Unconventional superconductivity in PdxBi2Se3 whiskers
Studies of temperature dependence of magnetoresistance for PdxBi2Se3 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/kBTc = 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 2ao, which indicates a strong fermionic interaction with phonons in the PdxBi2Se3 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 ⩽ Tc/TF ⩽ 0.1, which confirms the unconventional superconductivity in the investigated whiskers.
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