Superconductivity and topological aspects of the rock-salt carbides NbC and TaC

Abstract

Superconducting materials with a nontrivial band structure are potential candidates for topological superconductivity. Here, by combining muon-spin rotation and relaxation ($\mu$SR) methods with theoretical calculations, we investigate the superconducting and topological properties of the rock-salt-type compounds NbC and TaC (with$T_c$ = 11.5 and 10.3 K, respectively). At a macroscopic level, the magnetization and heat-capacity measurements under applied magnetic field provide an upper critical field of 1.93 and 0.65 T for NbC and TaC, respectively. The low-temperature superfluid density, determined by transverse-field $\mu$SR and electronic specific-heat data, suggest a fully-gapped superconducting state in both NbC and TaC, with a zero-temperature gap ${\Delta }_0=1.90$ and 1.45 meV, and a magnetic penetration depth ${\lambda }_0$ = 141 and 77 nm, respectively. Band-structure calculations suggest that the density of states at the Fermi level is dominated by the Nb $4d$- (or Ta $5d$-) orbitals, which are strongly hybridized with the C $p$-orbitals to produce large cylinder-like Fermi surfaces, similar to those of high-$T_c$ iron-based superconductors. Without considering the spin-orbit coupling (SOC) effect, the first Brillouin zone contains three closed node lines in the bulk band structure, protected by time-reversal and space-inversion symmetry. When considering SOC, its effects in the NbC case appear rather modest. Therefore, the node lines may be preserved in NbC, hence proposing it as a potential topological superconductor.

10 pages, 12 figures, accepted by Physical Review B

References in corpus (10)

• Superconducting proximity effect and Majorana fermions at the surface of a topological insulator
• Superconductivity in the vicinity of antiferromagnetic order in CrAs
• Pressure induced superconductivity on the border of magnetic order in MnP
• Upper critical field, Hall effect and magnetoresistance in the iron-based layered superconductor LaFeAsO_{0.9}F_{0.1-δ}
• Hall effect and magnetoresistance in the normal state of the superconductor LaO${}_{0.9}$F${}_{0.1-x}$FeAs
• Momentum space imaging of Cooper pairing in a half-Dirac-gas topological superconductor (a helical 2D topological superconductor)
• Topological semimetals and topological insulators in rare earth monopnictides
• Comparison of different methods for analyzing $\mu$SR line shapes in the vortex state of type-II superconductors
• Detection of an Unconventional Superconducting Phase in the Vicinity of the Strong First-Order Magnetic Transition in CrAs Using ^75As-Nuclear Quadrupole Resonance
• Superconductivity in the WP single crystal

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• High critical field superconductivity at ambient pressure in MoB${}_2$ stabilized in the P6/mmm structure via Nb substitution
• Superconducting ground state of nonsymmorphic superconducting compound Zr${}_2$Ir
• Time-reversal-symmetry Breaking in the Superconducting State of ScS
• Direct Observation of the Scale Relation between Density of States and Pairing Gap in a Dirty Superconductor
• ZrNb(CO) RF superconducting thin film with high critical temperature in the theoretical limit
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• Low-temperature thermal expansion of the topological material candidates $\beta$-PtBi${}_2$ and $\beta$-Bi${}_2$Pd
• Discovery of the Type-II Superconductor Ta${}_4$Rh${}_2$C${}_{1-\delta }$ with a High Upper Critical Field
• Nodeless superconductivity and topological nodal states in molybdenum carbide
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