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Clustered States as a New Paradigm of Condensed Matter Physics

Alvarez, G.; Dagotto, E.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
We argue that several materials of much current interest in condensed matter physics share common phenomenological aspects that only very recent investigations are unveiling. The list includes colossal magnetoresistance manganites, high temperature superconducting cuprates, diluted magnetic semiconductors, and others. The common aspect is the relevance of intrinsic inhomogeneities in the form of "clustered states", as explained in the text.; Comment: elsart3, 6 pages, 5 figures. Invited paper for the Conference Proceedings of the International Conference on Magnetism, Rome, July 2003

Two-dimensional delta potential wells and condensed-matter physics

de Llano, M.; Salazar, A.; Solis, M. A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
It is well-known that a delta potential well in 1D has only one bound state but that in 3D it supports an {\it infinite} number of bound states with {\it infinite} binding energy for the lowest level. We show how this also holds for the less familiar 2D case, and then discuss why this makes 3D delta potential wells unphysical as models of interparticle interactions for condensed-matter many-body systems. However, both 2D and 3D delta wells can be regularized'' to support a single bound level which in turn renders them conveniently simple single-parameter interactions, e.g., for modeling the pair-forming dynamics of quasi-2D superconductors such as the cuprates, or in 3D of other superconductors and of neutral-fermion superfluids such as ultra-cold trapped Fermi gases.; Comment: 19 pages including 5 figures

"Turbulent" electrical transport in Copper powders

Falcon, Eric; Castaing, Bernard; Laroche, Claude
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
Compressed copper powder has a very large electrical resistance (1MOhm), due to the oxide layer on grains (100 micro m). We observe that its voltage-current U-I characteristics are nonlinear, and undergo an instability, from an insulating to a conductive state at relatively small applied voltages. Current through the powder is then noisy, and the noise has interesting self-similar properties, including intermittency and scale invariance. We show that heat dissipation plays an essential role in the physics of the system. One piece of evidence is that the instability threshold always corresponds to the same Joule dissipated power whatever the applied stress. In addition, we observe long-time correlations which suggest that thermal expansion locally creates or destroys contacts, and is the driving mechanism behind the instability and noise observed in this granular system.; Comment: Final version. To be published in Europhysics Letters

Majorana and Condensed Matter Physics

Wilczek, Frank
Tipo: Artigo de Revista Científica
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449.4809%
Ettore Majorana contributed several ideas that have had significant, lasting impact in condensed matter physics, broadly construed. Here I will discuss, from a modern perspective, four important topics that have deep roots in Majorana's work: 1. Spin Response and Universal Connection; 2. Level Crossing and Generalized Laplace Transform; 3. Majorana Fermions, From Neutrinos to Electrons; 4. Majorinos and Emergent Symmetry.; Comment: 28 pages, no figures

A short guide to topological terms in the effective theories of condensed matter

Tanaka, Akihiro; Takayoshi, Shintaro
Tipo: Artigo de Revista Científica
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449.4809%
This article is meant as a gentle introduction to the "topological terms" that often play a decisive role in effective theories describing topological quantum effects in condensed matter systems. We first take up several prominent examples, mainly from the area of quantum magnetism and superfluids/superconductors. We then briefly discuss how these ideas are now finding incarnations in the studies of symmetry-protected topological phases, which are in a sense the generalization of the concept of topological insulators to a wider range of materials, including magnets and cold atoms.; Comment: 18 pages, 6 figures, Pedagogical review article written for the focus issue "Materials Science of Topological Insulators and Superconductors" of the journal, Science and Technology of Advanced Materials (STAM)

System of particles with interaction and the cluster formation in condensed matter

Krasnoholovets, Volodymyr; Lev, Bohdan
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
We investigate the behaviour of a system of particles with the different character of interaction. The approach makes it possible to describe systems of interacting particles by statistical methods taking into account a spatial nonhomogeneous distribution of particles, i.e. cluster formation. For these clusters are evaluated: their size, the number of particles in a cluster, and the temperature of phase transition to the cluster state. Three systems are under consideration: electrons on the liquid helium surface, particles interacting by the shielding Coulomb potential, which are found under the influence of an elastic field (e.g. nucleons in a nucleus), and gravitating masses with the Hubble expansion.; Comment: 17 pages, submitted to Condensed Matter Physics; References have been revised. Changes caused by the referee's criticism have been introduced

Condensed Matter Applications of Entanglement Theory

Schuch, Norbert
Tipo: Artigo de Revista Científica
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449.4809%
These are lecture notes from the 44th IFF Spring School "Quantum Information Processing" in Juelich, discussing applications of entanglement theory in condensed matter. The focus of the notes is on tensor network states, in particular Matrix Product States (MPS) and Projected Entangled Pair States (PEPS), which provide an efficient description of many-body states based on their entanglement structure; both numerical and analytical aspects of tensor networks are being covered. The notes close with a brief introduction to quantum complexity, which allows to assess the limitations to our ability to simulate quantum many-body systems.; Comment: Lecture notes for the 44th IFF Spring School "Quantum Information Processing" in Juelich, 2013. 29 pages

