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Peter Olsson

Publications and source records attributed to Peter Olsson.

At least 37 records · Page 2Linked to original sources
arXiv2013

Relaxation and Rheology in Dense Athermal Suspensions

We study relaxation and rheology of dense athermal suspensions of frictionless particles close below the jamming density. Our key quantity, the relaxation time---determined from the exponential decay of the energy after the shearing has suddenly been switched off---is argued to be a determining factor behind the algebraic divergence of various quantities as the jamming density is approached from below. We also define and measure the ``dissipation time'', which is obtained directly in shearing simulations and find that it behaves similarly to the relaxation time. Comparing shear viscosity with the expression for the dissipation time we identify a non-divergent factor that explains the need for correction terms in the scaling analyses of the shear viscosity.

cond-mat.soft↗
arXiv2012

Athermal Jamming vs Thermalized Glassiness in Sheared Frictionless Particles

Numerical simulations of soft-core frictionless disks in two dimensions are carried out to study behavior of a simple liquid as a function of thermal temperature $T$, packing fraction $ϕ$, and uniform applied shear strain rate $\dotγ$. Inferring the hard-core limit from our soft-core results, we find that it depends on the two parameters $ϕ$ and $T/\dotγ$. $T/\dotγ\to 0$ defines the athermal limit in which a shear driven jamming transition occurs at a well defined $ϕ_J$. $T/\dotγ\to\infty$ defines the thermalized limit where an equilibrium glass transition may take place at a $ϕ_G$. This conclusion argues that athermal jamming and equilibrium glassy behavior are not controlled by the same critical point. Preliminary results suggest $ϕ_G <ϕ_J$.

cond-mat.soft↗
arXiv2012

Duality in Shearing Rheology Near the Athermal Jamming Transition

We consider the rheology of soft-core frictionless disks in two dimensions in the neighborhood of the athermal jamming transition. From numerical simulations of bidisperse, overdamped, particles, we argue that the divergence of the viscosity below jamming is characteristic of the hard-core limit, independent of the particular soft-core interaction. We develop a mapping from soft-core to hard-core particles that recovers all the critical behavior found in earlier scaling analyses. Using this mapping we derive a duality relation that gives the exponent of the non-linear Herschel-Bulkley rheology above jamming in terms of the exponent of the diverging viscosity below jamming.

cond-mat.dis-nn↗
arXiv2011

Finite-Size-Scaling at the Jamming Transition: Corrections to Scaling and the Correlation Length Critical Exponent

We carry out a finite size scaling analysis of the jamming transition in frictionless bi-disperse soft core disks in two dimensions. We consider two different jamming protocols: (i) quench from random initial positions, and (ii) quasistatic shearing. By considering the fraction of jammed states as a function of packing fraction for systems with different numbers of particles, we determine the spatial correlation length critical exponent $ν\approx 1$, and show that corrections to scaling are crucial for analyzing the data. We show that earlier numerical results yielding $ν<1$ are due to the improper neglect of these corrections.

cond-mat.soft↗
arXiv2011

Glassiness, Rigidity and Jamming of Frictionless Soft Core Disks

The jamming of bi-disperse soft core disks is considered, using a variety of different protocols to produce the jammed state. In agreement with other works, we find that cooling and compression can lead to a broad range of jamming packing fractions $ϕ_J$, depending on cooling rate and initial configuration; the larger the degree of big particle clustering in the initial configuration, the larger will be the value of $ϕ_J$. In contrast, we find that shearing disrupts particle clustering, leading to a much narrower range of $ϕ_J$ as the shear strain rate varies. In the limit of vanishingly small shear strain rate, we find a unique non-trivial value for the jamming density that is independent of the initial system configuration. We conclude that shear driven jamming is a unique and well defined critical point in the space of shear driven steady states. We clarify the relation between glassy behavior, rigidity and jamming in such systems and relate our results to recent experiments.

cond-mat.soft↗
arXiv2010

Critical Scaling of Shearing Rheology at the Jamming Transition of Soft Core Frictionless Disks

