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## A Topological Framework for Local Structure Analysis in Condensed Matter

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 24/08/2015

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#Condensed Matter - Other Condensed Matter#Condensed Matter - Materials Science#Physics - Computational Physics

Physical systems are frequently modeled as sets of points in space, each
representing the position of an atom, molecule, or mesoscale particle. As many
properties of such systems depend on the underlying ordering of their
constituent particles, understanding that structure is a primary objective of
condensed matter research. Although perfect crystals are fully described by a
set of translation and basis vectors, real-world materials are never perfect,
as thermal vibrations and defects introduce significant deviation from ideal
order. Meanwhile, liquids and glasses present yet more complexity. A complete
understanding of structure thus remains a central, open problem. Here we
propose a unified mathematical framework, based on the topology of the Voronoi
cell of a particle, for classifying local structure in ordered and disordered
systems that is powerful and practical. We explain the underlying reason why
this topological description of local structure is better suited for structural
analysis than continuous descriptions. We demonstrate the connection of this
approach to the behavior of physical systems and explore how crystalline
structure is compromised at elevated temperatures. We also illustrate potential
applications to identifying defects in plastically deformed polycrystals at
high temperatures...

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## Non-equilibrium properties of a pumped-decaying Bose-condensed electron-hole gas in the BCS-BEC crossover region

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/06/2015

Relevância na Pesquisa

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#Condensed Matter - Strongly Correlated Electrons#Condensed Matter - Mesoscale and Nanoscale Physics#Condensed Matter - Other Condensed Matter#Condensed Matter - Quantum Gases#Condensed Matter - Superconductivity

We theoretically investigate a Bose-condensed exciton gas out of equilibrium.
Within the framework of the combined BCS-Leggett strong-coupling theory with
the non-equilibrium Keldysh formalism, we show how the Bose-Einstein
condensation (BEC) of excitons is suppressed to eventually disappear, when the
system is in the non-equilibrium steady state. The supply of electrons and
holes from the bath is shown to induce quasi-particle excitations, leading to
the partial occupation of the upper branch of Bogoliubov single-particle
excitation spectrum. We also discuss how this quasi-particle induction is
related to the suppression of exciton BEC, as well as the stability of the
steady state.; Comment: 7 pages, 2 figures, Proceedings of QFS-2015

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## Lattice Gauge Theory for Condensed Matter Physics: Ferromagnetic Superconductivity as its Example

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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Recent theoretical studies of various strongly-correlated systems in
condensed matter physics reveal that the lattice gauge theory(LGT) developed in
high-energy physics is quite a useful tool to understand physics of these
systems. Knowledges of LGT are to become a necessary item even for condensed
matter physicists. In the first part of this paper, we present a concise review
of LGT for the reader who wants to understand its basics for the first time.
For illustration, we choose the abelian Higgs model, a typical and quite useful
LGT, which is the lattice verison of the Ginzburg-Landau model interacting with
a U(1) gauge field (vector potential). In the second part, we present an
account of the recent progress in the study of ferromagnetic superconductivity
(SC) as an example of application of LGT to topics in condensed matter physics,
. As the ferromagnetism (FM) and SC are competing orders with each other, large
fluctuations are expected to take place and therefore nonperturbative methods
are required for theoretical investigation. After we introduce a LGT describing
the FMSC, we study its phase diagram and topological excitations (vortices of
Cooper pairs) by Monte-Carlo simulations.; Comment: 31 pages, 13 figures, Invited review article of Mod.Phys.Lett.B

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## Dynamics of Symmetry Breaking Out of Equilibrium: From Condensed Matter to QCD and the Early Universe

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/09/1999

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The dynamics of symmetry breaking during out of equilibrium phase transitions
is a topic of great importance in many disciplines, from condensed matter to
particle physics and early Universe cosmology with definite experimental
impact. In these notes we provide a summary of the relevant aspects of the
dynamics of symmetry breaking in many different fields with emphasis on the
experimental realizations. In condensed matter we address the dynamics of phase
ordering, the emergence of condensates, coarsening and dynamical scaling. In
QCD the possibility of disoriented chiral condensates of pions emerging during
a strongly out of equilibrium phase transition is discussed. We elaborate on
the dynamics of phase ordering in phase transitions in the Early Universe, in
particular the emergence of condensates and scaling in FRW cosmologies. We
mention some experimental efforts in different fields that study this wide
ranging phenomena and offer a quantitative theoretical description both at the
phenomenological level in condensed matter, introducing the scaling hypothesis
as well as at a microscopic level in quantum field theories. The emergence of
semiclassical condensates and a dynamical length scale is shown in detail, in
quantum field theory this length scale is constrained by causality. The large N
limit provides a natural bridge to compare the solutions in different settings
and to establish similarities and differences.; Comment: 35 pages...

