47,552 research outputs found
Correlations weak and strong: divers guises of the two-dimensional electron gas
The three-dimensional electron-gas model has been a major focus for many-body
theory applied to the electronic properties of metals and semiconductors.
Because the model neglects band effects, whereas electronic systems are
generally more strongly correlated in narrow band systems, it is most widely
used to describe the qualitative physics of weakly correlated metals with
unambiguous Fermi liquid properties. The model is more interesting in two space
dimensions because it provides a quantitative description of electrons in
quantum wells and because these can form strongly correlated many-particle
states. We illustrate the range of possible many-particle behaviors by
discussing the way correlations are manifested in 2D tunneling spectroscopy
experiments.Comment: Based on talk at MBIX conference, Sydney, July 1997. 12 pages, 3
figure
Spintronic Spin Accumulation and Thermodynamics
The spin degree of freedom can play an essential role in determining the
electrical transport properties of spin-polarized electron systems in metals or
semiconductors. In this article, I address the dependence of spin-subsystem
chemical potentials on accumulated spin-densities. I discuss both approaches
which can be used to measure this fundamental thermodynamic quantity and the
microscopic physics which determines its value in several different systems.Comment: 14 pages, 4 figures. Based on lecture given at the XVI Sitges
Conference, June 1999. Proceedings to be published by Springer-Verla
Orbital order in bilayer graphene at filling factor
In a graphene bilayer with Bernal stacking both and orbital
Landau levels have zero kinetic energy. An electronic state in the N=0 Landau
level consequently has three quantum numbers in addition to its guiding center
label: its spin, its valley index or , and an orbital quantum
number The two-dimensional electron gas (2DEG) in the bilayer supports
a wide variety of broken-symmetry states in which the pseudospins associated
these three quantum numbers order in a manner that is dependent on both filling
factor and the electric potential difference between the layers. In this
paper, we study the case of in an external field strong enough to
freeze electronic spins. We show that an electric potential difference between
layers drives a series of transitions, starting from interlayer-coherent states
(ICS) at small potentials and leading to orbitally coherent states (OCS) that
are polarized in a single layer. Orbital pseudospins carry electric dipoles
with orientations that are ordered in the OCS and have Dzyaloshinskii-Moriya
interactions that can lead to spiral instabilities. We show that the microwave
absorption spectra of ICSs, OCSs, and the mixed states that occur at
intermediate potentials are sharply distinct.Comment: 21 pages, 14 figure
Interactions suppress Quasiparticle Tunneling at Hall Bar Constrictions
Tunneling of fractionally charged quasiparticles across a two-dimensional
electron system on a fractional quantum Hall plateau is expected to be strongly
enhanced at low temperatures. This theoretical prediction is at odds with
recent experimental studies of samples with weakly-pinched
quantum-point-contact constrictions, in which the opposite behavior is
observed. We argue here that this unexpected finding is a consequence of
electron-electron interactions near the point contact.Comment: 4 page
Universal one-way light speed from a universal light speed over closed paths
This paper gives two complete and elementary proofs that if the speed of
light over closed paths has a universal value , then it is possible to
synchronize clocks in such a way that the one-way speed of light is c. The
first proof is an elementary version of a recent proof. The second provides
high precision experimental evidence that it is possible to synchronize clocks
in such a way that the one-way speed of light has a universal value. We also
discuss an old incomplete proof by Weyl which is important from an historical
perspective.Comment: RevTex4, 6 pages, 2 figures, uses psfrag. New sections added,
discussion expande
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