arXiv subjects

Jesko Sirker

Publications and source records attributed to Jesko Sirker.

26 records · Page 2Linked to original sources

arXiv2019

Equilibrium dynamics of the XX chain

The equilibrium dynamics of the spin-1/2 XX chain is re-examined within a recently developed formalism based on the quantum transfer matrix and a thermal form factor expansion. The transversal correlation function is evaluated in real time and space. The high-accuracy calculation reproduces several exact results in limiting cases as well as the well-known asymptotic formulas obtained by the matrix Riemann-Hilbert approach. Furthermore, comparisons to numerical data based on a direct evaluation of the Pfaffian as well as to asymptotic formulas obtained within non-linear Luttinger liquid theory are presented.

cond-mat.stat-mech↗

arXiv2018

Unique Spin Vortices in Quantum Dots with Spin-orbit Couplings

Spin textures of one or two electrons in a quantum dot with Rashba or Dresselhaus spin-orbit couplings reveal several intriguing properties. We show that even at the single-electron level spin vortices with different topological charges exist. These topological textures appear in the {\it ground state} of the dots. The textures are stabilized by time-reversal symmetry breaking and are robust against the eccentricity of the dot. The phenomenon persists for the interacting two-electron dot in the presence of a magnetic field.

cond-mat.mes-hall↗

arXiv2016

Conductance in inhomogeneous quantum wires: Luttinger liquid predictions and quantum Monte Carlo results

We study electron and spin transport in interacting quantum wires contacted by noninteracting leads. We theoretically model the wire and junctions as an inhomogeneous chain where the parameters at the junction change on the scale of the lattice spacing. We study such systems analytically in the appropriate limits based on Luttinger liquid theory and compare the results to quantum Monte Carlo calculations of the conductances and local densities near the junction. We first consider an inhomogeneous spinless fermion model with a nearest-neighbor interaction and then generalize our results to a spinful model with an onsite Hubbard interaction.

cond-mat.mes-hall↗

arXiv2016

Study of the cavity-magnon-polariton transmission line shape

We experimentally and theoretically investigate the microwave transmission line shape of the cavity-magnon-polariton (CMP) created by inserting a low damping magnetic insulator into a high quality 3D microwave cavity. While fixed field measurements are found to have the expected Lorentzian characteristic, at fixed frequencies the field swept line shape is in general asymmetric. Such fixed frequency measurements demonstrate that microwave transmission can be used to access magnetic characteristics of the CMP, such as the field line width $ΔH$. By developing an effective oscillator model of the microwave transmission we show that these line shape features are general characteristics of harmonic coupling. At the same time, at the classical level the underlying physical mechanism of the CMP is electrodynamic phase correlation and a second model based on this principle also accurately reproduces the experimental line shape features. In order to understand the microscopic origin of the effective coupled oscillator model and to allow for future studies of CMP phenomena to extend into the quantum regime, we develop a third, microscopic description, based on a Green's function formalism. Using this method we calculate the transmission spectra and find good agreement with the experimental results.

cond-mat.mtrl-sci↗

arXiv2012

Lightcone renormalization and quantum quenches in one-dimensional Hubbard models

The Lieb-Robinson bound implies that the unitary time evolution of an operator can be restricted to an effective light cone for any Hamiltonian with short-range interactions. Here we present a very efficient renormalization group algorithm based on this light cone structure to study the time evolution of prepared initial states in the thermodynamic limit in one-dimensional quantum systems. The algorithm does not require translational invariance and allows for an easy implementation of local conservation laws. We use the algorithm to investigate the relaxation dynamics of double occupancies in fermionic Hubbard models as well as a possible thermalization. For the integrable Hubbard model we find a pure power-law decay of the number of doubly occupied sites towards the value in the long-time limit while the decay becomes exponential when adding a nearest neighbor interaction. In accordance with the eigenstate thermalization hypothesis, the long-time limit is reasonably well described by a thermal average. We point out though that such a description naturally requires the use of negative temperatures. Finally, we study a doublon impurity in a Néel background and find that the excess charge and spin spread at different velocities, providing an example of spin-charge separation in a highly excited state.

cond-mat.str-el↗

arXiv2010

Non-Collinear Ferromagnetic Luttinger Liquids

The presence of electron-electron interactions in one dimension profoundly changes the properties of a system. The separation of charge and spin degrees of freedom is just one example. We consider what happens when a system consisting of a ferromagnetic region of non-collinearity, i.e. a domain wall, is coupled to interacting electrons in one-dimension (more specifically a Luttinger liquid). The ferromagnetism breaks spin charge separation and the presence of the domain wall introduces a spin dependent scatterer into the problem. The absence of spin charge separation and the effects of the electron correlations results in very different behaviour for the excitations in the system and for spin-transfer-torque effects in this model.

cond-mat.str-el↗

arXiv2009

Spin-wave theory for dimerized ferromagnetic chains

We describe a Peierls dimerization which occurs in ferromagnetic spin chains at finite temperature, within the modified spin-wave theory. Usual spin-wave theory is modified by introducing a Lagrange multiplier which enforces a nonmagnetic state at finite temperature. It is shown that this method gives results in excellent agreement with the density--matrix renormalization group applied to transfer matrices for dimerized ferromagnetic chains. We study bond correlation functions and explore the characteristic features of dimerization in the specific heat.

cond-mat.str-el↗

arXiv2005

Boundary susceptibility in the open XXZ-chain

In the first part we calculate the boundary susceptibility $χ_B$ in the open $XXZ$-chain at zero temperature and arbitrary magnetic field $h$ by Bethe ansatz. We present analytical results for the leading terms when $|h|\ll α$, where $α$ is a known scale, and a numerical solution for the entire range of fields. In the second part we calculate susceptibility profiles near the boundary at finite temperature $T$ numerically by using the density-matrix renormalization group for transfer matrices and analytically for $T\ll 1$ by field theoretical methods. Finally we compare $χ_B$ at finite temperature with a low-temperature asymptotics which we obtain by combining our Bethe ansatz result with recent predictions from bosonization.

cond-mat.str-el↗