Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_1677

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_1678

CiNii Books

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY  

We report evidence for Aharonov-Bohm (AB) oscillations with temporal current switching at 5.1 and 79K by using charge-density wave (CDW) loops in TaS3 ring crystals. The periodicity of the AB oscillations is h/2e, and this is confirmed by employing four samples with different diameters. This means that sliding CDWs carry 2e charge quanta. We observe current switching between the two states, namely the high and low current states, as a result of the separation of field-dependent and time-dependent fluctuations. The probability distribution of the switching oscillates also with a period of h/2e. We discover that the observed oscillations, which are a superposition of the current fluctuations and the switching behavior, have a period h/2e. Copyright (C) EPLA, 2012

DOI： 10.1209/0295-5075/97/57011

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have synthesized micrometer-scale polyhedral ring crystals of TaS(3) by the; chemical vapor transportation method. The polyhedral ring crystals are closed-loop crystals with several vertices. We investigated the crystallinity and flatness of the facets by the electron backscatter diffraction technique and found that the orientation of the crystal axis changed abruptly at several points. Observing the size of the crystals, we found a new phase of topological crystals and propose a phase diagram of ring-polyhedral crystals in terms of radius and thickness. We also propose a mechanism of polygonization in which the vertices of the polyhedral crystals are formed from concentrated dislocations as a result of distance-dependent interactions between them.

DOI： 10.1021/cg2004003

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J-GLOBAL

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We have found parity-violating current-voltage (I-V) curves in a single domain of Sr2RuO4 superconductors The Induced voltage V is an even function of bias current I below superconducting transition temperature The anomalous I-V curves show that positive voltage is detected regardless of the current direction The result implies the parity violation of I-V curves (C) 2009 Elsevier B V All rights reserved

DOI： 10.1016/j.physb.2009.11.101

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We measured the magnetic torque of the ring-shaped crystals of TaSe3 by using piezoresistive cantilevers to investigate the superconducting topological properties. We measured three ring samples and we observed that the magnetic torque of the ring crystals oscillates with increasing external magnetic field. The magnetic periods of Sample A (radius: 37.9 mu m), Sample B (24.5 mu m), and Sample C (15.6 mu m) were 2.16 +/- 6.6 x 10(-2) G, 4.69 +/- 1.8 x 10(-1) G, and 5.44 +/- 3.8 x 10(-1) G, respectively. We found that hundreds of vortices collectively and simultaneously penetrated the ring crystal. When such a phenomenon occurs, it is natural that the vortices in the ring crystal would be positioned along the circumference. From these results, we suggest that vortices exist as cylinder vortices in the rings, and this phenomenon provides unambiguous experimental evidence of the topological effect in a superconductor.

DOI： 10.1103/PhysRevB.81.184506

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We studied the nonlocal transport of a quasi-one-dimensional conductor o-TaS3. Electric transport phenomena in charge density waves include the thermally excited quasiparticles and collective motion of charge density waves (CDWs). In spite of its long-range correlation, the collective motion of a CDW does not extend far beyond the electrodes, where phase slippage breaks the correlation. We found that nonlocal voltages appeared in the CDW of o-TaS3, both below and above the threshold field for CDW sliding. The temperature dependence of the nonlocal voltage suggests that the observed nonlocal voltage originates from the CDW even below the threshold field. Moreover, our observation of nonlocal voltages in both the pinned and sliding states reveals the existence of a carrier with long-range correlation, in addition to sliding CDWs and thermally excited quasiparticles.

DOI： 10.1103/PhysRevB.81.113101

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arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We report our approach to measuring the transport properties in a single chiral order parameter domain of microscale Sr2RuO4 single crystals. Sr2RuO4 single crystals were grown by the solid-phase reaction. Microscale single crystals were deposited from a dispersed liquid, and selected from the result of the chemical composition and crystallinity of the dispersed crystals. The selected crystals attached to gold electrodes show superconducting properties. We also found the anomalous current-voltage characteristics that show that induced voltage is an even function of bias current. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.49.020209

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We studied the nonlocal transport of a quasi-one dimensional conductor<br />
$o$-TaS$_3$. Electric transport phenomena in charge density waves include the<br />
thermally-excited quasiparticles, and collective motion of charge density waves<br />
(CDW). In spite of its long-range correlation, the collective motion of a CDW<br />
does not extend far beyond the electrodes, where phase slippage breaks the<br />
correlation. We found that nonlocal voltages appeared in the CDW of<br />
$o$-TaS$_3$, both below and above the threshold field for CDW sliding. The<br />
temperature dependence of the nonlocal voltage suggests that the observed<br />
nonlocal voltage originates from the CDW even below the threshold field.<br />
Moreover, our observation of nonlocal voltages in both the pinned and sliding<br />
states reveals the existence of a carrier with long-range correlation, in<br />
addition to sliding CDWs and thermally-excited quasiparticles.