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## Cold Rydberg atoms for quantum simulation of exotic condensed matter interactions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 28/10/2013

Relevância na Pesquisa

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#Condensed Matter - Strongly Correlated Electrons#Condensed Matter - Superconductivity#Physics - Atomic Physics

Quantum simulators could provide an alternative to numerical simulations for
understanding minimal models of condensed matter systems in a controlled way.
Typically, cold atom systems are used to simulate e.g. Hubbard models. In this
paper, we discuss a range of exotic interactions that can be formed when cold
Rydberg atoms are loaded into optical lattices with unconventional geometries;
such as long-range electron-phonon interactions and extended Coulomb like
interactions. We show how these can lead to proposals for quantum simulators
for complex condensed matter systems such as superconductors. Continuous time
quantum Monte Carlo is used to compare the proposed schemes with the physics
found in traditional condensed matter Hamiltonians for systems such as high
temperature superconductors.

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## Zoology of condensed matter: Framids, ordinary stuff, extra-ordinary stuff

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 15/01/2015

Relevância na Pesquisa

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#High Energy Physics - Theory#Condensed Matter - Other Condensed Matter#General Relativity and Quantum Cosmology

We classify condensed matter systems in terms of the spacetime symmetries
they spontaneously break. In particular, we characterize condensed matter
itself as any state in a Poincar\'e-invariant theory that spontaneously breaks
Lorentz boosts while preserving at large distances some form of spatial
translations, time-translations, and possibly spatial rotations. Surprisingly,
the simplest, most minimal system achieving this symmetry breaking
pattern---the "framid"---does not seem to be realized in Nature. Instead,
Nature usually adopts a more cumbersome strategy: that of introducing internal
translational symmetries---and possibly rotational ones---and of spontaneously
breaking them along with their space-time counterparts, while preserving
unbroken diagonal subgroups. This symmetry breaking pattern describes the
infrared dynamics of ordinary solids, fluids, superfluids, and---if they
exist---supersolids. A third, "extra-ordinary", possibility involves replacing
these internal symmetries with other symmetries that do not commute with the
Poincar\'e group, for instance the galileon symmetry, supersymmetry or gauge
symmetries. Among these options, we pick the systems based on the galileon
symmetry, the "galileids", for a more detailed study. Despite some similarity...

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## Ultracold atomic gases in optical lattices: mimicking condensed matter physics and beyond

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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We review recent developments in the physics of ultracold atomic and
molecular gases in optical lattices. Such systems are nearly perfect
realisations of various kinds of Hubbard models, and as such may very well
serve to mimic condensed matter phenomena. We show how these systems may be
employed as quantum simulators to answer some challenging open questions of
condensed matter, and even high energy physics. After a short presentation of
the models and the methods of treatment of such systems, we discuss in detail,
which challenges of condensed matter physics can be addressed with (i)
disordered ultracold lattice gases, (ii) frustrated ultracold gases, (iii)
spinor lattice gases, (iv) lattice gases in "artificial" magnetic fields, and,
last but not least, (v) quantum information processing in lattice gases. For
completeness, also some recent progress related to the above topics with
trapped cold gases will be discussed.; Comment: Review article. v2: published version, 135 pages, 34 figures

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## The Onset of Phase Transitions in Condensed Matter and Relativistic QFT

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/01/2000

Relevância na Pesquisa

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Kibble and Zurek have provided a unifying causal picture for the appearance
of topological defects like cosmic strings or vortices at the onset of phase
transitions in relativistic QFT and condensed matter systems respectively.
There is no direct experimental evidence in QFT, but in condensed matter the
predictions are largely, but not wholly, supported in superfluid experiments on
liquid helium. We provide an alternative picture for the initial appearance of
strings/vortices that is commensurate with all the experimental evidence from
condensed matter and consider some of its implications for QFT.; Comment: 37 pages, to be published in Condensed Matter Physics, 2000

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## Visibility of the Amplitude (Higgs) Mode in Condensed Matter

