6,512 research outputs found
Tunneling transport in NSN junctions made of Majorana nanowires across the topological quantum phase transition
We theoretically consider transport properties of a normal metal (N)-
superconducting semiconductor nanowire (S)-normal metal (N) structure (NSN) in
the context of the possible existence of Majorana bound states in disordered
semiconductor-superconductor hybrid systems in the presence of spin-orbit
coupling and Zeeman splitting induced by an external magnetic field. We study
in details the transport signatures of the topological quantum phase transition
as well as the existence of the Majorana bound states in the electrical
transport properties of the NSN structure. Our theory includes the realistic
nonperturbative effects of disorder, which is detrimental to the topological
phase (eventually suppressing the superconducting gap completely), and the
effects of the tunneling barriers (or the transparency at the tunneling NS
contacts), which affect (and suppress) the zero bias conductance peak
associated with the zero energy Majorana bound states. We show that in the
presence of generic disorder and barrier transparency the interpretation of the
zero bias peak as being associated with the Majorana bound state is problematic
since the nonlocal correlations between the two NS contacts at two ends may not
manifest themselves in the tunneling conductance through the whole NSN
structure. We establish that a simple modification of the standard transport
measurements using conductance differences (rather than the conductance itself
as in a single NS junction) as the measured quantity can allow direct
observation of the nonlocal correlations inherent in the Majorana bound states
and enables the mapping out of the topological phase diagram (even in the
presence of considerable disorder) by precisely detecting the topological
quantum phase transition point.Comment: 34 pages, 7 figures, 1 table. New version with minor modifications
and more physical discussion
Spatial persistence and survival probabilities for fluctuating interfaces
We report the results of numerical investigations of the steady-state (SS)
and finite-initial-conditions (FIC) spatial persistence and survival
probabilities for (1+1)--dimensional interfaces with dynamics governed by the
nonlinear Kardar--Parisi--Zhang (KPZ) equation and the linear
Edwards--Wilkinson (EW) equation with both white (uncorrelated) and colored
(spatially correlated) noise. We study the effects of a finite sampling
distance on the measured spatial persistence probability and show that both SS
and FIC persistence probabilities exhibit simple scaling behavior as a function
of the system size and the sampling distance. Analytical expressions for the
exponents associated with the power-law decay of SS and FIC spatial persistence
probabilities of the EW equation with power-law correlated noise are
established and numerically verified.Comment: 11 pages, 5 figure
Spin-polarized transport in inhomogeneous magnetic semiconductors: theory of magnetic/nonmagnetic p-n junctions
A theory of spin-polarized transport in inhomogeneous magnetic semiconductors
is developed and applied to magnetic/nonmagnetic p-n junctions. Several
phenomena with possible spintronic applications are predicted, including
spinvoltaic effect, spin valve effect, and giant magnetoresistance. It is
demonstrated that only nonequilibrium spin can be injected across the
space-charge region of a p-n junction, so that there is no spin injection (or
extraction) at low bias.Comment: Minor Revisions. To appear in Phys. Rev. Let
Valley interference effects on a donor electron close to a Si/SiO2 interface
We analyze the effects of valley interference on the quantum control and
manipulation of an electron bound to a donor close to a Si/SiO2 interface as a
function of the valley-orbit coupling at the interface. We find that, for
finite valley-orbit coupling, the tunneling times involved in shuttling the
electron between the donor and the interface oscillate with the interface/donor
distance in much the same way as the exchange coupling oscillates with the
interdonor distance. These oscillations disappear when the ground state at the
interface is degenerate (corresponding to zero valley-orbit coupling).Comment: 7 pages, 5 figure
Spin Polarization Dependence of Carrier Effective Mass in Semiconductor Structures: Spintronic Effective Mass
We introduce the concept of a spintronic effective mass for spin-polarized
carriers in semiconductor structures, which arises from the strong
spin-polarization dependence of the renormalized effective mass in an
interacting spin-polarized electron system. The majority-spin many-body
effective mass renormalization differs by more than a factor of 2 at rs=5
between the unpolarized and the fully polarized two-dimensional system, whereas
the polarization dependence (~15%) is more modest in three dimensions around
metallic densities (rs~5). The spin-polarization dependence of the carrier
effective mass is of significance in various spintronic applications.Comment: Final versio
- …