arXiv subjects

X. Zotos

Publications and source records attributed to X. Zotos.

At least 19 recordsLinked to original sources

arXiv2026

Step conductance and spin selectivity in a one dimensional tailored conical magnet

Using an S-matrix formulation we evaluate the conductance of a one dimensional free electron gas in double exchange interaction with a classical conical magnet. We find integer conductance steps depending on the energy window of the incoming electrons for conical magnets described by a fictitious magnetic field of different orientations and modulated profile. The conductance windows, that we attribute to potential or diffractive scattering, are characterised by spin selectivity depending on the fictitious magnetic field direction and chirality. Furthermore, we study the conductance of a conical soliton lattice and discuss a rationalization of all the conductance data for an incoming electron with arbitrary spin direction in terms of scattering of an electron with spin along the conical axis.

cond-mat.mes-hall↗

arXiv2025

A note on the deformation of 1D ferromagnetic domain walls due to double exchange interaction with a free electron gas

Using an S-matrix formulation we evaluate the thermodynamic potential and conductance of a Bloch or Néel magnetic wall interacting with a one dimensional free electron gas via a double exchange interaction. The minimization of the elastic magnetic energy plus electronic thermodynamic potential indicates that for chemical potential larger than the magnetic interaction the domain wall is generally deformed to a thin wall, while for magnetic interaction larger than the chemical potential tends towards wide walls. In contrast, for a double wall configuration the deformation is always towards wide walls. For the single as well as the double magnetic wall configurations the conductance monotonically decreases with decreasing wall width. The thermodynamic potential and conductance of Bloch and Néel magnetic domain walls are identical within this prototype model.

cond-mat.mes-hall↗

arXiv2024

Magnetothermal transport in the spin-1/2 easy-axis antiferromagnetic chain

By an exact analytical approach we study the magnetothermal transport in the spin-1/2 easy-axis Heisenberg model, in particular the thermal conductivity and spin Seebeck effect as a function of anisotropy, magnetic field and temperature. We stress a distinction between the commnon spin Seebeck effect with fixed boundary conditions and the one (intrinsic) with open boundary conditions. In the open boundary spin Seebeck effect we find exceptional features at the critical fields between the low field antiferromagnetic phase, the gapless one and the ferromagnetic at high fields. We further study the development of these features as a function of easy-axis anisotropy and temperature. We point out the potential of these results to experimental studies in spin chain compounds, candidates for spin current generation in the field of spintronics.

cond-mat.str-el↗

arXiv2023

Spin Seebeck effect in the classical easy-axis antiferromagnetic chain

By molecular dymanics simulations we study the spin Seebeck effect as a function of magnetic field in the prototype classical easy-axis antiferromagnetic chain, in the far-out of equilibrium as well as linear response regime. We find distinct behavior in the low field antiferromagnetic, middle field canted and high field ferromagnetic phase. In particular, in the open boundary system at low temperatures, we observe a divergence of the spin current in the spin-flop transition between the antiferromagnetic and canted phase, accompanied by a change of sign in the generated spin current by the temperture gradient. These results are corroborated by a simple spin-wave phenomenological analysis and simulations in the linear response regime. They shed light on the spin current sign change observed in experiments in bulk antiferromagnetic materials.

cond-mat.stat-mech↗

arXiv2021

Operator growth in a quantum compass model on a Bethe lattice

The time evolution of local operators in quantum compass models is characterized by simplicity as it can be represented as expanding and contracting strings of operators. Here we present an analytical solution to the problem of growth of a local energy operator in a quantum compass model on a Bethe lattice. We find a linear increase in time of the average operator length and a diffusive spreading of the operator length distribution. By a moment method we evaluate the local energy autocorrelation function that shows a Lorentzian shape at low frequencies. Furthermore, by a stochastic method we visualize the expansion of the string cloud.

cond-mat.stat-mech↗

arXiv2021

Ballistic magnetic thermal transport coupled to phonons

Motivated by thermal conductivity experiments in spin chain compounds, we propose a phenomenological model to account for a ballistic magnetic transport coupled to a diffusive phononic one, along the line of the seminal two-temperature diffusive transport Sanders-Walton model. Although the expression for the effective thermal conductivity is identical to that of Sanders-Walton, the interpretation is entirely different, as the "magnetic conductivity" is replaced by an "effective transfer conductivity" between the magnetic and phononic component. This model also reveals the fascinating possibility of visualizing the ballistic character of magnetic transport, for appropriately chosen material parameters, as a two peak counter-propagating feature in the phononic temperature. It is also appropriate for the analysis of any thermal transport experiment involving a diffusive component coupled to a ballistic one.

