Strongly correlated electron systems

Reports on progress in physics. Physical Society (Great Britain), 2017

Solid state physics, 2006

2020

The understanding of material systems with strong electron-electron interactions is the central problem in modern condensed matter physics. Despite this, the essential physics of many of these materials is still not understood and we have no overall perspective on their properties. Moreover, we have very little ability to make predictions in this class of systems. In this manuscript we share our personal views of what the major open problems are in correlated electron systems and we discuss some possible routes to make progress in this rich and fascinating field. This manuscript is the result of the vigorous discussions and deliberations that took place at Johns Hopkins University during a three-day workshop January 27, 28, and 29, 2020 that brought together six senior scientists and 46 more junior scientists. Our hope, is that the topics we have presented will provide inspiration for others working in this field and motivation for the idea that significant progress can be made on v...

2009

Many important advances in the physics of strongly correlated electron systems have been driven by the development of new materials: for instance the filled skutterudites MT 4 X 12 (M ¼ alkali metal, alkaline earth, lanthanide, or actinide; T ¼ Fe, Ru, or Os; X ¼ P, As, or Sb), certain lanthanide and actinide intermetallic compounds such as URu 2Àx Re x Si 2 and CeTIn 5 (T ¼ Co, Rh, or Ir), and layered oxypnictides and related materials. These types of complex multinary d-and f-electron compounds have proven to be a vast reservoir of novel strongly correlated electron ground states and phenomena. In these materials, the occurrence of such a wide range of ground states and phenomena arises from a delicate interplay between competing interactions that can be tuned by partial or complete substitution of one element for another, as well as the application of pressure, and magnetic fields, resulting in rich and complex electronic phase diagrams in the hyperspace of temperature, chemical composition, pressure and magnetic field. It seems clear that this type of ''materials driven physics'' will continue to play a central role in the development of the field of strongly correlated electron systems in the future, through the discovery of new materials that exhibit unexpected phenomena and experiments on known materials in an effort to optimize their physical properties and test relevant theories.

Advanced Materials, 2012

2011

Science, 1988

Heavy-electron metals exhibit highly correlated electronic behavior at liquid helium temperatures, with conductionelectron masses some hundred times the free-electron mass. Whether "normal," antiferromagnetic, or superconducting, their electronic behavior differs drastically from their ordinary metallic counterparts. The physical origin ofthe large mass and unusual superconducting and magnetic properties is the strong coupling between the conduction electrons and the local f-electron moment fluctuations characteristic of these materials. T HE DISCOVERY AND EXPLORATION OF HIGHLY CORRELATed states of condensed matter in this century have opened new chapters in physics. Recent examples include the superfluidity of3He and the quantized Hall effect (2). In this article we review the properties of another set ofnew states, those found in heavy-electron systems, electrically conducting materials in which the conduction-electron specific heat is typically some 100 times larger than that found in most metals (3). As may be seen in , at low temperatures these systems either remain "normal," become antiferromagnetic, or become superconducting (4-17). Each of these highly correlated states displays properties that are dramatically different from their counterparts in ordinary metals.

Physica Scripta, 2012

The principal dilemma of real-space pairing versus pairing of electron-lattice (or other) origin can, in our view, be addressed properly for strongly correlated systems by explaining an overall phase diagram involving different magnetic and superconducting phases within a single consistent framework. In this comment, particular emphasis is put on the connection/coexistence with antiferromagnetism, as well as on the existence of the upper critical concentration for the disappearance of superconductivity in high-temperature superconductors. The analysis provides clear evidence for the kinetic exchange as being a natural origin of both phenomena, in conjunction with the strongly correlated motion (hopping) of the carriers. A subtle difference between the exchangeand the paramagnon-induced pairing is also noted. An analogical scenario is advocated briefly for heavy fermion systems. Some further tests are proposed in order to provide a convincing proof of the magnetic origin, combined with the strongly correlated nature of carriers, of this unconventional superconductivity and its universality in strongly correlated systems, solid-state or otherwise. The role of strong correlations among the fermions composing Cooper pairs is emphasized.

2006

The concept of electron pairing, central to the phenomenon of superconductivity, owes its origin to the earliest claim of high temperature superconductivity in a very light element system (an alkali ammine). The presence of high dynamic energy scales makes light element systems attractive from the standpoint of the standard electron-phonon pairing mechanisms, but among the elements themselves, and under normal conditions it is well known that superconducting transition temperatures (Tc) are quite limited. From the latecomer superconductor MgB 2 ((Tc) ∼ 40K) it is now clear that for the light elements in combination the situation can change radically. Structures admitting large numbers of electrons per unit cell (and a corresponding proliferation of occupied bands) can be especially favorable for superconductivity. It was already recognized by Kamerlingh Onnes that this important phenomenon could eventually impact the energy sector. Accordingly it is of interest to examine both the pathway and the prospects for higher temperature superconductivity in systems of light elements (for example high hydrides) particularly with a view towards invoking a concept of chemical pre-compression.

Revista de Indias, 2024

RESUMEN: El presente artículo tiene por objetivo analizar la vigilancia colonial y su relación con el desarrollo policial. Para realizar este propósito se reconstruye la polisemia conceptual de la noción de policía y se relaciona con la introducción de los alcaldes de barrio en Santafé de Bogotá en 1774. Con base en un análisis amplio de fuentes primarias, se diferencia policía como concepto, práctica e incipiente institución (Policía). Solo con esta claridad se trazan sus diferentes articulaciones en las prácticas de vigilancia en la vida cotidiana en Santafé. El trabajo señala la importancia de historizar la policía en los siglos XVII, XVIII y el umbral del siglo XIX y describe el surgimiento de una cultura de la vigilancia policial fundada en la construcción del enemigo, la interiorización de las normas, la sectorización del espacio urbano, la investigación del crimen, la captura de sospechosos y el apoyo en la administración de justicia. Con este resultado, esta investigación invita a reflexionar sobre los alcaldes de barrio, en medio de diacronías, como una futura herencia colonial en cuerpo de la Policía moderna como garante de privilegios sistémicos. PALABRAS CLAVE: alcaldes de barrio; control y administración de justicia; vigilancia; Nueva Granada; policía; siglos XVII y XVIII.