Unconventional superconductivity in PdxBi2Se3 whiskers

A.A. Druzhinin; I.P. Ostrovskii; Yu.M. Khoverko; M.P. Mykytiuk

doi:10.15330/pcss.24.3.558-563

Authors

A.A. Druzhinin Lviv Polytechnic National University, Lviv, Ukraine
I.P. Ostrovskii Lviv Polytechnic National University, Lviv, Ukraine
Yu.M. Khoverko Lviv Polytechnic National University, Lviv, Ukraine
M.P. Mykytiuk Lviv Polytechnic National University, Lviv, Ukraine

DOI:

https://doi.org/10.15330/pcss.24.3.558-563

Keywords:

whiskers, superconductivity, bismuth selenium, Curie temperature

Abstract

Studies of temperature dependence of magnetoresistance for Pd_xBi₂Se₃ whiskers in the temperature range 1.6-77K in magnetic field up to 10 T were carried out. Crystals were grown by chemical transport reaction method in closed bromide system. The source and crystallization zone temperatures were 1100 K and 780 K, respectively. Doping of the crystals was carried out during the growth process with palladium impurity to concentrations of (1 – 2) × 10¹⁹ cm⁻³. In the low-temperature region beginning at a temperature of 5 K and reaching a temperature 3.5 K, a sharp decrease in resistance was observed, which is associated with the transition to superconducting state. Based on the analysis of the temperature dependence of the resistance at fixed magnetic fields, the Curie temperature Tc₁=5.3 K and Tc₂=3.5 K as well as the upper critical magnetic field Bc₂=1.45 T and 0.25 T were determined. The established parameters indicates in II type supercondor. This is indicated by the ratio Δ₀/k_BT_c = 2.0, which exceeds BCS limit of 1.76 and indicates a relatively large value of the superconducting gap Δ₀=0.8 meV. The determined ratio A/γ², which establishes the relationship between the electron-electron and electron-phonon interaction, is about of 2a_o, which indicates a strong fermionic interaction with phonons in the Pd_xBi₂Se₃ superconductor. The estimated value of the ratio of the Curie temperature to the effective Fermi temperature equal to 0.04 also falls within the range of 0.01 ⩽ T_c/T_F ⩽ 0.1, which confirms the unconventional superconductivity in the investigated whiskers.

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