Yasuhiro Utsumi

Kondo Effect in Quantum Dots Coupled to Ferromagnetic Leads

Abstract The Kondo effects in transport through a quantum dot (QD) coupled to ferromagnetic leads are shown to be modified by the spin polarization of the electrodes. For parallel alignment of the magnetization of the leads the zero-bias anomaly in the differential conductance is split even in the absence of an external magnetic field. For antiparallel alignment the peaks are split only in the presence of a magnetic filed, but show a characteristic asymmetry.

Nonequilibrium Kondo effect in a quantum dot coupled to ferromagnetic leads

We study the Kondo effect in the electron transport through a quantum dot coupled to ferromagnetic leads, using a real-time diagrammatic technique that provides a systematic description of the nonequilibrium dynamics of a system with strong local electron correlations. We evaluate the theory in an extension of the “resonant tunneling approximation,” introduced earlier, by introducing the self-energy of the off-diagonal component of the reduced propagator in spin space. In this way we develop a charge and spin conserving approximation that accounts not only for Kondo correlations but also for the spin splitting and spin accumulation out of equilibrium. We show that the Kondo resonances, split by the applied bias voltage, may be spin polarized. A left-right asymmetry in the coupling strength and/or spin polarization of the electrodes significantly affects both the spin accumulation and the weight of the split Kondo resonances out of equilibrium. The effects are observable in the nonlinear differential conductance. We also discuss the influence of decoherence on the Kondo resonance in the frame of the real-time formulation.

Full counting statistics of interacting electrons

In order to fully characterize the noise associated with electron transport, with its severe consequences for solid-state quantum information systems, the theory of full counting statistics has been developed. It accounts for correlation effects associated with the statistics and effects of entanglement, but it remains a non-trivial task to account for interaction effects. In this article we present two examples: we describe electron transport through quantum dots with strong charging effects beyond perturbation theory in the tunneling, and we analyze current fluctuations in a diffusive interacting conductor.

Full Counting Statistics for a Single-Electron Transistor: Nonequilibrium Effects at Intermediate Conductance

We evaluate the current distribution for a single-electron transistor with intermediate strength tunnel conductance. Using the Schwinger-Keldysh approach and the drone (Majorana) fermion representation, we account for the renormalization of system parameters. Nonequilibrium effects induce a lifetime broadening of the charge-state levels, which suppress large current fluctuations.

Full counting statistics for the number of electrons in a quantum dot

Motivated by recent real-time electron counting experiments, we evaluate the full counting statistics for the probability distribution of the electron number inside a quantum dot which is weakly coupled to source and drain leads. A non-Gaussian exponential distribution appears when there is no dot state close to the lead chemical potentials. We propose the measurement of the joint probability distribution of current and electron number, which reveals correlations between the two observables. We also show that for increasing strength of tunneling, the quantum fluctuations qualitatively change the probability distribution of the electron number. In this paper, we derive the cumulant generating functions (CGFs) of the joint probability distribution for several cases. The Keldysh generating functional approach is adopted to obtain the CGFs for the resonant-level model and for the single-electron transistor in the intermediate conductance regime. The general form for the CGF of the joint probability distribution is provided within the Markov approximation in an extension of the master equation approach [D. A. Bagrets and Yu. V. Nazarov, Phys. Rev. B 67, 085316 (2003)].

Bulk and surface electronic properties of SmB6 : A hard x-ray photoelectron spectroscopy study

We have carried out bulk-sensitive hard x-ray photoelectron spectroscopy measurements on in situ cleaved and ex situ polished

Parity effect and tunnel magnetoresistance of ferromagnet/superconductor/ferromagnet single-electron tunneling transistors

{\mathrm{SmB}}_{6}

Contiguous 3 d and 4 f Magnetism: Strongly Correlated 3 d Electrons in YbFe 2 Al 10

single crystals. Using the multiplet structure in the Sm

Charge fluctuation between even and odd states of a superconducting island

3d

The effect of charge fluctuation on a normal-superconducting-normal single-electron transistor

core level spectra, we determined reliably that the valence of Sm in bulk