DOI： 10.1103/PhysRevB.81.113101

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report measurements of Little-Parks oscillation on the hierarchical honeycomb-superconducting network for investigating possible effects of hierarchical structure in terms of spatial symmetry, parity, and duality. We observed an asymmetric Little-Parks oscillation about Phi/Phi(0)=1/2, although spatial symmetry was kept in the network. In comparison with a regular honeycomb network, the asymmetric oscillation is attributed to hierarchy which induces mixture of commensurate and incommensurate regions. The asymmetric oscillation is found to indicate breaking of the duality of vortex configuration.

DOI： 10.1103/PhysRevB.80.094502

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Language：English   Publisher：Elsevier Ltd.  

DOI： 10.1016/j.ssc.2009.04.022

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We investigated Aharonov-Bohm (AB) oscillations from charge-density waves (CDWs) in TaS3 ring crystals and demonstrated that only sliding CDWs behave as a macroscopic quantum plane wave coupled to magnetic fields. The periodicity of the oscillations is h/2e within 10% accuracy. This means that sliding CDWs carry 2e charge quanta and that cannot be explained by quasi-particle interference. This is the first unambiguous experimental evidence for the AB effect in CDW loops. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2008.11.066

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We report a synchrotron X-ray study of charge density waves (CDWs) in an o-TaS3 crystal. CDW of o-TaS3 has been known to undergo a commensurate-incommensurate transition at 100 K, below which the wavevector locks in with the pristine lattice. However, the details of the commensurate-incommensurate transition remain open problems, the example being whether the discommensuration exists or not in the neighborhood of the transition. We exploited the beamline BL02B1 of SPring-8. A two-dimensional detector was placed at a distance of 1300mm from the sample, providing an angle resolution of 0.0076 degrees. Temperature dependence of the Bragg peak (0 0 2) and satellite peak (1 - 12) + q was measured from 7 to 180 K. We found that a new phase in the temperature range of 130-50 K, where two independent CDWs coexist. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c) = 0.252c* and 0.250c*, respectively. By lowering the temperature, intensity of the incommensurate CDW was decreased, while that of the commensurate CDW was increased. Below 50K, the incommensurate CDW was completely diminished. Based on the concept of discommensuration, we suggested the dislocation configuration from the intensity of the two CDWs. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2008.11.017

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We have investigated Little-Parks oscillation in a hierarchical superconducting network for searching possible effects of hierarchical structure in terms of spatial symmetry, parity and duality. We prepared a hierarchical honeycomb network, which is obtained to gather 6 hexagons around a hexagon and add 6 rhombuses to large hexagon repeatedly, by standard electron beam lithography and measured variation of superconducting transition temperature (T(c)) in a magnetic field. For comparison, we also fabricated regular honeycomb network and measured variation of T(c). The filling ratio f = Phi/Phi(0) is the magnetic flux Phi in units of the flux quantum Phi(0) per elementary hexagon. Downward cusps in T(c) curves of the regular honeycomb network are observed at f = 1/3, 2/5, 1/3, 3/5, 2/3. This result in range of 0 to 1 is symmetric about f = 1/2 and reminiscent of the report in the recent years. On the other hand, that of the hierarchical honeycomb network are observed at f = 1/5, 3/10, 4/9, 1/2, 5/9, 7/10, 3/4. The cusps at f = 1/5, 3/4 are not symmetric about f = 1/2. It is indicated that duality of vortex configuration on the network break down although system has symmetric structure. This behavior was not even obtained in the case of Sierpinski gasket, which is deterministic fractal form. Therefore this anti-symmetric pattern is due to the effect of hierarchical honeycomb structure in itself.