cond-mat.stat-mech↗

arXiv2019

Scattering of spinon excitations by potentials in the 1D Heisenberg model

By a semi-analytical Bethe ansatz method and a T-matrix approach we study the scattering of a spinon, the elementary quantum many-body topological excitation in the 1D Heisenberg model, by local and phonon potentials. In particular, we contrast the scattering of a spinon to that of a free spinless fermion in the XY model to highlight the effect of strong correlations. For the one spinon scattering in an odd-site chain, we find a regular behavior of the scattering coefficients. In contrast, in an even-site chain there is a transfer of transmission probability between the two spinon branches that grows exponentially with system size. We link the exponent of the exponential behavior to the dressed charge that characterizes the critical properties of the 1D Heisenberg model, an interplay of topological and critical properties. The aim of this study is a microscopic understanding of spinon scattering by impurities, barriers or phonons, modeled as prototype potentials, an input in the analysis of quantum spin transport experiments.

cond-mat.stat-mech↗

arXiv2019

Dressed excitations, thermodynamics and relaxation in the 1D XXZ Heisenberg model

In this note, we discuss the low and high temperature contribution of Thermodynamic Bethe Ansatz (TBA) dressed excitations in the thermodynamics and energy-magnetization relaxation within the Generalized Hydrodynamics approach in the linear response regime. In particular, we show how the temperature dependent dispersions of the excitations reproduce well known behavior of the specific heat, magnetic susceptibility, spin and energy Drude weights. In this context, we derive a further formulation of the Drude weights from the finite wavevector relaxation. Furthermore, we contrast the TBA description of thermodynamics and dynamics in terms of a multitude of string excitations to that in terms of a single quasi-particle in low energy effective theories.

cond-mat.stat-mech↗

arXiv2017

High temperature dynamics in quantum compass models

We analyze the high temperature spin dynamics of compass models using a moment expansion. We point out that the evaluation of moments maps to the enumeration of paths in a branching process on the lattice. This mapping to a statistical mechanics combinatorics problem provides an elegant visualization of the analysis. We present results for the time dependent spin correlation function (which is of relevance to NMR experiments) for two compass models: the Kitaev honeycomb model and two-dimensional compass model.

cond-mat.stat-mech↗

arXiv2016

A TBA description of thermal transport in the XXZ Heisenberg model

It is shown that the Bethe ansatz formulation of the easy-plane 1D Heisenberg model thermodynamics (TBA) by Takahashi and Suzuki and the subsequent analysis of the spin Drude weight, also reproduces the thermal Drude weight and magnetothermal coefficient obtained by the Quantum Transfer Matrix method (QTM). It can also be extended to study the far-out of equilibrium energy current generated at the interface between two semi-infinite chains held at different temperatures.

cond-mat.stat-mech↗

arXiv2016

Light induced magnetization in a spin S=1 easy-plane antiferromagnetic chain

The time evolution of magnetization induced by circularly polarized light in a $S=1$ Heisenberg chain with large, easy--plane anisotropy is studied numerically and analytically. Results at constant light frequency $Ω=Ω_0$ are interpreted in terms of absorption lines of the electronic spin resonance spectrum. Applying a time dependent light frequency $Ω=Ω(t)$, so called chirping, is shown to be an efficient procedure in order to obtain within a short time a large, controlled value of the magnetization $M^z$. Furthermore, comparison with a $2$ - level model provides a qualitative understanding of the induced magnetization process.

cond-mat.str-el↗

arXiv2015

Spin and magnetothermal transport in the S = 1/2 XXZ chain

We present a temperature and magnetic field dependence study of spin transport and magnetothermal corrections to the thermal conductivity in the spin S = 1/2 integrable easy-plane regime Heisenberg chain, extending an earlier analysis based on the Bethe ansatz method. We critically discuss the low temperature, weak magnetic field behavior, the effect of magnetothermal corrections in the vicinity of the critical field and their role in recent thermal conductivity experiments in 1D quantum magnets.

cond-mat.str-el↗

arXiv2014

Effective S=1/2 description of the S=1 chain with strong easy plane anisotropy

We present a study of the one-dimensional S=1 antiferromagnetic spin chain with large easy plane anisotropy, with special emphasis on field-induced quantum phase transitions. Temperature and magnetic field dependence of magnetization, specific heat, and thermal conductivity is presented using a combination of numerical methods. In addition, the original S=1 model is mapped into the low-energy effective S=1/2 XXZ Heisenberg chain, a model which is exactly solvable using the Bethe ansatz technique. The effectiveness of the mapping is explored, and we show that all considered quantities are in qualitative, and in some cases quantitative, agreement. The thermal conductivity of the considered S=1 model is found to be strongly influenced by the underlying effective description. Furthermore, we elucidate the low-lying electron spin resonance spectrum, based on a semi--analytical Bethe ansatz calculation of the effective S=1/2 model.