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

457.72773%

#Condensed Matter - Superconductivity#Condensed Matter - Quantum Gases#Condensed Matter - Statistical Mechanics#Condensed Matter - Strongly Correlated Electrons

The amplitude mode is a ubiquitous collective excitation in condensed matter
systems with broken continuous symmetry. It is expected in antiferromagnets,
short coherence length superconductors, charge density waves, and lattice Bose
condensates. Its detection is a valuable test of the corresponding field
theory, and its mass gap measures the proximity to a quantum critical point.
However, since the amplitude mode can decay into low-energy Goldstone modes,
its experimental visibility has been questioned. Here we show that the
visibility depends on the symmetry of the measured susceptibility. The
longitudinal susceptibility diverges at low frequency as \chi_{\sigma\sigma} ~
i/\omega (d=2) or log(1/|\omega|) (d=3), which can completely obscure the
amplitude peak. In contrast, the scalar susceptibility is suppressed by four
extra powers of frequency, exposing the amplitude peak throughout the ordered
phase. We discuss experimental setups for measuring the scalar susceptibility.
The conductivity of the O(2) theory (relativistic superfluid) is a scalar
response and therefore exhibits suppressed absorption below the Higgs mass
threshold, \sigma ~ \omega^{2d+1}. In layered, short coherence length
superconductors, (relevant e.g. to cuprates) this threshold is raised by the
interlayer plasma frequency.; Comment: 17 pages...

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## Proceedings of the 35th Annual Australian/New Zealand Condensed Matter and Materials Meeting

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 18/07/2011

Relevância na Pesquisa

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The 35th Australian/New Zealand Annual Condensed Matter and Materials Meeting
was held at the Charles Sturt University campus in Wagga Wagga, NSW, Australia
from the 1st to the 4th of February 2011. The conference was attended by 92
delegates from a range of universities across Australia, New Zealand and
further afield.
There were a total of 9 invited and 21 contributed talks during the three
days of scientific sessions, as well as 2 poster sessions with a total of 49
poster presentations. All presenters were invited to submit a manuscript for
publication in the conference proceedings. The length limits where six pages
for invited papers and four pages for contributed papers. Each manuscript was
reviewed by two anonymous referees and 18 papers were accepted for publication.
The accepted manuscripts are also available at the online publication section
of the Australian Institute of Physics national web site
(http://www.aip.org.au/).; Comment: A.P. Micolich (Editor), ISBN 978-0-646-55969-8 (2011). 18 papers from
35th Australian/New Zealand Annual Condensed Matter and Materials Meeting, 85
pages

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## Atomistic misconception of current model for condensed matter evaporation and new formulation

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/05/2014

Relevância na Pesquisa

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Even though the phenomenon of evaporation is omnipresent and has immense
scientific and technological importance, the research effort to unveil its
fundamentals remains inadequately low. As one particular consequence, the
textbooks and educational courses are lacking detailed explanation of
evaporation and its effects. In order to advance fundamental theory of
evaporation and increase accuracy of evaporation simulation a novel evaporation
theory is presented. This integrated Atomistic(Molecular)-Kinetics-Gasdynamics
theoretical model that combines statistical mechanics, gas dynamics and
thermodynamics approaches opens a path to detailed description of
nonstationary, nonequilibrium evaporation of condensed matter. The main
innovation of the proposed approach is that, unlike all previous and current
models of evaporation that are based on the assumption of evaporation as
emission of the particles that are not bound within the condense phase, the
described new model treats evaporation of condensed phase as escape of the
particles of sufficient kinetic energy out of potential well located at the
boundary of condensed and gaseous phases. Correspondingly, the re-condensation
of the vapor onto the surface is treated as entrapment of the vapor particles
with kietic energy lower than the depth of the potential well. The described
novel research will open new opportunities to substantially advance our
knowledge and provide needed contributions to chemical...

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## Amplitude / Higgs Modes in Condensed Matter Physics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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The order parameter and its variations in space and time in many different
states in condensed matter physics at low temperatures are described by the
complex function $\Psi({\bf r}, t)$. These states include superfluids,
superconductors, and a subclass of antiferromagnets and charge-density waves.
The collective fluctuations in the ordered state may then be categorized as
oscillations of phase and amplitude of $\Psi({\bf r}, t)$. The phase
oscillations are the {\it Goldstone} modes of the broken continuous symmetry.
The amplitude modes, even at long wavelengths, are well defined and decoupled
from the phase oscillations only near particle-hole symmetry, where the
equations of motion have an effective Lorentz symmetry as in particle physics,
and if there are no significant avenues for decay into other excitations. They
bear close correspondence with the so-called {\it Higgs} modes in particle
physics, whose prediction and discovery is very important for the standard
model of particle physics. In this review, we discuss the theory and the
possible observation of the amplitude or Higgs modes in condensed matter
physics -- in superconductors, cold-atoms in periodic lattices, and in uniaxial
antiferromagnets. We discuss the necessity for at least approximate
particle-hole symmetry as well as the special conditions required to couple to
such modes because...