DOI： 10.1088/1742-6596/150/2/022089

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We observed the power law and the critical exponent of quantum phase transitions by measuring a transient response in an Al/AlOx/Al junction of U(1) superconductors and Sr2RuO4 single crystals of SU(2) superconductors, when magnetic field decreased rapidly from more than the critical field to zero magnetic field below T = 0.1 K. In the Al/AlOx/Al junction, the result shows that the domain length xi is a power function of the quench time tau(Q). The critical exponent is 0.30 +/- 0.01. Moreover, in the Sr2RuO4 crystal, the result shows xi is a power function of tau(Q) and the critical exponent is 0.40 +/- 0.01. From the results of U(1) and SU(2) superconductors, we consider the critical exponents observed by the quenching are derived by a mean-field value in charged systems. Using typical U(1) and SU(2) superconductors, we find that the magnetic quench is efficient method to study formation processes of topological defects for a quantum phase transition near T = 0.
http://iopscience.iop.org/article/10.1088/1742-6596/150/5/052187/pdf

DOI： 10.1088/1742-6596/150/5/052187

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We report a synchrotron X-ray study of charge density waves (CDW) in an o-TaS3 crystal. CDW of o-TaS3 has been known to undergo a commensurate-incommensurate transition at 100 K, below which the wavevector locks in with the pristine lattice. We exploited the beamline BL02B1 of SPring-8. Temperature dependence of the Bragg peak (002) and satellite peak (1 -1 2)+(q) over right arrow was measured from 7 K to 180 K. We found that a new phase in a temperature range of 130-50 K, where two independent CDWs coexist. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c)=0.252c* and 0.250c*, respectively. By lowering the temperature, intensity of the incommensurate CDW was decreased, while that of the commensurate CDW was increased. At 50 K, the incommensurate CDW was completely diminished. Based on the concept of discommensuration, we determined the dislocation configuration from the intensity of the two CDWs.

DOI： 10.1088/1742-6596/150/4/042068

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We report the electron tunneling study on LaFeAsO1-xFx (x=0.07) using low temperature UHV-STM/STS. Tunneling spectra below T-c clearly shows the gap structure. We found three anomalies as kinks in the tunneling differential conductance curve: 1) Superconducting gap structure Delta(SC)=6 meV. 2) Small pseudogap Delta(PGS)=20 meV. 3) Large pseudogap Delta(PGL)=100-150 meV. Corresponding value of 2 Delta(SC)/k(B)T(c)=5.8 suggests strong coupling superconductivity. Tunneling spectra at T=80 K show dip structure. The kink around V=150 mV still exist.

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We observed quantum fluctuations of the superconducting phase ? in single domain Sr(2)RuO(4) single crystals using a transport measurement. The temperature dependence of the resistivity of submicron Sr2(R)uO(4) shows that a finite resistivity below the superconducting transition temperature of T(c) = 1.69 K. The results may suggest that the finite resistivity is occurred by the flow of vortices due to quantum fluctuations of the superconducting phase theta in the same way as one-dimensional Josephson junction array systems

DOI： 10.1088/1742-6596/129/1/012022

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We investigate topological effect of charge density wave (CDW). The Shapiro step measurement was performed on NbSe(3) topological (ring) crystals. We found that a beat-like splitting of Shapiro step spectrum. These results suggest that the circulating CDW current flows in the ring, and modifies the CDW fundamental frequency, namely narrow-band-noise frequency.

DOI： 10.1088/1742-6596/129/1/012024

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We investigate charge density wave (CDW) dynamics in ring-shaped crystals of NbSe3. We performed a measurement of the frequency dependence of resistance for a closed-ring topology (ring-shaped crystal without edge) and an open-ring topology (cut ring-shaped crystal with two edges) in the 300 kHz to 1.3 GHz frequency range. Comparison of the frequency dependence of the resistance indicated that the pinning potential in the closed-ring topology was smaller than that in the open-ring topology. This result suggests existence of a CDW circulating current in NbSe3 ring-shaped crystals.

DOI： 10.1142/9789812814623_0060

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We report studies of o-TaS(3) nanocrystals, including sample preparation of nanocrystals, fabrication of electrodes attached to the nanocrystals, and transport properties. Since the correlation length of a charge density wave (CDW) is in the range of several microns, electric properties of CDW in nanocrystals are expected to show significant difference. We have developed a new fabrication technique for electrodes by annealing with electron beam to reduce the contact resistance significantly. We applied this technique for the study of nanoscale CDW systems. Temperature dependence of resistance was measured in a o-TaS(3) nanocrystal with the electrode distance of several mu m. The observed resistance did not show a clear Peierls transition. The resistance was well described in terms of one-dimensional (1D) variable-range-hopping (VRH) conduction over the wide range of temperature. These behaviors are consistent with those of the previously reported nanoscale CDW systems. We also found a finite-size effect in current-voltage characteristics in nanoscale o-TaS(3) crystals with various sample dimensions. These results are consistent with the idea that electric transport phenomenon of the nanoscale o-TaS(3) crystals should be attributed to charged solitons in commensurate CDW systems.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We have studied a topological effect of a charge density wave (CDW) in niobium triselenide ring crystals. We measured the frequency dependence of AC conductivity in the range from 300 kHz to 1.3 GHz to investigate the dynamics of the CDW ring. We compared the dynamical properties of the CDW in the ring and in the cut-ring geometries. The experimental data shows that the pinning frequency of the cut-ring is larger than that of the ring. This result suggests that the dynamics of the CDW depend on the edges, i.e., the topological structure of the sample.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

