463 research outputs found
Multifractality at Anderson transitions with Coulomb interaction
We explore mesoscopic fluctuations and correlations of the local density of
states (LDOS) near localization transition in a disordered interacting
electronic system. It is shown that the LDOS multifractality survives in the
presence of Coulomb interaction. We calculate the spectrum of multifractal
dimensions in spatial dimensions and show that it differs from
that in the absence of interaction. The multifractal character of fluctuations
and correlations of the LDOS can be studied experimentally by scanning
tunneling microscopy of two-dimensional and three-dimensional disordered
structures.Comment: 16 pages, 2 figure
Mesoscopic fluctuations of the local density of states in interacting electron systems
We review our recent theoretical results for mesoscopic fluctuations of the
local density of states in the presence of electron-electron interaction. We
focus on the two specific cases: (i) a vicinity of interacting critical point
corresponding to Anderson-Mott transition, and (ii) a vicinity of
non-interacting critical point in the presence of a weak electron-electron
attraction. In both cases strong mesoscopic fluctuations of the local density
of states exist.Comment: A brief review based on arXiv:1305.2888, arXiv:1307.5811,
arXiv:1412.3306, arXiv:1603.0301
Local density of states and its mesoscopic fluctuations near the transition to a superconducting state in disordered systems
We develop a theory of the local density of states (LDOS) of disordered
superconductors, employing the non-linear sigma-model formalism and the
renormalization-group framework. The theory takes into account the interplay of
disorder and interaction couplings in all channels, treating the systems with
short-range and Coulomb interactions on equal footing. We explore 2D systems
that would be Anderson insulators in the absence of interaction and 2D or 3D
systems that undergo Anderson transition in the absence of interaction. We
evaluate both the average tunneling density of states and its mesoscopic
fluctuations which are related to the LDOS multifractality in normal disordered
systems. The obtained average LDOS shows a pronounced depletion around the
Fermi energy, both in the metallic phase (i.e., above the superconducting
critical temperature ) and in the insulating phase near the
superconductor-insulator transition (SIT). The fluctuations of the LDOS are
found to be particularly strong for the case of short-range interactions --
especially, in the regime when is enhanced by Anderson localization. On
the other hand, the long-range Coulomb repulsion reduces the mesoscopic LDOS
fluctuations. However, also in a model with Coulomb interaction, the
fluctuations become strong when the systems approaches the SIT
Superconductor-insulator transitions: Phase diagram and magnetoresistance
Influence of disorder-induced Anderson localization and of electron-electron
interaction on superconductivity in two-dimensional systems is explored. We
determine the superconducting transition temperature , the temperature
dependence of the resistivity, the phase diagram, as well as the
magnetoresistance. The analysis is based on the renormalization group (RG) for
a nonlinear sigma model. Derived RG equations are valid to the lowest order in
disorder but for arbitrary electron-electron interaction strength in
particle-hole and Cooper channels. Systems with preserved and broken
spin-rotational symmetry are considered, both with short-range and with
long-range (Coulomb) interaction. In the cases of short-range interaction, we
identify parameter regions where the superconductivity is enhanced by
localization effects. Our RG analysis indicates that the
superconductor-insulator transition is controlled by a fixed point with a
resistivity of the order of the quantum resistance . When
a transverse magnetic field is applied, we find a strong nonmonotonous
magnetoresistance for temperatures below .Comment: 34 pages, 20 figure
Strongly correlated two-dimensional plasma explored from entropy measurements
Charged plasma and Fermi liquid are two distinct states of electronic matter
intrinsic to dilute two-dimensional electron systems at elevated and low
temperatures, respectively. Probing their thermodynamics represents challenge
because of lacking an adequate technique. Here we report thermodynamic method
to measure the entropy per electron in gated structures. Our technique appears
to be three orders of magnitude superior in sensitivity to the ac calorimetry,
allowing entropy measurements with only electrons. This enables us to
investigate the correlated plasma regime, previously inaccessible
experimentally in two-dimensional electron systems in semiconductors. In
experiments with clean two-dimensional electron system in Si-based structures
we traced entropy evolution from the plasma to Fermi-liquid regime by varying
electron density. We reveal that the correlated plasma regime can be mapped
onto the ordinary non-degenerate Fermi gas with an interaction-enhanced
temperature dependent effective mass. Our method opens up new horizons in
studies of low-dimensional electron systems.Comment: 5 pages 3 figures + Supplementary Informatio
Temperature derivative of the chemical potential and its magnetooscillations in two-dimensional system
We report first thermodynamic measurements of the temperature derivative of
chemical potential (d{\mu}/dT) in two-dimensional (2D) electron systems. In
order to test the technique we have chosen Schottky gated GaAs/AlGaAs
heterojunctions and detected experimentally in this 2D system quantum
magnetooscillations of d{\mu}/dT. We also present a Lifshits-Kosevitch type
theory for the d{\mu}/dT magnetooscillations in 2D systems and compare the
theory with experimental data. The magnetic field dependence of the d{\mu}/dT
value appears to be sensitive to the density of states shape of Landau levels.