We perform numerical simulations to determine the shear stress and pressure of steady-state shear flow in a soft-disk model in two dimensions at zero temperature in the vicinity of the jamming transition ϕ_J. We use critical point scaling analyses to determine the critical behavior at jamming, and we find that it is crucial to include corrections to scaling for a reliable analysis. We find that the relative size of these corrections are much smaller for pressure than for shear stress. We furthermore find a superlinear behavior for pressure and shear stress above ϕ_J, both from the scaling analysis and from a direct analysis of pressure data extrapolated to the limit of vanishing shear rate.

cond-mat.soft↗
arXiv2010

Asymmetric velocity correlations in shearing media

A model of soft frictionless disks in two dimensions at zero temperature is simulated with a shearing dynamics to study various kinds of asymmetries in sheared systems. We examine both single particle properties, the spatial velocity correlation function, and a correlation function designed to separate clockwise and counter-clockwise rotational fields from one another. Among the rich and interesting behaviors we find that the velocity correlation along the two different diagonals corresponding to compression and dilation, respectively, are almost identical and, furthermore, that a feature in one of the correlation functions is directly related to irreversible plastic events.

cond-mat.soft↗
arXiv2009

Diffusion and Velocity Auto-Correlation in Shearing Granular Media

We perform numerical simulations to examine particle diffusion at steady shear in a model granular material in two dimensions at the jamming density and zero temperature. We confirm findings by others that the diffusion constant depends on shear rate as $D\sim\dotγ^{q_D}$ with $q_D<1$, and set out to determine a relation between $q_D$ and other exponents that characterize the jamming transition. We then examine the the velocity auto-correlation function, note that it is governed by two processes with different time scales, and identify a new fundamental exponent, $λ$, that characterizes an algebraic decay of correlations with time.

cond-mat.soft↗
arXiv2009

Unified Phase Diagram for the Three-Dimensional XY Model of a Point Disordered Type-II Superconductor

We carry out extensive Monte Carlo simulations of the three-dimensional (3D) uniformly frustrated XY model with uncorrelated randomly perturbed couplings, as a model for the equilibrium behavior of an extreme type-II superconductor with quenched uncorrelated random point vortex pinning, in the presence of a uniform applied magnetic field. We map out the resulting phase diagram as a function of temperature T and pinning strength p for a fixed value of the vortex line density. At low p we find a sharp first order vortex lattice melting phase boundary separating a vortex lattice from a vortex liquid. As p increases, it appears that this first order transition smears out over a finite temperature interval, due to the effects of the random pinning, in agreement with several recent experiments. At large p we find a second order transition from vortex liquid to vortex glass.

cond-mat.supr-con↗
arXiv2007

Critical Scaling of Shear Viscosity at the Jamming Transition

We carry out numerical simulations to study transport behavior about the jamming transition of a model granular material in two dimensions at zero temperature. Shear viscosity ηis computed as a function of particle volume density ρand applied shear stress σ, for diffusively moving particles with a soft core interaction. We find an excellent scaling collapse of our data as a function of the scaling variable σ/|ρ_c-ρ|^Δ, where ρ_c is the critical density at σ=0 ("point J"), and Δis the crossover scaling critical exponent. Our results show that jamming is a true critical phenomenon, extending to driven steady states along the non-equilibrium σaxis of the ρ-σphase diagram.

cond-mat.soft↗
arXiv2007

Vortex Line Ordering in the Driven Three-Dimensional Vortex Glass

Resistively-shunted-junction dynamics is applied to the three dimensional uniformly frustrated XY model with randomly perturbed couplings, as a model for driven steady states in a type-II superconductor with quenched point pinning. For a disorder strength p strong enough to produce a vortex glass in equilibrium, we map the phase diagram as a function of temperature T and uniform driving current I. We find that, within a finite current range I_{c1}(T)<I<I_{c2}(T), the system orders into a set of periodically spaced smectic planes of vortex lines. Smectic planes are short range correlated with neighboring planes; vortex lines within a given plane are periodic along the direction of motion, while disordered along the direction of the applied magnetic field.

