arXiv subjects

Hannes Meier

Publications and source records attributed to Hannes Meier.

4 recordsLinked to original sources

arXiv2019

Three-dimensional universality class of Ising model with power-law-correlated critical disorder

We use large-scale Monte Carlo simulations to test the Weinrib-Halperin criterion that predicts new universality classes in the presence of sufficiently slowly decaying power-law-correlated quenched disorder. While new universality classes are reasonably well established, the predicted exponents are controversial. We propose a method of growing such correlated disorder using the three-dimensional Ising model as benchmark systems both for generating disorder and studying the resulting phase transition. Critical equilibrium configurations of a disorder-free system are used to define the two-value distributed random bonds with a small power-law exponent given by the pure Ising exponent. Finite-size scaling analysis shows a new universality class with a single phase transition, but the critical exponents $ν_d=1.13(5), η_d=0.48(3)$ differ significantly from theoretical predictions. We find that depending on details of the disorder generation, disorder-averaged quantities can develop peaks at two temperatures for finite sizes. Finally, a layer model with the two values of bonds spatially separated to halves of the system genuinely has multiple phase transitions and thermodynamic properties can be flexibly tuned by adjusting the model parameters.

cond-mat.dis-nn↗

arXiv2015

Fluctuation-induced first order phase transitions in type-1.5 superconductors in zero external field

In a single-component Ginzburg-Landau model which possesses thermodynamically stable vortex excitations, the zero-field superconducting phase transition is second order even when fluctuations are included. Beyond the mean-field approximation the transition is described in terms of proliferation of vortex loops. Here we determine the order of the superconducting transition in an effective 3D vortex-loop model for the recently proposed multiband type-1.5 superconductors. The vortex interaction is nonmonotonic, i.e., exponentially screened and attractive at large separations, and short-range repulsive. We show that the details of the vortex interaction, despite its short-range nature, can lead to very different properties of the superconducting transition than found in type-1 and type-2 systems. Namely, the type-1.5 regime with nonmonotonic intervortex interaction can have a first-order vortex-driven phase transition not found in the single-band case.

cond-mat.supr-con↗

arXiv2012

Superfluid transition in a correlated defect network

Motivated by recent experiments on possible supersolid behavior of $^4$He solids at low temperature, we consider a model of superfluidity in a defected solid containing a system spaning network of correlated linear dislocations, or planar grain boundaries. Using arguments based on the Harris criterion, as well as numerical simulations, we find that such correlated quenched disorder shifts the familiar superfluid lambda transition to a new disordered universality class in which the correlation length exponent $ν\ge 1$. This results in the temperature-derivates for the superfluid density, $dρ_{\rm s}/dT$, and for the heat capacity, $dc/dT$, remaining finite at the transition $T_{\rm c}$, and thus a less singular transition, profoundly different from the usual lambda transition.

cond-mat.dis-nn↗

arXiv2011

Quantum Critical Dynamics Simulation of Dirty Boson Systems

Recently the scaling result $z=d$ for the dynamic critical exponent at the Bose glass to superfluid quantum phase transition has been questioned both on theoretical and numerical grounds. This motivates a careful evaluation of the critical exponents in order to determine the actual value of $z$. We study a model of quantum bosons at T=0 with disorder in 2D using highly effective worm Monte Carlo simulations. Our data analysis is based on a finite size scaling approach to determine the scaling of the quantum correlation time from simulation data for boson world lines. The resulting critical exponents are $z=1.8 \pm 0.05, ν=1.15 \pm 0.03,$ and $η=-0.3 \pm 0.1$, hence suggesting that $z=2$ is not satisfied.

cond-mat.dis-nn↗