Superluminal Spacetime Crystals Induced by Anomalous Velocity Modulation

TL;DR

This paper proposes a novel method to create optical spacetime crystals using anomalous velocity modulation in Weyl semimetals, enabling superluminal phase modulation and advanced light control at optical frequencies.

Contribution

It introduces a new approach to photonic spacetime crystals based on anomalous velocity in Weyl semimetals, demonstrating superluminal modulation and active nonreciprocal photonic effects.

Findings

Ultrafast superluminal phase modulation in Weyl semimetals

Unidirectional light transport below optical gap

Stimulated emission of volume plasmons near epsilon-near-zero point

Abstract

Time-modulated media offer powerful opportunities for controlling light, yet extending such concepts to optical frequencies has remained challenging. Here we propose a different route to photonic spacetime crystals based on modulation of the anomalous velocity in low-symmetry conductors, particularly Weyl semimetals. We show that when driven by a strong optical pump, the anomalous velocity of Bloch electrons induces an ultrafast spacetime modulation that propagates with a superluminal phase velocity relative to the dielectric background. This self-induced modulation enables unidirectional light transport below the optical gap and, near the epsilon-near-zero point, gives rise to collective parametric resonance and stimulated emission of volume plasmons. These findings identify Weyl semimetals as a promising platform for realizing optical spacetime crystals and open a pathway toward active and nonreciprocal photonic systems governed by quantum geometric effects.