634 research outputs found
Josephson response of a conventional and a noncentrosymmetric superconductor coupled via a double quantum dot
We consider transport through a Josephson junction consisting of a
conventional s-wave superconductor coupled via a double quantum dot to a
noncentrosymmetric superconductor with both, singlet and triplet pairing. We
calculate the Andreev bound state energies and the associated Josephson
current. We demonstrate that the current-phase relation is a sensitive probe of
the singlet-triplet ratio in the noncentrosymmetric superconductor. In
particular, in the presence of an inhomogeneous magnetic field the system
exhibits a -junction behavior.Comment: 8 pages, 7 figures, published versio
Model for the magnetoresistance and Hall coefficient of inhomogeneous graphene
We show that when bulk graphene breaks into n-type and p-type puddles, the
in-plane resistivity becomes strongly field dependent in the presence of a
perpendicular magnetic field, even if homoge- neous graphene has a
field-independent resistivity. We calculate the longitudinal resistivity
\rho_{xx} and Hall resistivity \rho_{xy} as a function of field for this
system, using the effective-medium approximation. The conductivity tensors of
the individual puddles are calculated using a Boltzmann approach suit- able for
the band structure of graphene near the Dirac points. The resulting resistivity
agrees well with experiment, provided that the relaxation time is weakly
field-dependent. The calculated Hall resistivity has the sign of the majority
carrier and vanishes when there are equal number of n and p type puddles.Comment: 5 pages, 4 figure
Numerical Study of Energy Loss by a Nanomechanical Oscillator Coupled to a Cooper Pair Box
We calculate the dynamics of a nanomechanical oscillator (NMO) coupled
capacitively to a Cooper pair box (CPB), by solving a stochastic Schrodinger
equation with two Lindblad operators. Both the NMO and the CPB are assumed
dissipative, and the coupling is treated within the rotating wave
approximation. We show numerically that, if the CPB decay time is smaller than
the NMO decay time, the coupled NMO will lose energy faster, and the coupled
CPB more slowly, than do the uncoupled NMO and CPB. The results show that the
efficiency of energy loss by an NMO can be substantially increased if the NMO
is coupled to a CPB.Comment: 10 pages, 3 figure
Signatures of tunable Majorana-fermion edge states
Chiral Majorana-fermion modes are shown to emerge as edge excitations in a
superconductor--topological-insulator hybrid structure that is subject to a
magnetic field. The velocity of this mode is tunable by changing the
magnetic-field magnitude and/or the superconductor's chemical potential. We
discuss how quantum-transport measurements can yield experimental signatures of
these modes. A normal lead coupled to the Majorana-fermion edge state through
electron tunneling induces resonant Andreev reflections from the lead to the
grounded superconductor, resulting in a distinctive pattern of
differential-conductance peaks.Comment: (13 pages, Accepted for publication in New Journal of Physics, an
extension of and expansion on our previous work arXiv:1210.4057). arXiv admin
note: text overlap with arXiv:1210.405
Spin transport in a graphene normal-superconductor junction in the quantum Hall regime
The quantum Hall regime of graphene has many unusual properties. In
particular, the presence of a Zeeman field opens up a region of energy within
the zeroth Landau level, where the spin-up and spin-down states localized at a
single edge propagate in opposite directions. We show that when these edge
states are coupled to an s-wave superconductor, the transport of charge
carriers is spin-filtered. This spin-filtering effect can be traced back to the
interplay of specular Andreev reflections and Andreev retro-reflections in the
presence of a Zeeman field.Comment: 6 pages, 7 figure
Tunable Band Gap in Graphene with a Non-Centrosymmetric Superlattice Potential
We show that, if graphene is subjected to the potential from an external
superlattice, a band gap develops at the Dirac point provided the superlattice
potential has broken inversion symmetry. As a numerical example, we calculate
the band structure of graphene in the presence of an external potential due to
periodically patterned gates arranged in a triangular graphene superlattice
(TGS) with broken inversion symmetry, and find that a band gap is created at
both the original and "second generation" Dirac point. The gap can be
controlled, in principle, by changing the external potential and the lattice
constant of the TGS.Comment: 6 figures, Phys. Rev. B 79, 20543
MOLECULAR DYNAMICS STUDY OF NON-HYDROGEN-BONDING BASE-PAIR DNA DUPLEX d(GTCDNAM GCGCCGTGGC). d(GCCACGGCGCD5SICSGAC)
Objective: The objective of the study was to elucidate the structural activity of a natural DNA sequence modified by a hydrophobic base-pair which didn't form Watson-Crick (W-C) hydrogen-bond. The modified unnatural base-pair (DNAM-D5SICS) was introduced in DNA sequences of 14-mer for molecular dynamics study in water solution.Methods: A 200 ns molecular-dynamics-simulation in orthogonal-box-water-solvent, using Particle-mesh-Ewald-method (PME) within periodic-boundary-condition (PBC) was performed by using AMBER-14 code. The force-field-ff12SB-force-field was used during the simulation while the force-field-parameters of modified base-pair, compatible to ff12SB-force-field, were calculated by Gaussian-09-code using ab-inito/Hartree-Fock-methodology. The code CPPTRAJ, (a module of AMBER-14) CURVE and Chimera were used in the analysis of the data.Results: Root mean square deviation (RMSD) of heavy atoms of the trajectory revealed that the structure of the equilibrated duplex was stable, sequence-dependent and had mixed DNA-conformation. A little distortion near to the neighbor of the modified base-pair in the duplex strand was observed. However, we got a stabilized structure of such type of duplex if we placed modified base-pair after the third place in the strand.Conclusion: The study concluded that the distortion produced by modified-base-pair in the overall structure of duplex was local while the confirmation of such type of duplex was mixed and maintained the Watson-Crick (W-C) integrity of DNA. The study would help in the use of hydrophobic base-pair materials in biotechnological applications and the understanding of their structure-function relationship
Quantum charge pumping through fractional Fermions in charge density modulated quantum wires and Rashba nanowires
We study the phenomenon of adiabatic quantum charge pumping in systems
supporting fractionally charged fermionic bound states, in two different
setups. The first quantum pump setup consists of a charge-density-modulated
quantum wire, and the second one is based on a semiconducting nanowire with
Rashba spin-orbit interaction, in the presence of a spatially oscillating
magnetic field. In both these quantum pumps transport is investigated in a
N-X-N geometry, with the system of interest (X) connected to two normal-metal
leads (N), and the two pumping parameters are the strengths of the effective
wire-lead barriers. Pumped charge is calculated within the scattering matrix
formalism. We show that quantum pumping in both setups provides a unique
signature of the presence of the fractional-fermion bound states, in terms of
asymptotically quantized pumped charge. Furthermore, we investigate shot noise
arising due to quantum pumping, verifying that quantized pumped charge
corresponds to minimal shot noise.Comment: This is the published versio
Quantum transport signatures of chiral edge states in SrRuO
We investigate transport properties of a double quantum dot based Cooper pair
splitter, where the superconducting lead consists of SrRuO. The
proposed device can be used to explore the symmetry of the superconducting
order parameter in SrRuO by testing the presence of gapless chiral edge
states, which are predicted to exist if the bulk superconductor is described by
a chiral --wave state. The odd orbital symmetry of the bulk order parameter
ensures that we can realize a regime where the electrons tunneling into the
double dot system come from the chiral edge states and thereby leave their
signature in the conductance. The proposed Cooper pair splitter has the
potential to probe order parameters in unconventional superconductors.Comment: 5 page
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