Página 1 dos resultados de 209552 itens digitais encontrados em 0.088 segundos

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

Lazar, Emanuel A.; Han, Jian; Srolovitz, David J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.86%
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...

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

Ichinose, Ikuo; Matsui, Tetsuo
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.86%
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

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

Boyanovsky, D.; de Vega, H. J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.86%
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...

## Quantum phase transition for the BEC--BCS crossover in condensed matter physics and CPT violation in elementary particle physics

Klinkhamer, F. R.; Volovik, G. E.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.92%
We discuss the quantum phase transition that separates a vacuum state with fully-gapped fermion spectrum from a vacuum state with topologically-protected Fermi points (gap nodes). In the context of condensed-matter physics, such a quantum phase transition with Fermi point splitting may occur for a system of ultracold fermionic atoms in the region of the BEC-BCS crossover, provided Cooper pairing occurs in the non-s-wave channel. For elementary particle physics, the splitting of Fermi points may lead to CPT violation, neutrino oscillations, and other phenomena.; Comment: 13 pages, 1 figure, v3: published version

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

Hague, J. P.; Downes, S.; MacCormick, C.; Kornilovitch, P. E.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.89%
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.

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

Nicolis, Alberto; Penco, Riccardo; Piazza, Federico; Rattazzi, Riccardo
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.86%
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...

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

Lewenstein, Maciej; Sanpera, Anna; Ahufinger, Veronica; Damski, Bogdan; De, Aditi Sen; Sen, Ujjwal
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.89%
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

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

Rivers, R. J.; Kavoussanaki, E.; Karra, G.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.89%
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

## Theory of the colossal Van-der-Waals binding in soft and hard condensed matter

Georgiev, Mladen; Gochev, Alexander; Singh, Jai
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.9%
A simple theory is proposed for the dispersive molecular binding of unusually high magnitude due to an enhanced polarizability. Two alternative ways have so far been considered in the literature leading to the polarizability enhancement: (i) a vibronic energy level gap narrowing, as proposed by us with regard to a hypothetical exciton matter, and (ii) a giant electric dipole in a Rydberg state of constituent atoms, as proposed by Gilman with regard to an enigmatic substance building the ball lightning. We now combine the two mechanisms to obtain concrete expressions for the colossal binding energy. The problem is exemplified for a three-level system coupled to the umbrella mode of an ammonia molecule. Other possibilities for the design of enhanced-polarizability molecules are also discussed. The colossal Van-der-Waals binding is most likely to materialize in hard condensed matter and perhaps less so in soft condensed matter.; Comment: 20 pages, 3 figures, pdf format

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

Podolsky, Daniel; Auerbach, Assa; Arovas, Daniel P.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.89%
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...

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

Radhanpura, K.; Hargreaves, S.; Lewis, R. A.; Krüger, H.; Rey, E.; Si, P. -Z.; Söhnel, T.; Jovic, V.; Metson, J. B.; Waterhouse, G. I. N.; Abiona, A. A.; Kemp, W. J.; Byrne, A. P.; Ridgeway, M. C.; Timmers, H.; Cashion, J. D.; Gates, W. P.; Greaves, T.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.89%
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

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

Semak, V. V.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.89%
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...

## Amplitude / Higgs Modes in Condensed Matter Physics

Pekker, David; Varma, C. M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.92%
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...

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

Sachdev, Subir
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.87%
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...

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

Sivasubramanian, S.; Widom, A.; Srivastava, Y. N.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.89%
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

## Spin-polarized muons in condensed matter physics

Blundell, S. J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.89%
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

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

Levin, K.; Hulet, Randall G.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.88%
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

## Shock (Blast) Mitigation by "Soft" Condensed Matter

Nesterenko, Vitali F.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.9%
It is a common point that "soft" condensed matter (like granular materials or foams) can reduce damage caused by impact or explosion. It is attributed to their ability to absorb significant energy. This is certainly the case for a quasistatic type of deformation at low velocity of impact where such materials are widely used for packing of fragile devices. At the same time a mitigation of blast phenomena must take into account shock wave properties of "soft" matter which very often exhibit highly nonlinear, highly heterogeneous and dissipative behavior. This paper considers applications of "soft" condensed matter for blast mitigation using simplified approach, presents analysis of some anomalous effects and suggestions for future research in this exciting area.; Comment: 12 pages, 12 figures

## Non-equilibrium phase transitions in condensed matter and cosmology: spinodal decomposition, condensates and defects

Boyanovsky, D.; de Vega, H. J.; Holman, R.
Tipo: Artigo de Revista Científica