arXiv subjects

Aichi Yamashita

Publications and source records attributed to Aichi Yamashita.

51 records · Page 3Linked to original sources

arXiv2020

Superconducting properties of high-entropy-alloy tellurides M-Te (M: Ag, In, Cd, Sn, Sb, Pb, Bi) with a NaCl-type structure

High-entropy-alloy-type tellurides M-Te, which contain five different metals of M = Ag, In, Cd, Sn, Sb, Pb, and Bi, were synthesized using high pressure synthesis. Structural characterization revealed that all the obtained samples have a cubic NaCl-type structure. Six samples, namely AgCdSnSbPbTe5, AgInSnSbPbTe5, AgCdInSnSbTe5, AgCdSnPbBiTe5, AgCdInPbBiTe5, and AgCdInSnBiTe5 showed superconductivity. The highest transition temperature (Tc) among those samples was 1.4 K for AgInSnSbPbTe5. A sample of AgCdInSbPbTe5 showed a semiconductor-like transport behavior. From the relationship between Tc and lattice constant, it was found that a higher Tc is observed for a telluride with a larger lattice constant.

cond-mat.supr-con↗

arXiv2019

Synthesis of Hg-based cuprate superconductors $HgBa_{2}Ca_{n-1}Cu_{n}O_{2(n+1)+δ}$ by CsCl flux additional method

We have succeeded in the synthesis of Re-doped $HgBa_{2}Ca_{n-1}Cu_{n}O_{2(n+1)+δ}$ quickly by a sealed tube technique with a bit of CsCl flux. Powder X-ray diffraction measurement revealed that the single phases of Re-doped $HgBa_{2}CuO_{4+δ}$ (Hg1201), $HgBa_{2}CaCu_{2}O_{6+δ}$ (Hg1212), and $HgBa_{2}Ca_{2}Cu_{3}O_{8+δ}$ (Hg1223) formed in 4 h. The sample grains exhibited plate-like crystals with the sizes of 20$\times$20$\times$1 $μm^{3}$ and the chemical compositions of Hg1201, Hg1212, and Hg1223. The superconducting transitions were observed at 25 K for Hg1201, 122 for Hg1212, and 133 K for Hg1223 in the magnetic susceptibility. These results indicate that the developed method is useful for the fabrication of Hg-based superconducting wires.

cond-mat.supr-con↗

arXiv2018

Single Crystal Growth of Cuprate Superconductor (Lu$_{0.8}$Nd$_{0.2}$)Ba$_2$Cu$_4$O$_8$ by KOH Flux Method

Single crystals of Nd-substituted LuBa$_2$Cu$_4$O$_8$ were successfully grown by the KOH flux method. The single phase of Lu$_{1-x}$Nd$_x$Ba$_2$Cu$_4$O$_8$ [(Lu,Nd)124] formed at $x = 0.2$. The compound crystallized as orthorhombic Ammm structure with lattice constants of a = 3.835(3) Å, b = 3.879(2) Å and c = 27.195(6) Å. Single crystal structural analysis demonstrated that the Nd ion partially occupied the Lu site. The (Lu,Nd)124 exhibited the superconducting transition at ~75 K in the magnetic susceptibility and resistivity. The $T_c$ and the c-axis of the (Lu,Nd)124 corresponded to Tm124. These results indicate that RE124 equivalent to the one composed of single RE element is obtained by combination of two RE elements.

cond-mat.supr-con↗

arXiv2018

Universal scaling behavior of the upper critical field in strained FeSe0.7Te0.3 thin films

Revealing the universal behaviors of iron-based superconductors (FBS) is important to elucidate the microscopic theory of superconductivity. In this work, we investigate the effect of in-plane strain on the slope of the upper critical field Hc2 at the superconducting transition temperature Tc (i.e. -dHc2/dT) for FeSe0.7Te0.3 thin films. The in-plane strain tunes Tc in a broad range, while the composition and disorder are almost unchanged. We show that -dHc2/dT scales linearly with Tc, indicating that FeSe0.7Te0.3 follows the same universal behavior as observed for pnictide FBS. The observed behavior is consistent with a multiband superconductivity paired by interband interaction such as sign change s+- superconductivity.

