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Researchers used intense mid-infrared laser pulses to study high-harmonic generation in Sr2CuO3, a one-dimensional cuprate material that behaves as a Mott insulator. Above a critical electric field of 6 MV/cm, they observed characteristic redshifts in harmonic frequencies that indicate the material is transitioning from its insulating state to a metallic one. Theoretical simulations using dynamical mean-field theory suggest these frequency shifts arise from electronic structure changes occurring within each cycle of the oscillating laser field, a phenomenon unique to strongly correlated electron systems.
Why it matters
This work demonstrates that high-harmonic spectroscopy can track ultrafast electronic transitions in strongly correlated materials on sub-cycle timescales, potentially enabling new methods to study and control quantum materials. The technique could provide insights into phase transitions in complex materials that are relevant for future electronic and quantum computing applications.
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⚠️ Preprint – Noch nicht peer-reviewed
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Abstract: Solids in an intense laser field show high-harmonic generation (HHG), which can provide information on carrier dynamics and band structures in weakly correlated systems. In strongly correlated systems, a laser field can induce a transition between the various electronic phases formed by the entanglement of charge, spin, and orbital degrees of freedom via carrier generation. The HHG accompanying this process can reflect information on the nonequilibrium electronic-state dynamics along the oscillating field-an aspect that remains unresolved to date. Here, we show that an intense mid-infrared (MIR) pulse induces melting of a Mott-insulator state in a one-dimensional cuprate, Sr2CuO3, the evolution of which leaves a trace in the HH spectra. When the electric-field amplitude exceeds 6 MV/cm, carriers are efficiently generated and each harmonic frequency decreases from odd multiples of the MIR frequency. Dynamical mean-field theory (DMFT) presents a possibility that these redshifts originate from a series of electronic-structure reconstructions in each electric-field cycle during the melting of the Mott-insulator state, which modifies the radiation phase from carrier recombination cycle-by-cycle. This phenomenon is negligible in rigid-band systems. This experimental-theoretical study suggests that HH spectroscopy has the potential to obtain information on the cycle-by-cycle dynamics of nonequilibrium transitions in correlated materials.
Source: High-harmonic generation during ultrafast melting of a Mott insulating state