Dirac-Weyl fermions with arbitrary spin in two-dimensional optical superlattices

TL;DR

This paper proposes a quantum simulation platform using ultracold atoms in optical lattices to realize Dirac-Weyl fermions with arbitrary pseudospin, revealing novel phases and quantum effects.

Contribution

It introduces a method to simulate Dirac-Weyl fermions with any pseudospin in optical lattices, expanding the understanding of relativistic particles in engineered quantum systems.

Findings

Identification of semimetallic phase for half-integer pseudospin s

Discovery of metallic phase with flat zero-energy band for integer s

Observation of rich anomalous quantum Hall effects and multirefringent Klein tunneling

Abstract

Dirac-Weyl fermions are massless relativistic particles with a well-defined helicity which arise in the context of high-energy physics. Here we propose a quantum simulation of these paradigmatic fermions using multicomponent ultracold atoms in a two-dimensional square optical lattice. We find that laser-assisted spin-dependent hopping, specifically tuned to the $(2s+1)$-dimensional representations of the $\mathfrak{su}$(2) Lie algebra, directly leads to a regime where the emerging massless excitations correspond to Dirac-Weyl fermions with arbitrary pseudospin $s$. We show that this platform hosts two different phases: a semimetallic phase that occurs for half-integer $s$, and a metallic phase that contains a flat zero-energy band at integer $s$. These phases host a variety of interesting effects, such as a very rich anomalous quantum Hall effect and a remarkable multirefringent Klein tunneling. In addition we show that these effects are directly related to the number of underlying Dirac-Weyl species and zero modes.