658 research outputs found
Finite-temperature conductance of strongly interacting quantum wire with a nuclear spin order
We study the temperature dependence of the electrical conductance of a clean
strongly interacting quantum wire in the presence of a helical nuclear spin
order. The nuclear spin helix opens a temperature-dependent partial gap in the
electron spectrum. Using a bosonization framework we describe the gapped
electron modes by sine-Gordon-like kinks. We predict an internal resistivity
caused by an Ohmic-like friction these kinks experience via interacting with
gapless excitations. As a result, the conductance rises from at
temperatures below the critical temperature when nuclear spins are fully
polarized to at higher temperatures when the order is destroyed,
featuring a relatively wide plateau in the intermediate regime. The theoretical
results are compared with the experimental data for GaAs quantum wires obtained
recently by Scheller et al. [Phys. Rev. Lett. 112, 066801 (2014)].Comment: 18 pages, 10 figure
Lifetime of Majorana qubits in Rashba nanowires with non-uniform chemical potential
We study the lifetime of topological qubits based on Majorana bound states
hosted in a one-dimensional Rashba nanowire (NW) with proximity-induced
superconductivity and non-uniform chemical potential needed for manipulation
and read-out. If nearby gates tune the chemical potential locally so that part
of the NW is in the trivial phase, Andreev bound states (ABSs) can emerge which
are localized at the interface between topological and trivial phases with
energies significantly less than the gap. The emergence of such subgap states
strongly decreases the Majorana qubit lifetime at finite temperatures due to
local perturbations that can excite the system into these ABSs. Using Keldysh
formalism, we study such excitations caused by fluctuating charges in
capacitively coupled gates and calculate the corresponding Majorana lifetimes
due to thermal noise, which are shown to be much shorter than those in NWs with
uniform chemical potential.Comment: 9 pages, 8 figure
Stabilization of the surface CDW order parameter by long-range Coulomb interaction
We study theoretically formation of two-dimensional (2D) charge density wave
(CDW) in a system of conducting chains at the surface of an insulator due to
interaction of quasi 1D surface electrons with phonons. We show that the
unscreened long-range Coloumb interaction between the charges induced by
fluctuations of the CDW phase stabilizes the finite order parameter value at
finite temperatures, and thus the long-range order (LRO) exists. In the case of
screened Coloumb interaction the phase fluctuations suppress the phase
transition, but decay of the order parameter is rather slow, it obeys a
power-law with small exponent
$\gamma
A Dynamic Model of Stochastic Innovation Race: Leader-Follower Case
We provide steps towards analysis of rational behaviors of innovators acting on a market of a technological product. The situation when a technological leader competes with a large number of identical followers is in the focus. The process of development of new generations of the product is treated as a Poisson-type cyclic stochastic process. The technology spillovers effect acts as a driving force of the technological progress. We obtain an analytic characterization of optimal leaders R&D and manufacturing investment policies. Numerical simulations and economic interpretations are presented as well
Degeneracy lifting of Majorana bound states due to electron-phonon interactions
We study theoretically how electron-phonon interaction affects the energies
and level broadening (inverse lifetime) of Majorana bound states (MBSs) in a
clean topological nanowire at low temperatures. At zero temperature, the energy
splitting between the right and left MBSs remains exponentially small with
increasing nanowire length . At finite temperatures, however, the absorption
of thermal phonons leads to the broadening of energy levels of the MBSs that
does not decay with system length, and the coherent absorption/emission of
phonons at opposite ends of the nanowire results in MBSs energy splitting that
decays only as an inverse power-law in . Both effects remain exponential in
temperature. In the case of quantized transverse motion of phonons, the
presence of Van Hove singularities in the phonon density of states causes
additional resonant enhancement of both the energy splitting and the level
broadening of the MBSs. This is the most favorable case to observe the
phonon-induced energy splitting of MBSs as it becomes much larger than the
broadening even if the topological nanowire is much longer than the coherence
length. We also calculate the charge and spin associated with the energy
splitting of the MBSs induced by phonons. We consider both a spinless
low-energy continuum model, which we evaluate analytically, as well as a
spinful lattice model for a Rashba nanowire, which we evaluate numerically
Heavy-Ion Beam Acceleration of Two-Charge States from an Ecr Ion Source
This paper describes a design for the front end of a superconducting (SC) ion
linac which can accept and simultaneously accelerate two charge states of
uranium from an ECR ion source. This mode of operation increases the beam
current available for the heaviest ions by a factor of two. We discuss the 12
MeV/u prestripper section of the Rare Isotope Accelerator (RIA) driver linac
including the LEBT, RFQ, MEBT and SC sections, with a total voltage of 112 MV.
The LEBT consists of two bunchers and electrostatic quadrupoles. The
fundamental frequency of both bunchers is half of the RFQ frequency. The first
buncher is a multiharmonic buncher, designed to accept more than 80% of each
charge state and to form bunches of extremely low longitudinal emittance (rms
emittance is lower than 0.2 keV/u nsec) at the output of the RFQ. The second
buncher is located directly in front of the RFQ and matches the velocity of
each charge-state bunch to the design input velocity of the RFQ. We present
full 3D simulations of a two-charge-state uranium beam including space charge
forces in the LEBT and RFQ, realistic distributions of all electric and
magnetic fields along the whole prestripper linac, and the effects of errors,
evaluated for several design options for the prestripper linac. The results
indicate that it is possible to accelerate two charge states while keeping
emittance growth within tolerable limits.Comment: LINAC2000, MOD0
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