86 research outputs found
Dielectric anomaly in coupled rotor systems
The correlated dynamics of coupled quantum rotors carrying electric dipole
moment is theoretically investigated. The energy spectra of coupled rotors as a
function of dipolar interaction energy is analytically solved. The calculated
dielectric susceptibilities of the system show the peculiar temperature
dependence different from that of isolated rotors.Comment: 5 pages, 4 figures (Figure 2 is available on request from
[email protected]
Glass-like Thermal-Transport in Symmetry-Broken Clathrates
We present the quantitative interpretation for the glass-like behavior of
thermal conductivities for type-I clathrate compounds involving
off-centered guest ions. It is shown that the dipole-dipole interaction
generated in cage/guest-ion systems is crucial to reproduce the characteristics
of thermal conductivities for these symmetry-broken clathrates. The above
scenario also explains well the difference of between the -type
and the -type -BGS found recently by K. Suekuni et al. [Phys. Rev. B,
77 (2008) 235119.
Phonon-glass electron-crystal thermoelectric clathrates: Experiments and theory
Type-I clathrate compounds have attracted a great deal of interest in
connection with the search for efficient thermoelectric materials. These
compounds constitute networked cages consisting of nano-scale
tetrakaidecahedrons (14 hedrons) and dodecahedrons (12 hedrons), in which the
group 1 or 2 elements in the periodic table are encaged as the so-called
rattling guest atom. It is remarkable that, though these compounds have
crystalline cubic-structure, they exhibit glass-like phonon thermal
conductivity over the whole temperature range depending on the states of
rattling guest atoms in the tetrakaidecahedron. In addition, these compounds
show unusual glass-like specific heats and THz-frequency phonon dynamics,
providing a remarkable broad peak almost identical to those observed in
topologically disordered amorphous materials or structural glasses, the
so-called Boson peak. An efficient thermoelectric effect is realized in
compounds showing these glass-like characteristics. This decade, a number of
experimental works dealing with type-I clathrate compounds have been published.
These are diffraction experiments, thermal and spectroscopic experiments in
addition to those based on heat and electronic transport. These form the raw
materials for this article based on advances this decade. The subject of this
article involves interesting phenomena from the viewpoint of not only physics
but also from the view point of the practical problem of elaborating efficient
thermoelectric materials. This review presents a survey of a wide range of
experimental investigations of type-I clathrate compounds, together with a
review of theoretical interpretations of the peculiar thermal and dynamic
properties observed in these materials.Comment: 51pages, 43 figure
Critical behavior of ac conductivity near the Anderson transition
We investigate the dynamic scaling behavior of ac conductivity () in three-dimensional ͑3D͒ unitary and symplectic systems in addition to orthogonal one by means of large-scale simulations. It is demonstrated that the ac conductivity near the Anderson transition behave as ()ϰ ␦ (␦Ӎ1/3) for all of the above systems. Numerical calculations are performed by an efficient algorithm based on the forced oscillator method ͑FOM͒, which enables us to accurately treat large-scale quantum systems with less computational effort. The values of the exponents ␦ are determined by the finite-time scaling method for the FOM. ͓S0163-1829͑99͒11943-X
Orienting coupled quantum rotors by ultrashort laser pulses
We point out that the non-adiabatic orientation of quantum rotors, produced
by ultrashort laser pulses, is remarkably enhanced by introducing dipolar
interaction between the rotors. This enhanced orientation of quantum rotors is
in contrast with the behavior of classical paired rotors, in which dipolar
interactions prevent the orientation of the rotors. We demonstrate also that a
specially designed sequence of pulses can most efficiently enhances the
orientation of quantum paired rotors.Comment: 7 pages, 5 figures, to appear in Phys. Rev.
Spin Seebeck Effect in Asymmetric Four-Terminal Systems with Rashba Spin-Orbit Coupling
We propose a new type of the spin Seebeck effect (SSE) emerging from the
Rashba spin-orbit coupling in asymmetric four-terminal electron systems. This
system generates spin currents or spin voltages along the longitudinal
direction parallel to the temperature gradient in the absence of magnetic
fields. The remarkable result arises from the breaking of reflection symmetry
along the transverse direction. In the meantime, the SSE along the transverse
direction, so-called the spin Nernst effect, with spin currents or spin
voltages perpendicular to the temperature gradient can be simultaneously
realized in our system. We further find that it is possible to use the
temperature differences between four leads to tune the spin Seebeck
coefficients.Comment: 14 pages, 4 figure
- …