944 research outputs found
Spin Current in p-wave Superconducting Rings
A formula of the spin current in mesoscopic superconductors is derived from
the mean-field theory of superconductivity. The spin flow is generated by the
spatial fluctuations of which represents a spin state of spin-triplet
superconductors. We discuss a possibility of the circulating spin current in
isolated p-wave superconducting rings at the zero magnetic field. The direction
of the spin current depends on topological numbers which characterize the
spatial configuration of on the ring.Comment: 4page
Interplay of Kondo and superconducting correlations in the nonequilibrium Andreev transport through a quantum dot
Using the modified perturbation theory, we theoretically study the
nonequilibrium Andreev transport through a quantum dot coupled to normal and
superconducting leads (N-QD-S), which is strongly influenced by the Kondo and
superconducting correlations. From the numerical calculation, we find that the
renormalized couplings between the leads and the dot in the equilibrium states
characterize the peak formation in the nonequilibrium differential conductance.
In particular, in the Kondo regime, the enhancement of the Andreev transport
via a Kondo resonance occurs in the differential conductance at a finite bias
voltage, leading to an anomalous peak whose position is given by the
renormalized parameters. In addition to the peak, we show that the energy
levels of the Andreev bound states give rise to other peaks in the differential
conductance in the strongly correlated N-QD-S system. All these features of the
nonequilibrium transport are consistent with those in the recent experimental
results [R. S. Deacon {\it et al.}, Phys. Rev. Lett. {\bf 104}, 076805 (2010);
Phys. Rev. B {\bf 81}, 12308 (2010)]. We also find that the interplay of the
Kondo and superconducting correlations induces an intriguing pinning effect of
the Andreev resonances to the Fermi level and its counter position.Comment: 22 pages, 23 figure
Quantum Hall effects of graphene with multi orbitals: Topological numbers, Boltzmann conductance and Semi-classical quantization
Hall conductance as the Chern numbers of the Berry connection
in the magnetic Brillouin zone is calculated for a realistic multi band
tight-band model of graphene with non-orthogonal basis. It is confirmed that
the envelope of coincides with a semi-classical result when
magnetic field is sufficiently small.
The Hall resistivity from the weak-field Boltzmann theory also
explains the overall behaviour of the if the Fermi surface is
composed of a single energy band. The plateaux of are explained
from semi-classical quantization and necessary modification is proposed for the
Dirac fermion regimes.Comment: 5pages, 3figure
Detection of spin polarization with a side coupled quantum dot
We propose realistic methods to detect local spin polarization, which utilize
a quantum dot side coupled to the target system. By choosing appropriate states
in the dot, we can put spin selectivity to the dot and detect spins in the
target with small disturbance. We also present an experiment which realizes one
of the proposed spin detection schemes in magnetic fields.Comment: 5 pages, 6 figure
Spin filtering by a periodic nanospintronic devices
For a linear chain of diamond-like elements, we show that the Rashba
spin-orbit interaction (which can be tuned by a perpendicular gate voltage) and
the Aharonov-Bohm flux (due to a perpendicular magnetic field) can combine to
select only one propagating ballistic mode, for which the electronic spins are
fully polarized along a direction that can be tuned by the electric and
magnetic fields and by the electron energy. All the other modes are evanescent.
For a wide range of parameters, this chain can serve as a spin filter.Comment: Published versio
Reevaluation of Neutron Electric Dipole Moment with QCD Sum Rules
We study the neutron electric dipole moment in the presence of the
CP-violating operators up to the dimension five in terms of the QCD sum rules.
It is found that the OPE calculation is robust when exploiting a particular
interpolating field for neutron, while there exist some uncertainties on the
phenomenological side. By using input parameters obtained from the lattice
calculation, we derive a conservative limit for the contributions of the CP
violating operators. We also show the detail of the derivation of the sum
rules.Comment: 33 pages, 5 figure
Josephson pi-state in a ferromagnetic insulator
We predict anomalous atomic-scale 0-pi transitions in a Josephson junction
with a ferromagnetic-insulator (FI) barrier. The ground state of such junction
alternates between 0- and pi-states when thickness of FI is increasing by a
single atomic layer. We find that the mechanism of the 0-pi transition can be
attributed to thickness-dependent phase-shifts between the wave numbers of
electrons and holes in FI. Based on these results, we show that stable pi-state
can be realized in junctions based on high-Tc superconductors with
LaBaCuO barrier.Comment: 4 pages, 3 figures, Phys. Rev. Lett. (2010) in pres
Filtering and analyzing mobile qubit information via Rashba-Dresselhaus-Aharonov-Bohm interferometers
Spin-1/2 electrons are scattered through one or two diamond-like loops, made
of quantum dots connected by one-dimensional wires, and subject to both an
Aharonov-Bohm flux and (Rashba and Dresselhaus) spin-orbit interactions. With
some symmetry between the two branches of each diamond, and with appropriate
tuning of the electric and magnetic fields (or of the diamond shapes) this
device completely blocks electrons with one polarization, and allows only
electrons with the opposite polarization to be transmitted. The directions of
these polarizations are tunable by these fields, and do not depend on the
energy of the scattered electrons. For each range of fields one can tune the
site and bond energies of the device so that the transmission of the fully
polarized electrons is close to unity. Thus, these devices perform as ideal
spin filters, and these electrons can be viewed as mobile qubits; the device
writes definite quantum information on the spinors of the outgoing electrons.
The device can also read the information written on incoming polarized
electrons: the charge transmission through the device contains full information
on this polarization. The double-diamond device can also act as a realization
of the Datta-Das spin field-effect transistor.Comment: 13 pages, 8 figure
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