95 research outputs found
Spectral Statistics: From Disordered to Chaotic Systems
The relation between disordered and chaotic systems is investigated. It is
obtained by identifying the diffusion operator of the disordered systems with
the Perron-Frobenius operator in the general case. This association enables us
to extend results obtained in the diffusive regime to general chaotic systems.
In particular, the two--point level density correlator and the structure factor
for general chaotic systems are calculated and characterized. The behavior of
the structure factor around the Heisenberg time is quantitatively described in
terms of short periodic orbits.Comment: uuencoded file with 1 eps figure, 4 page
Magnetic fluctuations in 2D metals close to the Stoner instability
We consider the effect of potential disorder on magnetic properties of a
two-dimensional metallic system (with conductance ) when interaction in
the triplet channel is so strong that the system is close to the threshold of
the Stoner instability. We show, that under these conditions there is an
exponentially small probability for the system to form local spin droplets
which are local regions with non zero spin density. Using a non-local version
of the optimal fluctuation method we find analytically the probability
distribution and the typical spin of a local spin droplet (LSD). In particular,
we show that both the probability to form a LSD and its typical spin are
independent of the size of the droplet (within the exponential accuracy). The
LSDs manifest themselves in temperature dependence of observable quantities. We
show, that below certain cross-over temperature the paramagnetic susceptibility
acquires the Curie-like temperature dependence, while the dephasing time
(extracted from magneto-resistance measurements) saturates.Comment: 15 pages, 4 figure
Conductance of Mesoscopic Systems with Magnetic Impurities
We investigate the combined effects of magnetic impurities and applied
magnetic field on the interference contribution to the conductance of
disordered metals. We show that in a metal with weak spin-orbit interaction,
the polarization of impurity spins reduces the rate of electron phase
relaxation, thus enhancing the weak localization correction to conductivity.
Magnetic field also suppresses thermal fluctuations of magnetic impurities,
leading to a recovery of the conductance fluctuations. This recovery occurs
regardless the strength of the spin-orbit interaction. We calculate the
magnitudes of the weak localization correction and of the mesoscopic
conductance fluctuations at an arbitrary level of the spin polarization induced
by a magnetic field. Our analytical results for the ``'' Aharonov-Bohm
conductance oscillations in metal rings can be used to extract spin and
gyromagnetic factor of magnetic impurities from existing experimental data.Comment: 18 pages, 8 figure
Nonohmic conductivity as a probe of crossover from diffusion to hopping in two dimensions
We show that the study of conductivity nonlinearity gives a possibility to
determine the condition when the diffusion conductivity changes to the hopping
one with increasing disorder. It is experimentally shown that the conductivity
of single quantum well GaAs/InGaAs/GaAs heterostructures behaves like diffusive
one down to value of order .Comment: 4 pages, 2 figure
Inelastic Scattering Time for Conductance Fluctuations
We revisit the problem of inelastic times governing the temperature behavior
of the weak localization correction and mesoscopic fluctuations in one- and
two-dimensional systems. It is shown that, for dephasing by the electron
electron interaction, not only are those times identical but the scaling
functions are also the same.Comment: 10 pages Revtex; 5 eps files include
Long-Range Coulomb Interaction and the Crossover between Quantum and Shot Noise in Diffusive Conductors
Frequency-dependent nonequilibrium noise in quantum-coherent diffusive
conductors is calculated with account taken of long-range Coulomb interaction.
For long and narrow contacts with strong external screening the crossover
between quantum and shot noise takes place at frequencies much smaller than the
voltage drop across the contact. We also show that under certain frequency
limitations, the semiclassical and quantum-coherent approaches to shot noise
are mathematically equivalent.Comment: 13 pages, RevTex, 7 ps figures, more details of derivation give
Superconductive proximity effect in interacting disordered conductors
We present a general theory of the superconductive proximity effect in
disordered normal--superconducting (N-S) structures, based on the recently
developed Keldysh action approach. In the case of the absence of interaction in
the normal conductor we reproduce known results for the Andreev conductance G_A
at arbitrary relation between the interface resistance R_T and the diffusive
resistance R_D. In two-dimensional N-S systems, electron-electron interaction
in the Cooper channel of normal conductor is shown to strongly affect the value
of G_A as well as its dependence on temperature, voltage and magnetic field. In
particular, an unusual maximum of G_A as a function of temperature and/or
magnetic field is predicted for some range of parameters R_D and R_T. The
Keldysh action approach makes it possible to calculate the full statistics of
charge transfer in such structures. As an application of this method, we
calculate the noise power of an N-S contact as a function of voltage,
temperature, magnetic field and frequency for arbitrary Cooper repulsion in the
normal metal and arbitrary values of the ratio R_D/R_T.Comment: RevTeX, 28 pages, 18 PostScript figures; added and updated reference
Interaction-Induced Magnetization of the Two-Dimensional Electron Gas
We consider the contribution of electron-electron interactions to the orbital
magnetization of a two-dimensional electron gas, focusing on the ballistic
limit in the regime of negligible Landau-level spacing. This regime can be
described by combining diagrammatic perturbation theory with semiclassical
techniques. At sufficiently low temperatures, the interaction-induced
magnetization overwhelms the Landau and Pauli contributions. Curiously, the
interaction-induced magnetization is third-order in the (renormalized) Coulomb
interaction. We give a simple interpretation of this effect in terms of
classical paths using a renormalization argument: a polygon must have at least
three sides in order to enclose area. To leading order in the renormalized
interaction, the renormalization argument gives exactly the same result as the
full treatment.Comment: 11 pages including 4 ps figures; uses revtex and epsf.st
Electron transport and energy relaxation in dilute magnetic alloys
We consider the effect of the RKKY interaction between magnetic impurities on
the electron relaxation rates in a normal metal. The interplay between the RKKY
interaction and the Kondo effect may result in a non-monotonic temperature
dependence of the electron momentum relaxation rate, which determines the Drude
conductivity. The electron phase relaxation rate, which determines the
magnitude of the weak localization correction to the resistivity, is also a
non-monotonic function of temperature. For this function, we find the
dependence of the position of its maximum on the concentration of magnetic
impurities. We also relate the electron energy relaxation rate to the
excitation spectrum of the system of magnetic impurities. The energy relaxation
determines the distribution function for the out-of-equilibrium electrons.
Measurement of the electron distribution function thus may provide information
about the excitations in the spin glass phase.Comment: 15 pages, 5 figure
Fate of the extended states in a vanishing magnetic field: the role of spins in strongly-interacting 2D electron systems
In non-interacting or weakly-interacting 2D electron systems, the energy of
the extended states increases as the perpendicular magnetic field approaches
zero: the extended states "float up" in energy, giving rise to an insulator.
However, in those 2D systems where metallic conductivity has been recently
observed in zero magnetic field, the energy of the extended states remains
constant or even decreases as B -> 0, thus allowing conduction in the limit of
zero temperature. Here we show that aligning the electrons' spins causes the
extended states to once more "float up" in energy in the vanishing
perpendicular magnetic field, as they do for non- or weakly-interacting
electrons. The difference between extended states that float up (an insulator)
or remain finite (a metal) is thus tied to the existence of the spins
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