Goldstone and Pseudo-Goldstone Bosons in Nuclear, Particle and Condensed-Matter Physics

Burgess, C. P.
Tipo: Artigo de Revista Científica
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449.4809%
These notes review the effective lagrangian treatment of Goldstone and pseudo-Goldstone bosons, taking examples from high-energy/nuclear and condensed-matter physics. The contents are: 1. Goldstone Bosons 2. Pions: A Relativistic Application 3. Magnons: Nonrelativistic Applications 4. SO(5) Invariance and Superconductors 5. Bibliography; Comment: 119 pages, LaTeX, five figures included with epsf. Lectures given to NUSS98, Seoul National University, June 1998. Typos cleaned up and minor changes to improve the presentation

Effective Holographic Theories for low-temperature condensed matter systems

Charmousis, C.; Goutéraux, B.; Kim, B. S.; Kiritsis, E.; Meyer, Rene
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
The IR dynamics of effective holographic theories capturing the interplay between charge density and the leading relevant scalar operator at strong coupling are analyzed. Such theories are parameterized by two real exponents $(\gamma,\delta)$ that control the IR dynamics. By studying the thermodynamics, spectra and conductivities of several classes of charged dilatonic black hole solutions that include the charge density back reaction fully, the landscape of such theories in view of condensed matter applications is characterized. Several regions of the $(\gamma,\delta)$ plane can be excluded as the extremal solutions have unacceptable singularities. The classical solutions have generically zero entropy at zero temperature, except when $\gamma=\delta$ where the entropy at extremality is finite. The general scaling of DC resistivity with temperature at low temperature, and AC conductivity at low frequency and temperature across the whole $(\gamma,\delta)$ plane, is found. There is a codimension-one region where the DC resistivity is linear in the temperature. For massive carriers, it is shown that when the scalar operator is not the dilaton, the DC resistivity scales as the heat capacity (and entropy) for planar (3d) systems. Regions are identified where the theory at finite density is a Mott-like insulator at T=0. We also find that at low enough temperatures the entropy due to the charge carriers is generically larger than at zero charge density.; Comment: (v3): Added discussion on the UV completion of the solutions...

Horizons, holography and condensed matter

Hartnoll, Sean A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
The holographic correspondence creates an interface between classical gravitational physics and the dynamics of strongly interacting quantum field theories. This chapter will relate the physics of charged, asymptotically Anti-de Sitter spacetimes to the phenomenology of low temperature critical phases of condensed matter. Common essential features will characterise both the gravitational and field theoretic systems. Firstly, an emergent scaling symmetry at the lowest energy scales appears as an emergent isometry in the interior, near horizon' regime of the spacetime. Secondly, the field theoretic distinction between fractionalized and mesonic phases appears as the presence or absence of a charge-carrying horizon in the spacetime. A perspective grounded in these two characteristics allows a unified presentation of holographic superconductors', electron stars' and charged dilatonic spacetimes'.; Comment: 34 pages. Chapter of the book `Black Holes in Higher Dimensions' to be published by Cambridge University Press (editor: G. Horowitz). v2 typos corrected, references added

Internal Space Renormalization Group Methods for Atomic and Condensed Matter Physics

Polonyi, Janos
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
The functional renormalization group method is used to take into account the vacuum polarization around localized bound states generated by external potential. The application to Atomic Physics leads to improved Hartree-Fock and Kohn-Sham equations in a systematic manner within the framework of the Density Functional Theory. Another application to Condensed Matter Physics consists of an algorithm to compute quenched averages with or without Coulomb interaction in a non-perturbative manner.; Comment: Talk presented at the Conference "Renormalization Group 2002 (RG-2002)" Strba, Slovakia, March 2002, 6 pages no figures

String Defects in Condensed Matter Systems as Optical Fibers

Srivastava, Ajit Mohan
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
We analyze the core structure of string defects in various condensed matter systems, such as nematic liquid crystals and superfluid helium, and argue that in certain cases the variation of the refractive index near the core is such that it can lead to total internal reflection of light travelling along the string core. These strings thus behave as optical fibers providing a qualitatively new approach to optical fibers. We present a candidate for such a fiber by looking at string segments in a thin nematic liquid crystal film on water. We discuss various possibilities for constructing such fibers as well as possible technological applications.; Comment: 8 pages, in LATEX, 1 figure (not included)

Various condensed matter Hamiltonians in terms of U(2/2) operators and their symmetry structures

Okumura, Ko
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
We rewrite various lattice Hamiltonian in condensed matter physics in terms of U(2/2) operators that we introduce. In this representation the symmetry structure of the models becomes clear. Especially, the Heisenberg, the supersymmetric t-J and a newly proposed high-$T_c$ superconducting Hamiltonian reduce to the same form $H=$$-t\sum_{}\sum_{ac}X^{ac}_j X^{ca}_k (-1)^{F(c)}$. This representation also gives us a systematic way of searching for the symmetries of the system.; Comment: 13 pages, LatTeX, CCNY-HEP-92/7

