arXiv subjects

Peter Prelovsek

Publications and source records attributed to Peter Prelovsek.

At least 19 recordsLinked to original sources

arXiv2020

Similarity of thermodynamic properties of Heisenberg model on triangular and kagome lattices

Derivation of a reduced effective model allows for a unified treatment and discussion of the $J_1$-$J_2$ Heisenberg model on a triangular and kagome lattice. Calculating thermodynamic quantities, i.e. the entropy $s(T)$ and uniform susceptibility $χ_0(T)$, numerically on systems up to effectively $N=48$ sites we show by comparing to full-model results that low-$T$ properties are well represented within the reduced model. Moreover, we find in the spin-liquid regime similar variation of $s(T)$ as well as $χ_0(T)$ in both models down to $T \ll J_1$. In particular, the spin liquid appears to be characterized by Wilson ratio vanishing at low $T$, indicating on the low-lying singlet dominating over the triplet excitations.

cond-mat.str-el↗

arXiv2018

Spin subdiffusion in disordered Hubbard chain

We derive and study the effective spin model that explains the anomalous spin dynamics in the one-dimensional Hubbard model with strong potential disorder. Assuming that charges are localized, we show that spins are delocalized and their subdiffusive transport originates from a singular random distribution of spin exchange interactions. The exponent relevant for the subdiffusion is determined by the Anderson localization length and the density of electrons. While the analytical derivations are valid for low particle density, numerical results for the full model reveal a qualitative agreement up to half-filling.

cond-mat.str-el↗

arXiv2017

Counting local integrals of motion in disordered spinless-fermion and Hubbard chains

We develop a procedure which systematically generates all conserved operators in the disordered models of interacting fermions. Among these operators, we identify and count the independent and local integrals of motion (LIOM) which represent the hallmark of the many-body localization (MBL). The method is tested first on the prototype disordered chain of interacting spinless fermions. As expected for full MBL, we find for large enough disorder $N_M=2^M-1$ independent and quasi-local LIOM with support on $M$ consecutive sites. On the other hand, the study of the disordered Hubbard chain reveals that $3^M-1< N_M < 4^M/2$ which is less than required for full MBL but much more than in the case of spinless fermions.

cond-mat.str-el↗

arXiv2017

A new high-temperature quantum spin liquid with polaron spins

The existence of a quantum spin liquid (QSL) in which quantum fluctuations of spins are sufficiently strong to preclude spin ordering down to zero temperature was originally proposed theoretically more than 40 years ago, but its experimental realisation turned out to be very elusive. Here we report on an almost ideal spin liquid state that appears to be realized by atomic-cluster spins on the triangular lattice of a charge-density wave (CDW) state of 1T-TaS$_2$. In this system, the charge excitations have a well-defined gap of $\sim 0.3$ eV, while nuclear magnetic quadrupole resonance and muon spin relaxation experiments reveal that the spins show gapless quantum spin liquid dynamics and no long range magnetic order down to 70~mK. Canonical $T^{2}$ power-law temperature dependence of the spin relaxation dynamics characteristic of a QSL is observed from 200~K to $T_f= 55$ K. Below this temperature we observe a new gapless state with reduced density of spin excitations and high degree of local disorder signifying new quantum spin order emerging from the QSL.

cond-mat.str-el↗

arXiv2016

Distinctive response of many-body localized systems to strong electric field

We study systems which are close to or within the many-body localized (MBL) regime and are driven by strong electric field. In the ergodic regime, the disorder extends applicability of the equilibrium linear--response theory to stronger drivings, whereas the response of the MBL systems is very distinctive, revealing currents with damped oscillations. The oscillation frequency is independent of driving and the damping is not due to heating but rather due to dephasing. The details of damping depend on the system's history reflecting nonergodicity of the MBL phase, while the frequency of the oscillations remains a robust hallmark of localization. We show that the distinctive characteristic of the driven MBL phase is also a logarithmic increase of the energy and the polarization with time.

cond-mat.str-el↗

arXiv2015

Approximate conservation laws in perturbed integrable lattice models

We develop a numerical algorithm for identifying approximately conserved quantities in models perturbed away from integrability. In the long-time regime, these quantities fully determine correlation functions of local observables. Applying the algorithm to the perturbed XXZ model we find that the main effect of perturbation consists in expanding the support of conserved quantities. This expansion follows quadratic dependence on the strength of perturbation. The latter result together with correlation functions of conserved quantities obtained from the memory function analysis confirm feasibility of the perturbation theory.

cond-mat.str-el↗

arXiv2015

Local and Quasilocal Conserved Quantities in Integrable Systems

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 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. Besides 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.

cond-mat.stat-mech↗

arXiv2014

Breakdown of the generalized Gibbs ensemble for current-generating quenches

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.

