Superconductivity
2019/03
Ashish Chhaganlal Gandhi, Shrikrushna Shivaji Gaikwad, Jen-Chih Peng, Chin-Wei Wang, Ting Shan Chan, Sheng Yun Wu
APL Materials 7(3), 031111, 2019
We report on the nanosized effect on superconducting properties of Bi nanoparticles (NPs) that extracted from the temperature and applied magnetic field dependent magnetization measurements of bismuth NPs, and revealed an enhanced TC and stronger coupling strength because of increased density of state and softened phonons ωln. A strong electron-phonon coupling (λep = 1.639) to low-lying phonons (ωln = 58 K) is found to be the leading mechanism behind the observed superconductivity with an enhanced TC ∼ 8.22 K and a strong superconducting coupling strength of α = 2.32(1) of 15 nm Bi NPs. Our results are well described by the Allen and Dynes formula within the framework of the McMillan formalism and are in agreement with the Ginzburg-Landau theory calculations.
Full Paper: https://aip.scitation.org/doi/full/10.1063/1.5068687
2018/12
Ashish Chhaganlal Gandhi and Sheng Yun Wu
Inorganic Chemistry 58 (1), 794-802, 2019
We report the crystal structure and superconducting phase diagram for InpSn1–p (0.01 ≤ p ≤ 0.99) bimetallic alloys. A weak electron–phonon coupling was observed in intergranular linked InSn superconductors over an infinite range mediated by high-energy phonons. An enhanced TC(0) ∼ 6.2 K and critical field HC(0) ∼ 2.7 kOe were determined from intermediate (γ-Sn + β-InSn) composite alloys attributed to internal strain possibly originating from thermal expansion effect of constituent phases.
Full Paper: https://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.8b02941
2018/07
Ashish Chhaganlal Gandhi and Sheng Yun Wu
Inorganic Chemistry 57(15), 9306-9315, 2018
Electron–phonon coupling is a fundamental inelastic interaction in solid-state physics and superconductors. Here we probe electron–phonon and superconducting coupling strength by tuning the indium composition in InqPb1–q superconducting bimetallic alloys. A crossover from weak to strong coupling strength was observed through the analysis of crystal structure and superconducting phase diagrams. The hole-doped Pb solid solution showed suppressed TC and subverted coupling strength due to decreased density of state N(0) and hardened phonons, while the electron-doped In solid solution revealed enhanced TC and stronger coupling strength because of increased N(0) and softened phonons. Our results are in agreement with the Ginzburg–Landau theory calculations regarding the dirty limits and are well described by the Allen and Dynes formula within the framework of the McMillan formalism.
Full Paper: https://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.8b01303
2018/03
Ashish Chhaganlal Gandhi and Jauyn Grace Lin
Superconductor Science and Technology 31(5), 055002, 2018
A new cost effective scheme of a microwave-assisted sol–gel route followed by a short annealing time is proposed to synthesize YBCO nanoparticles (NPs) of various sizes. The advanced techniques of synchrotron radiation x-ray diffraction (SRXRD) and electron spin resonance (ESR) are used to analyze the size effects on their magnetic/superconducting properties. The major interesting finding is that the size of YBCO NPs could confine the amount of oxygen content and consequently change the superconducting transition temperature (T C) of YBCO NPs. The ESR result demonstrates a sensitive probe to characterize surface defects in the oxygen-deficient YBCO NPs.
Full Paper: https://iopscience.iop.org/article/10.1088/1361-6668/aab0c5/meta
2017/09
Ashish Chhaganlal Gandhi, Ting Shan Chan, Sheng Yun Wu
Superconductor Science and Technology 30(10), 105010, 2017
We report on the crystal structure transformation and superconducting phase diagrams for a Pb m Bi 100− m (0< m< 100 in%) alloy. The superconducting coupling strength is resolved by analyzing the dependency of T C on the applied magnetic field. The phase diagram shows evidence for strong-coupling s-wave superconductivity for all alloys of Pb m Bi 100− m and the dependency of the superconducting parameters on the weight percent of each constituent phase is discussed in the phase diagram. Very strong coupling of 2Δ o/k B T C~ 5.174 is observed in the present Pb m Bi 100− m phase diagram.
