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Search Results: 1 - 10 of 22575 matches for " Roberto Raimondi "
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Resonant Andreev Tunneling in Strongly Interacting Quantum Dots
Rosario Fazio,Roberto Raimondi
Physics , 1997, DOI: 10.1103/PhysRevLett.80.2913
Abstract: We study resonant Andreev tunneling through a strongly interacting quantum dot connected to a normal and to a superconducting lead. We obtain a formula for the Andreev current and apply it to discuss the linear and non-linear transport in the nonperturbative regime, where the effects of the Kondo resonance on the two particle tunneling arise. In particular we notice an enhancement of the Kondo anomaly in the $I-V$ characteristics due to the superconducting electrode.
Interplay of intrinsic and extrinsic mechanisms to the spin Hall effect in a two-dimensional electron gas
Roberto Raimondi,Peter Schwab
Physics , 2009, DOI: 10.1016/j.physe.2009.10.047
Abstract: In order to describe correctly the interplay of extrinsic and intrinsic spin-orbit mechanisms to the spin Hall effect, it is necessary to consider different sources of spin relaxation. We take into account the spin relaxation time $\tau_{DP}$ due to the Dyakonov-Perel mechanism as well as the Elliot-Yafet spin-relaxation time $\tau_s$ due to the spin-orbit scattering from impurities. The total spin Hall conductivity depends crucially on the ratio $\tau_s /\tau_{DP}$.
Spin-Hall effect in a disordered 2D electron-system
Roberto Raimondi,Peter Schwab
Physics , 2004, DOI: 10.1103/PhysRevB.71.033311
Abstract: We calculate the spin-Hall conductivity for a two-dimensional electron gas within the self-consistent Born approximation, varying the strength and type of disorder. In the weak disorder limit we find both analytically and numerically a vanishing spin-Hall conductivity even when we allow a momentum dependent scattering. Separating the reactive from the disspative current response, we find the universal value $\sigma^R_{sH} = e/8 \pi$ for the reactive response, which cancels however with the dissipative part $\sigma^D_{sH} = -e/8 \pi$.
Disordered Electron Systems
Carlo Di Castro,Roberto Raimondi
Physics , 2004,
Abstract: These lectures provide an introduction to the theory of disordered interacting electron systems. In particular, we concentrate on those aspects which are fundamental for the problem of the metal-insulator transition due to the interplay of disorder and interaction. After reviewing the problem of disordered non-interacting electrons, we examine the past and recent experimental urgency to take into account interaction effects. We describe, by using the language of standard perturbation theory, how these interactions effects lead to the picture of the renormalized disordered Fermi liquid. This allows us to obtain the renormalization group equations for the disordered interacting electron liquid. The group equations are then discussed by the light of the existing experimental evidence.
Transport properties of a two-dimensional electron liquid at high magnetic field
Roberto D'Agosta,Roberto Raimondi,Giovanni Vignale
Physics , 2003, DOI: 10.1103/PhysRevB.68.035314
Abstract: The chiral Luttinger liquid model for the edge dynamics of a two-dimensional electron gas in a strong magnetic field is derived from coarse-graining and a lowest Landau level projection procedure at arbitrary filling factors $\nu<1$ -- without reference to the quantum Hall effect. Based on this model, we develop a formalism to calculate the Landauer-B\"uttiker conductances in generic experimental set-ups including multiple leads and voltage probes. In the absence of tunneling between the edges the "ideal" Hall conductances ($G_{ij}= \frac{e^2 \nu}{h}$ if lead $j$ is immediately upstream of lead $i$, and $G_{ij}=0$ otherwise) are recovered. Tunneling of quasiparticles of fractional charge $e^*$ between different edges is then included as an additional term in the Hamiltonian. In the limit of weak tunneling we obtain explicit expressions for the corrections to the ideal conductances. As an illustration of the formalism we compute the current- and temperature-dependent resistance $R_{xx}(I,T)$ of a quantum point contact localized at the center of a gate-induced constriction in a quantum Hall bar. The exponent $\alpha$ in the low-current relation $R_{xx}(I,0) \sim I^{\alpha -2}$ shows a nontrivial dependence on the strength of the inter-edge interaction, and its value changes as $e^*V_H$, where $V_H = \frac{h I}{\nu e^2}$ is the Hall voltage, falls below a characteristic crossover energy $\frac{\hbar c}{d}$, where $c$ is the edge wave velocity and $d$ is the length of the constriction. The consequences of this crossover are discussed vis-a-vis recent experiments in the weak tunneling regime.
Temperature Dependence of the Tunneling Amplitude between Quantum Hall Edges
Roberto D'Agosta,Giovanni Vignale,Roberto Raimondi
Physics , 2004, DOI: 10.1103/PhysRevLett.94.086801
Abstract: Recent experiments have studied the tunneling current between the edges of a fractional quantum Hall liquid as a function of temperature and voltage. The results of the experiment are puzzling because at "high" temperature (600-900 mK) the behavior of the tunneling conductance is consistent with the theory of tunneling between chiral Luttinger liquids, but at low temperature it strongly deviates from that prediction dropping to zero with decreasing temperature. In this paper we suggest a possible explanation of this behavior in terms of the strong temperature dependence of the tunneling amplitude.
Specific Heat Anomaly and Adiabatic Hysteresis in Disordered Electron Systems in a Magnetic Field
Peter Schwab,Roberto Raimondi,Claudio Castellani
Physics , 1998, DOI: 10.1007/s100510050601
Abstract: We consider the thermodynamic behavior of a disordered interacting electron system in two dimensions. We show that the corrections to the thermodynamic potential in the weakly localized regime give rise to a non monotonic behavior of the specific heat both in temperature and magnetic field. From this effect we predict the appearance of adiabatic hysteresis in the magnetoconductance. Our results can be interpreted as precursor effect of formation of local moments in disordered electron systems. We also comment on the relevance of our analysis in three dimensional systems.
Parity-dependent Kondo effect in ultrasmall metallic grains
Giancarlo Franzese,Roberto Raimondi,Rosario Fazio
Physics , 2002, DOI: 10.1209/epl/i2003-00355-6
Abstract: We study the Kondo effect in an ultrasmall metallic grain, i.e. small enough to have a discrete energy-level spectrum, by calculating the susceptibility chi of the magnetic impurity. Our quantum Monte Carlo simulations, and analytic solution of a simple model, show that the behavior changes dramatically depending on whether the number of electrons in the grain is even or odd. We suggest that the measurements of chi provide an effective experimental way of probing the grain's number parity.
Spin Hall effects due to phonon skew scattering
Cosimo Gorini,Ulrich Eckern,Roberto Raimondi
Physics , 2015, DOI: 10.1103/PhysRevLett.115.076602
Abstract: A diversity of spin Hall effects in metallic systems is known to rely on Mott skew scattering. In this work its high-temperature counterpart, phonon skew scattering, which is expected to be of foremost experimental relevance, is investigated. In particular, the phonon skew scattering spin Hall conductivity is found to be practically $T$-independent for temperatures above the Debye temperature $T_D$. As a consequence, in Rashba-like systems a high-$T$ linear behavior of the spin Hall angle demonstrates the dominance of extrinsic spin-orbit scattering only if the intrinsic spin splitting is smaller than the temperature.
Spin polarization induced by an electric field in the presence of weak localization effects
Daniele Guerci,Juan Borge,Roberto Raimondi
Physics , 2015, DOI: 10.1016/j.physe.2015.09.046
Abstract: We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.
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