One of the pivotal questions in the physics of high-temperature superconductors is whether the low-energy dynamics of the charge carriers is mediated by bosons with a characteristic timescale. This issue has remained elusive as electronic correlations are expected to greatly accelerate the electron-boson scattering processes, confining them to the very femtosecond timescale that is hard to access even with state-of-the-art ultrafast techniques. Here we simultaneously push the time resolution and frequency range of transient reflectivity measurements up to an unprecedented level, enabling us to directly observe the ∼16 fs build-up of the e ective electron-boson interaction in hole-doped copper oxides. This extremely fast timescale is in agreement with numerical calculations based on the t-J model and the repulsive Hubbard model, in which the relaxation of the photo-excited charges is achieved via inelastic scattering with short-range antiferromagnetic excitations.A fter almost 30 years of intensive experimental and theoretical efforts to understand the origin of high-temperature superconductivity in copper oxides, a consensus about the microscopic process responsible for the superconducting pairing is still lacking. The large Coulomb repulsion U 1 eV between two electrons occupying the same lattice site is believed to have fundamental consequences for the normal state of these systems 1 , and it is not clear whether a BCS-like bosonic glue that mediates the electron interactions and eventually leads to pairing can still be defined [2][3][4] . The fundamental issue can be reduced to the question whether the electronic interactions are essentially unmediated and instantaneous, or whether the low-energy physics, including superconductivity, can be effectively described in terms of interactions among the fermionic charge carriers mediated by the exchange of bosons. The problem can be rationalized by considering the Hubbard model, in which the instantaneous virtual hopping of holes into already occupied sites (with an energy cost of U ) inherently favours an antiferromagnetic (AF) coupling J = 4t 2 h /U between neighbouring sites, where t h is the nearestneighbour hopping energy. As a consequence, antiferromagnetic fluctuations with a high-energy cutoff of 2J U naturally emerge as a candidate 5 for mediating the low-energy electronic interactions, on a characteristic retarded timescale of the order ofh/2J .In principle, time-resolved optical spectroscopy 6 may be used to prove the existence of an effective retarded boson-mediated interaction, provided that the temporal resolution is of the order of the inverse bosonic-fluctuation scale (for example,h/2J for AF fluctuations) and the optical properties are probed over a sufficiently broad frequency range, to extract the dynamics of the electron-boson coupling. Recent advances in ultrafast optical spectroscopy have succeeded in separately fulfilling these requirements. For example, high-temporal-resolution (<15 fs) experiments 7,8 have been carried out to investigate the...

We study real-time dynamics of a charge carrier introduced into undoped Mott insulator propagating under a constant electric field F on the t-J ladder and square lattice. We calculate quasistationary current. In both systems adiabatic regime is observed followed by the positive differential resistivity (PDR) at moderate fields where carrier mobility is determined. Quantitative differences between ladder and 2-dimensional (2D) system emerge when at large fields both systems enter negative differential resistivity (NDR) regime. In the ladder system Bloch-like oscillations prevail, while in 2D the current remains finite, proportional to 1/F . The crossover between PDR and NDR regime in 2D is accompanied by a change of the spatial structure of the propagating spin polaron. [12,13] and the relaxation of correlated systems after the photoexcitations [14,15], represent the well-studied examples of nonequilibrium phenomena which are important both for fundamental understanding of strongly correlated systems as well as for their potential applications.Most of theoretical studies so far considered the breakdown of undoped MI, when threshold value of the electric field exceeds experimental value [9] by a few orders of magnitude (see discussion in Ref. [11]). It indicates that other transport mechanism becomes active at energies much lower than the Mott-Hubbard gap. In this Letter we inveqstigate a nonequilibrium response of a charge carrier doped into the insulator and driven by an uniform electric field F . Understanding of this subject on one hand widens our knowledge of a charge carrier doped into the antiferromagnetic (AFM) background [16,17], on the other, it represents a fundamental problem of a quantum particle moving in a dissipative medium [18].Having in mind strongly correlated systems, we investigate the t-J model where the particle driven by a constant electric field dissipates the energy by inelastic scattering on spin degrees of freedom. We use numerical approaches to treat t-J model at zero temperature on two different system geometries, i.e., a ladder with periodic boundary conditions and an infinite 2-dimensional (2D)

Nonlinear real-time response of interacting particles is studied on the example of a one-dimensional tight-binding model of spinless fermions driven by electric field. Using equations of motion and numerical methods we show that for a nonintegrable case at finite temperatures the major effect of nonlinearity can be taken into account within the linear response formalism extended by a renormalization of the kinetic energy due to the Joule heating. On the other hand, integrable systems show on constant driving a different universality with a damped oscillating current whereby the frequency is related but not equal to the Bloch oscillations.

