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Anharmonic multi-phonon nonradiative transition: An ab initio calculation approach
Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering. In this article, we provide a revised analysis of Huang’s original nonradiative multi-phonon (NMP) theory with ab initio calculations. First, we confirmed at the first-principles level that Huang’s concise formula gives the same results as the matrix-based formula, and that Huang’s high-temperature formula provides an analytical expression for the coupling constant in Marcus theory. Secondly, we correct for anharmonic effects by taking into account local phonon-mode variations for different charge states of a defect. The corrected capture rates for defects in GaN and SiC agree well with experiments
Moving Defects in AdS/CFT
We study defects of various dimensions moving through Anti-de Sitter space.
Using the AdS/CFT correspondence this allows us to probe aspects of the dual
quantum field theory. We focus on the energy loss experienced by these defects
as they move through the CFT plasma. We find that the behavior of these
physical quantities is governed by induced world-volume horizons. We identify
world-volume analogs for several gravitational phenomena including black holes,
the Hawking-Page phase transition and expanding cosmological horizons.Comment: 24 pages, 7 figures. Version 2 contains two added reference
On the Beaming of Gluonic Fields at Strong Coupling
We examine the conditions for beaming of the gluonic field sourced by a heavy
quark in strongly-coupled conformal field theories, using the AdS/CFT
correspondence. Previous works have found that, contrary to naive expectations,
it is possible to set up collimated beams of gluonic radiation despite the
strong coupling. We show that, on the gravity side of the correspondence, this
follows directly (for arbitrary quark motion, and independently of any
approximations) from the fact that the string dual to the quark remains
unexpectedly close to the AdS boundary whenever the quark moves
ultra-relativistically. We also work out the validity conditions for a related
approximation scheme that proposed to explain the beaming effect though the
formation of shock waves in the bulk fields emitted by the string. We find that
these conditions are fulfilled in the case of ultra-relativistic uniform
circular motion that motivated the proposal, but unfortunately do not hold for
much more general quark trajectories.Comment: 1+33 pages, 2 figure
The Gluonic Field of a Heavy Quark in Conformal Field Theories at Strong Coupling
We determine the gluonic field configuration sourced by a heavy quark
undergoing arbitrary motion in N=4 super-Yang-Mills at strong coupling and
large number of colors. More specifically, we compute the expectation value of
the operator tr[F^2+...] in the presence of such a quark, by means of the
AdS/CFT correspondence. Our results for this observable show that signals
propagate without temporal broadening, just as was found for the expectation
value of the energy density in recent work by Hatta et al. We attempt to shed
some additional light on the origin of this feature, and propose a different
interpretation for its physical significance. As an application of our general
results, we examine when the quark undergoes oscillatory motion,
uniform circular motion, and uniform acceleration. Via the AdS/CFT
correspondence, all of our results are pertinent to any conformal field theory
in 3+1 dimensions with a dual gravity formulation.Comment: 1+38 pages, 16 eps figures; v2: completed affiliation; v3: corrected
typo, version to appear in JHE
Early-Time Energy Loss in a Strongly-Coupled SYM Plasma
We carry out an analytic study of the early-time motion of a quark in a
strongly-coupled maximally-supersymmetric Yang-Mills plasma, using the AdS/CFT
correspondence. Our approach extracts the first thermal effects as a small
perturbation of the known quark dynamics in vacuum, using a double expansion
that is valid for early times and for (moderately) ultrarelativistic quark
velocities. The quark is found to lose energy at a rate that differs
significantly from the previously derived stationary/late-time result: it
scales like T^4 instead of T^2, and is associated with a friction coefficient
that is not independent of the quark momentum. Under conditions representative
of the quark-gluon plasma as obtained at RHIC, the early energy loss rate is a
few times smaller than its late-time counterpart. Our analysis additionally
leads to thermally-corrected expressions for the intrinsic energy and momentum
of the quark, in which the previously discovered limiting velocity of the quark
is found to appear naturally.Comment: 39 pages, no figures. v2: Minor corrections and clarifications.
