15 research outputs found
History dependence, memory and metastability in electron glasses
We discuss the history dependence and memory effects which are observed in
the out-of-equilibrium conductivity of electron glasses. The experiments can be
understood by assuming that the local density of states retains a memory of the
sample history. We provide analytical arguments for the consistency of this
assumption, and discuss the saturation of the memory effect with increasing
gate voltage change. This picture is bolstered by numerical simulations at zero
temperature, which moreover demonstrate the incompressibility of the Coulomb
glass on short timescales.Comment: 4 pages, 1 figur
Non Equilibrium Noise as a Probe of the Kondo Effect in Mesoscopic Wires
We study the non-equilibrium noise in mesoscopic diffusive wires hosting
magnetic impurities. We find that the shot-noise to current ratio develops a
peak at intermediate source-drain biases of the order of the Kondo temperature.
The enhanced impurity contribution at intermediate biases is also manifested in
the effective distribution. The predicted peak represents increased inelastic
scattering rate at the non-equilibrium Kondo crossover.Comment: 4+ pages, 4 figures, published versio
Conserving many body approach to the fully screened, infinite U Anderson model
Using a Luttinger Ward scheme for interacting gauge particles, we present a
conserving many body treatment of a family of fully screened infinite U
Anderson models that has a smooth cross-over into the Fermi liquid state, with
a finite scattering phase shift at zero temperature and a Wilson ratio greater
than one. We illustrate our method, computing the temperature dependence of the
thermodynamics, resistivity and electron dephasing rate and discuss its future
application to non-equilibrium quantum dots and quantum critical mixed valent
systems
Coulomb blockade and Non-Fermi-liquid behavior in quantum dots
The non-Fermi-liquid properties of an ultrasmall quantum dot coupled to a
lead and to a quantum box are investigated. Tuning the ratio of the tunneling
amplitudes to the lead and box, we find a line of two-channel Kondo fixed
points for arbitrary Coulomb repulsion on the dot, governing the transition
between two distinct Fermi-liquid regimes. The Fermi liquids are characterized
by different values of the conductance. For an asymmetric dot, spin and charge
degrees of freedom are entangled: a continuous transition from a spin to a
charge two-channel Kondo effect evolves. The crossover temperature to the
two-channel Kondo effect is greatly enhanced away from the local-moment regime,
making this exotic effect accessible in realistic quantum-dot devices.Comment: 5 figure
The Memory Effect in Electron Glasses
We present a theory for the memory effect in electron glasses. In fast gate
voltage sweeps it is manifested as a dip in the conductivity around the
equilibration gate voltage. We show that this feature, also known as anomalous
field effect, arises from the long-time persistence of correlations in the
electronic configuration. We argue that the gate voltage at which the memory
dip saturates is related to an instability caused by the injection of a
critical number of excess carriers. This saturation threshold naturally
increases with temperature. On the other hand, we argue that the gate voltage
beyond which memory is erased, is temperature independent. Using standard
percolation arguments, we calculate the anomalous field effect as a function of
gate voltage, temperature, carrier density and disorder. Our results are
consistent with experiments, and in particular, they reproduce the observed
scaling of the width of the memory dip with various parameters.Comment: Accepted version, to be published in PR
Enhancement of the Two-channel Kondo Effect in Single-Electron boxes
The charging of a quantum box, coupled to a lead by tunneling through a
single resonant level, is studied near the degeneracy points of the Coulomb
blockade. Combining Wilson's numerical renormalization-group method with
perturbative scaling approaches, the corresponding low-energy Hamiltonian is
solved for arbitrary temperatures, gate voltages, tunneling rates, and energies
of the impurity level. Similar to the case of a weak tunnel barrier, the shape
of the charge step is governed at low temperatures by the non-Fermi-liquid
fixed point of the two-channel Kondo effect. However, the associated Kondo
temperature TK is strongly modified. Most notably, TK is proportional to the
width of the level if the transmission through the impurity is close to unity
at the Fermi energy, and is no longer exponentially small in one over the
tunneling matrix element. Focusing on a particle-hole symmetric level, the
two-channel Kondo effect is found to be robust against the inclusion of an
on-site repulsion on the level. For a large on-site repulsion and a large
asymmetry in the tunneling rates to box and to the lead, there is a sequence of
Kondo effects: first the local magnetic moment that forms on the level
undergoes single-channel screening, followed by two-channel overscreening of
the charge fluctuations inside the box.Comment: 21 pages, 19 figure
Fermi liquid identities for the Infinite U Anderson Model
We show how the electron gas methods of Luttinger, Ward and Nozi\`eres can be
applied to the infinite U Anderson impurity model within a Schwinger boson
treatment. Working to all orders in a 1/N expansion, we show how the Friedel
Langreth relationship, the Yamada-Yosida-Yoshimori and the Shiba-Korringa
relations can be derived, under the assumption that the spinon and holon fields
are gapped. One of the remarkable features of this treatment, is that the
Landau amplitudes depend on the exchange of low energy virtual spinons and
holons. We end the paper with a discussion on the extension of our approach to
the lattice, where the spinon-holon is expected to close at a quantum critical
point.Comment: 18 pages. Version 2 revised after referees comment
Kondo effect in coupled quantum dots: a Non-crossing approximation study
The out-of-equilibrium transport properties of a double quantum dot system in
the Kondo regime are studied theoretically by means of a two-impurity Anderson
Hamiltonian with inter-impurity hopping. The Hamiltonian, formulated in
slave-boson language, is solved by means of a generalization of the
non-crossing approximation (NCA) to the present problem. We provide benchmark
calculations of the predictions of the NCA for the linear and nonlinear
transport properties of coupled quantum dots in the Kondo regime. We give a
series of predictions that can be observed experimentally in linear and
nonlinear transport measurements through coupled quantum dots. Importantly, it
is demonstrated that measurements of the differential conductance , for the appropriate values of voltages and inter-dot tunneling
couplings, can give a direct observation of the coherent superposition between
the many-body Kondo states of each dot. This coherence can be also detected in
the linear transport through the system: the curve linear conductance vs
temperature is non-monotonic, with a maximum at a temperature
characterizing quantum coherence between both Kondo states.Comment: 20 pages, 17 figure