Robust Floquet-induced gap in irradiated graphite

Abstract

Floquet engineering provides an emerging pathway for tailoring the electronic states of quantum materials through time-periodic drive. A critical step along this direction is achieving light-induced modifications of the dynamical electronic structure, such as avoided-crossing gap at the Floquet Brillouin zone boundary, via efficient coupling of electrons with the coherent light-field. Here, we report robust Floquet-induced gap in bulk graphite that persists despite the presence of interlayer coupling and photo-excitation. Using time- and angle-resolved photoemission spectroscopy with intense mid-infrared pumping, we directly reveal Floquet-induced gaps at resonance points both in the valence and conduction bands, accompanied by coherent Floquet sidebands. The gap and sidebands coexist with photo-excited carriers, yet their distinct timescales allow us to disentangle their origins. Our demonstration of robust Floquet-induced gaps establishes graphite as a platform for coherent manipulation of Dirac fermions and realization of light-engineered quantum phases.

Figures (4)

• Figure : Fig. 1. Schematic illustration for light-induced avoided-crossing gap in Dirac cone of graphene/graphite. (a) Schematic of MIR pumped TrARPES experiment. The inset shows the Brillouin zone of graphite and dispersions near H and K. (b,c) Conical dispersion in the equilibrium state (b) and light-induced gap opening at the Floquet resonance points upon resonant driving with $\hbar\omega$ (c).
• Figure : Fig. 2. Observation of light-induced gap, Floquet-Volkov sideband, photo-excited carriers and their dynamical evolution upon pumping. (a)-(g) Dispersion images measured at different delay times upon pumping with photon energy $\hbar\omega$ = 415 meV at pump fluence of 5.2 mJ/cm$^2$. The inset shows the optical image of the graphite sample and the Brillouin zone. The white dot in the optical image represents the probe beam spot size. (h)-(m) Differential image obtained by subtracting data measured at $\Delta$t = -200 fs (a) from data in (b)-(g). (n) Integrated intensity of the photo-excited CB (P1), Floquet-Volkov sideband (S2, S3) and VB (G4) as a function of delay time over regions marked in (c) and (i). (o) A schematic summary of the observed dispersion upon pumping.
• Figure : Fig. 3. Observation of light-induced gap in the conduction band and valence band, and extraction of the gap size from EDC analysis. (a)-(b) Dispersion image measured upon pumping (a) and at 200 fs after pumping (b). (c)-(d) EDCs extracted from (a) and (b)respectively. Tick marks indicate peak positions in the EDCs. (e)-(h) Zoom-in EDCs at resonance points of VB and CB with fitting peaks appended. (i)-(j) Schematic summary of dispersions upon and at 200 fs with fitting data appended.
• Figure : Fig. 4. Dynamical evolution of the light-induced gap, confirming its Floquet origin. (a)-(e) The second-derivative images measured at different delay times. (f)-(j) EDCs extracted from data in Fig. 2(a) and 2(d)-(g) respectively. Tick marks indicate peak positions in the EDCs. (k) EDCs at resonance points for various delays, with fitted results appended. (l) Extracted Floquet-induced gap at different delay times. The black curve is the same as S3 in Fig. 2(n).