References added. Version to be published in JHE
Dipole Coupling Effect of Holographic Fermion in the Background of Charged Gauss-Bonnet AdS Black Hole
We investigate the holographic fermions in the charged Gauss-Bonnet
black hole background with the dipole coupling between fermion and gauge field
in the bulk. We show that in addition to the strength of the dipole coupling,
the spacetime dimension and the higher curvature correction in the gravity
background also influence the onset of the Fermi gap and the gap distance. We
find that the higher curvature effect modifies the fermion spectral density and
influences the value of the Fermi momentum for the appearance of the Fermi
surface. There are richer physics in the boundary fermion system due to the
modification in the bulk gravity.Comment: 16 pages, accepted for publication in JHE
Phase transitions and critical behavior of black branes in canonical ensemble
We study the thermodynamics and phase structure of asymptotically flat
non-dilatonic as well as dilatonic black branes in a cavity in arbitrary
dimensions (). We consider the canonical ensemble and so the charge inside
the cavity and the temperature at the wall are fixed. We analyze the stability
of the black brane equilibrium states and derive the phase structures. For the
zero charge case we find an analog of Hawking-Page phase transition for these
black branes in arbitrary dimensions. When the charge is non-zero, we find that
below a critical value of the charge, the phase diagram has a line of
first-order phase transition in a certain range of temperatures which ends up
at a second order phase transition point (critical point) as the charge attains
the critical value. We calculate the critical exponents at that critical point.
Although our discussion is mainly concerned with the non-dilatonic branes, we
show how it easily carries over to the dilatonic branes as well.Comment: 37 pages, 6 figures, the validity of using the effective action
discussed, references adde
A spin triplet supercurrent through the half-metallic ferromagnet CrO2
In general, conventional superconductivity should not occur in a ferromagnet,
though it has been seen in iron under pressure. Moreover, theory predicts that
the current is always carried by pairs of electrons in a spin singlet state, so
conventional superconductivity decays very rapidly when in contact with a
ferromagnet, which normally prohibits the existence of singlet pairs. It has
been predicted that this rapid spatial decay would not occur when spin triplet
superconductivity could be induced in the ferromagnet. Here we report a
Josephson supercurrent through the strong ferromagnet CrO2, from which we infer
that it is a spin triplet supercurrent. Our experimental setup is different
from those envisaged in the earlier predictions, but we conclude that the
underlying physical explanation for our result is a conversion from spin
singlet to spin triplets at the interface. The supercurrent can be switched
with the direction of the magnetization, analogous to spin valve transistors,
and therefore could enable magnetization-controlled Josephson junctions.Comment: 14 pages, including 3 figure
A 10-year study reveals clinical and laboratory evidence for the 'semi-invasive' properties of chronic pulmonary aspergillosis
published_or_final_versio
Phase structure of black branes in grand canonical ensemble
This is a companion paper of our previous work [1] where we studied the
thermodynamics and phase structure of asymptotically flat black -branes in a
cavity in arbitrary dimensions in a canonical ensemble. In this work we
study the thermodynamics and phase structure of the same in a grand canonical
ensemble. Since the boundary data in two cases are different (for the grand
canonical ensemble boundary potential is fixed instead of the charge as in
canonical ensemble) the stability analysis and the phase structure in the two
cases are quite different. In particular, we find that there exists an analog
of one-variable analysis as in canonical ensemble, which gives the same
stability condition as the rather complicated known (but generalized from black
holes to the present case) two-variable analysis. When certain condition for
the fixed potential is satisfied, the phase structure of charged black
-branes is in some sense similar to that of the zero charge black -branes
in canonical ensemble up to a certain temperature. The new feature in the
present case is that above this temperature, unlike the zero-charge case, the
stable brane phase no longer exists and `hot flat space' is the stable phase
here. In the grand canonical ensemble there is an analog of Hawking-Page
transition, even for the charged black -brane, as opposed to the canonical
ensemble. Our study applies to non-dilatonic as well as dilatonic black
-branes in space-time dimensions.Comment: 32 pages, 2 figures, various points refined, discussion expanded,
references updated, typos corrected, published in JHEP 1105:091,201
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