Restoration of superconductivity in high magnetic fields in UTe2

It was theoretically predicted more than 20 years ago [A. G. Lebed and K. Yamaji, Phys. Rev. Lett. 80, 2697 (1998)], that a triplet quasi-two-dimensional (Q2D) superconductor could restore its superconducting state in parallel magnetic fields, which are higher than its upper critical magnetic field, [Formula: see text]. It is very likely that, recently, such phenomenon has been experimentally discovered in the Q2D superconductor UTe2 by Nicholas Butch, Sheng Ran, and their colleagues and has been confirmed by Japanese–French team. We review our previous theoretical results using such a general method that it describes the reentrant superconductivity in the abovementioned compound and will hopefully describes the similar phenomena, which can be discovered in other Q2D superconductors.

Evaluating Superconductors through Current Induced Depairing

The phenomenon of superconductivity occurs in the phase space of three principal parameters: temperature T, magnetic field B, and current density j. The critical temperature T c is one of the first parameters that is measured and in a certain way defines the superconductor. From the practical applications point of view, of equal importance is the upper critical magnetic field B c 2 and conventional critical current density j c (above which the system begins to show resistance without entering the normal state). However, a seldom-measured parameter, the depairing current density j d , holds the same fundamental importance as T c and B c 2 , in that it defines a boundary between the superconducting and normal states. A study of j d sheds unique light on other important characteristics of the superconducting state such as the superfluid density and the nature of the normal state below T c , information that can play a key role in better understanding newly-discovered superconducting materials. From a measurement perspective, the extremely high values of j d make it difficult to measure, which is the reason why it is seldom measured. Here, we will review the fundamentals of current-induced depairing and the fast-pulsed current technique that facilitates its measurement and discuss the results of its application to the topological-insulator/chalcogenide interfacial superconducting system.

Electrical and Thermal Transport Properties of Layered Superconducting Ca10(Pt4As8)((Fe0.86Pt0.14)2As2)5 Single Crystal

We have synthesized single crystals of iron-based superconducting Ca10(Pt4As8)((Fe0.86Pt0.14)2As2)5 and performed extensive measurements on their transport properties. A remarkable difference in the behavior and a large anisotropy between in-plane and out-of-plane resistivity was observed. Disorder could explain the in-plane square-root temperature dependence resistivity, and interlayer incoherent scattering may contribute to the out-of-plane transport property. Along the ab plane, the estimated value of the coherence length is 15.5 Å. From measurements of the upper critical magnetic field Hc2 (T ≥ 20 K), we estimate Hc2(0) = 313 T. Thermal conductivity for Ca10(Pt4As8)((Fe0.86Pt0.14)2As2)5 is relatively small, which can be accounted for by the disorder in the crystal and the low-charge carrier density as verified by the Hall effect.