Mechanism of ultrafast relaxation of a photo-carrier in antiferromagnetic spin background

Abstract

We study the relaxation mechanism of a highly excited charge carrier propagating in the antiferromagnetic background modeled by the t-J Hamiltonian on a square lattice. We show that the relaxation consists of two distinct stages. The initial ultrafast stage with the relaxation time τ ∼( /t0)(J/t0) −2/3 (where t0 is the hopping integral and J is the exchange interaction) is based on generation of string states in the close proximity of the carrier. This unusual scaling of τ is obtained by means of comparison of numerical results with a simplified t-Jz model on a Bethe lattice. In the subsequent (much slower) stage local antiferromagnetic excitations are carried away by magnons. The relaxation time on the two-leg ladder system is an order of magnitude longer due to the lack of string excitations. This further reinforces the importance of string excitations for the ultrafast relaxation in the two-dimensional system.In a large number of generic time-dependent manybody systems, it is conjectured that strong electronic correlations give rise to extremely fast timescales of relevant relaxation processes. In general, the nonequlibrium evolution of a simple quantum system is a complex problem with only a few exactly solvable cases, and strong interactions between charge carriers usually make the problem even harder. Although advanced numerical approaches give important information about nonequlibrium dynamics, this dynamics is in many cases too complex to be comprehended in terms of a simple physical picture. Distinguishing different elementary excitations in time domain therefore represents one of the major goals of the present research of nonequilibirum many-body systems. In this context, a rapid development of time-resolved experiments in condensed-matter systems [1][2][3][4][5][6][7] and cold atomic gases [8] provide both a challenge for theory as well as a testbed for new ideas. A large body of current theoretical research is based on studies of Hubbard-like models far from equilibrium, and it focuses both on relaxation dynamics after a sudden quench [9-13] and steadystate properties as a consequence of constant driving [14][15][16][17][18][19][20][21][22][23][24][25][26].Understanding the dynamics of photo-induced charge carriers in Mott insulators may contribute to unravelling still elusive mechanism of high-T C superconductivity, in addition, it is as well indispensable for applications of novel materials in future electronic and photovoltaic technologies. Many recent studies focused on dynamics of photo-induced carriers, i.e., doublons and holons [27][28][29][30][31][32][33][34][35][36][37][38], in particular on their nonradiative recombination process [37][38][39][40][41][42][43]. Experimentally, photo-induced carriers have been observed in, e.g., insulating cuprates, where they decay within a few hundreds of femtoseconds [44].In this manuscript, we investigate a phenomenon which precedes the recombination of photo-induced carriers, i.e., we consider a rapid exchange of energy between photo-induced carriers and...

Snapshots of the retarded interaction of charge carriers with ultrafast fluctuations in cuprates

“…The advantage of this method over the standard ED in the equilibrium regime follows from a systematic construction of states with distinct configurations of local antiferromagnetic excitations in the proximity of the hole. In addition, it remains efficient even when applied to non-equilibrium systems on short and intermediate timescales, as long as the antiferromagnetic disturbance caused by the local quench remains within the boundaries of generated excitations 26,27 . We first construct the parent state where H kin represents the kinetic energy term of the t-J model andH J represents the spin-flip term of the Heisenberg part of the t-J model (spin-flip denotes overturned spins with respect to the Néel state;H J erases two neighbouring spin-flips created by the propagating hole).…”

“…The latter method was recently successfully applied to describe non-equilibrium properties of a charge carrier propagating in a local antiferromagnetic background 26,27 . The advantage of this method over the standard ED in the equilibrium regime follows from a systematic construction of states with distinct configurations of local antiferromagnetic excitations in the proximity of the hole.…”

Dynamics of screening in photodoped Mott insulators

“…Therefore updated Weiss fields can be obtained from the impurity Dyson equations (9) and (10) by replacing the impurity Green's functions with the local lattice Green's functions. The solution of the impurity problem (8) via (11), the impurity and lattice Dyson equations (9) and (10) and (12) and (13), the EDMFT approximation for the lattice self-energies, and the EDMFT self-consistency equations for G loc and W loc form the closed set of nonequilibrium EDMFT equations. The nonequilibrium EDMFT calculation is implemented as a stepwise time-propagation, which starts from an equilibrium EDMFT solution at time t = 0.…”

“…In a system with sufficiently large gap, the relaxation proceeds in two stages. In the first stage, the photodoped carriers "thermalize" within the Hubbard band due to electron-electron scattering, or loose their kinetic energy due to scattering with phonons [10,11] or spins [12][13][14]. Scattering processes, which change the number of doublon-hole pairs, necessary for thermalization, depend exponentially on the gap size [15,16].…”

Delocalized carriers in the t−J model with strong charge disorder

“…In a case of single carrier instead of diagonalizing the Hamiltonian in the full Hilbert space we use the limited functional Hilbert space [68]. Such approach has successfully been applied to the studies on the real-time dynamics of t-J and Holstein models [69][70][71][72] and it is briefly explained also in the Supplemental material [73]. In this approach one accounts for all spin excitations in the closest vicinity of the holde but only for a selected more distant excitations.…”