Attosecond spectral singularities in solid-state high-harmonic generation

Abstract

Strong field driven electric currents in condensed matter systems open new frontiers in petahertz electronics. In this regime new challenges arise as the role of the band structure and the quantum nature of electron-hole dynamics have yet to be resolved. Here we reveal the underlying attosecond dynamics that dictates the temporal evolution of carriers in multi-band solid state systems, via high harmonic generation (HHG) spectroscopy. We demonstrate that when the electron-hole relative velocity approaches zero, enhanced quantum interference leads to the appearance of spectral caustics in the HHG spectrum. Introducing the role of the dynamical joint density of states (JDOS) we identify its direct mapping into the spectrum, exhibiting singularities at the spectral caustics. By probing these singularities, we visualize the structure of multiple unpopulated high conduction bands. Our results open a new path in the control and study of attosecond quasi-particle interactions within the field dressed band structure of crystals.Induced by the strong field interaction, HHG provides a unique spectroscopic scheme to visualize the coherent evolution of petahertz currents inside solids.Since the first observation [1], solid HHG opened a door into the study of the electronic structure and dynamics in crystals [2,3,4,5,6,7], multiple band dynamics [8,9,10,11] and complex many-body phenomena [12] in crystalline and amorphous systems [9]. For a moderate field strength the electron-hole dynamics are often described semi-classicaly by a single valence and conduction band of

Super-resolution lightwave tomography of electronic bands in quantum materials

“…Angle-resolved photoelectron spectroscopy has championed electronic band-structure mapping (10)(11)(12)(13) in samples of sufficient size, measured at ultrahigh vacuum conditions. All-optical techniques, such as harmonic sideband (HSB) (14-17) and highharmonic generation (HHG) (18)(19)(20)(21)(22)(23)(24)(25)(26)(27), promise in situ probing of even microscopically small and/or atomically thin solids in ambient. Yet, HHG mapping encounters challenges: Atomically strong lightwaves inherently spread electrons broadly throughout the Brillouin zone (BZ) (20) and induce electronic interferences (21) as well as transport among multiple bands.…”

Neighboring Atom Collisions in Solid-State High Harmonic Generation

“…Subsequent investigation about delocalization of HHG in ZnO predicted by a Wannier-Bloch approach, whereby an electron ionized from one site in the periodic lattice may recombine at another one, seems to support this viewpoint [23]. Very recently, similar angular dependence of HHG has also been observed in Reference [30] (see Figure 2 of the supplementary information in [30]), where the angular dependence of the enhancement of HHG was attributed to an enhanced constructive interference of the interband currents at Van Hove singularities.…”

“…The imaginary parts of TDM are shown in Figure S1 in Supplementary Materials. The driving laser wavelength we used in our simulation is 1.3 μm, the same as in the experiments [21,30]. The pulse duration is 10 laser cycles and the peak field amplitude is 1.2 VÅ −1 , which are chosen to correspond to the experimental conditions.…”

Crystal-momentum-resolved contributions to multiple plateaus of high-order harmonic generation from band-gap materials

“…High-order harmonic generation (HHG) in solids has attracted great attention since its experimental observation in 2011 [1], and its underlying mechanism is still being debated [2][3][4][5][6][7][8][9][10][11][12]. HHG from band-gap materials can be used to produce novel vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) light sources [5,13], to study the dynamics of electrons on their natural timescales [6,14], and to investigate the properties of these materials [15][16][17][18][19][20].…”