Tailored-light photocurrent spectroscopy for probing time-reversal symmetry-broken phases

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. We employ combinations of bichromatic linearly-polarized laser beams that individually respect mirror and time-reversal symmetry (TRS). Hence they do not lead to a field-driven photocurrent individually, but when superposed can break individual symmetries and generate photocurrents. For unique choices of the relative polarization angle and two-color phase the tailored light exhibits TRS while breaking all other crystal symmetries, which imposes a forbidden photocurrent selection rule in TRS-invariant systems as we show both theoretically and experimentally. We employ state-of-the-art \textit{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.