Nonlinear Dirac Cones

TL;DR

This paper introduces a new class of nonlinear Dirac cones in a 2D Chern insulator model that are robust to perturbations, with tunable Berry phase and observable topological phases, revealing a nonlinear-induced topological transition.

Contribution

It demonstrates the existence of nonlinear Dirac cones with non-quantized Berry phase and a novel topological phase transition induced by mean-field nonlinearity.

Findings

Nonlinear Dirac cones are robust to local perturbations.

Berry phase of these cones can be continuously tuned.

A nonlinear-induced topological phase transition occurs.

Abstract

Physics arising from two-dimensional~(2D) Dirac cones has been a topic of great theoretical and experimental interest to studies of gapless topological phases and to simulations of relativistic systems. Such $2$D Dirac cones are often characterized by a $\pi$ Berry phase and are destroyed by a perturbative mass term. By considering mean-field nonlinearity in a minimal two-band Chern insulator model, we obtain a novel type of Dirac cones that are robust to local perturbations without symmetry restrictions. Due to a different pseudo-spin texture, the Berry phase of the Dirac cone is no longer quantized in $\pi$, and can be continuously tuned as an order parameter. Furthermore, in an Aharonov-Bohm~(AB) interference setup to detect such Dirac cones, the adiabatic AB phase is found to be $\pi$ both theoretically and computationally, offering an observable topological invariant and a fascinating example where the Berry phase and AB phase are fundamentally different. We hence discover a nonlinearity-induced quantum phase transition from a known topological insulating phase to an unusual gapless topological phase.