850 research outputs found
Nonlocal Damping of Helimagnets in One-Dimensional Interacting Electron Systems
We investigate the magnetization relaxation of a one-dimensional helimagnetic
system coupled to interacting itinerant electrons. The relaxation is assumed to
result from the emission of plasmons, the elementary excitations of the
one-dimensional interacting electron system, caused by slow changes of the
magnetization profile. This dissipation mechanism leads to a highly nonlocal
form of magnetization damping that is strongly dependent on the
electron-electron interaction. Forward scattering processes lead to a spatially
constant damping kernel, while backscattering processes produce a spatially
oscillating contribution. Due to the nonlocal damping, the thermal fluctuations
become spatially correlated over the entire system. We estimate the
characteristic magnetization relaxation times for magnetic quantum wires and
nuclear helimagnets.Comment: Final version accepted by Physical Review
From Classical to Quantum and Back: Hamiltonian Adaptive Resolution Path Integral, Ring Polymer, and Centroid Molecular Dynamics
Path integral-based simulation methodologies play a crucial role for the
investigation of nuclear quantum effects by means of computer simulations.
However, these techniques are significantly more demanding than corresponding
classical simulations. To reduce this numerical effort, we recently proposed a
method, based on a rigorous Hamiltonian formulation, which restricts the
quantum modeling to a small but relevant spatial region within a larger
reservoir where particles are treated classically. In this work, we extend this
idea and show how it can be implemented along with state-of-the-art path
integral simulation techniques, such as ring polymer and centroid molecular
dynamics, which allow the approximate calculation of both quantum statistical
and quantum dynamical properties. To this end, we derive a new integration
algorithm which also makes use of multiple time-stepping. The scheme is
validated via adaptive classical--path-integral simulations of liquid water.
Potential applications of the proposed multiresolution method are diverse and
include efficient quantum simulations of interfaces as well as complex
biomolecular systems such as membranes and proteins
Current-induced gap opening in interacting topological insulator surfaces
Two-dimensional topological insulators (TIs) host gapless helical edge states
that are predicted to support a quantized two-terminal conductance.
Quantization is protected by time-reversal symmetry, which forbids elastic
backscattering. Paradoxically, the current-carrying state itself breaks the
time-reversal symmetry that protects it. Here we show that the combination of
electron-electron interactions and momentum-dependent spin polarization in
helical edge states gives rise to feedback through which an applied current
opens a gap in the edge state dispersion, thereby breaking the protection
against elastic backscattering. Current-induced gap opening is manifested via a
nonlinear contribution to the system's characteristic, which persists
down to zero temperature. We discuss prospects for realizations in recently
discovered large bulk band gap TIs, and an analogous current-induced gap
opening mechanism for the surface states of three-dimensional TIs.Comment: 6 pages, 2 figures, published versio
Spin-orbit-induced strong coupling of a single spin to a nanomechanical resonator
We theoretically investigate the deflection-induced coupling of an electron
spin to vibrational motion due to spin-orbit coupling in suspended carbon
nanotube quantum dots. Our estimates indicate that, with current capabilities,
a quantum dot with an odd number of electrons can serve as a realization of the
Jaynes-Cummings model of quantum electrodynamics in the strong-coupling regime.
A quantized flexural mode of the suspended tube plays the role of the optical
mode and we identify two distinct two-level subspaces, at small and large
magnetic field, which can be used as qubits in this setup. The strong intrinsic
spin-mechanical coupling allows for detection, as well as manipulation of the
spin qubit, and may yield enhanced performance of nanotubes in sensing
applications.Comment: 5 pages, 3 figures + appendix; published versio
Exploring Business-to-Business Marketsites
Business-to-business (B2B) marketsites are quickly becoming one of the major issues for companies in their search for opportunities to improve visibility of their trading activities and sources of further cost reduction. The paper begins with a synthesis of potential benefits resulting from participation in marketsites and then provides a number of initial classifications of marketsites. The paper then introduces some of the major inhibitors and enablers of marketsites and views these from a number of perspectives such as the structure of marketsites, the degree of centricity and the types of products purchased through such marketsites. Finally, some recommendations for further research are made
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