Superconductivity in the repulsive Hubbard model: an asymptotically exact weak-coupling solution

TL;DR

This paper provides an asymptotically exact weak-coupling solution for the superconducting transition temperature in the Hubbard model, revealing unconventional pairing states across various densities.

Contribution

It introduces a novel RG-based method to compute T$_c$ in the weak-coupling limit, valid for arbitrary densities and independent of initial cutoff.

Findings

Explicit T$_c$ calculations for different densities

Identification of unconventional superconducting states

Validation of cutoff independence in the RG approach

Abstract

We study the phase diagram of the Hubbard model in the limit where U, the onsite repulsive interaction, is much smaller than the bandwidth. We present an asymptotically exact expression for T$_c$, the superconducting transition temperature, in terms of the correlation functions of the non-interacting system which is valid for arbitrary densities so long as the interactions are sufficiently small. Our strategy for computing T$_c$ involves first integrating out all degrees of freedom having energy higher than an unphysical initial cutoff $\Omega_0$. Then, the renormalization group (RG) flows of the resulting effective action are computed and T$_c$ is obtained by determining the scale below which the RG flows in the Cooper channel diverge. We prove that T$_c$ is independent of $\Omega_0$. Using this method, we find a variety of unconventional superconducting ground states in two and three dimensional lattice systems and present explicit results for T$_c$ and pairing symmetries as a function of the electron concentration.