Signatures of bosonic excitations in high-harmonic spectra of Mott insulators

Abstract

The high-harmonic spectrum of the Mott insulating Hubbard model has recently been shown to exhibit plateau structures with cutoff energies determined by nth-nearest-neighbor doublon-holon recombination processes. The spectrum thus allows one to extract the on-site repulsion U. Here, we consider generalizations of the single-band Hubbard model and discuss the signatures of bosonic excitations in high-harmonic spectra. Specifically, we study an electron-plasmon model which captures the essential aspects of the dynamically screened Coulomb interaction in solids and a multiorbital Hubbard model with Hund coupling which allows one to analyze the effect of local spin excitations. For the electron-plasmon model, we show that the high-harmonic spectrum can reveal information about the screened and bare on-site interaction, the boson frequency, as well as the relation between boson coupling strength and boson frequency. In the multiorbital case, string states formed by local spin excitations result in an increase of the radiation intensity and cutoff energy associated with higher-order recombination processes.

High-harmonic generation in spin-orbit coupled systems

“…It is a nonlinear process in which a system driven by light at a certain frequency can give rise to emission at multiples of this fundamental frequency [5,6]. In the condensed matter context, one of the interesting aspects is that the harmonic spectrum carries information about the microscopic model, like the band structure or interaction parameters [6][7][8][9].…”

“…Which of these two processes dominates the emission has been debated for a long time, and a unified HHG mechanism applicable to a wide range of solids is still lacking [12]. Recently, the scope of HHG studies has been extended to strongly correlated systems [8,9,[13][14][15][16], disordered systems [17][18][19][20], the effects of spin-polarized defects [21], spin or multiferroic systems [22,23], HHG in graphene and transition metal dicalchogenides [24,25], to mention a few.…”

High-order nonlinear optical response of a twisted bilayer graphene

“…This phenomenon has attracted interest not only for compact frequency converter applications [12,13] but also as a probe of electron dynamics in intense optical fields [14]. Among various systems such as semiconductors [15][16][17][18][19][20][21][22][23][24][25], superconductors [26][27][28], strongly correlated systems [29][30][31][32][33][34], quantum magnets [35][36][37], and topological insulators [38,39], Dirac materials have turned out to have extremely large nonlinear susceptibility from the mid-infrared [40][41][42] down to the teraherz [43][44][45] frequency regimes. In particular, nonlinear response of graphene has been studied extensively [46][47][48][49][50].…”

Correlation effects in high-harmonic generation from finite systems

“…In the finite-size limit, however, electron-electron correlations are of importance as alluded to in HHG experiments with monolayer materials [21] and predicted for pump-probe HHG [31,32]. To investigate beyond mean-field electronelectron correlations in HHG, several effective Hamiltonian models have been developed and applied [2,[33][34][35][36][37][38].…”