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## What can gauge-gravity duality teach us about condensed matter physics?

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

456.05973%

I discuss the impact of gauge-gravity duality on our understanding of two
classes of systems: conformal quantum matter and compressible quantum matter.
The first conformal class includes systems, such as the boson Hubbard model
in two spatial dimensions, which display quantum critical points described by
conformal field theories. Questions associated with non-zero temperature
dynamics and transport are difficult to answer using conventional field
theoretic methods. I argue that many of these can be addressed systematically
using gauge-gravity duality, and discuss the prospects for reliable computation
of low frequency correlations.
Compressible quantum matter is characterized by the smooth dependence of the
charge density, associated with a global U(1) symmetry, upon a chemical
potential. Familiar examples are solids, superfluids, and Fermi liquids, but
there are more exotic possibilities involving deconfined phases of gauge fields
in the presence of Fermi surfaces. I survey the compressible systems studied
using gauge-gravity duality, and discuss their relationship to the condensed
matter classification of such states. The gravity methods offer hope of a
deeper understanding of exotic and strongly-coupled compressible quantum
states.; Comment: 34 pages...

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## Thermodynamic QED Coherence in Condensed Matter: Microscopic Basis of Thermal Superradiance

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 26/09/2002

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Electromagnetic superradiant field coherence exists in a condensed matter
system if the electromagnetic field oscillators undergo a mean displacement.
Transitions into thermal states with ordered superradiant phases have been
shown to theoretically exist in Dicke-Preparata models. The theoretical
validity of these models for condensed matter has been called into question due
to non-relativistic diamagnetic terms in the electronic Hamiltonian. The
microscopic bases of Dicke-Preparata thermal superradiance for realistic
macroscopic systems are explored in this work. The impossibility of diaelectric
correlations in condensed matter systems (via the Landau-Lifshitz theorem)
provides a strong theoretical basis for understanding the physical reality of
condensed matter thermodynamic superradiant phases.; Comment: 11 pages, no figures, LaTeX format

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## Finite temperature effects in Bose-Einstein Condensed dark matter halos

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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#Astrophysics - Astrophysics of Galaxies#Condensed Matter - Quantum Gases#General Relativity and Quantum Cosmology

Once the critical temperature of a cosmological boson gas is less than the
critical temperature, a Bose-Einstein Condensation process can always take
place during the cosmic history of the universe. Zero temperature condensed
dark matter can be described as a non-relativistic, Newtonian gravitational
condensate, whose density and pressure are related by a barotropic equation of
state, with barotropic index equal to one. In the present paper we analyze the
effects of the finite dark matter temperature on the properties of the
Bose-Einstein Condensed dark matter halos. We formulate the basic equations
describing the finite temperature condensate, representing a generalized
Gross-Pitaevskii equation that takes into account the presence of the thermal
cloud. The static condensate and thermal cloud in thermodynamic equilibrium is
analyzed in detail, by using the Hartree-Fock-Bogoliubov and Thomas-Fermi
approximations. The condensed dark matter and thermal cloud density and mass
profiles at finite temperatures are explicitly obtained. Our results show that
when the temperature of the condensate and of the thermal cloud are much
smaller than the critical Bose-Einstein transition temperature, the zero
temperature density and mass profiles give an excellent description of the dark
matter halos. However...

