Synthesizing Strong-Coupling Kohn-Luttinger Superconductivity in 2D Van der Waals materials

TL;DR

This paper demonstrates a novel inter-layer s-wave Kohn-Luttinger superconductivity with high transition temperatures in layered 2D materials, driven by strong inter-layer interactions and robust against Coulomb repulsion.

Contribution

It reveals a strong-coupling inter-layer Kohn-Luttinger superconductivity mechanism with elevated $T_c$ in multi-layer Hubbard models, supported by simulations and ab initio predictions.

Findings

Strong pairing attraction $V^{*}$ emerges without collective mode mediation.

Transition from quadratic to linear $V^{*}$ scaling with $U$, enhancing $T_c$.

Proposes real 2D van der Waals materials to realize this superconductivity.

Abstract

The Kohn-Luttinger (KL) mechanism of pairing, which describes superconductivity emergent from repulsive interactions, typically yields Cooper pairs at high angular-momentum ($\ell > 0$) and extremely low transition temperatures ($T_c$). Here, we reveal an inter-layer s-wave ($\ell=0$) KL superconductivity with greatly elevated $T_c$ in a multi-layer Hubbard model, which prototypes stacked two-dimensional (2D) electrons in layered van der Waals materials. By employing determinant quantum Monte Carlo and dynamical mean-field theory simulations, we show that a strong pairing attraction $V^{*}$, without the mediation of collective modes, can emerge between inter-layer electrons in the system. As inter-layer repulsion $U$ increases, $V^{*}$ evolves from a conventional KL relation of $V^{*} \propto -U^2$, to a linear strong-coupling scaling of $V^{*} \propto -U$, resulting in enhanced superconductivity at large $U$. This strong-coupling KL pairing is robust against changes in lattice geometries and dimensionalities, and it can persist, in the presence of a large remnant Coulomb repulsion $U^{*}$ between pairing electrons. Using \textit{ab initio} calculations, we propose a few 2D layered van der Waals materials that can potentially realize and control this unconventional superconductivity.