We have investigated the pressure effects near the phase boundary between the CDW and the pressure-induced reentrant-superconductivity (r-SC) in ZrTe3, where, simultaneously with the collapse of the CDW state, appears again the SC. Fluctuations of the CDW and the SC have become stronger as both transitions approach to the phase boundary. We discuss the possible exsitence of a novel state between the CDW and the r-SC phases.

DOI： 10.1051/jp4:2005131087

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We successfully synthesized new crystal forms of a charge-density-wave conductor, NbSe3. The new forms are basically a loop of diameters 10-200 mum with/without a twist (ex. ring, Mobius strip). Their distinctive topology seems to offer systems for studying possible new quantum phenomena. Samples were obtained by chemical vapor transportation method and identified as NbSe3 Crystals by electron diffraction. SEM studies revealed that a loop is formed from a NbSe3 whisker that wraps around a droplet of selenium by forces of surface tension during crystal growth. Also we observed that a twist is introduced during this spooling process. Moreover, we performed transport measurements on the materials and found that, exclusively in samples with a twist, T-CDW is lower by a few K than that of NbSe3 whiskers. We suggest that the anomaly originates in local strain due to the twisted topology. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02287-1

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We have investigated structural and electrical properties of "ribbon-knot" crystals of TaSe3 (superconductor) having nontrivial topological structures. They are shaped a ring, a Mobius strip and a 2pi-twisted loop, so they can be categorized by a ribbon knot topological invariant in the mathematics field. For investigation of structural property of the ring crystals, cutting operation was performed for 45 specimens of the TaSe3 ring crystal using focused ion beam milling. The cutting operation transformed them to arc-shape crystals having homogeneous curvatures. At low temperature, thin ring crystals of TaSe3 showed superconductivity, however, thick rings showed nonmetallic behavior. The experimental results suggest that the ring-shape structure affect the electrical behavior in the TaSe3 ring crystal. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02290-1

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Nanoscale electrical transport properties have attracted attentions because of new phenomena such as ballistic transport, quantized resistance, and Coulomb blockade. For measurement of nanoscale resistance, we have been developing a cryogenic atomic force microscope that can operate at 1.8 K. To use it as an electrode, we coated the cantilever with conductive oxides of TiO and indium tin oxide (ITO). We verified that TiO and ITO thin films remain conductive even at 4.2 K. Also we measured I V characteristics of the tip-sample contact with a standard sample of NbSe2 single crystal, and found that the conductive coats were not lost under large stresses due to the tip-sample contact. Moreover, we succeeded in obtaining a room temperature nano-potentiometry of a gold thin film with the ITO coated cantilever. In conclusion, the TiO and ITO coated cantilevers are applicable to cryogenic nano-potentiometry. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02435-3

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We found new types of niobium triselenide (NbSe3) crystal that have the shapes of a loop with a twist of n pi (n = 0, 1,2) with a size on scale of 10-100 micrometers. We named them "topological crystals" after their distinctive topologies. The crystals were synthesized by direct vapor phase reaction of selenium and niobium. We revealed that a droplet of liquid selenium is responsible for the formation of the crystals, acting as a spool that takes up a NbSe3 whisker by the force of surface tension. As a result, a loop crystal wrapping around the droplet is formed. Twisted loops, such as a Mobius strip, are produced through similar spooling mechanisms that involve either a double spooling or an autonomous twisting of a whisker. We performed electrical transport measurements on the crystal and confirmed the transitions into charge-density-wave (CDW) phases that are characteristic of the substance, NbSe3. It was revealed that loops without a twist and with a twist exhibit qualitatively different behaviors; CDW transition temperatures decrease and the width of transitions broaden for some of twisted rings, while none of the twist-free rings shows such features. The electronic properties seem to be affected by crystallographic difference due to their variant topologies.

