Multiple topological electronic phases in superconductor MoC

Abstract

The search for a superconductor with non-s-wave pairing is important not only for understanding unconventional mechanisms of superconductivity but also for finding new types of quasiparticles such as Majorana bound states. Materials with both topological band structure and superconductivity are promising candidates as p + ip superconducting states can be generated through pairing the spin-polarized topological surface states. In this work, the electronic and phonon properties of the superconductor molybdenum carbide (MoC) are studied with first-principles methods. Our calculations show that nontrivial band topology and superconductivity coexist in both structural phases of MoC, namely, the cubic α and hexagonal γ phases. The α phase is a strong topological insulator and the γ phase is a topological nodal line semimetal with drumhead surface states. In addition, hole doping can stabilize the crystal structure of the α phase and elevate the transition temperature in the γ phase. Therefore, MoC in different structural forms can be a practical material platform for studying topological superconductivity and elusive Majorana fermions.

Superconductivity enhancement in phase-engineered molybdenum carbide/disulfide vertical heterostructures

“…Indeed, through the Lifshitz-Kosevich formalism, we extract fairly light effective masses, that is, m α = (0.3 ± 0.3) m 0 , m β = (0.13 ± 0.05) m 0 , and m γ = (0.7 ± 0.3) m 0 , where m 0 is the bare electron mass. Recent DFT calculations indicate that γ-MoC might display a nontrivial electronic topology, being a Dirac nodal line semimetal, which could become superconducting upon hole doping (12). The same calculations indicate that the Fermi surface should be composed of additional, larger Fermi surface sheets not detected in this study, probably because the measurements should be performed under higher fields.…”

“…Therefore, transition metal carbides (TMCs) stand as an attractive platform for studying the intrinsic properties of superconductivity in two dimensions (11). It is interesting to notice that the different phases of molybdenum carbide, including α, β, and γ phases, were recently predicted to display topologically nontrivial electronic bulk bands that would lead to unconventional topological surface states (12,13). These bulk and related surface states could be harvested to induce unconventional, and hopefully topological, superconductivity through the proximity effect (14) with a superconductor such as α-phase Mo 2 C.…”

Superconductivity and topological aspects of the rocksalt carbides NbC and TaC

“…Only recently, the carbon-defective δ and γ phase of MoC 1−x (with T c = 14.3 and 8.5 K) could be synthesized under high-temperature highpressure conditions (1700 • C, 6-17 GPa), and their crystal structures and physical properties be studied via different techniques [19][20][21]. Moreover, in both δ and γ MoC, firstprinciples calculations could show the coexistence of SC with nontrivial band topology [22].…”

Topologically nontrivial phases in superconducting transition metal carbides

“…However, the superconductivity of VC, CrC, NbC, and TaC follows the BCS theory, so these materials are not strongly correlated systems. Additionally, many previous studies have succesfully used GGA and LDA exchange correlation functionals to compute the properties of similar superconducting transition metal carbides 11,[36][37][38][39] . Consequently, we do not need to make use of DFT+U or DMFT for our calculations.…”

“…TSHs, however, can be complex and consequently difficult to create, which hinders further research into these types of TSCs. In addition, most TSHs have relatively low SC transition temperatures, usually below 4 K 11 .…”