7,799 research outputs found
Mesoscopic mechanism of adiabatic charge transport
We consider adiabatic charge transport through mesoscopic metallic samples
caused by a periodically changing external potential. We find that both the
amplitude and the sign of the charge transferred through a sample per period
are random sample specific quantities. The characteristic magnitude of the
charge is determined by the quantum interference.Comment: 4 pages, 2 figure
Events, processes, and the time of a killing
The paper proposes a novel solution to the problem of the time of a killing (ToK), which persistently besets theories of act-individuation. The solution proposed claims to expose a crucial wrong-headed assumption in the debate, according to which ToK is essentially a problem of locating some event that corresponds to the killing. The alternative proposal put forward here turns on recognizing a separate category of dynamic occurents, viz. processes. The paper does not aim to mount a comprehensive defense of process ontology, relying instead on extant defenses. The primary aim is rather to put process ontology to work in diagnosing the current state of play over ToK, and indeed in solving it
Condensation of Cavity Polaritons in a Disordered Environment
A model for direct two band excitons in a disordered quantum well coupled to
light in a cavity is investigated. In the limit in which the exciton density is
high, we assess the impact of weak `pair-breaking' disorder on the feasibility
of condensation of cavity polaritons. The mean-field phase diagram shows a
`lower density' region, where the condensate is dominated by electronic
excitations and where disorder tends to close the condensate and quench
coherence. Increasing the density of excitations in the system, partially due
to the screening of Coulomb interaction, the excitations contributing to the
condensate become mainly photon-like and coherence is reestablished for any
value of disorder. In contrast, in the photon dominated region of the phase
diagram, the energy gap of the quasi-particle spectrum still closes when the
disorder strength is increased. Above mean-field, thermal, quantum and
fluctuations induced by disorder are considered and the spectrum of the
collective excitations is evaluated. In particular, it is shown that the angle
resolved photon intensity exhibits an abrupt change in its behaviour, going
from the condensed to the non-condensed region.Comment: 17 pages, 9 eps figures; published versio
Correlations and fluctuations of a confined electron gas
The grand potential and the response of a phase-coherent confined noninteracting electron gas depend
sensitively on chemical potential or external parameter . We compute
their autocorrelation as a function of , and temperature. The result
is related to the short-time dynamics of the corresponding classical system,
implying in general the absence of a universal regime. Chaotic, diffusive and
integrable motions are investigated, and illustrated numerically. The
autocorrelation of the persistent current of a disordered mesoscopic ring is
also computed.Comment: 12 pages, 1 figure, to appear in Phys. Rev.
Universal parametric correlations in the transmission eigenvalue spectra of disordered conductors
We study the response of the transmission eigenvalue spectrum of disordered
metallic conductors to an arbitrary external perturbation. For systems without
time-reversal symmetry we find an exact non-perturbative solution for the
two-point correlation function, which exhibits a new kind of universal behavior
characteristic of disordered conductors. Systems with orthogonal and symplectic
symmetries are studied in the hydrodynamic regime.Comment: 10 pages, written in plain TeX, Preprint OUTP-93-36S (University of
Oxford), to appear in Phys. Rev. B (Rapid Communication
Measurement of the charged pion mass using X-ray spectroscopy of exotic atoms
The transitions in pionic nitrogen and muonic oxygen were measured
simultaneously by using a gaseous nitrogen-oxygen mixture at 1.4\,bar. Due to
the precise knowledge of the muon mass the muonic line provides the energy
calibration for the pionic transition. A value of
(139.57077\,\,0.00018)\,MeV/c (\,1.3ppm) is derived for the
mass of the negatively charged pion, which is 4.2ppm larger than the present
world average
A Brownian Motion Model of Parametric Correlations in Ballistic Cavities
A Brownian motion model is proposed to study parametric correlations in the
transmission eigenvalues of open ballistic cavities. We find interesting
universal properties when the eigenvalues are rescaled at the hard edge of the
spectrum. We derive a formula for the power spectrum of the fluctuations of
transport observables as a response to an external adiabatic perturbation. Our
formula correctly recovers the Lorentzian-squared behaviour obtained by
semiclassical approaches for the correlation function of conductance
fluctuations.Comment: 19 pages, written in RevTe
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