cond-mat.supr-con↗
arXiv2006

Pinning and Depinning of the Bragg Glass in a Point Disordered Model Superconductor

The three-dimensional frustrated anisotropic XY model with point disorder is studied with both Monte Carlo simulations and resistively-shunted-junction dynamics to model the dynamics of a type-II superconductor with quenched point pinning in a magnetic field and a weak applied current. Both the collective pinning and the depinning of the Bragg glass is examined. We find a critical current I_c that separates a creep region with unmeasurable low voltage from a region with a voltage V \sim I-I_c, and also identify the mechanism behind this behavior. It is further found to be possible to collapse the data obtained at a fixed disorder strength by plotting the voltage versus TI, where T is the temperature, though the reason for this behavior is unclear.

cond-mat.supr-con↗
arXiv2005

Vortex glass transitions in disordered three-dimensional XY models: Simulations for several different sets of parameters

The anisotropic frustrated 3D XY model with strong disorder in the coupling constants is studied as a model of a disordered superconductor in an applied magnetic field. Simulations with the exchange Monte Carlo method are performed for frustrations f=1/5 and f=1/4, corresponding to two different values of the magnetic field along the z direction. The anisotropy is also varied. The determination of the helicity modulus from twist histograms is discussed in some detail and the helicity modulus is used in finite size scaling analyses of the vortex glass transition. The general picture is that the behavior in [Phys. Rev. Lett. 91, 077002 (2003)] is confirmed. For strong (e.g. isotropic) coupling in the z direction the helicity modulus fails to scale and it is argued that this is due to a too small effective randomness of such systems for the accessible system sizes.

cond-mat.supr-con↗
arXiv2003

Vortex glass transition in a frustrated 3D XY model with disorder

The anisotropic frustrated three dimensional (3D) XY model with disorder in the coupling constants is simulated as a model of a point disordered superconductor in an applied magnetic field. From a finite size scaling analysis of the helicity modulus it is concluded that the data is consistent with a finite temperature transition with isotropic scaling and the correlation length exponent is found to be ν=1.50+/-0.12, consistent with 3D gauge glass universality.

cond-mat.supr-con↗
arXiv2001

A Zero-Temperature Study of Vortex Mobility in Two-Dimensional Vortex Glass Models

Three different vortex glass models are studied by examining the energy barrier against vortex motion across the system. In the two-dimensional gauge glass this energy barrier is found to increase logarithmically with system size which is interpreted as evidence for a low-temperature phase with zero resistivity. Associated with the large energy barriers is a breaking of ergodicity which explains why the well established results from equilibrium studies could fail. The behavior of the more realistic random pinning model is however different with decreasing energy barriers a no finite critical temperature.

cond-mat.supr-con↗
arXiv2001

Critical exponent η_ϕof the Lattice London Superconductor and vortex loops in the 3D XY model

The anomalous dimension of the lattice London superconductor is determined from finite size scaling of the susceptibility to be η_ϕ= -0.79(1). Indirect determinations of η_ϕfrom properties of the vortex loops in the 3D XY model are also attempted, but it is found that the results are sensitive to details in the simulations related to vortex loop intersections. It is suggested that the same value of η_ϕcan at most be obtained from vortex loop properties in the limit of low vortex density.

cond-mat.stat-mech↗
arXiv2000

The Transition in the Two-Dimensional Step Model: A Kosterlitz-Thouless Transition in Disguise

Evidence for a Kosterlitz-Thouless transition in the 2D step model is obtained from Monte Carlo determinations of the helicity modulus. It is argued that the free energy of a single vortex at the center of the system depends logarithmically on the system size in spite of the fact that the spin interaction is not harmonic for small differences in the spin angles. We conclude that this is the reason for the Kosterlitz-Thouless transition in the 2D step model and that the harmonic spin interaction not is a necessary requirement.

cond-mat.stat-mech↗