Interband versus intraband currents in high-harmonic generation from solids
In plain words
An intense infrared laser shining on a crystal makes it emit light at many multiples of the laser frequency (high harmonics). Two pictures compete: electrons accelerating within one energy band, or electrons and holes recombining across the band gap.
Precise statement
Bulk or monolayer crystals (ZnO, $\mathrm{SiO_2}$, GaSe, $\mathrm{MoS_2}$) driven by a mid-infrared field with Keldysh parameter $\gamma < 1$ below the damage threshold. Quantity: the fraction of the harmonic yield in each order from the interband polarization (electron-hole recollision) versus the intraband current (nonparabolic band motion, Bloch-like oscillation), as a function of order, field strength and wavelength. An answer is an experimental observable that separates the two contributions unambiguously (harmonic phase, ellipticity or two-color response) in at least one material, matched by a parameter-free microscopic calculation.
What would settle it
Phase-resolved harmonic measurements in a well-characterized crystal compared with ab initio time-dependent calculations that include propagation through the sample.
Status in the literature
Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
Different materials and drive wavelengths have been reported to favor different dominant mechanisms; no unified microscopic account exists as of 2024.
Problems built on this one
Special cases
- Can harmonic spectra measure Berry curvature of a crystal? · open
- Why solid-state harmonic models need femtosecond dephasing times · open
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