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## Spin-polarized muons in condensed matter physics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/07/2002

Relevância na Pesquisa

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#Condensed Matter - Strongly Correlated Electrons#Condensed Matter - Materials Science#Condensed Matter - Superconductivity

A positive muon is a spin-1/2 particle. Beams of muons with all their spins
polarized can be prepared and subsequently implanted in various types of
condensed matter. The subsequent precession and relaxation of their spins can
then be used to investigate a variety of static and dynamic effects in a sample
and hence to deduce properties concerning magnetism, superconductivity and
molecular dynamics. Though strictly a lepton, and behaving essentially like a
heavy electron, it is convenient to think of a muon as a light proton, and it
is often found with a captured electron in a hydrogen-like atom known as
muonium. This article outlines the principles of various experimental
techniques which involve implanted muons and describes some recent
applications. The use of muons in condensed matter physics has shed new light
on subjects as diverse as passivation in semiconductors, frustrated spin
systems, vortex lattice melting, and quantum diffusion of light particles.; Comment: 17 pages, 21 figures, review article

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## The Fermi Gases and Superfluids: Short Review of Experiment and Theory for Condensed Matter Physicists

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/02/2012

Relevância na Pesquisa

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The study of ultracold atomic Fermi gases is a rapidly exploding subject
which is defining new directions in condensed matter and atomic physics. Quite
generally what makes these gases so important is their remarkable tunability
and controllability. Using a Feshbach resonance one can tune the attractive
two-body interactions from weak to strong and thereby make a smooth crossover
from a BCS superfluid of Cooper pairs to a Bose-Einstein condensed superfluid.
Furthermore, one can tune the population of the two spin states, allowing
observation of exotic spin-polarized superfluids, such as the Fulde Ferrell
Larkin Ovchinnikov (FFLO) phase. A wide array of powerful characterization
tools, which often have direct condensed matter analogues, are available to the
experimenter. In this Chapter, we present a general review of the status of
these Fermi gases with the aim of communicating the excitement and great
potential of the field.; Comment: 34 pages, 15 figures. To appear as a chapter in "Contemporary
Concepts of Condensed Matter Science", Elsevier

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## Microscopic theory of non-adiabatic response in real and imaginary time

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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We present a general approach to describe slowly driven quantum systems both
in real and imaginary time. We highlight many similarities, qualitative and
quantitative, between real and imaginary time evolution. We discuss how the
metric tensor and the Berry curvature can be extracted from both real and
imaginary time simulations as a response of physical observables. For quenches
ending at or near the quantum critical point, we show the utility of the
scaling theory for detecting the location of the quantum critical point by
comparing sweeps at different velocities. We briefly discuss the universal
relaxation to equilibrium of systems after a quench. We finally review recent
developments of quantum Monte Carlo methods for studying imaginary-time
evolution. We illustrate our findings with explicit calculations using the
transverse field Ising model in one dimension.; Comment: 22 pages, 10 figures, revised version, contribution to the special
issue of J. Phys. Condensed Matter: "Condensed matter analogues of
cosmology", edited by T. Kibble and Ajit Srivastava

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## Planetary Atmospheres as Non-Equilibrium Condensed Matter

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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#Condensed Matter - Statistical Mechanics#Physics - Atmospheric and Oceanic Physics#Physics - Fluid Dynamics

Planetary atmospheres, and models of them, are discussed from the viewpoint
of condensed matter physics. Atmospheres are a form of condensed matter, and
many interesting phenomena of condensed matter systems are realized by them.
The essential physics of the general circulation is illustrated with idealized
2-layer and 1-layer models of the atmosphere. Equilibrium and non-equilibrium
statistical mechanics are used to directly ascertain the statistics of these
models.; Comment: 23 pages, 10 figures, to appear in Annual Reviews of Condensed Matter
Physics (2012). Rhines scale (Eq. 25) corrected, one reference moved, and
updates to other citations

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## Causality and non-equilibrium second-order phase transitions in inhomogeneous systems

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

549.4809%

When a second-order phase transition is crossed at fine rate, the evolution
of the system stops being adiabatic as a result of the critical slowing down in
the neighborhood of the critical point. In systems with a topologically
nontrivial vacuum manifold, disparate local choices of the ground state lead to
the formation of topological defects. The universality class of the transition
imprints a signature on the resulting density of topological defects: It obeys
a power law in the quench rate, with an exponent dictated by a combination of
the critical exponents of the transition. In inhomogeneous systems the
situation is more complicated, as the spontaneous symmetry breaking competes
with bias caused by the influence of the nearby regions that already chose the
new vacuum. As a result, the choice of the broken symmetry vacuum may be
inherited from the neighboring regions that have already entered the new phase.
This competition between the inherited and spontaneous symmetry breaking
enhances the role of causality, as the defect formation is restricted to a
fraction of the system where the front velocity surpasses the relevant sound
velocity and phase transition remains effectively homogeneous. As a
consequence, the overall number of topological defects can be substantially
suppressed. When the fraction of the system is small...

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