Ultrafast Charge Recombination in a Photoexcited Mott-Hubbard Insulator

Lenarčič, Zala; Prelovšek, P.

doi:10.1103/physrevlett.111.016401

Cited by 92 publications

(126 citation statements)

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“…In the absence of such a bath the only possible decay paths involve kinetic energy transfer (creation of particle-hole pairs) or spin excitations within the Hubbard model itself, where the relevant energy scales are the bandwidth t and the exchange coupling t 2 =ðU − VÞ, respectively [17]. For U ≫ V, t a large number of scattering events is required for recombination, leading to a decay rate that is exponentially small with U=t [17][18][19][20]. Owing to the weak electronphonon coupling in ET-F 2 TCNQ [5], and lack of efficient radiative emission, it is reasonable to assume that highfrequency molecular modes are the primary scattering partner for the rapid decay of hot quasiparticles observed in our experiment.…”

Section: (D)mentioning

confidence: 99%

Pressure-Dependent Relaxation in the Photoexcited Mott InsulatorET–F2TCNQ: Influence of Hopping and Correlations on Quasiparticle Recombination Rates

et al. 2014

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We measure the ultrafast recombination of photoexcited quasiparticles (holon-doublon pairs) in the one dimensional Mott insulator ET-F 2 TCNQ as a function of external pressure, which is used to tune the electronic structure. At each pressure value, we first fit the static optical properties and extract the electronic bandwidth t and the intersite correlation energy V. We then measure the recombination times as a function of pressure, and we correlate them with the corresponding microscopic parameters. We find that the recombination times scale differently than for metals and semiconductors. A fit to our data based on the time-dependent extended Hubbard Hamiltonian suggests that the competition between local recombination and delocalization of the Mott-Hubbard exciton dictates the efficiency of the recombination. The recombination of hot carriers in solids is a fundamental process of interest to nonlinear optics and to device applications, as well as a spectroscopic tool that exposes the physics of interacting microscopic degrees of freedom. "Hot electron" spectroscopy has been applied extensively to metals and semiconductors, for which well-established models have been developed.For direct gap semiconductors recombination occurs at a rate that depends on the joint density of states between valence and conduction bands ∝ð∂E v =∂kÞð∂E c =∂kÞ, and is thus expected to slow down with the square of the bandwidth τ ∝ t 2 . On the other hand, in the case of metals, the dynamics are well captured by the two-temperature model [1,2], which considers the energy stored in the optically excited nonequilibrium electron distribution as flowing into the lattice at a rate determined by the electronphonon coupling strength and by the electronic and lattice heat capacities. As the relaxation of hot electrons accelerates with smaller electronic specific heat, and because c e v is proportional to the density of states at the Fermi level [3], for metals relaxation should accelerate linearly with the reciprocal of the bandwidth τ ∝ 1=t.For solids with strongly correlated electrons, the dependence of nonequilibrium quasiparticle recombination rates on the microscopic parameters has not been systematically investigated and it is not well understood. In this Letter, we study the recombination of impulsively excited quasiparticles in a one dimensional Mott insulator, in which we tune electronic bandwidth and intersite correlation energy by applying external pressure. We find that the recombination of quasiparticles accelerates for increasing bandwidth, as expected for a metal, but with a dependence on microscopic parameters that is unique to the physics of electronic insulators in one dimension and that descends from a competition between local decay and coherent delocalization of photoexcited holon-doublon pairs [4].We study bis-(ethylendithyo)-tetrathiafulvalenedifluorotetracyano-quinodimethane (ET-F 2 TCNQ), a half filled organic salt with quasi-1D electronic structure, negligible electron-phonon interaction [5], and with electronic pr...

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Section: (D)mentioning

confidence: 99%

Pressure-Dependent Relaxation in the Photoexcited Mott InsulatorET–F2TCNQ: Influence of Hopping and Correlations on Quasiparticle Recombination Rates

et al. 2014

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“…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].…”

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

et al. 2014

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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...

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“…It was recently demonstrated that after such an interaction quench the order parameter m quickly relaxes to a quasistationary but nonthermal value [17] that is protected from further decay by the slow recombination rate of doublons and holes [27][28][29][30]. This transient state resembles properties of a photodoped system in which charge carriers are created by a short laser pulse.…”

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Ultrafast Quenching of the Exchange Interaction in a Mott Insulator

Mentink

Eckstein

2014

Phys. Rev. Lett.

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We investigate how fast and how effective photocarrier excitation can modify the exchange interaction Jex in the prototype Mott-Hubbard insulator. We demonstrate an ultrafast quenching of Jex both by evaluating exchange integrals from a time-dependent response formalism, and by explicitly simulating laser-induced spin precession in an antiferromagnet that is canted by an external magnetic field. In both cases, the electron dynamics is obtained from nonequilibrium dynamical mean-field theory. We find that the modified Jex emerges already within a few electron hopping times after the pulse, with a reduction that is comparable to the effect of chemical doping. PACS numbers: 75.78.Jp,71.10.Fd Magnetic long-range order and the dynamics of spins in magnetic materials are governed by the exchange interaction J ex , the strongest force of magnetism. Because J ex emerges from the Pauli principle and the electrostatic Coulomb repulsion between electrons, it is sensitive to purely nonmagnetic perturbations. This fact implies intriguing and largely unexplored possibilities for the ultrafast control of magnetism by femtosecond laser pulses, which is currently a very active research area [1]. In principle, laser-excitation can effect J ex by modulating the electronic structure (electron hopping, Coulomb repulsion) and by creating a nonequilibrium distribution of photoexcited carriers (photodoping). A modification of J ex has been discussed within the context of experiments on manganites [2-4], magnetic semi-conductors [5], and, using static field gradients, ultracold atoms in optical lattices [6,7]. While it might play a role as well in metallic ferromagnets [8][9][10][11], ultrafast demagnetization [12] and laser-induced magnetization reversal [13][14][15] seem at least partly understood in terms of a given time-independent J ex . Clearly, more theoretical work is needed to understand how effective a modification of J ex under nonequilibrium conditions can be, and how fast J ex can be modified. The latter touches the fundamental question for the time scale at which the description of spin dynamics in terms of a J ex emerges from the full electronic dynamics, before which J ex is not a valid concept at all. Although this question has not been directly addressed in the experiments mentioned above, an investigation of this ultimate limit of spin dynamics is in range using today's femtosecond laser technology.In general, the exchange interaction arises from a lowenergy description of the electronic states in terms of magnetic degrees of freedom. Recently, Secchi et al. defined the nonequilibrium exchange interaction via an effective action that governs the spin dynamics out of equilibrium, leading to an expression in terms of nonequilibrium electronic Green's functions [16]. Here, we apply this framework to the paradigm single-band Mott-Hubbard insulator at half-filling, for which the concept of exchange interaction in equilibrium is very well understood. To directly assess the nonequilibrium electron dynamics and evaluate th...

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Ultrafast Charge Recombination in a Photoexcited Mott-Hubbard Insulator

Cited by 92 publications

References 38 publications

Pressure-Dependent Relaxation in the Photoexcited Mott InsulatorET–F2TCNQ: Influence of Hopping and Correlations on Quasiparticle Recombination Rates

Pressure-Dependent Relaxation in the Photoexcited Mott InsulatorET–F2TCNQ: Influence of Hopping and Correlations on Quasiparticle Recombination Rates

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

Ultrafast Quenching of the Exchange Interaction in a Mott Insulator

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