1,368 research outputs found
On The Mobile Behavior of Solid He at High Temperatures
We report studies of solid helium contained inside a torsional oscillator, at
temperatures between 1.07K and 1.87K. We grew single crystals inside the
oscillator using commercially pure He and He-He mixtures containing
100 ppm He. Crystals were grown at constant temperature and pressure on the
melting curve. At the end of the growth, the crystals were disordered,
following which they partially decoupled from the oscillator. The fraction of
the decoupled He mass was temperature and velocity dependent. Around 1K, the
decoupled mass fraction for crystals grown from the mixture reached a limiting
value of around 35%. In the case of crystals grown using commercially pure
He at temperatures below 1.3K, this fraction was much smaller. This
difference could possibly be associated with the roughening transition at the
solid-liquid interface.Comment: 15 pages, 6 figure
A Field Effect Transitor based on the Mott Transition in a Molecular Layer
Here we propose and analyze the behavior of a FET--like switching device, the
Mott transition field effect transistor, operating on a novel principle, the
Mott metal--insulator transition. The device has FET-like characteristics with
a low ``ON'' impedance and high ``OFF'' impedance. Function of the device is
feasible down to nanoscale dimensions. Implementation with a class of organic
charge transfer complexes is proposed.Comment: Revtex 11pages, Figures available upon reques
Stochastic Tunneling of Two Mutations in a Population of Cancer Cells
Cancer initiation, progression, and the emergence of drug resistance are driven by specific genetic and/or epigenetic alterations such as point mutations, structural alterations, DNA methylation and histone modification changes. These alterations may confer advantageous, deleterious or neutral effects to mutated cells. Previous studies showed that cells harboring two particular alterations may arise in a fixed-size population even in the absence of an intermediate state in which cells harboring only the first alteration take over the population; this phenomenon is called stochastic tunneling. Here, we investigated a stochastic Moran model in which two alterations emerge in a cell population of fixed size. We developed a novel approach to comprehensively describe the evolutionary dynamics of stochastic tunneling of two mutations. We considered the scenarios of large mutation rates and various fitness values and validated the accuracy of the mathematical predictions with exact stochastic computer simulations. Our theory is applicable to situations in which two alterations are accumulated in a fixed-size population of binary dividing cells
Electronic Orders Induced by Kondo Effect in Non-Kramers f-Electron Systems
This paper clarifies the microscopic nature of the staggered scalar order,
which is specific to even number of f electrons per site. In such systems,
crystalline electric field (CEF) can make a singlet ground state. As exchange
interaction with conduction electrons increases, the CEF singlet at each site
gives way to Kondo singlets. The collective Kondo singlets are identified with
itinerant states that form energy bands. Near the boundary of itinerant and
localized states, a new type of electronic order appears with staggered Kondo
and CEF singlets. We present a phenomenological three-state model that
qualitatively reproduces the characteristic phase diagram, which have been
obtained numerically with use of the continuous-time quantum Monte Carlo
combined with the dynamical mean-field theory. The scalar order observed in
PrFe_4P_{12} is ascribed to this staggered order accompanying charge density
wave (CDW) of conduction electrons. Accurate photoemission and tunneling
spectroscopy should be able to probe sharp peaks below and above the Fermi
level in the ordered phase.Comment: 7 pages, 8 figure
On the origin of multiple ordered phases in PrFe4P12
The nature of multiple electronic orders in skutterudite PrFe_4P_{12} is
discussed on the basis of a model with antiferro-quadrupole (AFQ) interaction
of \Gamma_3 symmetry. The high-field phase can be reproduced qualitatively
provided (i) ferro-type interactions are introduced between the dipoles as well
as between the octupoles of localized f-electrons, and (ii) separation is
vanishingly small between the \Gamma_1-\Gamma_4^{(1)} crystalline electric
field (CEF) levels. The high-field phase can have either the same ordering
vector q=(1,0,0) as in the low-field phase, or a different one q=0 depending on
the parameters. In the latter case, distortion of the crystal perpendicular to
the (111) axis is predicted. The corresponding anomaly in elastic constants
should also appear. The electrical resistivity is calculated with account of
scattering within the CEF quasi-quartet. It is found that the resistivity as a
function of the direction of magnetic field shows a sharp maximum around the
(111) axis at low temperatures because of the level crossing.Comment: 16 pages, 5 figure
Quantitative analysis of electronic transport through weakly-coupled metal/organic interfaces
Using single-crystal transistors, we have performed a systematic experimental
study of electronic transport through oxidized copper/rubrene interfaces as a
function of temperature and bias. We find that the measurements can be
reproduced quantitatively in terms of the thermionic emission theory for
Schottky diodes, if the effect of the bias-induced barrier lowering is
included. Our analysis emphasizes the role of the coupling between metal and
molecules, which in our devices is weak due to the presence of an oxide layer
at the surface of the copper electrodes.Comment: 4 pages, 3 figure
Role of p-f Hybridization in the Metal-Non-Metal Transition of PrRu4P12
Electronic state evolution in the metal-non-metal transition of PrRu4P12 has
been studied by X-ray and polarized neutron diffraction experiments. It has
been revealed that, in the low-temperature non-metallic phase, two inequivalent
crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2)
ground states are located at Pr1 and Pr2 sites forming the bcc unit cell
surrounded by the smaller and larger cubic Ru-ion sublattices, respectively.
This modulated electronic state can be explained by the p-f hybridization
mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f
hybridization effect plays an important role for the electronic energy gain in
the metal-non-metal transition originated from the Fermi surface nesting.Comment: 5 pages, 5 figures. Accepted by J. Phys. Soc. Jp
Microscopic Mechanism for Staggered Scalar Order in PrFe4P12
A microscopic model is proposed for the scalar order in PrFe4P12 where f2
crystalline electric field (CEF) singlet and triplet states interact with two
conduction bands. By combining the dynamical mean-field theory and the
continuous-time quantum Monte Carlo, we obtain an electronic order with
staggered Kondo and CEF singlets with the total conduction number being unity
per site. The ground state becomes semimetallic provided that the two
conduction bands have different occupation numbers. This model naturally
explains experimentally observed properties in the ordered phase of PrFe4P12
such as the scalar order parameter, temperature dependence of the resistivity,
field-induced staggered moment, and inelastic features in neutron scattering.
The Kondo effect plays an essential role for ordering, in strong contrast with
ordinary magnetic orders by the RKKY interaction.Comment: 4 pages, 4figure
Infrared spectra of one- and two-dimensional fullerene polymer structures: RbC60 and rhombohedral C-60
We compare the infrared spectra of two types of fullerene polymers: the linear-chain RbC60 and the two-dimensional pressure-polymerized rhombohedral C-60. Both the splitting of the F-1u modes and the structure of newly activated Lines are in agreement with fully ordered structures of molecular symmetry D-2h and D-3d, respectively
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