Friedel oscillations and chiral superconductivity in monolayer NbSe<sub>2</sub>.

Siegl, Julian; Bleibaum, Anton; Wan, Wen; Kurpas, Marcin; Schliemann, John; Ugeda, Miguel M; Marganska, Magdalena; Grifoni, Milena · Nat Commun · 2025

basic_science · Level V

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Abstract

The nature of the dominant pairing mechanism in some two-dimensional transition metal dichalcogenides is still debated. Focusing on monolayer 1H-NbSe<sub>2</sub>, we show that superconductivity can be induced by the Coulomb interaction when accounting for screening effects on the trigonal lattice with multiple orbitals. Using ab initio based tight-binding parametrizations for the relevant low-energy d-bands, we evaluate the screened interaction microscopically. In the direct space, we find pronounced Friedel oscillations, a key to the Kohn-Luttinger mechanism for superconductivity. The momentum-resolved gap equations predict at the critical temperature T<sub>c</sub> two degenerate solutions of <math xmlns="http://www.w3.org/1998/Math/MathML"> <msup><mrow><mi>E</mi></mrow> <mrow><mo>'</mo></mrow> </msup> </math> symmetry, signalling the unconventional nature of the pairing. Their complex linear combination, i.e., a chiral gap with p-like symmetry, provides the ground state of the model. Our prediction of a fully gapped chiral phase well below T<sub>c</sub> is in good agreement with the spectral function extracted from tunnelling spectroscopy measurements.