Ising Superconductivity and Magnetism in NbSe2

Abstract

Recent studies on superconductivity in NbSe2 have demonstrated a large anisotropy in the superconducting critical field when the material is reduced to a single monolayer. Motivated by this recent discovery, we use density-functional theory (DFT) calculations to quantitatively address the superconducting properties of bulk and monolayer NbSe2. We demonstrate that NbSe2 is close to a ferromagnetic instability, and analyze our results in the context of experimental measurements of the spin susceptibility in NbSe2. We show how this magnetic instability, which is pronounced in a single monolayer, can enable sizable singlet-triplet mixing of the superconducting order parameter, contrary to contemporary considerations of the pairing symmetry in monolayer NbSe2, and discuss approaches as to how this degree of mixing can be addressed quantitatively within our DFT framework. Our calculations also enable a quantitative description of the large anisotropy of the superconducting critical field, using DFT calculations of monolayer NbSe2 in the normal state.

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