The data in low magnetic field domain demonstrate brilliant agreement with
theory for non-interacting Fermi gas with Lorentzian Landau level shape.Comment: 4 pages, 3 figure
Critical behavior of transport and magnetotransport in 2D electron system in Si in the vicinity of the metal-insulator transition
We report on studies of the magnetoresistance in strongly correlated 2D
electron system in Si in the critical regime, in the close vicinity of the 2D
metal-insulator transition. We performed self-consistent comparison of our data
with solutions of two equations of the cross-over renormalization group (CRG)
theory which describes temperature evolutions of the resistivity and
interaction parameters for 2D electron system. We found a good agreement
between the \rho(T,B) data and the RG theory in a wide range of the in-plane
fields, 0-2.1 T. This agreement supports the interpretation of the observed 2D
MIT as the true quantum phase transition.Comment: 5 pages, 4 figures, uses jetpl.cl
Residual bulk viscosity of a disordered 2D electron gas
The nonzero bulk viscosity signals breaking of the scale invariance. We
demonstrate that a disorder in two-dimensional noninteracting electron gas in a
perpendicular magnetic field results in the nonzero disorder-averaged bulk
viscosity. We derive analytic expression for the bulk viscosity within the
self-consistent Born approximation. This residual bulk viscosity provides the
lower bound for the bulk viscosity of 2D interacting electrons at low enough
temperatures.Comment: 10 pages, 2 figure
Berezinskii-Kosterlitz-Thouless transition in homogeneously disordered superconducting films
We develop a theory for the vortex unbinding transition in homogeneously
disordered superconducting films. This theory incorporates the effects of
quantum, mesoscopic and thermal fluctuations stemming from length scales
ranging from the superconducting coherence length down to the Fermi wavelength.
In particular, we extend the renormalization group treatment of the diffusive
nonlinear sigma model to the superconducting side of the transition.
Furthermore, we explore the mesoscopic fluctuations of parameters in the
Ginzburg-Landau functional. Using the developed theory, we determine the
dependence of essential observables (including the vortex unbinding
temperature, the superconducting density, as well as the temperature-dependent
resistivity and thermal conductivity) on microscopic characteristics such as
the disorder-induced scattering rate and bare interaction couplings
Probing spin susceptibility of a correlated two-dimensional electron system by transport and magnetization measurements
We report temperature and density dependences of the spin susceptibility of
strongly interacting electrons in Si inversion layers. We measured (i) the
itinerant electron susceptibility from the Shubnikov-de Haas
oscillations in crossed magnetic fields and (ii) thermodynamic susceptibility
sensitive to all the electrons in the layer. Both and
are strongly enhanced with lowering the electron density in the
metallic phase. However, there is no sign of divergency of either quantity at
the density of the metal-insulator transition . Moreover, the value of
, which can be measured across the transition down to very low
densities deep in the insulating phase, increases with density at , as
expected. In the absence of magnetic field, we found the temperature dependence
of to be consistent with Fermi-liquid-based predictions, and to be
much weaker than the power-law, predicted by non-Fermi-liquid models. We
attribute a much stronger temperature dependence of to localized
spin droplets. In strong enough in-plane magnetic field, we found the
temperature dependence of to be stronger than that expected for the
Fermi liquid interaction corrections.Comment: 16 pages, 13 figure
- …