22,846 research outputs found
Specific heats of quantum double-well systems
Specific heats of quantum systems with symmetric and asymmetric double-well
potentials have been calculated. In numerical calculations of their specific
heats, we have adopted the combined method which takes into account not only
eigenvalues of for obtained by the
energy-matrix diagonalization but also their extrapolated ones for ( or 30). Calculated specific heats are shown to be rather
different from counterparts of a harmonic oscillator. In particular, specific
heats of symmetric double-well systems at very low temperatures have the
Schottky-type anomaly, which is rooted to a small energy gap in low-lying
two-level eigenstates induced by a tunneling through the potential barrier. The
Schottky-type anomaly is removed when an asymmetry is introduced into the
double-well potential. It has been pointed out that the specific-heat
calculation of a double-well system reported by Feranchuk, Ulyanenkov and
Kuz'min [Chem. Phys. 157, 61 (1991)] is misleading because the zeroth-order
operator method they adopted neglects crucially important off-diagonal
contributions.Comment: 27 pages, 12 figures; Correted figure numbers (accepted in Phys. Rev.
E
Recombination kinetics of a dense electron-hole plasma in strontium titanate
We investigated the nanosecond-scale time decay of the blue-green light
emitted by nominally pure SrTiO following the absorption of an intense
picosecond laser pulse generating a high density of electron-hole pairs. Two
independent components are identified in the fluorescence signal that show a
different dynamics with varying excitation intensity, and which can be
respectively modeled as a bimolecular and unimolecolar process. An
interpretation of the observed recombination kinetics in terms of interacting
electron and hole polarons is proposed
Specific heat and entropy of -body nonextensive systems
We have studied finite -body -dimensional nonextensive ideal gases and
harmonic oscillators, by using the maximum-entropy methods with the - and
normal averages (: the entropic index). The validity range, specific heat
and Tsallis entropy obtained by the two average methods are compared. Validity
ranges of the - and normal averages are ,
respectively, where , and
() for ideal gases (harmonic oscillators). The energy and
specific heat in the - and normal averages coincide with those in the
Boltzmann-Gibbs statistics, % independently of , although this coincidence
does not hold for the fluctuation of energy. The Tsallis entropy for obtained by the -average is quite different from that derived by the
normal average, despite a fairly good agreement of the two results for . It has been pointed out that first-principles approaches previously
proposed in the superstatistics yield -body entropy () which is in contrast with the Tsallis entropy.Comment: 27 pages, 8 figures: augmented the tex
Low temperature metallic state induced by electrostatic carrier doping of SrTiO
Transport properties of SrTiO-channel field-effect transistors with
parylene organic gate insulator have been investigated. By applying gate
voltage, the sheet resistance falls below 10 k at low
temperatures, with carrier mobility exceeding 1000 cm/Vs. The temperature
dependence of the sheet resistance taken under constant gate voltage exhibits
metallic behavior (/ 0). Our results demonstrate an insulator to
metal transition in SrTiO driven by electrostatic carrier density control.Comment: 3 pages, 4 figure
Continuous Transition of Defect Configuration in a Deformed Liquid Crystal Film
We investigate energetically favorable configurations of point disclinations
in nematic films having a bump geometry. Gradual expansion in the bump width
{\Delta} gives rise to a sudden shift in the stable position of the
disclinations from the top to the skirt of the bump. The positional shift
observed across a threshold {\Delta}th obeys a power law function of
|{\Delta}-{\Delta}th|, indicating a new class of continuous phase transition
that governs the defect configuration in curved nematic films.Comment: 8pages, 3figure
Classical small systems coupled to finite baths
We have studied the properties of a classical -body system coupled to a
bath containing -body harmonic oscillators, employing an model
which is different from most of the existing models with . We have
performed simulations for -oscillator systems, solving
first-order differential equations with and , in order to calculate the time-dependent energy exchange between the
system and the bath. The calculated energy in the system rapidly changes while
its envelope has a much slower time dependence. Detailed calculations of the
stationary energy distribution of the system (: an energy per
particle in the system) have shown that its properties are mainly determined by
but weakly depend on . The calculated is analyzed with the
use of the and - distributions: the latter is derived with
the superstatistical approach (SSA) and microcanonical approach (MCA) to the
nonextensive statistics, where stands for the entropic index. Based on
analyses of our simulation results, a critical comparison is made between the
SSA and MCA. Simulations have been performed also for the -body ideal-gas
system. The effect of the coupling between oscillators in the bath has been
examined by additional () models which include baths consisting of
coupled linear chains with periodic and fixed-end boundary conditions.Comment: 30 pages, 16 figures; the final version accepted in Phys. Rev.
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