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We have investigated structural and electrical properties of ribbon-knot crystals of low-dimensional conductors, such as TaSe3 (superconductor) and NbSe3 (charge-density-waves conductor), having some topological invariant characteristics. We cut some specimens of TaSe3 ring crystals using focused ion beam sputtering to obtain the structural property (e.g., elasticity and plasticity). The cut specimens of ring crystal transformed to arc-shape with homogeneous curvatures, and the cut thick rings had a tendency to keep strongly their shapes. From result of electrical measurement at low temperature, whisker and thin ring crystals of TaSe3 show superconductivity, however, thick rings show increase resistance with decreasing temperature. The geometrical parameter, thickness, dominates the structural and the electrical properties in the ring crystals.

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Hall coefficients and resistivities of a series of Bi2+xSr2-xCuOy single crystals were measured to investigate the relation between the carrier concentration n and the resistivity-minimum temperature T-min. The T-min was found to obey a simple linear relation: T-min proportional to n(c)-n, where n(c)similar or equal to4.2x10(21) cm(-3) is a critical carrier concentration. A model of two-dimensional electron systems with a mobility edge was introduced to explain this linear relation, and the presence of a mobility edge in two-dimensional copper-oxide-based metals was suggested. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1509842

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：E D P SCIENCES  

The charge-density-wave (CDW) order of low-dimensional inorganic conductor ZrTe3 is found to increase with increasing pressure, while the superconductivity with filamentary nature is significantly suppressed. It was evidenced in resistivity measurements under pressure up to 0.8 Gpa. The present results suggest that competition between the superconductivity and the CDW is not simply explained by a nesting effect of the Fermi surface, but other origin is needed. Non-metallic behaviour is also found below 4K under high pressures above 0.6 Gpa. The relationship between the non-metallic state and the pressure-enhanced CDW is expected, although yet inexplicable.

DOI： 10.1051/jp4:20020369

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We propose a technique based on ultrasonic force microscopy that exploits the hysteresis in cantilever jumping to and from a sample while varying the ultrasonic amplitude. Both the elastic modulus and the work of adhesion can be determined by comparision with a relation derived between their ratio and the cantilever shift at the jump-in point. The method is applied to measurements on an aluminum thin film. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1463212

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Hall coefficients and resistivities of a series of Bi2+xSr2-xCuOy single crystals were measured to investigate the relation between the carrier concentration and the disorder of the system in the superconductor-insulator transition. Excimer-laser cutting technique was applied to fabricate the Hall-bar shaped samples in order to determine precisely the transport properties of the single crystals. The Hall coefficients were found to be independent of the temperature, which suggests Coulomb interaction was negligible in the localized regime of Bi2+xSr2-xCuOy. We found the Ioffe-Legel condition k(F)l similar to 1 laid around n(0) similar to 8 x 10(20) cm(-3) in this system, and the carriers in the localized regime were essentially ''metallic.'' (C) 1996 American Institute of Physics.

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Transport properties, such as electric conductivity, magnetoresistance, and Hall coefficient are measured in Bi2Sr2CuO6 single crystals. The conductivity drops at low temperature proportional to log T. This behavior is interpreted as the weakly localized regime of Anderson localization, since we observe log T, log E and log H dependences of the conductivity. The coefficients of log T and log E come close to the expected values by treating the sample as consisting of stacked two-dimensional conduction planes, However, the coefficient of log H is much less than the universal value which is expected from theories of the weakly localized regime. From the results of Hall measurement, we show that electron-electron interaction does not play a major role.

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Transport properties of Bi2Sr2CuO6 single crystals, including the electric conductivity magnetoresistance, and Hall coefficient, were measured. Characteristics of the conductivity in the weakly localized regime, which includes temperature, electric field, and magnetic field, were also measured. The coefficient of In H was found to be much smaller than the theoretical value predicted for the weakly localized regime. Measurement of the Hall coefficient indicates that the electron-electron interaction does not play a significant role in the conductivity. Rather, interplane coupling appears to play a role in the transport properties of this system.

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We have measured temperature-dependent resistivities of a set of Pb ultrathin films by repeating in situ deposition at liquid-He temperature. Observed conductance in the fermion region can be described by a single-parameter scaling function (beta function) with a self-consistent theory for localization in two dimensions. Based on estimated values of electrical localization length (xi(loc)) and superconducting coherence length (xi(super)), the superconductor-insulator transition is confirmed to occur at the point where xi(loc)similar to 2 xi(super). Moreover, only samples exhibiting lnT dependence in the fermion region become global coherent superconductors at low temperature.