cond-mat.str-el↗

arXiv2014

Unusual Two-stage Dynamics of the Spin-Lattice Polaron Formation

We follow the formation of a spin-lattice polaron after a quantum quench that simulates absorption of the pump{pulse in the time-resolved experiments. We discover a two-stage relaxation where spin and lattice degrees of freedom represent an integral part of the relaxation mechanism. In the first stage the kinetic energy of the spin-lattice polaron relaxes towards its ground state value while relaxation processes via spin and phonon degrees of freedom remain roughly independent. In the second, typically much longer stage, a subsequent energy transfer between lattice and spin degrees of freedom via the charge carrier emerges. The excess local spin energy radiates away via magnon excitations.

cond-mat.str-el↗

arXiv2011

Integrable Mott insulators driven by finite electric field

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

cond-mat.str-el↗

arXiv2011

Nonequilibrium quantum dynamics of a charge carrier doped into a Mott insulator

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.

cond-mat.str-el↗

arXiv2011

Nonequilibrium dynamics of the Holstein polaron driven by external electric field

This work represents a fundamental study of a Holstein polaron in one dimension driven away from the ground state by a constant electric field. Taking fully into account quantum effects we follow the time-evolution of the system from its ground state as the constant electric field is switched on at t = 0, until it reaches a steady state. At weak electron phonon coupling (EP) the system experiences damped Bloch oscillations (BO) characteristic for noninteracting electron band. An analytic expression of the steady state current is proposed in terms of weak EP coupling and large electric field. For moderate values of EP coupling the oscillations are almost critically damped and the system reaches the steady state after a short time. In the strong coupling limit weakly damped BO, consistent with nearly adiabatic evolution within the polaron band, persist up to extremely large electric fields. A traveling polaron under the influence of the electric field leaves behind a trail of phonon excitations absorbing the excess energy gained from the electric field. The shape of the traveling polaron is investigated in details.

cond-mat.other↗

arXiv2010

Nonlinear current response of an isolated system of interacting fermions

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 non-integrable 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.

cond-mat.str-el↗

arXiv2010

Freezing of spin dynamics and omega/T scaling in underdoped cuprates

The memory function approach to spin dynamics in doped antiferromagnetic insulator combined with the assumption of temperature independent static spin correlations and constant collective mode damping leads to omega/T scaling in a broad range. The theory involving a non universal scaling parameter is used to analyze recent inelastic neutron scattering results for underdoped cuprates. Adopting modified damping function also the emerging central peak in low-doped cuprates at low temperatures can be explained within the same framework.

cond-mat.str-el↗

arXiv2008

Many body localization in Heisenberg XXZ magnet in a random field

We numerically investigate Heisenberg XXZ spin-1/2 chain in a spatially random static magnetic field. We find that tDMRG simulations of time evolution can be performed efficiently, namely the dimension of matrices needed to efficiently represent the time-evolution increases linearly with time and entanglement entropies for typical chain bipartitions increase logarithmically. As a result, we show that for large enough random fields infinite temperature spin-spin correlation function displays exponential localization in space indicating insulating behavior of the model.

quant-ph↗

arXiv2005

Self-localization of composite spin-lattice polarons

Self-localization of holes in the Holstein t-J model is studied in the adiabatic limit using exact diagonalization and the retraceable path approximation. It is shown that the critical electron-phonon coupling λ_c decreases with increasing J and that this behavior is determined mainly by the incoherent rather than by the coherent motion of the hole. The obtained spin correlation functions in the localized region can be understood within a percolation picture where antiferromagnetic order can persist up to a substantial hole doping. These results restrict the possibility of self-localization of holes in lightly doped cuprates.

cond-mat.str-el↗

arXiv2002

Temperature Dependence of Hall Response in Doped Antiferromagnets

Using finite-temperature Lanczos method the frequency-dependent Hall response is calculated numerically for the t-J model on the square lattice and on ladders. At low doping, both the high-frequency RH* and the d.c. Hall coefficient RH0 follow qualitatively similar behavior at higher temperatures: being hole-like for T > Ts~1.5J and weakly electron-like for T < Ts. Consistent with experiments on cuprates, RH0 changes, in contrast to RH*, again to the hole-like sign below the pseudogap temperature T*, revealing a strong temperature variation for T->0.

cond-mat.str-el↗

arXiv2000

On the universal optical conductivity and single-particle relaxation in cuprates

The origin of the universal optical conductivity form sigma(omega) ~ (1-e^(omega/T))/omega established in numerical model studies of doped antiferromagnets and consistent with experiments on cuprates near optimal doping is discussed. It is shown that such a behaviour appears quite generally when the single-particle excitations are overdamped and their relaxation follows the marginal Fermi liquid concept. Relation to recent ARPES experiments is also discussed.

cond-mat.str-el↗