98 research outputs found
Ising nematic fluid phase of hard-core dimers on the square lattice
We present a model of classical hard-core dimers on the square lattice that
contains an Ising nematic phase in its phase diagram. We consider a model with
an attractive interaction for parallel dimers on a given plaquette of the
square lattice and an attractive interaction for neighboring parallel dimers on
the same row ({\it viz} column) of the lattice. By extensive Monte carlo
simulations we find that with a finite density of holes the phase diagram has,
with rising temperatures, a columnar crystalline phase, an Ising nematic liquid
phase and a disordered fluid phase, separated by Ising continuous phase
transitions. We present strong evidence for the Ising universality class of
both transitions. The Ising nematic phase can be interpreted as either an
intermediate classical thermodynamic phase (possibly of a strongly correlated
antiferromagnet) or as a phase of a 2D quantum dimer model using the
Rokhsar-Kivelson construction of exactly solvable quantum Hamiltonians.Comment: 13 pages, 24 figure
Learning local, quenched disorder in plasticity and other crackling noise phenomena
When far from equilibrium, many-body systems display behavior that strongly depends on the initial conditions. A characteristic such example is the phenomenon of plasticity of crystalline and amorphous materials that strongly depends on the material history. In plasticity modeling, the history is captured by a quenched, local and disordered flow stress distribution. While it is this disorder that causes avalanches that are commonly observed during nanoscale plastic deformation, the functional form and scaling properties have remained elusive. In this paper, a generic formalism is developed for deriving local disorder distributions from field- response (e.g., stress/strain) timeseries in models of crackling noise. We demonstrate the efficiency of the method in the hysteretic random-field Ising model and also, models of elastic interface depinning that have been used to model crystalline and amorphous plasticity. We show that the capacity to resolve the quenched disorder distribution improves with the temporal resolution and number of samples
Learning local, quenched disorder in plasticity and other crackling noise phenomena
When far from equilibrium, many-body systems display behavior that strongly depends on the initial conditions. A characteristic such example is the phenomenon of plasticity of crystalline and amorphous materials that strongly depends on the material history. In plasticity modeling, the history is captured by a quenched, local and disordered flow stress distribution. While it is this disorder that causes avalanches that are commonly observed during nanoscale plastic deformation, the functional form and scaling properties have remained elusive. In this paper, a generic formalism is developed for deriving local disorder distributions from field- response (e.g., stress/strain) timeseries in models of crackling noise. We demonstrate the efficiency of the method in the hysteretic random-field Ising model and also, models of elastic interface depinning that have been used to model crystalline and amorphous plasticity. We show that the capacity to resolve the quenched disorder distribution improves with the temporal resolution and number of samples
Nodal-antinodal dichotomy from pairing disorder in d-wave superconductors
We study the basic features of the local density of states (LDOS) observed in
STM experiments on high-T d-wave superconductors in the context of a
minimal model of a d-wave superconductor which has {\it weakly} modulated
off-diagonal disorder. We show that the low and high energy features of the
LDOS are consistent with the observed experimental patterns and in particular,
the anisotropic local domain features at high energies. At low energies, we
obtain not only the scattering peaks predicted by the octet model, but also
weak features that should be experimentally accessible. Finally, we show that
the emerging features of the LDOS lose their correspondence with the features
of the imposed disorder, as its complexity increases spatially
Isostaticity at Frictional Jamming
Amorphous packings of frictionless, spherical particles are isostatic at
jamming onset, with the number of constraints (contacts) equal to the number of
degrees of freedom. Their structural and mechanical properties are controlled
by the interparticle contact network. In contrast, amorphous packings of
frictional particles are typically hyperstatic at jamming onset. We perform
extensive numerical simulations in two dimensions of the geometrical asperity
(GA) model for static friction, to further investigate the role of
isostaticity. In the GA model, interparticle forces are obtained by summing up
purely repulsive central forces between periodically spaced circular asperities
on contacting grains. We compare the packing fraction, contact number,
mobilization distribution, and vibrational density of states using the GA model
to those generated using the Cundall-Strack (CS) approach. We find that static
packings of frictional disks obtained from the GA model are mechanically stable
and isostatic when we consider interactions between asperities on contacting
particles. The crossover in the structural and mechanical properties of static
packings from frictionless to frictional behavior as a function of the static
friction coefficient coincides with a change in the type of interparticle
contacts and the disappearance of a peak in the density of vibrational modes
for the GA model. These results emphasize that mesoscale features of the model
for static friction play an important role in determining the properties of
granular packings.Comment: 4.5 pages, 5 figures, http://prl.aps.org/covers/110/1
Straining the Identity of Majorana Fermions
We propose an experimental setup of an interferometer for the observation of
neutral Majorana fermions on topological insulator - superconductor -
ferromagnet junctions. We show that the extended lattice defects naturally
present in materials, dislocations, induce spin currents on the edges while
keeping the bulk time-reversal symmetry intact. We propose a simple two
terminal conductance measurement in an interferometer formed by two edge point
contacts, which reveals the nature of Majorana states through the effect of
dislocations. The zero temperature magneto-conductance changes from even
oscillations with period phi/2 (phi is the flux quantum hc/e) to odd
oscillations with period phi, when non-trivial dislocations are present and the
Majorana states are sufficiently strongly coupled. Additionally, the
conductance acquires a notable asymmetry as a function of the incident electron
energy, due to the topological influence of the dislocations, while resonances
appear at the coupling energy of Majorana states.Comment: 5 pages, 3 figures, three-point bending setup with Hg(Cd)Te analyze
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