Proposal for realizing unpaired Weyl points in a three-dimensional periodically driven optical Raman lattice

TL;DR

This paper proposes a method to realize and control unpaired Weyl points in a 3D optical Raman lattice with ultracold atoms, enabling the study of chiral anomaly and topological phenomena in a highly tunable, nonequilibrium setting.

Contribution

It introduces a scheme to generate unpaired Weyl points using periodic driving in ultracold atom systems, overcoming static lattice constraints and enabling experimental exploration of chiral effects.

Findings

Eight Weyl points with tunable net chirality are demonstrated in the quasienergy spectrum.

A synthetic magnetic field induces a quantized charge current, evidencing the chiral magnetic effect.

The proposed setup is feasible with current ultracold-atom experimental techniques.

Abstract

In static lattice systems, the Nielsen-Ninomiya theorem enforces the pairing of Weyl points with opposite chiralities, which precludes the chiral magnetic effect (CME) in equilibrium. Periodic driving provides a viable route to circumvent this no-go constraint. Here, we propose a scheme to realize and control unpaired Weyl points using ultracold atoms in a three-dimensional (3D) optical Raman lattice under continuous periodic driving. By engineering distinct relative symmetries between the lattice and multiple Raman potentials, the configuration generates an effective 3D spin-orbit coupling and yields a tunable topological-insulator phase. Through adiabatic periodic modulation of this system, we show that eight Weyl points emerge in the quasienergy spectrum of the low-energy sector, whose net chirality can be precisely tuned. A nonzero total chirality directly corresponds to the formation of unpaired Weyl points. Furthermore, by implementing a synthetic magnetic field via laser-assisted tunneling in this setup, we demonstrate that the chirality imbalance drives a quantized charge current in the weak-field regime, providing a direct signature of the CME. We verify that the adiabatic condition of the driving protocol, as well as the proposed experimental preparation and detection techniques, are within reach of current ultracold-atom experiments. This work establishes a realistic and controllable platform for exploring chiral-anomaly physics and nonequilibrium topological phenomena linked to Weyl fermions.