Effect of alloying in monolayer niobium dichalcogenide superconductors

Abstract

When sulfur and silicon are incorporated in monolayer 2H-NbSe2 the superconducting transition temperature, Tc, has been found to vary non-monotonically. This was assumed to be a manifestation of fractal superconductivity. Using first-principles calculations, we show that the nonmonotonic dependence of Tc is insufficient evidence for multifractality. A unifying aspect in our study are selenium vacancies in NbSe2, which are magnetic pair-breaking defects that we propose can be present in considerable concentrations in as-grown NbSe2. We show that sulfur and silicon can occupy the selenium sites and reduce the pair-breaking effect. Furthermore, when sulfur is incorporated in NbSe2, the density of states at the Fermi level and the proximity to magnetism in the alloy are both reduced compared to the parent compound. Based on our results, we propose an alternative explanation of the non-monotonic change in Tc which does not require the conjecture of multifractality.

van der Waals Self-Epitaxial Growth of Inch-Sized Superconducting Niobium Diselenide Films

“…It is noteworthy that the Se vacancies and residual oxides of NbSe 2 affect the superconducting transition temperature. 46,47 The ratio of Nb to Se in our NbSe 2 films is 1:1.98 according to the XPS results, which confirms the high quality of the synthesized NbSe 2 films.…”

“…The in-plane HRTEM image (Figure c) exhibits the distinct hexagonal lattice without the presence of moiré patterns, and the SAED patterns obtained from different domains in the NbSe 2 film (Figure S7d–f) also testify the lattice structure and orientation remain consistent from top to bottom, thereby demonstrating the top-down epitaxial selenization process. It is noteworthy that the Se vacancies and residual oxides of NbSe 2 affect the superconducting transition temperature. , The ratio of Nb to Se in our NbSe 2 films is 1:1.98 according to the XPS results, which confirms the high quality of the synthesized NbSe 2 films.…”

Controllable growth of wafer-scale monolayer transition metal dichalcogenides ternary alloys with tunable band gap

“…There are various methods to tune the band gap of TMDCs, such as strain engineering, alloying, functionalization, electrostatic gating [25][26][27][28][29][30][31]. Alloy is a flexible approach to tune the band structure and physical properties [32][33][34][35][36][37][38]. In the field of semiconductor science, scientists have been able to achieve continuously tunable electronic structures by alloying different semiconductors, such as CuIn x Ga 1−x Se 2 [39].…”