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Transport properties of (Formula presented)(Formula presented)Cu(Formula presented) single crystals, including the electric conductivity magnetoresistance, and Hall coefficient, were measured. Characteristics of the conductivity in the weakly localized regime, which includes temperature, electric field, and magnetic field, were also measured. The coefficient of (Formula presented) was found to be much smaller than the theoretical value predicted for the weakly localized regime. Measurement of the Hall coefficient indicates that the electron-electron interaction does not play a significant role in the conductivity. Rather, interplane coupling appears to play a role in the transport properties of this system. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.53.R8902

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We have observed the nonlinear current-voltage characteristics of Bi2Sr2CuO6 single crystals in the weakly localized regime (WLR), in which the conductivity indicates a logarithmic dependence both on temperature and on magnetic fields. The conductivity in low voltage remaines constant (Ohmic behavior). Upon application of a voltage higher than the threshold electric field 0.1V/cm, the conductivity begins to increase. The observed threshold of the electric field is much smaller than the value of 200V/cm estimated from the model which Anderson et al. (1979) introduced to explain the nonlinear conductivity shown in the WLR of thin metal films. © 1994.

DOI： 10.1016/0921-4534(94)91905-4

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CiNii Books

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CiNii Books

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We investigate the spectrally resolved transient reflectivity changes Delta R(T,tau,lambda) in the charge density wave (CDW) conductor o-TaS3. A distinct near-infrared resonance in this compound emphasizes the characteristic Delta R(lambda) resonances, and allows a selection of coexisting CDW phases with different nonequilibrium carrier dynamics. Furthermore, the spectrally resolved Delta R(tau) characterizes the collective oscillations associated with the individual states. We believe that this demonstration paves the way for the optical selection of the multiphase order that plays an important role in various macroscopic quantum systems.

DOI： 10.1103/PhysRevB.80.121103

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The Aharonov-Bohm (AB) effect has been accepted and has promoted<br />
interdisciplinary scientific activities in modern physics. To observe the AB<br />
effect in condensed matter physics, the whole system needs to maintain phase<br />
coherence, in a tiny ring of the diameter 1 micrometer and at low temperatures<br />
below 1 K. We report that AB oscillations have been measured at high<br />
temperature 79 K by use of charge-density wave (CDW) loops in TaS3 ring<br />
crystals. CDW condensate maintained macroscopic quantum coherence, which<br />
extended over the ring circumference 85 micrometer. The periodicity of the<br />
oscillations is h/2e in accuracy within a 10 percent range. The observation of<br />
the CDW AB effect implies Frohlich superconductivity in terms of macroscopic<br />
coherence and will provide a novel quantum interference device running at room<br />
temperature.

DOI： 10.1209/0295-5075/97/57011

arXiv

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：English   Publisher：AMER PHYSICAL SOC  

We investigate the topological effect of charge density wave (CDW). We found a "beat" Shapiro step structure in NbSe3 topological (ring) crystals. We interpreted it as an evidence of the circulating CDW current that flows in the rings and modifies the CDW fundamental frequency, namely, narrow-band-noise frequency. This result also implied that a precursor of Frohlich&apos;s CDW supercurrent emerged in the ring system.

DOI： 10.1103/PhysRevB.79.014304

Web of Science

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Language：English   Publisher：PHYSICAL SOC JAPAN  

We report a synchrotron X-ray Study of charge density waves (CDWs) in an o-TaS3 crystal. We found that two independent CDWs coexist ill the temperature range of 130-50K. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c) = 0.252c* and 0.250c*, respectively. The temperature and electric current dependences of the intensity of the two CDW satellites were measured. We found that the commensurate CDW was converted to the incommensurate CDW at 80 K by inducing current flow. Our observation was interpreted in terms of the dynamics of topological defects. We determined the edge dislocation configuration from the electric Current dependence of the intensity of the two CDWs. The result implies Cor the first time that discommensurations are induced ill the commensurate CDW by applying an electric field.

DOI： 10.1143/JPSJ.77.093708

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

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Language：Japanese   Publisher：社団法人日本物理学会  

CiNii Books

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

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Language：Japanese   Publisher：社団法人日本物理学会  

CiNii Books

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

CiNii Books

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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We studied the differences of the charge density wave (CDW) dynamics in closed-ring and open-ring topologies by measuring the frequency-dependent resistance in the radio-frequency range. We performed a two-probe ac resistance measurement for a ring-shaped crystal of niobium triselenide (NbSe3) in the 300 kHz to 1.3 GHz frequency range. We compared the frequency dependence of the resistance of closed-ring and open-ring crystals and found that the pinning potential in the former is smaller than that in the latter. The open-ring crystal was obtained by changing of the topology of the closed-ring crystal. We believe that the reduction in the pinning effect is caused by a CDW circulating current in the closed-ring topology.