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...

We establish a relation between two hallmarks of integrable systems: the relaxation towards the generalized Gibbs ensemble (GGE) and the dissipationless charge transport. We show that the former one is possible only if the so called Mazur bound on the charge stiffness is saturated by local conserved quantities. As an example we show how a non-GGE steady state with a current can be generated in the one-dimensional model of interacting spinless fermions with a flux quench. Moreover an extended GGE involving the quasi-local conserved quantities can be formulated for this case.PACS numbers: 75.10.Pq, 05.60.Gg,05.70.Ln Recent advances in experiments on ultracold atoms together with new computational techniques have significantly broadened our understanding of relaxation processes in closed many-body quantum systems. It is commonly accepted that in generic macroscopic systems the long-time averages of local observables coincide with the results for the statistical Gibbs ensemble [1][2][3][4] and are uniquely determined by few parameters related to conserved quantities, in particular the system's energy and particle number. Due to the presence of macroscopic number of conserved quantities such a simple scenario is not applicable to integrable systems [5][6][7]. However, there is a large and still growing evidence that relaxation in the latter systems is consistent with the generalized Gibbs ensemble (GGE) [8][9][10][11][12], where the density matrix is determined not only by the Hamiltonian H and particle number N but also by other local conserved quantitiesIn this Letter we focus on the relaxation dynamics of one of the most studied integrable models: the model of interacting spinless fermions, being equivalent to the anisotropic Heisenberg (XXZ) model for which the set of Q i has been established [13,14]. We show that ρ GGE as generated only by local integrals of motion Q i doesn't exhaust all generic stationary states in the metallic (easy plane) regime. Instead, there are cases for which one should lift the requirement of locality of the conserved quantities and allow also for quasi-local integrals of motion [15,16]. In this Letter we call them non-GGE states, however we stress that these states can be viewed also as "extended GGE", where the extension concerns the locality of operators. Such operators have the parity opposite to local ones Q i . We identify one of such quasi-local quantities as the time-averaged particle current operator and we construct as well as verify it explicitly.It has been well recognized that integrable systems in spite of interaction reveal anomalous transport properties at finite inverse temperatures β = 1/T , e.g. the dissipationless particle current. This property is manifested by a nonvanishing charge stiffness D(β < ∞) [17][18][19], which in turn is bounded from below by the local conservation laws via the Mazur bound [18,20]. The dissipationless transport and the relaxation towards GGE are probably the most prominent hallmarks of integrability, still they have been studied indep...

We report the electric transport and thermodynamic properties of the skutterudite-related La3Co4Sn13 and La3Rh4Sn13 superconductors. Applying an external pressure to La3Rh4Sn13, the resistive superconducting critical temperature Tc decreases, while the critical temperature of La3Co4Sn13 is enhanced with increasing pressure. The positive pressure coefficient dTc/dP correlates with a subtle structural transition in La3Co4Sn13 and is discussed in the context of lattice instabilities. Specific heat data show that both compounds are typical BCS superconductors. However, La3Rh4Sn13 also exhibits a second superconducting phase at higher temperatures, which is characteristic of inhomogeneous superconductors. We calculate the specific heat for an inhomogeneous superconducting phase, which agrees well with experimental C(T ) data for La3Rh4Sn13. We also found that an applied pressure reduces this second superconducting phase.

We outline a procedure for counting and identifying a complete set of local and quasilocal conserved operators in integrable lattice systems. The method yields a systematic generation of all independent, conserved quasilocal operators related to the time average of local operators with a support on up to M consecutive sites. As an example, we study the anisotropic Heisenberg spin-1/2 chain and show that the number of independent conserved operators grows linearly with M. In addition to the known local operators, there exist novel quasilocal conserved quantities in all the parity sectors. The existence of quasilocal conserved operators is shown also for the isotropic Heisenberg model. Implications for the anomalous relaxation of quenched systems are discussed as well.

We develop a method for extracting the steady nonequilibrium current from studies of driven isolated systems, applying it to the model of a one-dimensional Mott insulator at high temperatures. While in the nonintegrable model the nonequilibrium conditions can be accounted for by internal heating, the integrability leads to a strongly nonlinear dc response with a vanishingly small dc conductivity in the linear-response regime. The finding is consistent with equilibrium results for the dc limit of the optical conductivity determined in the presence of a weak and decreasing perturbation.