Probing broken time-reversal symmetry with tailored-light photocurrents

TL;DR

This paper demonstrates a novel method using tailored laser fields to generate and analyze photocurrents for probing broken time-reversal symmetry in materials, advancing ultrafast spectroscopy techniques.

Contribution

It introduces a new approach combining bichromatic laser fields to selectively break symmetries and detect TRS-breaking phases without external magnetic fields.

Findings

Tailored light can induce forbidden photocurrents in TRS-invariant systems.

The method can distinguish materials with intrinsic TRS-breaking.

The approach is validated through ab-initio simulations and experiments.

Abstract

Light-field-driven photocurrents represent a powerful tool for generating photocurrents without external bias in light-matter systems that lack inversion symmetry. While these photocurrents are used in electronic applications, such as current sources, switches, and photovoltaics, their presence can also be used to probe material properties in and out of equilibrium, such as topology. Here we advance this path of light-field-driven photocurrent spectroscopy by utilizing tailored laser fields for ultrafast photocurrent generation to study time-reversal symmetry (TRS) broken phases. We employ combinations of bichromatic linearly-polarized laser beams that individually respect mirror (spatial) and time-reversal symmetry, individually precluding photocurrents, but when combined can break symmetries and generate photocurrents. We show, both theoretically and experimentally, that unique choices of the relative polarization angle and two-color phase imposes a forbidden photocurrent selection rule in TRS-invariant systems, as the tailored light maintains TRS while breaking all other spatial symmetries. We then employ state-of-the-art ab-initio simulations to validate this physical mechanism, and, crucially, predict its breaking in materials with intrinsically-broken TRS, creating a background free signal for magnetism and Chern physics. Our work paves way for probing TRS-broken phases of matter in an ultrafast time-resolved manner, not requiring the application of external magnetic fields or even circularly-polarized electric fields.