A5074247366- Physics of Superconductivity and Magnetism
- Theoretical and Computational Physics
- Advanced Condensed Matter Physics
- Quantum many-body systems
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum and electron transport phenomena
- Quantum, superfluid, helium dynamics
- Topological Materials and Phenomena
- Magnetic properties of thin films
- Graphene research and applications
- Magnetic and transport properties of perovskites and related materials
- Surface and Thin Film Phenomena
- Advanced Chemical Physics Studies
- Organic and Molecular Conductors Research
- Advanced Thermodynamics and Statistical Mechanics
- Atomic and Subatomic Physics Research
- Quasicrystal Structures and Properties
- Magnetism in coordination complexes
- Opinion Dynamics and Social Influence
- Quantum Information and Cryptography
- Strong Light-Matter Interactions
- Stochastic processes and statistical mechanics
- Spectroscopy and Quantum Chemical Studies
- Quantum chaos and dynamical systems
- Advanced NMR Techniques and Applications
RWTH Aachen University
2016-2025
Jülich Aachen Research Alliance
2015-2024
Max Planck Institute for Solid State Research
2020
University Medical Center Groningen
2018-2019
University of Groningen
2018-2019
University of Stuttgart
2005-2011
Adam Mickiewicz University in Poznań
2006
Institute of Physics
2006
Université Paris-Sud
2006
Laboratoire de physique des Solides
2006
We present release 2.0 of the ALPS (Algorithms and Libraries for Physics Simulations) project, an open source software project to develop libraries application programs simulation strongly correlated quantum lattice models such as magnets, bosons, fermion systems. The code development is centered on common XML HDF5 data formats, simplify speed up development, evaluation plotting tools, programs. enable non-experts start carrying out serial or parallel numerical simulations by providing basic...
We determine the phase diagram of hard-core bosons on a triangular lattice with nearest-neighbor repulsion, paying special attention to stability supersolid phase. Similar same model square we find that for densities rho<1/3 or rho>2/3 is unstable and transition between commensurate solid superfluid first order. At intermediate fillings 1/3<rho<2/3 an extended even at half filling rho=1/2. The emergence reflects novel interesting way quantum system avoid classical frustration, similar...
Using the adaptive time-dependent density-matrix renormalization group method, we study time evolution of strongly correlated spinless fermions on a one-dimensional lattice after sudden change interaction strength. For certain parameter values, two different initial states (e.g., metallic and insulating) lead to observables which become indistinguishable relaxation. We find that resulting quasistationary state is nonthermal. This result holds for both integrable nonintegrable variants system.
Efficient quantum Monte Carlo update schemes called directed loops have recently been proposed, which improve the efficiency of simulations lattice models. We propose to generalize detailed balance equations at local level during loop construction by accounting for matrix elements operators associated with open world-line segments. Using linear programming techniques solve generalized equations, we look optimal loops. This also allows an extension scheme general models, such as high-spin or...
We study properties of ultra-cold bosonic atoms in one, two and three dimensional optical lattices by large scale quantum Monte Carlo simulations the Bose Hubbard model parabolic confinement potentials. Local phase structures are shown to be accessible via a well defined local compressibility, quantifying global response system perturbation. An indicator for presence extended Mott plateaux is stem from shape coherent component momentum distribution function, amenable experimental detection....
We study the two-dimensional Kane-Mele-Hubbard model at half filling by means of quantum Monte Carlo simulations. present a refined phase boundary for spin liquid. The topological insulator finite Hubbard interaction strength is adiabatically connected to groundstate Kane-Mele model. In presence spin-orbit coupling, magnetic order large U restricted transverse direction. transition from band antiferromagnetic Mott in universality class three-dimensional XY numerical data suggest that liquid...
We investigate the edge-state magnetism of graphene nanoribbons using projective quantum Monte Carlo simulations and a self-consistent mean-field approximation Hubbard model. The static magnetic correlations are found to be short ranged. Nevertheless, correlation length increases with width ribbon such that already for ribbons moderate widths we observe strong trend towards mean-field-type ferromagnetic at zigzag edge. These accompanied by dominant low-energy peak in local spectral function...
The magnetic properties of graphene on finite geometries are studied using a self-consistent mean-field theory the Hubbard model. This approach is known to predict ferromagnetic edge states close zigzag edges in single-layer quantum dots and nanoribbons. In order assess accuracy this method, we perform complementary exact diagonalization Monte Carlo simulations. We observe good quantitative agreement for all quantities investigated provided that Coulomb interaction not too strong.
Using large scale quantum Monte Carlo simulations and dual vortex theory, we analyze the ground state phase diagram of hard-core bosons on kagome lattice with nearest-neighbor repulsion. In contrast case a triangular lattice, no supersolid emerges for strong interactions. While uniform superfluid prevails at half filling, two novel solid phases emerge densities $\ensuremath{\rho}=1/3$ $\ensuremath{\rho}=2/3$. These solids exhibit an only partial ordering bosonic density, allowing local...
Using the adaptive time-dependent density-matrix renormalization group, we study time evolution of density correlations interacting spinless fermions on a one-dimensional lattice after sudden change in interaction strength. Over broad range model parameters, correlation function exhibits characteristic light-cone-like representative ballistic transport information. Such behavior is observed both when quenching an insulator into metallic region and also within insulating region. However,...
