Two-bands Ising superconductivity from Coulomb interactions in monolayer NbSe2
Sebastian Hörhold, Juliane Graf, Magdalena Margańska, Milena Grifoni
Abstract
Abstract The nature of superconductivity in monolayer transition metal dichalcogenides is still under debate. It has already been argued that repulsive Coulomb interactions, combined with the disjoint Fermi surfaces around the K , K ʹ valleys and at the Γ point, can lead to superconducting instabilities in monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mtext>NbSe</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> . Here, we demonstrate the two-bands nature of superconductivity in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mtext>NbSe</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> . It arises from the competition of repulsive long range intravalley and short range intervalley interactions together with Ising spin–orbit coupling. The two distinct superconducting gaps, one for each spin-orbit split band, consist of a mixture of s -wave and f -wave components. Their different amplitudes are due to the difference between the normal densities of states of the two bands at the Fermi level. Using a microscopic multiband BCS approach, we derive and self-consistently solve the gap equation, demonstrating the stability of nontrivial solutions in a realistic parameter range. We find a universal behavior of the temperature dependence of the gaps and of the critical in-plane field which is consistent with various sets of existing experimental data.