6,519 research outputs found
Subthreshold characteristics of pentacene field-effect transistors influenced by grain boundaries.
Grain boundaries in polycrystalline pentacene films significantly affect the electrical characteristics of pentacene field-effect transistors (FETs). Upon reversal of the gate voltage sweep direction, pentacene FETs exhibited hysteretic behaviours in the subthreshold region, which was more pronounced for the FET having smaller pentacene grains. No shift in the flat-band voltage of the metal-insulator-semiconductor capacitor elucidates that the observed hysteresis was mainly caused by the influence of localized trap states existing at pentacene grain boundaries. From the results of continuous on/off switching operation of the pentacene FETs, hole depletion during the off period is found to be limited by pentacene grain boundaries. It is suggested that the polycrystalline nature of a pentacene film plays an important role on the dynamic characteristics of pentacene FETs
Sparticle masses in deflected mirage mediation
We discuss the sparticle mass patterns that can be realized in deflected
mirage mediation scenario of supersymmetry breaking, in which the moduli,
anomaly, and gauge mediations all contribute to the MSSM soft parameters.
Analytic expression of low energy soft parameters and also the sfermion mass
sum rules are derived, which can be used to interpret the experimentally
measured sparticle masses within the framework of the most general mixed
moduli-gauge-anomaly mediation. Phenomenological aspects of some specific
examples are also discussed.Comment: 43 pages, 17 figures, references adde
Supersymmetry Breaking and Moduli Stabilization with Anomalous U(1) Gauge Symmetry
We examine the effects of anomalous U(1)_A gauge symmetry on soft
supersymmetry breaking terms while incorporating the stabilization of the
modulus-axion multiplet responsible for the Green-Schwarz (GS) anomaly
cancellation mechanism. In case of the KKLT stabilization of the GS modulus,
soft terms are determined by the GS modulus mediation, the anomaly mediation
and the U(1)_A mediation which are generically comparable to each other,
thereby yielding the mirage mediation pattern of superparticle masses at low
energy scale. Independently of the mechanism of moduli stabilization and
supersymmetry breaking, the U(1)_A D-term potential can not be an uplifting
potential for de Sitter vacuum when the gravitino mass is smaller than the
Planck scale by many orders of magnitude. We also discuss some features of the
supersymmetry breaking by red-shifted anti-brane which is a key element of the
KKLT moduli stabilization.Comment: 32 pages; references are adde
Interplay between carrier and impurity concentrations in annealed GaMnAs intrinsic anomalous Hall Effect
Investigating the scaling behavior of annealed GaMnAs anomalous
Hall coefficients, we note a universal crossover regime where the scaling
behavior changes from quadratic to linear, attributed to the anomalous Hall
Effect intrinsic and extrinsic origins, respectively. Furthermore, measured
anomalous Hall conductivities when properly scaled by carrier concentration
remain constant, equal to theoretically predicated values, spanning nearly a
decade in conductivity as well as over 100 K in T. Both the qualitative
and quantitative agreement confirms the validity of new equations of motion
including the Berry phase contributions as well as tunablility of the intrinsic
anomalous Hall Effect.Comment: 4 pages, 5 figure
Charge states and magnetic ordering in LaMnO3/SrTiO3 superlattices
We investigated the magnetic and optical properties of
[(LaMnO3)n/(SrTiO3)8]20 (n = 1, 2, and 8) superlattices grown by pulsed laser
deposition. We found a weak ferromagnetic and semiconducting state developed in
all superlattices. An analysis of the optical conductivity showed that the
LaMnO3 layers in the superlattices were slightly doped. The amount of doping
was almost identical regardless of the LaMnO3 layer thickness up to eight unit
cells, suggesting that the effect is not limited to the interface. On the other
hand, the magnetic ordering became less stable as the LaMnO3 layer thickness
decreased, probably due to a dimensional effect.Comment: 17 pages including 4 figures, accepted for publication in Phys. Rev.
Phenomenology of Mixed Modulus-Anomaly Mediation in Fluxed String Compactifications and Brane Models
In some string compactifications, for instance the recently proposed KKLT
set-up, light moduli are stabilized by nonperturbative effects at
supersymmetric AdS vacuum which is lifted to a dS vacuum by supersymmetry
breaking uplifting potential. In such models, soft supersymmetry breaking terms
are determined by a specific mixed modulus-anomaly mediation in which the two
mediations typically give comparable contributions to soft parameters. Similar
pattern of soft terms can arise also in brane models to stabilize the radion by
nonperturbative effects. We examine some phenomenological consequences of this
mixed modulus-anomaly mediation, including the pattern of low energy sparticle
spectrum and the possibility of electroweak symmetry breaking. It is noted that
adding the anomaly-mediated contributions at amounts to replacing the
messenger scale of the modulus mediation by a mirage messenger scale
where
for denoting the
modulus-mediated contribution to the gaugino mass at . The minimal
KKLT set-up predicts . As a consequence, for ,
the model can lead to a highly distinctive pattern of sparticle masses at TeV
scale, particularly when .Comment: 20 pages, 15 figures, some notations are changed, typos are corrected
and discussions on the CP phase from and B are adde
Evidence of metallic clustering in annealed Ga1-xMnxAs from atypical scaling behavior of the anomalous Hall coefficient
We report on the anomalous Hall coefficient and longitudinal resistivity
scaling relationships on a series of annealed Ga1-xMnxAs epilayers (x~0.055).
As-grown samples exhibit scaling parameter n of ~ 1. Near the optimal annealing
temperature, we find n ~ 2 to be consistent with recent theories on the
intrinsic origins of anomalous Hall Effect in Ga1-xMnxAs. For annealing
temperatures far above the optimum, we note n > 3, similar behavior to certain
inhomogeneous systems. This observation of atypical behavior agrees well with
characteristic features attributable to spherical resonance from metallic
inclusions from optical spectroscopy measurements.Comment: 3 pages, 3 figure
Sequestered uplifting and the pattern of soft supersymmetry breaking terms
We examine the pattern of soft supersymmetry breaking terms in moduli
stabilization, where an uplifting potential is provided by spontaneously broken
supersymmetry in a generic sequestered sector. From stationary conditions, we
derive the relation between moduli F-term vacuum expectation values which does
not depend on the details of sequestered uplifting. This moduli F-term relation
is crucial for identifying the dominant source of soft terms of visible fields.Comment: 11 pages; references adde
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