Local topological phase transitions in periodic condensed matter systems

Budich, Jan Carl; Trauzettel, Björn
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
Topological properties of a periodic condensed matter system are global features of its Brillouin zone (BZ). In contrast, the validity of effective low energy theories is usually limited to the vicinity of a high symmetry point in the BZ. We derive a general criterion under which the control parameter of a topological phase transition localizes the topological defect in an arbitrarily small neighbourhood of a single point in $k$-space upon approaching its critical value. Such a local phase transition is associated with a Dirac-like gap closing point, whereas a flat band transition is not localized in $k$-space. This mechanism and its limitations are illustrated with the help of experimentally relevant examples such as HgTe/CdTe quantum wells and bilayer graphene nanostructures.

Theoretical spectroscopy of realistic condensed matter systems

Caramella, Lucia
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
This thesis is devoted to ab initio calculations of ground and excited state properties of different systems within density functional theory and time dependent density functional theory. From the numerical point of view we implemented an original method in the DP code to calculate the independent particle response function. Moreover, we generalized the DP code to the spin degree of freedom in order to study the magnetic properties of realistic condensed matter systems. We studied reflectance anisotropy and energy loss spectra of a clean and oxidized surface, and we performed an analysis of the origin of the main spectral features. Thanks to the comparison between experimental and theoretical energy loss spectra, we roule out the p(2x1) reconstruction for the Si(100) surface. Moreover, in the case of a simple BeH molecule we evidenced the problem of correctly describing the excitation spectra for open shell systems within the TDDFT framework. In the second part of the thesis, we presented the study of the optical properties of magnetic systems such as FeS2, CoS2 or NiS2, interesting materials for possible technological applications in the growing field of spintronics. Within this context we calculated ground state properties and optical condictivity of BCC bulk iron...

Lectures on holographic methods for condensed matter physics

Hartnoll, Sean A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
These notes are loosely based on lectures given at the CERN Winter School on Supergravity, Strings and Gauge theories, February 2009 and at the IPM String School in Tehran, April 2009. I have focused on a few concrete topics and also on addressing questions that have arisen repeatedly. Background condensed matter physics material is included as motivation and easy reference for the high energy physics community. The discussion of holographic techniques progresses from equilibrium, to transport and to superconductivity.; Comment: 1+85 pages. 15 figures. v2: typos fixed and references added. v3: another typo fixed

Determination of the effective transverse coherence of the neutron wave packet as employed in reflectivity investigations of condensed matter structures Part I: Measurements

Majkrzak, Charles F.; Metting, Christopher; Maranville, Brian B.; Dura, Joseph A.; Satija, Sushil; Udovic, Terrence; Berk, Norman F.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
The primary purpose of this investigation is to determine the effective coherent extent of the neutron wave packet transverse to its mean propagation vector k, when it is prepared in a typical instrument used to study the structure of materials in thin film form via specular reflection. There are two principal reasons for doing so. One has to do with the fundamental physical interest in the characteristics of a free neutron as a quantum object while the other is of a more practical nature, relating to the understanding of how to interpret elastic scattering data when the neutron is employed as a probe of condensed matter structure on an atomic or nanometer scale. Knowing such a basic physical characteristic as the neutron's effective transverse coherence can dictate how to properly analyze specular reflectivity data obtained for material film structures possessing some amount of in-plane inhomogeneity. In this study we describe a means of measuring the effective transverse coherence length of the neutron wave packet by specular reflection from a series of diffraction gratings of different spacings. Complementary non-specular measurements of the widths of grating reflections were also performed which corroborate the specular results. (Part I principally describes measurements interpreted according to the theoretical picture presented in Part II.) Each grating was fabricated by lift-off photo-lithography patterning of a nickel film (approximately 1000 Angstroms thick) formed by physical vapor deposition on a flat silicon crystal surface. The grating periods ranged from 10 microns (5 microns Ni stripe...

Finite temperature many-particle theory of condensed matter systems in the functional Schroedinger picture

Noh, Hyun Sik; You, Sang Koo; Kim, Chul Koo
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.4809%
A finite temperature many-particle theory of condensed matter systems is formulated using the functional Schroedinger picture. Using the interacting electron gas as a model system, we solve the equation of motion for the density matrix variationally with a Gaussian type trial density matrix. We show that the present formalism yields the finite temperature Hartree-Fock results both for the para- and ferromagnetic states in a simple and convenient fashion. Implications of the present results and future prospects are also discussed.; Comment: 12pages, to appear in Int. J. Mod. Phys. B

Effective Field Theory in Condensed Matter Physics

Shankar, R.
Tipo: Artigo de Revista Científica
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449.4809%
Some personal reminiscences are followed by a brief illustration of how effective field theories are used in condensed matter physics. Examples include Landau's Fermi liquid, sigma models with topological terms, Dirac fermions and the Gross Neveu model.; Comment: 10 pages , 4 eps figures Latex Typos fixed

Affleck, Ian