Superconductivity with Topological Non-trivial Surface States in NbC

Abstract

Quantum materials with non-trivial band topology and bulk superconductivity are considered superior materials to realize topological superconductivity. In this regard, we report detailed Density Functional Theory (DFT) calculations for NbC superconductor which shows the topologically non-trivial band structure. Bulk superconductivity at 8.9K is confirmed through DC magnetization measurements under Field Cooled (FC) and Zero Field Cooled (ZFC) protocols. This superconductivity is found to be of type-II nature as revealed by isothermal M-H measurements and thus calculated the Ginzberg-Landau parameter. A large intermediate state is evident from phase diagram, showing NbC to be a strong type-II superconductor. When compared with earlier reports on superconducting NbC, a non-monotonic relationship of critical temperature with lattice parameters is seen. In conclusion, it is clear that NbC is a type-II around 10K superconductor with topological non-trivial surface states.

Comprehensive review on topological superconducting materials and interfaces

“…Both NbC and TaC show superconductivity at relatively higher temperature which are 11.5K and 10.5K respectively [92][93][94][95][96][97]. These materials are found to have a type-II Dirac semimetal like band structure, which has been confirmed through both DFT calculations and ARPES measurements [93][94][95][96][97].…”

“…Other examples of centrosymmetric superconductors, which are supposed to show topological superconductivity, are transition metal carbides (TMCs) viz. NbC and TaC [92][93][94][95][96][97].…”

“…Both NbC and TaC show superconductivity at relatively higher temperature which are 11.5K and 10.5K respectively [92][93][94][95][96][97]. These materials are found to have a type-II Dirac semimetal like band structure, which has been confirmed through both DFT calculations and ARPES measurements [93][94][95][96][97]. NbC has a NaCl type crystal structure and its superconducting temperature strongly depend on the lattice parameters [98,99] which increases or decreases with stoichiometry of carbon [100].…”

“…(c) Evolutionof Wannier charge centers in various K-planes. Adapted from ref [97]. with permission of Springer nature.…”

Superconductivity and topological states in hexagonal TaC and NbC

“…The general experiment-detected Young's moduli were B537 GPa for TaC [26][27][28] and B493 GPa for NbC, 29,30 which can be explained by the bonding characters between the d orbitals of transition metal atoms and p orbitals of carbon atoms. Besides, NaCl-type TaC and NbC show superconductivity at a critical temperature in the range of 8 to 11 K. [31][32][33][34][35] Recently, several different research groups reported the topological properties and the nodal line characteristic in rocksalt-type NbC, 36,37 while another group reported NbC as a Dirac semimetal by combining theoretical calculations and angle resolved photoemission spectroscopy (ARPES) measurements. 34 In addition, the isostructural TaC is proposed as a topological superconductor candidate.…”