cond-mat.str-el↗

arXiv2012

Magnetic excitations in the spin-1 anisotropic antiferromagnet $NiCl_2-4SC(NH_2)_2$

The spin-1 anisotropic antiferromagnet NiCl_2-4SC(NH2)_2 exhibits a field-induced quantum phase transition that is formally analogous to Bose-Einstein condensation. Here we present results of systematic high-field electron spin resonance (ESR) experimental and theoretical studies of this compound with a special emphasis on single-ion two-magnon bound states. In order to clarify some remaining discrepancies between theory and experiment, the frequency-field dependence of magnetic excitations in this material is reanalyzed. In particular, a more comprehensive interpretation of the experimental signature of single-ion two-magnon bound states is shown to be fully consistent with theoretical results. We also clarify the structure of the ESR spectrum in the so-called intermediate phase.

cond-mat.str-el↗

arXiv2012

Spinon heat transport and spin-phonon interaction in the antiferromagnetic spin-1/2 Heisenberg chain cuprates Sr2CuO3 and SrCuO2

We have investigated the thermal conductivity κ_mag of high-purity single crystals of the spin chain compound Sr2CuO3 which is considered an excellent realization of the one-dimensional spin-1/2 antiferromagnetic Heisenberg model. We find that the spinon heat conductivity κ_mag is strongly enhanced as compared to previous results obtained on samples with lower chemical purity. The analysis of κ_mag allows to compute the spinon mean free path l_mag as a function of temperature. At low-temperature we find l_mag\sim0.5\mum, corresponding to more than 1200 chain unit cells. Upon increasing the temperature, the mean free path decreases strongly and approaches an exponential decay ~1/T*exp(T*/T) which is characteristic for umklapp processes with the energy scale k_B T*. Based on Matthiesen's rule we decompose l_mag into a temperature-independent spinon-defect scattering length l0 and a temperature dependent spinon-phonon scattering length l_sp(T). By comparing l_mag(T) of Sr2CuO3 with that of SrCuO2, we show that the spin-phonon interaction, as expressed by l_sp is practically the same in both systems. The comparison of the empirically derived l_sp with model calculations for the spin-phonon interaction of the one-dimensional spin-1/2 XY model yields reasonable agreement with the experimental data.

cond-mat.str-el↗

arXiv2010

On the nonlinear response of a particle interacting with fermions in a 1D lattice

By the Bethe ansatz method we study the energy dispersion of a particle interacting by a local interaction with fermions (or hard core bosons) of equal mass in a one dimensional lattice. We focus on the period of the Bloch oscillations which turns out to be related to the Fermi wavevector of the Fermi sea and in particular on how this dispersion emerges as a collective effect in the thermodynamic limit. We show by symmetry that the dispersion is temperature independent for a half-filled system. We also discuss the adiabatic coherent collective response of the particle to an applied field.

cond-mat.str-el↗

arXiv2010

Thermal transport in a spin-1/2 Heisenberg chain coupled to a (non) magnetic impurity

We explore the effect of a (non) magnetic impurity on the thermal transport of the spin-1/2 Heisenberg chain model. This unique system allows to probe Kondo-type phenomena in a prototype strongly correlated system. Using numerical diagonalization techniques we study the scaling of the frequency dependent thermal conductivity with system size and host-impurity coupling strength as well as the dependence on temperature. We focus in particular on the analysis of cutting-healing of weak links or a magnetic impurity by the host chain via Kondo-like screening as the temperature is lowered.

cond-mat.str-el↗

arXiv2009

Finite temperature transport in disordered Heisenberg chains

Using numerical diagonalization techniques, we explore the effect of local and bond disorder on the finite temperature spin and thermal conductivities of the one dimensional anisotropic spin-1/2 Heisenberg model. High-temperature results for local disorder show that the dc conductivties are finite, apart from the uncorrelated - XY case - where dc transport vanishes. Moreover, at strong disorder, we find finite dc conductivities at all temperatures $T$, except T=0. The low frequency conductivities are characterized by a nonanalytic cusp shape. Similar behavior is found for bond disorder.

cond-mat.str-el↗