52 research outputs found
‘… a metal conducts and a non-metal doesn't’
In a letter to one of the authors, Sir Nevill Mott, then in his tenth decade, highlighted the fact that the statement ‘… a metal conducts, and a non-metal doesn’t’ can be true only at the absolute zero of temperature, T=0 K. But, of course, experimental studies of metals, non-metals and, indeed, the electronic and thermodynamic transition between these canonical states of matter must always occur above T=0 K, and, in many important cases, for temperatures far above the absolute zero. Here, we review the issues—theoretical and experimental—attendant on studies of the metal to non-metal transition in doped semiconductors at temperatures close to absolute zero (T=0.03 K) and fluid chemical elements at temperatures far above absolute zero (T>1000 K)
Random-phase approximation and its applications in computational chemistry and materials science
The random-phase approximation (RPA) as an approach for computing the
electronic correlation energy is reviewed. After a brief account of its basic
concept and historical development, the paper is devoted to the theoretical
formulations of RPA, and its applications to realistic systems. With several
illustrating applications, we discuss the implications of RPA for computational
chemistry and materials science. The computational cost of RPA is also
addressed which is critical for its widespread use in future applications. In
addition, current correction schemes going beyond RPA and directions of further
development will be discussed.Comment: 25 pages, 11 figures, published online in J. Mater. Sci. (2012
Stellar structure and compact objects before 1940: Towards relativistic astrophysics
Since the mid-1920s, different strands of research used stars as "physics
laboratories" for investigating the nature of matter under extreme densities
and pressures, impossible to realize on Earth. To trace this process this paper
is following the evolution of the concept of a dense core in stars, which was
important both for an understanding of stellar evolution and as a testing
ground for the fast-evolving field of nuclear physics. In spite of the divide
between physicists and astrophysicists, some key actors working in the
cross-fertilized soil of overlapping but different scientific cultures
formulated models and tentative theories that gradually evolved into more
realistic and structured astrophysical objects. These investigations culminated
in the first contact with general relativity in 1939, when J. Robert
Oppenheimer and his students George Volkoff and Hartland Snyder systematically
applied the theory to the dense core of a collapsing neutron star. This
pioneering application of Einstein's theory to an astrophysical compact object
can be regarded as a milestone in the path eventually leading to the emergence
of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal
A Natural Supersymmetric Model with MeV Dark Matter
It has previously been proposed that annihilating dark matter particles with
MeV-scale masses could be responsible for the flux of 511 keV photons observed
from the region of the Galactic Bulge. The conventional wisdom, however, is
that it is very challenging to construct a viable particle physics model
containing MeV dark matter. In this letter, we challenge this conclusion by
describing a simple and natural supersymmetric model in which the lightest
supersymmetric particle naturally has a MeV-scale mass and the other
phenomenological properties required to generate the 511 keV emission. In
particular, the small ( ) effective couplings between dark
matter and the Standard Model fermions required in this scenario naturally lead
to radiative corrections that generate MeV-scale masses for both the dark
matter candidate and the mediator particle.Comment: 4 pages, 1 figure. v2: Small modification to discussion of spectru
Statistical Mechanics and the Physics of the Many-Particle Model Systems
The development of methods of quantum statistical mechanics is considered in
light of their applications to quantum solid-state theory. We discuss
fundamental problems of the physics of magnetic materials and the methods of
the quantum theory of magnetism, including the method of two-time temperature
Green's functions, which is widely used in various physical problems of
many-particle systems with interaction. Quantum cooperative effects and
quasiparticle dynamics in the basic microscopic models of quantum theory of
magnetism: the Heisenberg model, the Hubbard model, the Anderson Model, and the
spin-fermion model are considered in the framework of novel
self-consistent-field approximation. We present a comparative analysis of these
models; in particular, we compare their applicability for description of
complex magnetic materials. The concepts of broken symmetry, quantum
protectorate, and quasiaverages are analyzed in the context of quantum theory
of magnetism and theory of superconductivity. The notion of broken symmetry is
presented within the nonequilibrium statistical operator approach developed by
D.N. Zubarev. In the framework of the latter approach we discuss the derivation
of kinetic equations for a system in a thermal bath. Finally, the results of
investigation of the dynamic behavior of a particle in an environment, taking
into account dissipative effects, are presented.Comment: 77 pages, 1 figure, Refs.37
Toward a history-based model for scientific invention: Problem-solving practices in the invention of the transistor and the development of the theory of superconductivity
problem-solving, scientific thinking, physics, creativity, superconductivity, transistor, analogy, decomposition,
- …