6,100 research outputs found
Extending Linear Response: Inferences from Electron-Ion Structure Factors
Linear response methods applied to electron systems often display a level of
accuracy which is notable when viewed in terms of the strengths of perturbing
interactions. Neglect of higher response terms is in fact justifiable in many
cases and it can be shown to stem from an intrinsic interference between atomic
and electronic length scales. For fluid metallic systems it can be further
shown that electron-ion structure (increasingly accessible experimentally) can
be understood from an application of linear response in the electron system,
combined with hard-sphere like correlation for the ionic component.Comment: 5 pages, 2 figure
Observability of a projected new state of matter: a metallic superfluid
Dissipationless quantum states, such as superconductivity and superfluidity,
have attracted interest for almost a century. A variety of systems exhibit
these macroscopic quantum phenomena, ranging from superconducting electrons in
metals to superfluid liquids, atomic vapours, and even large nuclei. It was
recently suggested that liquid metallic hydrogen could form two new unusual
dissipationless quantum states, namely the metallic superfluid and the
superconducting superfluid. Liquid metallic hydrogen is projected to occur only
at an extremely high pressure of about 400 GPa, while pressures on hydrogen of
320 GPa having already been reported. The issue to be adressed is if this state
could be experimentally observable in principle. We propose four experimental
probes for detecting it.Comment: in print in Phys. Rev. Let
Self-organized circular flow of classical point particles
We consider newtonian dynamics of charged particles on the circle with
nearest neigbour interaction with Coulomb repulsive potential . Also
there is an external accelerating force which is nonzero only on a small part
of the circle. We construct homogeneous solutions where the velocities of all
particles are approximately equal and their density is approximately uniform.
This gives a qualitative mathematical model for some features of the direct
electric current (DC), in agreement with a suggestion by R. Feynman
Lucid : a formal system for writing and proving programs
Lucid is both a programming language and a formal system for proving properties of Lucid programs. The programming language is unconventional in many ways, although programs are readily understood as using assignment statements and loops in a 'structured' fashion. Semantically, an assignment statement is really an equation between 'histories', and a whole program is simply an unordered set of such equations.
From these equations, properties of the program can be derived by straightforward mathematical reasoning, using the Lucid formal system. The rules of this system are mainly those of first order logic, together with extra axioms and rules for the special Lucid functions.
This paper formally describes the syntax and semantics of programs and justifies the axioms and rules of the formal system
Metals get an awkward cousin
A newly predicted state of matter is a simple theoretical example of a phase
that conducts electricity but is not smoothly connected to our conventional
model of metals. A viewpoint on arXiv:1201.5998.Comment: Physics 5, 82 (2012
Diagrammatic quantum field formalism for localized electrons
We introduce a diagrammatic quantum field formalism for the evaluation of
normalized expectation values of operators, and suitable for systems with
localized electrons. It is used to develop a convergent series expansion for
the energy in powers of overlap integrals of single-particle orbitals. This
method gives intuitive and practical rules for writing down the expansion to
arbitrary order of overlap, and can be applied to any spin configuration and to
any dimension. Its applicability for systems with well localized electrons has
been illustrated with examples, including the two-dimensional Wigner crystal
and spin-singlets in the low-density electron gas.Comment: 13 pages, 0 figure
Electronic Properties of Strained Si/Ge Core-Shell Nanowires
We investigated the electronic properties of strained Si/Ge core-shell
nanowires along the [110] direction using first principles calculations based
on density-functional theory. The diameter of the studied core-shell wire is up
to 5 nm. We found the band gap of the core-shell wire is smaller than that of
both pure Si and Ge wires with the same diameter. This reduced band gap is
ascribed to the intrinsic strain between Ge and Si layers, which partially
counters the quantum confinement effect. The external strain is further applied
to the nanowires for tuning the band structure and band gap. By applying
sufficient tensile strain, we found the band gap of Si-core/Ge-shell nanowire
with diameter larger than ~3 nm experiences a transition from direct to
indirect gap.Comment: 4 figure
Thermoelectric efficiency of topological insulators in a magnetic field
We study the thermoelectric properties of three-dimensional topological
insulators in magnetic fields with many holes (or pores) in the bulk. We find
that at high density of these holes in the transport direction the
thermoelectric figure of merit, ZT, can be large due to the contribution of the
topologically protected conducting surfaces and the suppressed phonon thermal
conductivity. By applying an external magnetic field a subgap can be induced in
the surface states spectrum. We show that the thermoelectric efficiency can be
controlled by this tunable subgap leading to the values of ZT much greater than
1. Such high values of ZT for reasonable system parameters and its tunability
by magnetic field make this system a strong candidate for applications in heat
management of nanodevices, especially at low temperatures.Comment: 9 pages, 4 figures, Proceedings of MMM 201
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