DOI： 10.1103/PhysRevB.73.165118

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We discover a supercluster of electrons in the ultrathin TaSe2 crystals synthesized by our developed de-chalcogenide method. The supercluster has all unexpected structure containing 61 electrons denoted by root 61 x root 61, in addition to a root 49 x root 49 supercluster based on root 7 x root 7 clusters expected in triangle lattices. This new hierarchal structure and successive clustering cannot be explained by a conventional electron clustering mechanism assisted by background lattice distortions, i.e., charge-density-wave formation mechanism based on Fermi surface nesting. We propose an alternative possible formation mechanism based on saddle-point nesting, taking into account a trigonal symmetry as well as lattice distortion energy.

DOI： 10.1143/JPSJ.75.024706

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Language：English   Publisher：EDP SCIENCES S A  

We report studies of o-TaS3 nanocrystals, including sample preparation of nanocrystals, fabrication of electrodes attached to the nanocrystals, and transport properties. Absence of the clear Peierls transition and one-dimensional variable-range-hopping conduction were observed. We also found finite-size effect of soliton transport in nanoscale o-TaS3 crystals. These results are consistent with the idea that electric transport phenomenon of the nanoscale o-TaS3 crystals should be attributed to soliton nucleation.

DOI： 10.1051/jp4:2005130016

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Language：English   Publisher：AMER CHEMICAL SOC  

Electrostatic assembly of cationic nanoparticles onto the negatively charged backbone of double-stranded DNA has been shown to produce one-dimensional chains with potential use as nanoelectronic components. In this paper, micron long DNA templates stretched on aminosilane- and hexamethyldisilazane-modified silicon surfaces are used to assemble 3.5 nm gold nanoparticles passivated with cationic thiocholine. Atomic force microscopy is used to analyze the density and defects along the similar to 5 nm high structures, with comparison between positively charged and neutral surfaces. Low background adsorption of nanoparticles is facilitated by both these surface chemistries, while the neutral surface yields a more densely packed assembly.

DOI： 10.1021/la0515367

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PubMed

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Language：English   Publisher：ELSEVIER SCIENCE BV  

The reduction of the system size may lead to new developments in macroscopic quantum systems such as superconductors and charge-density-wave systems. In order to investigate such effects, thin films and thin wires are generally fabricated by an evaporation technique. However, this technique can only be applied to a limited number of materials; hence, a more versatile technique is required. In this study, we provide the results of our recent study on the fabrication of electrodes on nanoscale crystals. Gold electrodes, which were 400 nm in width, were fabricated by a standard lift-off technique on o-TaS3 charge-density-wave nanocrystals, which were prepared by deposition on silicon substrates. The interface resistance was higher than 100 G Omega just after evaporation and was decreased significantly by electron beam irradiation. The electrodes were tested down to 80 mK and were found to be fairly durable for cryogenic measurement. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2005.01.083

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Language：English   Publisher：ELSEVIER SCIENCE BV  

We investigate the ac conductivity of charge density wave (CDW) rings, which are topologically different from whiskers. We synthesize ring crystals of NbSe3, a CDW material, by the selenium droplet spooling method. The ac conductivity is measured for both the rings and the whiskers in the frequency range of 10 kHz- 150 MHz. We analyze the frequency dependence of the ac conductivity of the CDW rings and the whiskers using a simple washboard potential model. The result suggests that the CDW rings have a larger effective mass and a higher pinning frequency than the CDW in the whiskers and that the topology of the crystals plays an important role in CDW dynamics. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2005.02.141

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Reduction of the sample size leads to a new phenomena through a change in system dimensionality. Progress of nanotechnology allows us to seek for such a size-driven effect of quasi-one-dimensional materials. Here we report recent studies of o-TaS3 nanocrystals. We found that the nonlinear conduction due to soliton transport in the charge-density-wave system became independent of temperature below 2 K. The observed I-v curves were classified to two kinds. One kind of the samples exhibit the standard activation formula, I proportional to exp[-E-0/E-2], whereas other kind of the samples show a modified form, I proportional to exp[-(E-0/E)(2)], where E-0 is a constant, and E is an applied field. Since both kinds of the samples were synthesized in a same batch, it is plausible to attribute the difference of the I-V curves to that of the sample sizes. We interpreted it as the dimensional crossover of soliton transport, in the framework provided by Hatakenaka et al. They predicted the quantum nucleation possibility of the solutions T, which is proportional to the current, obeys a dimensionality-dependent formula, F proportional to exp(const./E-D), where D is the system dimension. According to this, our observation suggests that the system dimension relevant to soliton transport was either D = 1 or D = 2, which depends on the system size. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2005.05.058