Full Paper: https://iopscience.iop.org/article/10.1088/1361-6668/aa83d7/meta
2017/08
Ashish Chhaganlal Gandhi and Sheng Yun Wu
Scientific reports 7(1), 9442, 2017
We report the observation of strong electron-phonon coupling in intergranular linked BiIn superconductors over an infinite range mediated by low-lying phonons. An enhanced superconducting transition temperature was observed from the magnetization, revealing a main diamagnetic Meissner state below T C (0)= 5.86 (1) K and a critical field H C (0)= 1355 (15) Oe with an In 2 Bi phase of the composite sample. The electron-phonon coupling to low lying phonons is found to be the leading mechanism for observed strong-coupling superconductivity in the BiIn system. Our findings suggest that In 2 Bi is in the strong-coupling region with T C (0)= 5.62 (1) K, λ ep= 1.45, ω ln= 45.92 K and α= 2.23. The estimated upper critical field can be well-described by a power law with α value higher than 2, consistent with the strong electron-phonon coupling.
Full Paper: https://www.nature.com/articles/s41598-017-09831-9
2016/06
Ashish Chhaganlal Gandhi, Ting Shan Chan, Sheng Yun Wu
Journal of Alloys and Compounds 688, 61-68, 2016
We report on the influence of the nanosized effect on the structural transformation and superconducting properties of InSn nanoalloys with mean sizes ranging from ∼14 to 23 nm fabricated by controlling the argon pressure with the thermal evaporation method. A reversible process of phase transition between γ-Sn and β-InSn was observed using high energy synchrotron x-ray diffraction. An enhanced superconducting transition temperature was observed revealing the main diamagnetic Meissner state to be below TC = 6.22(5) K for the 14(2) nm InSn nanoalloys. Our experimental findings provide important information for controlling the superconducting properties and constituent phases in InSn nanoalloys.
Full Paper: https://www.sciencedirect.com/science/article/abs/pii/S0925838816320023
2016/01
Ashish Chhaganlal Gandhi and Sheng Yun Wu
Journal of Magnetism and Magnetic Materials 407, 155-159, 2016
Single phase ε-PbBi microcubes were synthesized using a simple thermal evaporation method. Synchrotron x-ray measurement of the crystal structure of the ε-PbBi microcubes revealed a space group of P63/mmc. Enhanced superconducting transitions were observed from the temperature dependent magnetization, showing a main diamagnetic Meissner state below a TC of ~8.66(2) K. An extremely strong superconducting strength (α=2.51(1)) and electron-phonon constant (λEP=2.25) are obtained from the modified Allen and Dynes theory, which give rise to higher TC superconductivity in this type of structure. The electron–phonon coupling to low lying phonons is found to be the leading mechanism for the observed strong-coupling superconductivity in the PbBi system.
Full Paper: https://www.sciencedirect.com/science/article/abs/pii/S0304885316300786
2015/05
Po-Yu Lin, Ashish Chhaganlal Gandhi, Sheng Yun Wu
Journal of Applied Physics 117(17), 17E316, 2015
We report the influence of the nanosized effect on the superconducting properties of bimetallic In2Bi nanoparticles. In this study, the temperature- and applied magnetic field-dependence of the magnetization were utilized to investigate the electron-phonon coupling effect while controlling particle sizes 〈d〉 from 21(2) to 42(5) nm. As the particle size decreases, the electron-phonon constant λEP decreases rapidly, signaling the short-range electron-phonon coupling effect which acts to confine the electrons within a smaller volume, thereby giving rise to a higher superconducting transition temperature TC. An enhanced superconducting transition was observed from the temperature dependence of magnetization, revealing a main diamagnetic Meissner state below TC ∼ 5.72(5) K for 〈d〉 = 31(1) nm In2Bi nanoparticles. The variation of the TC is very sensitive to the particle size, which might be due to crystallinity and size uniformity of the samples. The electron-phonon coupling to low lying phonons is found to be the leading mechanism for the observed strong-coupling superconductivity in the In2Bi system.
Full Paper: https://aip.scitation.org/doi/full/10.1063/1.4916106
2012/08
Ashish Chhaganlal Gandhi, Po-Hsun Shih, Sheng Yun Wu
Superconductor Science and Technology 25(10), 105006, 2012
Single crystal InSn nanocubes were synthesized using a simple thermal evaporation method and observed using high-resolution transmission electron microscope images. Enhanced superconducting transitions were observed from the magnetization, revealing a main diamagnetic Meissner state below 6.02 (5) K with β-InSn phase. The transition temperature reduced to zero as the applied magnetic field H a neared 2 T and a critical field H C0= 2.05 (5) T was obtained. An extremely weak superconducting strength α= 0.35 was obtained and revealed the coupling strength in InSn nanocubes to be weakened more than the BCS expectations indicated.
Full Paper:https://iopscience.iop.org/article/10.1088/0953-2048/25/10/105006/meta
