Topologically nontrivial phases in superconducting transition metal carbides

Abstract

Topological superconductors have shown great potential in the search for unique quasiparticles such as Majorana fermions. Combining nontrivial band topology and superconductivity can lead to topological superconductivity due to the proximity effect. In this work, we used first principle calculations to predict that rock-salt phases of VC and CrC are superconducting with topologically nontrivial states. The phonon dispersions of these transition metal carbides displayed no imaginary frequencies, which suggests dynamic stability. Additionally, the presence of soft acoustic phonon bands supports the existence of Bardeen-Cooper-Schrieffer (BCS) superconductivity in rock-salt VC and CrC. Therefore, these transition metal carbides are practical candidates for studying topological superconductors and their associated Majorana bound states.

A general route to form topologically-protected surface and bulk Dirac fermions along high-symmetry lines

“…The study of their evolution with time-reversal symmetry breaking may be possible in compounds with ferromagnetic ground states. For example, the transition metal carbides, {Nb, Ta, V, Cr}C (O h ), have been recently verified to host k-mediated bulk Dirac cones within their metal d-orbital manifolds [43]. Whilst this compound series is non-magnetic, analogous physics can be expected to occur in the similarly structured transition metal nitride compounds, {Sc, Ti, V, Cr, Zr, Nb}N. These share remarkably similar band structures to the carbides [44], but CrN has a ferromagnetic ground state.…”

Superconductivity and topological aspects of the rocksalt carbides NbC and TaC

“…Other TMCs, such as δ-type VC and CrC, are also predicted to be superconductors with nontrivial topological band structures and, therefore, are candidates for searching for topological superconductivity [23]. Although both VC and CrC should exhibit relatively high critical temperatures [24][25][26][27], to date experimental evidence is inconsistent.…”

Time-reversal symmetry breaking in the superconducting state of ScS

“…the carbon, pnictogen, or chalcogen group, have been widely studied as they provide an exciting family of candidate materials where a range of exotic features has been observed over the years. For instance, NbC, TaC, MoC, VC, and CrC [21][22][23] exhibit superconductivity together with a nontrivial topological band structure. These compounds crystallize in a centrosymmetric cubic structure known as the rocksalt structure.…”