2,974 research outputs found
Green's and spectral functions of the small Frolich polaron
According to recent Quantum Monte Carlo simulations the small polaron theory
is practically exact in a wide range of the long-range (Frohlich)
electron-phonon coupling and adiabatic ratio. We apply the Lang-Firsov
transformation to convert the strong-coupling term in the Hamiltonian into the
form of an effective hopping integral and derive the single-particle Green's
function describing propagation of the small Frohlich polaron. One and two
dimensional spectral functions are studied by expanding the Green's function
perturbatively. Numerical calculations of the spectral functions are produced.
Remarkably, the coherent spectral weight (Z) and effective mass (Z')
renormalisation exponents are found to be different with Z'>>Z, which can
explain a small coherent spectral weight and a relatively moderate mass
enhancement in oxides.Comment: RevTeX, 5 pages, 2 postscript figures, LaTeX processing problems
correcte
From Hurwitz numbers to Kontsevich-Witten tau-function: a connection by Virasoro operators
In this letter,we present our conjecture on the connection between the
Kontsevich--Witten and the Hurwitz tau-functions. The conjectural formula
connects these two tau-functions by means of the group element. An
important feature of this group element is its simplicity: this is a group
element of the Virasoro subalgebra of . If proved, this conjecture
would allow to derive the Virasoro constraints for the Hurwitz tau-function,
which remain unknown in spite of existence of several matrix model
representations, as well as to give an integrable operator description of the
Kontsevich--Witten tau-function.Comment: 13 page
Spectral analysis of electron transfer kinetics II
Electron transfer processes in Debye solvents are studied using a spectral
analysis method recently proposed. Spectral structure of a nonadiabatic
two-state diffusion equation is investigated to reveal various kinetic regimes
characterized by a broad range of physical parameters; electronic coupling,
energy bias, reorganization energy, and solvent relaxation rate. Within this
unified framework, several kinetic behaviors of the electron transfer kinetics,
including adiabatic Rabi oscillation, crossover from the nonadiabatic to
adiabatic limits, transition from the incoherent to coherent kinetic limits,
and dynamic bath effect, are demonstrated and compared with results from
previous theoretical models. Dynamics of the electron transfer system is also
calculated with the spectral analysis method. It is pointed out that in the
large reorganization energy case the nonadiabatic diffusion equation exhibits a
non-physical behavior, yielding a negative eigenvalue.Comment: submitted for a publication in Journal of Chemical Physic
On the total mean curvature of non-rigid surfaces
Using Green's theorem we reduce the variation of the total mean curvature of
a smooth surface in the Euclidean 3-space to a line integral of a special
vector field and obtain the following well-known theorem as an immediate
consequence: the total mean curvature of a closed smooth surface in the
Euclidean 3-space is stationary under an infinitesimal flex.Comment: 4 page
Polaron and bipolaron transport in a charge segregated state of doped strongly correlated 2D semiconductor
The 2D lattice gas model with competing short and long range interactions is
appliedused for calculation of the incoherent charge transport in the classical
strongly-correlated charge segregated polaronic state. We show, by means of
Monte-Carlo simulations, that at high temperature the transport is dominated by
hopping of the dissociated correlated polarons, where with thetheir mobility is
inversely proportional to the temperature. At the temperatures below the
clustering transition temperature the bipolaron transport becomes dominant. The
energy barrier for the bipolaron hopping is determined by the Coulomb effects
and is found to be lower than the barrier for the single-polaron hopping. This
leads to drastically different temperature dependencies of mobilities for
polarons and bipolarons at low temperatures
Emergent order in the spin-frustrated system DyxTb2-xTi2O7 studied by ac susceptibility measurements
We report the a.c. susceptibility study of Dy_xTb_{2-x}Ti_2O_7 with x in [0,
2]. In addition to the single-ion effect at Ts (single-ion effect peak
temperature) corresponding to the Dy3+ spins as that in spin ice Dy_2Ti_2O_7
and a possible spin freezing peak at Tf (Tf < 3 K), a new peak associated with
Tb^{3+} is observed in at nonzero magnetic field with a
characteristic temperature T^* (Tf < T^* < Ts). T^* increases linearly with x
in a wide composition range (0 < x < 1.5 at 5 kOe). Both application of a
magnetic field and increasing doping with Dy3+ enhance T^*. The T^* peak is
found to be thermally driven with an unusually large energy barrier as
indicated from its frequency dependence. These effects are closely related to
the crystal field levels, and the underlying mechanism remains to be
understood.Comment: 7 pages, 5 figure
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