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Language：English   Publisher：AMERICAN PHYSICAL SOC  

A charge-density-wave material NbSe3 with thickness less than 1 mu m shows a distinct peak in the low temperature transverse magnetoresistance when the magnetic field is applied along the c axis. The resistance peak is less pronounced as the field is tilted away from the c axis to the a* axis. The peak height also decreases as the temperature increases, although the magnetic field at the peak shows no appreciable dependence on temperature. The resistance peak is attributed to surface diffuse scattering of normal carriers which remain even below the lower charge-density-wave transition temperature.

DOI： 10.1103/PhysRevB.71.134409

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Language：English   Publisher：AMER INST PHYSICS  

Nanoscale charge density wave systems of quasi-one-dimensional o-TaS3 crystals were fabricated. Gold electrodes 400 nm wide were made by standard lift-off technique on o-TaS3 nanocrystals prepared by deposition on silicon substrates. Interface resistance was higher than 100 GOmega just after evaporation, and were significantly reduced by electron-beam irradiation. The electrodes were tested down to 80 mK, and were found quite durable for cryogenic measurement. The temperature dependence of the resistance of the nanocrystal was represented as the variable-range-hopping-type conduction with one dimension over the wide range of temperature, from 4.2 to 100 K. This behavior was different from that of conventional bulk samples. (C) 2005 American Institute of Physics.

DOI： 10.1063/1.1862782

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We report novel experimental results of chemical doping effect on Ag-doped DNA conductor. The prepared Ag-doped DNA samples were confirmed by EXAFS that Ag+ was doped into pi-way. In I-V measurements at room temperature, nonlinear I-V curves with hysteresis emerged and systematic change in electrical conductivity a was observed from 10(-10) to 10(-6) Omega(-1) cm(-1) under doping condition [Ag+]/[Base pair] = 10(-6)-10. The relation between the conductivity and dopant concentration showed a weak dependence a proportional to [Ag+](0.5). This 'weakly doping effect' may be caused by the long-range correlated randomness of sequence in DNA, in contrast with usual doped organic conductors. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2004.08.061

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J-GLOBAL

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We succeed in synthesizing NbSe2 nanotubes along with nanofibers by chemical vapor transportation. They are stable crystalline systems and can be synthesized reproducibly in a nearly equilibrium reacting process. We have investigated these nanosize structures of NbSe2 by transmission electron microscopy and electron diffraction. Both of the structures have a similar size of 100-200 nm in diameter. While nanotubes consist of rolled-up NbSe2 layers, nanofibers are a pile of thin flat layers. We propose a mechanism of the formation of NbSe2 nanotubes and nanofibers on the basis of deseleniditive transition from a NbSe3 fiber-shaped crystal. We also measured electrical resistance of the nanofibers with conductive atomic force microscopy and demonstrated that the material show metallic behavior at room temperature. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cap.2003.07.002

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Low-temperature specific heat of CDW compounds ZrTe3 and NbTe4, measured between 1.5 and 10 K, exhibited an anomaly which deviates from the regular phonon term; an excess specific-heat contribution appeared around T = 6 K. The excess contribution was well presented in terms of the phason contribution of CDW. The pinning frequency estimated from the analysis was quite high in comparison to the value of common CDW conductors, which is not inconsistent with the linear relation between current and voltage. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02252-4

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DOI： 10.1038/417397a

Scopus

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Language：English   Publisher：AMER INST PHYSICS  

We present measurements using ultrasonic force microscopy at similar to 60 MHz, operating in a "waveguide" mode in which the cantilever base is vibrated and flexural ultrasonic vibrations are launched down the cantilever without exciting any particular cantilever resonance. The nonlinearity of the tip-sample force-distance curve allows the conversion of a modulated ultrasonic frequency into a low frequency vibration of the cantilever, detected in a conventional atomic force microscope. Images of Ge quantum dots on a Si substrate show contrast related to elasticity and adhesion differences, and this is interpreted with the Johnson-Kendall-Roberts model of the force-distance curve. (C) 2000 American Institute of Physics. [S0003-6951(00)03114-4].

DOI： 10.1063/1.126184

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