cond-mat.supr-con↗

arXiv2018

Pressure-induced Superconductivity in Sulfur-doped SnSe Single Crystal Using Boron-doped Diamond Electrode-prefabricated Diamond Anvil Cell

Sulfur-doped SnSe single crystal was successfully synthesized using a melt and slow-cooling method. The chemical composition and valence state of the obtained sample were analyzed by X-ray photoelectron spectroscopy. The pressure range of a diamond anvil cell with boron-doped diamond electrodes was upgraded to 104 GPa using nano-polycrystalline diamond anvil to investigate a pressure effect for the sample. Electrical resistivity measurements of sulfur-doped SnSe single crystal showed the insulator-metal-superconductor transition by applying high pressure up to 75.9 GPa.

cond-mat.supr-con↗

arXiv2018

Diamond anvil cell using boron-doped diamond electrodes covered with undoped diamond insulating layer

Diamond anvil cell using boron-doped metallic diamond electrodes covered with undoped diamond insulating layer have been developed for electrical transport measurements under high pressure. These designed diamonds were grown on a bottom diamond anvil via a nanofabrication process combining microwave plasma-assisted chemical vapor deposition and electron beam lithography. The resistance measurements of high quality FeSe superconducting single crystal under high pressure were successfully demonstrated by just putting the sample and gasket on the bottom diamond anvil directly. The superconducting transition temperature of FeSe single crystal was enhanced up to 43 K by applying uniaxial-like pressure.

cond-mat.supr-con↗

arXiv2017

Observation of Zero Resistance in As-Electrodeposited FeSe

Superconducting FeSe films were electrochemically deposited on rolling-assisted biaxially textured substrate (RABiTS) tape. We observed zero resistivity in the as-electrodeposited FeSe film prepared on the RABiTS when the appropriate voltage was applied while it was dipped into the solution. When the RABiTS tape was dipped in the solution without applying voltage, a thin Se film was deposited on the substrate. The compositional ratio of the FeSe film got closer to the stoichiometric ratio with decreasing the dipping time before applying voltage.

cond-mat.supr-con↗

arXiv2017

Electronic Transport Properties of Carrier Controlled SnSe Single Crystals

We found that the electronic transport property of SnSe single crystals was sensitive to oxygen content. Semiconducting SnSe single crystals were obtained by using Sn of grain form as a starting material while powder Sn resulted in metallic SnSe. X-ray photoelectron spectroscopy analysis revealed that the surfaces of raw Sn were oxidized, where the volume fraction was relatively low in grain Sn. This demonstrates that contamination of oxygen causes metallic behavior in grown SnSe single crystals.

cond-mat.mtrl-sci↗

arXiv2017

The influence of the in-plane lattice constant on the superconducting transition temperature of FeSe0.7Te0.3 thin films

Epitaxial Fe(Se,Te) thin films were prepared by pulsed laser deposition on (La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT), CaF2-buffered LSAT and bare CaF2 substrates, which exhibit an almost identical in-plane lattice parameter. The composition of all Fe(Se,Te) films were determined to be FeSe0.7Te0.3 by energy dispersive X-ray spectroscopy, irrespective of the substrate. Albeit the lattice parameters of all templates have comparable values, the in-plane lattice parameter of the FeSe0.7Te0.3 films varies significantly. We found that the superconducting transition temperature (Tc) of FeSe0.7Te0.3 thin films is strongly correlated with their a-axis lattice parameter. The highest Tc of over 19 K was observed for the film on bare CaF2 substrate, which is related to unexpectedly large in-plane compressive strain originating mostly from the thermal expansion mismatch between the FeSe0.7Te0.3 film and the substrate.

