20 research outputs found
Metal-Insulator Transition in Disordered Two-Dimensional Electron Systems
We present a theory of the metal-insulator transition in a disordered
two-dimensional electron gas. A quantum critical point, separating the metallic
phase which is stabilized by electronic interactions, from the insulating phase
where disorder prevails over the electronic interactions, has been identified.
The existence of the quantum critical point leads to a divergence in the
density of states of the underlying collective modes at the transition, causing
the thermodynamic properties to behave critically as the transition is
approached. We show that the interplay of electron-electron interactions and
disorder can explain the observed transport properties and the anomalous
enhancement of the spin susceptibility near the metal-insulator transition
Branch-cut Singularities in Thermodynamics of Fermi Liquid Systems
The recently measured spin susceptibility of the two dimensional electron gas
exhibits a strong dependence on temperature, which is incompatible with the
standard Fermi liquid phenomenology. Here we show that the observed temperature
behavior is inherent to ballistic two dimensional electrons. Besides the
single-particle and collective excitations, the thermodynamics of Fermi liquid
systems includes effects of the branch-cut singularities originating from the
edges of the continuum of pairs of quasiparticles. As a result of the
rescattering induced by interactions, the branch-cut singularities generate
non-analyticities in the thermodynamic potential which reveal themselves in
anomalous temperature dependences. Calculation of the spin susceptibility in
such a situation requires a non-perturbative treatment of the interactions. As
in high-energy physics, a mixture of the collective excitations and pairs of
quasiparticles can be effectively described by a pole in the complex momentum
plane. This analysis provides a natural explanation for the observed
temperature dependence of the spin susceptibility, both in sign and magnitude.Comment: 8 pages, 3 figure
Dilute electron gas near the metal-insulator transition in two dimensions
In recent years systematic experimental studies of the temperature dependence
of the resistivity in a variety of dilute, ultra clean two dimensional
electron/hole systems have revived the fundamental question of localization or,
alternatively, the existence of a metal-insulator transition in the presence of
strong electron-electron interactions in two dimensions. We argue that under
the extreme conditions of ultra clean systems not only is the electron-electron
interaction very strong but the role of other system specific properties are
also enhanced. In particular, we emphasize the role of valleys in determining
the transport properties of the dilute electron gas in silicon inversion layers
(Si-MOSFETs). It is shown that for a high quality sample the temperature
behavior of the resistivity in the region close to the critical region of the
metal-insulator transition is well described by a renormalization group
analysis of the interplay of interaction and disorder if the electron band is
assumed to have two distinct valleys. The decrease in the resistivity up to
five times has been captured in the correct temperature interval by this
analysis, without involving any adjustable parameters. The considerable
variance in the data obtained from different Si-MOSFET samples is attributed to
the sample dependent scattering rate across the two valleys, presenting thereby
with a possible explanation for the absence of universal behavior in Si-MOSFET
samples of different quality
Suppression of \bbox{T_c} in superconducting amorphous wires
The suppression of the mean field temperature of the superconducting
transition, , in homogeneous amorphous wires is studied. We develop a
theory that gives in situations when the dynamically enhanced Coulomb
repulsion competes with the contact attraction. The theory accurately describes
recent experiments on --suppression in superconducting wires, after a
procedure that minimizes the role of nonuniversal mechanisms influencing
is applied.Comment: RevTeX, 4 pages, 3 figure
A Single Impurity in Tomonaga-Luttinger Liquids
The problem of a single impurity in one dimensional Tomonaga-Luttinger
liquids with a repulsive electron-electron interaction is discussed. We find
that the renormalization group flow diagram for the parameters characterizing
the impurity is rather complex. Apart from the fixed points corresponding to
two weakly connected semi-infinite wires, the flow diagram contains additional
fixed points which control the low temperature physics when the bare potential
of the impurity is not strong.Comment: To be published in the Philosophical Magazine in the Proceedings of
the "MINERVA WORKSHOP on MESOSCOPICS, FRACTALS and NEURAL NETWORKS", Eilat,
Israel, March 199
Valley current in graphene through electron-phonon interaction
We discuss valley current, which is carried by quasiparticles in graphene. We
show that the valley current arises owing to a peculiar term in the
electron-phonon collision integral that mixes the scalar and vector
gauge-field-like vertices in the electron-phonon interaction. This mixing makes
collisions of phonons with electrons sensitive to their chirality, which is
opposite in two valleys. As a result of collisions with phonons, electrons of
the different valleys deviate in opposite directions. Breaking the spatial
inversion symmetry is not needed for a valley-dependent deviation of the
quasiparticle current. The effect exists both in pristine graphene or bilayer
graphene samples, and it increases with temperature owing to a higher rate of
collisions with phonons at higher temperatures. The valley current carried by
quasiparticles could be detected by measuring the electric current using a
nonlocal transformer of a suitable design.Comment: 5 pages, 2 figures. To be published as a Rapid Communication in
Physical Review
Dephasing time in graphene due to interaction with flexural phonons
We investigate decoherence of an electron in graphene caused by
electron-flexural phonon interaction. We find out that flexural phonons can
produce dephasing rate comparable to the electron-electron one. The problem
appears to be quite special because there is a large interval of temperature
where the dephasing induced by phonons can not be obtain using the golden rule.
We evaluate this rate for a wide range of density () and temperature ()
and determine several asymptotic regions with temperature dependence crossing
over from to when
temperature increases. We also find to be a non-monotonous
function of . These distinctive features of the new contribution can provide
an effective way to identify flexural phonons in graphene through the
electronic transport by measuring the weak localization corrections in
magnetoresistance.Comment: 13 pages, 8 figure
Odd-frequency spin-triplet instability in disordered electron liquid
We consider a two-dimensional disordered conductor in the regime when the
superconducting phase is destroyed by the magnetic field. We observe that the
end point of the superconductivity is a quantum critical point separating the
conventional superconducting phase from a state with the odd-frequency
spin-triplet pairing instability. We speculate that this could shed light on a
rather mysterious insulating state observed in strongly disordered
superconducting films in a broad region of the magnetic fields.Comment: 27 pages, 8 figure