Study of Nb_0.18Re_0.82non-centrosymmetric superconductor in the normal and superconducting states

Abstract

We examine the evidence for multiband superconductivity and non s-wave pairing in the noncentrosymmetric superconductor Nb 0.18 Re 0.82 , using electrical transport, magnetization and specific heat measurements. In the normal state, both the evolution of resistivity with temperature and with magnetic field support a multiband picture. In the superconducting state, the Werthamer, Helfand and Hohenberg (WHH) model cannot adequately describe the temperature dependence of the upper critical field, H c2 (T ), over the whole temperature range measured. In addition, the observed H c2 (0) exceeds the Pauli limit, suggesting non-s-wave pairing. Interestingly, the Kadowaki-Woods ratio and Uemura plot reveal a behavior in Nb 0.18 Re 0.82 which is similar to that found in unconventional superconductors. The temperature dependence of the lower critical field, H c1 (T ), follows an anomalous T 3 behavior and the derived normalized superfluid density (ρ s ) is well explained using a nodeless two-gap description. Phase-fluctuation analysis conducted on the reversible magnetization data, reveals a significant deviation from the mean-field conventional s-wave behavior. This trend is interpreted in terms of a non s-wave spin-triplet component in the pairing symmetry as might be anticipated in a non-centrosymmetric superconductor where anti-symmetric spin-orbit coupling plays a dominant role.

Unconventional superconductivity in CuxBi2Se3 from magnetic susceptibility and electrical transport

“…In NbN, the phase fluctuations are proposed to be important for forming a pseudogap state [14]. For Cu x Bi 2 Se 3 , we also find a similar trend according to the results reported by Kriener [80,81], high-T c cuprates [80,81,112], high-T c iron-based superconductors [82][83][84][85][86], noncentrosymmetric superconductors [56,57,113,114], conventional metal superconductors [81,113], and 4 He [82].…”

“…To study the temperature dependence of the superfluid density n s (T), we have analyzed the μ 0 H c1 (T) extracted in criterion I. The n s (T) is related to the λ as well as equivalently the μ 0 H c1 , which is given by [56,57]…”

Upper critical magnetic field in NbRe and NbReN micrometric strips

“…217) [9][10][11][12]. This non-centrosymmetric nature of the material leads to intriguing and unconventional physical properties such as the time-reversal symmetry breaking observed with muon-spin rotation and relaxation studies [13] and large values of the upper critical magnetic fields [11,14], which are above the Pauli paramagnetic limit [15,16]. In the case of thin films, the structure of NbRe is polycrystalline with grains of small dimensions, typically of the order of 2-3 nm [7,8,17].…”

“…When λ so = 0, it is [23]. The WHH theory has been used to interpret the temperature dependence of the critical fields of several superconductors [20,[24][25][26][27][28][29][30][31][32][33][34][35][36], including non-centrosymmetric materials for which experiments give contradictory results [14,[37][38][39][40][41][42][43]. In particular, values of the critical field larger than H p (0) have been experimentally observed.…”

Nonrelativistic axion electrodynamics in $p+is$ superconductors

“…A mixture of triplet and singlet Cooper pairings which breaks time reversal symmetry has been theoretically studied in different contexts, showing exotic properties including nontrivial bulk electromagnetic and gravitational responses 52,53 , quantized surface thermal Hall effects 52,[54][55][56] , chiral Majorana fermions propagating along the magnetic domain wall on the surface 24 , and high order topology 57 . Recently, there has been experimental evidence of triplet pairing gap functions with spontaneous time reversal symmetry breaking in real materials 58,59 .…”