313 research outputs found
An intermediate state between the kagome-ice and the fully polarized state in DyTiO
DyTiO is at present the cleanest example of a spin-ice material.
Previous theoretical and experimental work on the first-order transition
between the kagome-ice and the fully polarized state has been taken as a
validation for the dipolar spin-ice model. Here we investigate in further depth
this phase transition using ac-susceptibility and dc-magnetization, and compare
this results with Monte-Carlo simulations and previous magnetization and
specific heat measurements. We find signatures of an intermediate state between
the kagome-ice and full polarization. This signatures are absent in current
theoretical models used to describe spin-ice materials.Comment: 7 pages, 4 figure
Specific heat anomaly in a supercooled liquid with amorphous boundary conditions
We study the specific heat of a model supercooled liquid confined in a
spherical cavity with amorphous boundary conditions. We find the equilibrium
specific heat has a cavity-size-dependent peak as a function of temperature.
The cavity allows us to perform a finite-size scaling (FSS) analysis, which
indicates that the peak persists at a finite temperature in the thermodynamic
limit. We attempt to collapse the data onto a FSS curve according to different
theoretical scenarios, obtaining reasonable results in two cases: a
"not-so-simple" liquid with nonstandard values of the exponents {\alpha} and
{\nu}, and random first-order theory, with two different length scales.Comment: Includes Supplemental Materia
Dynamic relaxation of a liquid cavity under amorphous boundary conditions
The growth of cooperatively rearranging regions was invoked long ago by Adam
and Gibbs to explain the slowing down of glass-forming liquids. The lack of
knowledge about the nature of the growing order, though, complicates the
definition of an appropriate correlation function. One option is the
point-to-set correlation function, which measures the spatial span of the
influence of amorphous boundary conditions on a confined system. By using a
swap Monte Carlo algorithm we measure the equilibration time of a liquid
droplet bounded by amorphous boundary conditions in a model glass-former at low
temperature, and we show that the cavity relaxation time increases with the
size of the droplet, saturating to the bulk value when the droplet outgrows the
point-to-set correlation length. This fact supports the idea that the
point-to-set correlation length is the natural size of the cooperatively
rearranging regions. On the other hand, the cavity relaxation time computed by
a standard, nonswap dynamics, has the opposite behavior, showing a very steep
increase when the cavity size is decreased. We try to reconcile this difference
by discussing the possible hybridization between MCT and activated processes,
and by introducing a new kind of amorphous boundary conditions, inspired by the
concept of frozen external state as an alternative to the commonly used frozen
external configuration.Comment: Completely rewritten version. After the first submission it was
realized that swap and nonswap dynamics results are qualitatively different.
This version reports the results of both dynamics and discusses the different
behaviors. 17 pages, 18 figure
A phase-separation perspective on dynamic heterogeneities in glass-forming liquids
We study dynamic heterogeneities in a model glass-former whose overlap with a
reference configuration is constrained to a fixed value. The system
phase-separates into regions of small and large overlap, so that dynamical
correlations remain strong even for asymptotic times. We calculate an
appropriate thermodynamic potential and find evidence of a Maxwell's
construction consistent with a spinodal decomposition of two phases. Our
results suggest that dynamic heterogeneities are the expression of an ephemeral
phase-separating regime ruled by a finite surface tension
Pressure study of nematicity and quantum criticality in SrRuO for an in-plane field
We study the relationship between the nematic phases of SrRuO and
quantum criticality. At ambient pressure, one nematic phase is associated with
a metamagnetic quantum critical end point (QCEP) when the applied magnetic
field is near the \textit{c}-axis. We show, however, that this metamagnetic
transition does not produce the same nematic signatures when the QCEP is
reached by hydrostatic pressure with the field applied in the
\textit{ab}-plane. Moreover, a second nematic phase, that is seen for field
applied in the \textit{ab}-plane close to, but not right at, a second
metamagnetic anomaly, persists with minimal change to the highest applied
pressure, 16.55 kbar. Taken together our results suggest that metamagnetic
quantum criticality may not be necessary for the formation of a nematic phase
in SrRuO
Static correlations functions and domain walls in glass-forming liquids: the case of a sandwich geometry
The problem of measuring nontrivial static correlations in deeply supercooled
liquids made recently some progress thanks to the introduction of amorphous
boundary conditions, in which a set of free particles is subject to the effect
of a different set of particles frozen into their (low temperature) equilibrium
positions. In this way, one can study the crossover from nonergodic to ergodic
phase, as the size of the free region grows and the effect of the confinement
fades. Such crossover defines the so-called point-to-set correlation length,
which has been measured in a spherical geometry, or cavity. Here, we make
further progress in the study ofcorrelations under amorphous boundary
conditions by analyzing the equilibrium properties of a glass-forming liquid,
confined in a planar ("sandwich") geometry. The mobile particles are subject to
amorphous boundary conditions with the particles in the surrounding walls
frozen into their low temperature equilibrium configurations. Compared to the
cavity, the sandwich geometry has three main advantages: i) the width of the
sandwich is decoupled from its longitudinal size, making the thermodynamic
limit possible; ii) for very large width, the behaviour off a single wall can
be studied; iii) we can use "anti-parallel" boundary conditions to force a
domain wall and measure its excess energy. Our results confirm that amorphous
boundary conditions are indeed a very useful new tool inthe study of static
properties of glass-forming liquids, but also raise some warning about the fact
that not all correlation functions that can be calculated in this framework
give the same qualitative results.Comment: Submited to JCP special issue on the glass transisio
Glassy dynamics, metastability limit and crystal growth in a lattice spin model
We introduce a lattice spin model where frustration is due to multibody
interactions rather than quenched disorder in the Hamiltonian. The system has a
crystalline ground state and below the melting temperature displays a dynamic
behaviour typical of fragile glasses. However, the supercooled phase loses
stability at an effective spinodal temperature, and thanks to this the Kauzmann
paradox is resolved. Below the spinodal the system enters an off-equilibrium
regime corresponding to fast crystal nucleation followed by slow activated
crystal growth. In this phase and in a time region which is longer the lower
the temperature we observe a violation of the fluctuation-dissipation theorem
analogous to structural glasses. Moreover, we show that in this system there is
no qualitative difference between a locally stable glassy configuration and a
highly disordered polycrystal
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