We determine the optimal scaling of local-update flat-histogram methods with system size by using a perfect scheme based on exact density states 2D Ising models.The typical tunneling time needed to sample entire bandwidth does not scale number spins N as minimal N^2 an unbiased random walk in energy space. While is power law for ferromagnetic and fully frustrated model, +/- J nearest-neighbor spin glass distribution times governed fat-tailed Frechet extremal value that obeys exponential...
We present the ALPS (Algorithms and Libraries for Physics Simulations) project, an international open source software project to develop libraries application programs simulation of strongly correlated quantum lattice models such as magnets, bosons, fermion systems. Development is centered on common XML binary data formats, simplify speed up code development, full-featured programs. The enable non-experts start carrying out numerical simulations by providing basic implementations important...
We study the properties of spin systems realized by cold polar molecules interacting via dipole-dipole interactions in two dimensions. Using a wave theory, that allows for full treatment characteristic long-distance tail dipolar interaction, we find several anomalous features ground state correlations and excitation spectrum, which are absent their counterparts with short-range interaction. The most striking consequence is existence true long-range order at finite temperature two-dimensional...
We present an analysis of neural network-based machine learning schemes for phases and phase transitions in theoretical condensed matter research, focusing on networks with a single hidden layer. Such shallow were previously found to be efficient classifying locating various basic model systems. In order rationalize the emergence classification process identifying any underlying physical quantities, it is feasible examine weight matrices convolutional filter kernels that result from such...
The scaling of the transition temperature into an ordered phase close to a quantum critical point as well order parameter fluctuations inside region provide valuable information about universal properties underlying point. Here, we employ Monte Carlo simulations examine these relations in detail for two-dimensional systems that exhibit finite-temperature Ising-transition line vicinity belongs universality class either (i) three-dimensional Ising model case transverse magnetic field on square...
We present a generalization of the classical Wang-Landau algorithm [Phys. Rev. Lett. 86, 2050 (2001)]] to quantum systems. The proceeds by stochastically evaluating coefficients high temperature series expansion or finite perturbation arbitrary order. Similar their counterpart, algorithms are efficient at thermal and phase transitions, greatly reducing tunneling problem first order allow direct calculation free energy entropy.
We consider the physics of lattice bosons affected by disordered on-site interparticle interactions. Characteristic qualitative changes in zero-temperature phase diagram are observed when compared to case randomness chemical potential. The Mott-insulating regions shrink and eventually vanish for any finite disorder strength beyond a sufficiently large filling factor. Furthermore, at low values potential both superfluid Mott insulator stable towards formation Bose glass leading possibly...
Using a combination of quantum Monte Carlo simulations, functional renormalization group calculations and mean-field theory, we study the Hubbard model on Bernal-stacked honeycomb bilayer at half-filling as system for graphene. The free bands consisting two Fermi points with quadratic dispersions lead to finite density states level, which triggers an antiferromagnetic instability that spontaneously breaks sublattice spin rotational symmetry once local Coulomb repulsions are introduced. Our...
We study the quantum phases of fermions with an explicit $\mathrm{SU}(N)$-symmetric, Heisenberg-like nearest-neighbor flavor exchange interaction on honeycomb lattice at half filling. Employing projective (zero temperature) Monte Carlo simulations for even values $N$, we explore evolution from a weak-coupling semimetal into strong-coupling, insulating regime. Furthermore, compare our numerical results to saddle-point approximation in large-$N$ limit. From regime down SU(6) case, state is...
We examine the entanglement properties of spin-half Heisenberg model on two-dimensional square-lattice bilayer based quantum Monte Carlo calculations second R\'enyi entropy. In particular, we extract dominant area-law contribution to bipartite entropy that shows a non-monotonous behavior upon increasing inter-layer exchange interaction: local maximum in coefficient is located at critical point separating antiferromagnetically ordered region from disordered dimer-singlet regime. Furthermore,...
It is argued that the subtle crossover from decoherence-dominated classical magnetism to fluctuation-dominated quantum experimentally accessible in graphene nanoribbons. We show width of a nanoribbon determines whether edge on side, or between. In regime, decoherence dominant and leads static spin polarizations at ribbon edges, which are well described by mean-field theories. The Zeno effect identified as basic mechanism responsible for polarization thereby enables application spintronics....
In a $D=2+1$ quantum critical system, the entanglement entropy across boundary with corner contains subleading logarithmic scaling term universal coefficient. It has been conjectured that this coefficient is, to leading order, proportional number of field components $N$ in associated $\text{O}(N)$ continuum ${\ensuremath{\phi}}^{4}$ theory. Using density matrix renormalization group calculations combined powerful numerical linked cluster expansion technique, we confirm scenario for...
Using quantum Monte Carlo simulations along with higher-order spin-wave theory, bond-operator and strong-coupling expansions, we analyse the dynamical spin structure factor of spin-half Heisenberg model on square-lattice bilayer. We identify distinct contributions from low-energy Goldstone modes in magnetically ordered phase gapped triplon disordered phase. In antisymmetric (with respect to layer inversion) channel, exhibits a continuous evolution spectral features across transition,...