Nodeless superconducting gaps in noncentrosymmetric superconductorPbTaSe2with topological bulk nodal lines

Abstract

Low-temperature thermal conductivity measurements were performed on single crystal of PbTaSe2, a noncentrosymmetric superconductor with topological bulk nodal lines in the electronic band structure. It is found that the residual linear term κ0/T is negligible in zero magnetic field. Furthermore, the field dependence of κ0/T exhibits a clear "S"-shape curve. These results suggest that PbTaSe2 has multiple nodeless superconducting gaps. Therefore, the spin-triplet state with gap nodes does not play an important role in this noncentrosymmetric superconductor with strong spin-orbital coupling. The fully gapped superconducting state also meets the requirement of a topological superconductor, if PbTaSe2 is indeed the case.

μSR study of the noncentrosymmetric superconductor PbTaSe2

“…While our data alone cannot distinguish the isotropic 2-gap state from such a mixed state, comparison with data from other groups makes the fully gapped state most likely. STM measurements show fully gapped superconductivity 31 , while thermal conductivity 30 and H C2 measurments 29 are both consistent with multiple fully gapped bands. This picture also matches the theoretical expectations of Samokhin et al 18 where a noncentrosymmetric superconductor with pairing caused by phonons should exhibit two-band nodeless superconductivity.…”

“…As H C2 (T = 0) is still below the Pauli limit, this has been interpreted as evidence of multi-band superconductivity rather than exotic pairing symmetry. Furthermore, thermal conductivity measurements are consistent with fully gapped superconductivity as there is no linear term at low temperature, and the field dependence suggests multi-band superconductivity 30 . STM 31 and ARPES 32 results support this multi-band picture as they both show multiple relevant bands near the Fermi surface.…”

“…30 and the relation H c2 = φ 0 /(2πξ 2 ) to determine ξ. The resultant penetration depth is shown in Figure 4.…”

Superconducting topological surface states in the noncentrosymmetric bulk superconductor PbTaSe 2

“…However, the existence of a Dirac point and the spin texture of these two surface bands have not yet been confirmed because the Dirac point energy ( E D ) is located at several hundred millielectron volts above E F and, hence, not accessible to ARPES. For the bulk superconducting state, although all recent bulk measurements indicate that PbTaSe 2 is likely a conventional BCS s-wave superconductor ( 20 , 22 – 25 ), it has been proposed that the superconductivity on TSSs induced by the proximity effect in PbTaSe 2 can be stronger than that in TI/s-wave superconductor heterostructures ( 26 ). Therefore, it is critically important to confirm the existence of a superconducting TSS and to investigate the potential signature of any MBS in PbTaSe 2 .…”

Unconventional superconductors with spin-orbit interaction

“…Superconductivity has also been observed in nodal line semimetal PdTaSe 2 [131,146]. Experimental results of the London penetration depth [147] and thermal conductivity [148] have indicated fully gapped superconductivity. The peculiar doughnut-shaped Fermi surface in the nodal line semimetals may induce topological superconductivity.…”