cond-mat.supr-con↗

arXiv2017

Phase Diagram of FeSe Deposited by Electrochemical Technique with Different Temperature and Voltage

High-quality crystalline FeSe is successfully synthesized in 5 minutes by an electrochemical deposition technique via increasing the solution temperature. The synthesis of FeSe have been controlled by the applied voltage, synthesis time and pH value. The obtained samples were summarized as a phase diagram at each temperature and applied voltage. The best synthesis temperature to produce high-quality crystalline samples was found to be 70°C.

cond-mat.supr-con↗

arXiv2017

Phase-separation control of K$_x$Fe$_{2-y}$Se$_2$ superconductor through rapid-quenching process

K$_x$Fe$_{2-y}$Se$_2$ exhibits an iron-vacancy ordering at $T_{\rm s} {\sim}270°$C and separates into two phases: a minor superconducting (iron-vacancy-disordered) phase and a major non-superconducting (iron-vacancy-ordered) phase. The microstructural and superconducting properties of this intermixture can be tuned by an appropriate control of the quenching process through $T_{\rm s}$. A faster quenching rate leads to a finer microstructure and a suppression of formation of the non-superconducting phase by up to 50%. Nevertheless, such a faster cooling rate does induce a monotonic reduction in the superconducting transition temperature (from 30.7 K down to 26.0 K) and, simultaneously, a decrease in the iron content within the superconducting phase such that the compositional ratio changed from K$_{0.35}$Fe$_{1.83}$Se$_2$ to K$_{0.58}$Fe$_{1.71}$Se$_2$.

cond-mat.supr-con↗

arXiv2015

Electrochemical deposition of FeSe on RABiTS tapes

FeSe film is successfully fabricated onto Rolling Assisted Biaxially Textured Substrate (RABiTS) tapes by an electrochemical deposition technique. The deposited FeSe films tend to become high crystallinity with a decrease in the applied voltage to -1.0 V, and the compositional ratio of Fe to Se approaches 1:1. The sample deposited at -1.0 V shows a superconducting transition approximately 8.0 K in the magnetic susceptibility.

cond-mat.supr-con↗

arXiv2014

Superconductivity in FeTe{1-x}S_x induced by electrochemical reaction using ionic liquid solution

Superconductivity in FeTe0.8S0.2 is successfully induced by an electrochemical reaction using an ionic liquid solution. A clear correlation between the Fe concentration in the solution and the manifestation of superconductivity was confirmed, suggesting that superconductivity was induced by the deintercalation of excess iron.

cond-mat.supr-con↗

arXiv2014

Superconductivity in FeTe0.8S0.2 induced by battery-like reaction

Superconductivity is successfully induced by utilizing a battery-like reaction found in a typical Li-ion battery. Excess Fe in FeTe0.8S0.2 is electrochemically de-intercalated by applying a voltage in a citric acid solution. The superconducting properties improve with an increase in the applied voltage up to 1.5 V. This result suggests that an electrochemical reaction can be used as a novel method to develop new superconducting materials.

cond-mat.supr-con↗

arXiv2013

Coexistence of bulk superconductivity and ferromagnetism in CeO1-xFxBiS2

We show the observation of the coexistence of bulk superconductivity and ferromagnetism in CeO1-xFxBiS2(x = 0 - 1.0) prepared by annealing under high-pressure. In CeO1-xFxBiS2 system, both superconductivity and two types of ferromagnetism with respective magnetic transition temperatures of 4.5 K and 7.5 K are induced upon systematic F substitution. This fact suggests that carriers generated by the substitution of O by F are supplied to not only the BiS2 superconducting layers but also the CeO blocking layers. Furthermore, the highest superconducting transition temperature is observed when the ferromagnetism is also enhanced, which implies that superconductivity and ferromagnetism are linked to each other in the CeO1-xFxBiS2 system.

cond-mat.supr-con↗