A direct transition between a Neel ordered Mott insulator and a $d_{x^2-y^2}$ superconductor on the square lattice

TL;DR

This paper investigates a unique, continuous phase transition between a Neel ordered Mott insulator and a $d_{x^2-y^2}$ superconductor on the square lattice, challenging traditional Landau theory by involving charged vortices and topological band insulator properties.

Contribution

It introduces a novel theoretical framework for a direct transition between these phases, highlighting the role of vortex quantum numbers and topological aspects.

Findings

Identifies a continuous transition forbidden by Landau theory.

Shows vortices carry charge and spin, enabling the transition.

Connects ordered phases to a topological band insulator.

Abstract

In this paper we study a bandwidth-controlled direct, continuous, phase transition from a Mott insulator, with easy plane Neel order, to a fully gapped $d_{x^2-y^2}$ superconductor with a doubled unit cell on the square lattice, a transition that is forbidden according to the Landau paradigm. This transition is made possible because the vortices of the antiferromagnet are charged and the vortices of the superconductor carry spins. These nontrivial vortex quantum numbers arise because the ordered phases are intimately related to a topological band insulator. We describe the lattice model as well as the effective field theory.