385 research outputs found
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
Resistivity as a function of temperature for models with hot spots on the Fermi surface.
We calculate the resistivity as a function of temperature for two
models currently discussed in connection with high temperature
superconductivity: nearly antiferromagnetic Fermi liquids and models with van
Hove singularities on the Fermi surface. The resistivity is calculated
semiclassicaly by making use of a Boltzmann equation which is formulated as a
variational problem. For the model of nearly antiferromagnetic Fermi liquids we
construct a better variational solution compared to the standard one and we
find a new energy scale for the crossover to the behavior at
low temperatures. This energy scale is finite even when the spin-fluctuations
are assumed to be critical. The effect of additional impurity scattering is
discussed. For the model with van Hove singularities a standard ansatz for the
Boltzmann equation is sufficient to show that although the quasiparticle
lifetime is anomalously short, the resistivity .Comment: Revtex 3.0, 8 pages; figures available upon request. Submitted to
Phys. Rev. B
Effect of band filling in the Kondo lattice: A mean-field approach
The usual Kondo-lattice, including an antiferromagnetic exchange interaction
between nearest-neighboring localized spins, is treated here in a mean-field
scheme that introduces two mean-field parameters: one associated with the local
Kondo effect, and the other related to the magnetic correlations between
localized spins. Phases with short-range magnetic correlations or coexistence
between those and the Kondo effect are obtained. By varying the number of
electrons in the conduction band, we notice that the Kondo effect tends to be
suppressed away from half filling, while magnetic correlations can survive if
the Heisenberg coupling is strong enough. An enhanced linear coefficient of the
specific heat is obtained at low temperatures in the metallic state.Comment: 7 pages, ReVTeX two-column, 7 figure
Instability of Anisotropic Fermi Surfaces in Two Dimensions
The effect of strong anisotropy on the Fermi line of a system of correlated
electrons is studied in two space dimensions, using renormalization group
techniques. Inflection points change the scaling exponents of the couplings,
enhancing the instabilities of the system. They increase the critical dimension
for non Fermi liquid behavior, from 1 to 3/2. Assuming that, in the absence of
nesting, the dominant instability is towards a superconducting ground state,
simple rules to discern between d-wave and extended s-wave symmetry of the
order parameter are given.Comment: 5 pages, revte
Saddle-point pairing: an electronic mechanism for superconductivity
It is shown that the interactions in a strongly correlated quasi-two-dimensional electron gas with the Fermi level lying at a saddle point (Van Hove singularity) in εk can give rise to superconductivity by exchange of excitations with a characteristic low electronic energy scale E∗. Application to cuprate superconductors shows that this mechanism along with a conventional electron-phonon interaction can explain the high Tc's and the anomalous behavior of the isotope shift as a function of doping
The Energetics of Li Off-Centering in KLiTaO; First Principles Calculations
KLiTaO (KLT) solid solutions exhibit a variety of
interesting physical phenomena related to large displacements of Li-ions from
ideal perovskite A-site positions. First-principles calculations for KLT
supercells were used to investigate these phenomena. Lattice dynamics
calculations for KLT exhibit a Li off-centering instability. The energetics of
Li-displacements for isolated Li-ions and for Li-Li pairs up to 4th neighbors
were calculated. Interactions between nearest neighbor Li-ions, in a Li-Li
pair, strongly favor ferroelectric alignment along the pair axis. Such Li-Li
pairs can be considered "seeds" for polar nanoclusters in KLT.
Electrostriction, local oxygen relaxation, coupling to the KT soft-mode, and
interactions with neighboring Li-ions all enhance the polarization from Li
off-centering. Calculated hopping barriers for isolated Li-ions and for nearest
neighbor Li-Li pairs are in good agreement with Arrhenius fits to experimental
dielectric data.Comment: 14 pages including 10 figures. To Physical Review B. Replaced after
corrections due to referees' remark
Quantum Monte Carlo Evidence for d-wave Pairing in the 2D Hubbard Model at a van Hove Singularity
We implement a Quantum Monte Carlo calculation for a repulsive Hubbard model
with nearest and next-nearest neighbor hopping interactions on clusters up to
12x12. A parameter region where the Fermi level lies close to the van Hove
singularity at the Saddle Points in the bulk band structure is investigated. A
pairing tendency in the symmetry channel, but no other channel,
is found. Estimates of the effective pairing interaction show that it is close
to the value required for a 40 K superconductor. Finite-size scaling compares
with the attractive Hubbard model.Comment: 11 pages, REVTex, 4 figures, postscrip
Multilevel information storage using magnetoelastic layer stacks
The use of voltages to control magnetisation via the inverse magnetostriction effect in piezoelectric/ferromagnet heterostructures holds promise for ultra-low energy information storage technologies. Epitaxial galfenol, an alloy of iron and gallium, has been shown to be a highly suitable material for such devices because it possesses biaxial anisotropy and large magnetostriction. Here we experimentally investigate the properties of galfenol/spacer/galfenol structures in which the compositions of the galfenol layers are varied in order to produce different strengths of the magnetic anisotropy and magnetostriction constants. Based upon these layers, we propose and simulate the operation of an information storage device that can operate as an energy efficient multilevel memory cell
Superconducting and pseudogap phases from scaling near a Van Hove singularity
We study the quantum corrections to the Fermi energy of a two-dimensional
electron system, showing that it is attracted towards the Van Hove singularity
for a certain range of doping levels. The scaling of the Fermi level allows to
cure the infrared singularities left in the BCS channel after renormalization
of the leading logarithm near the divergent density of states. A phase of
d-wave superconductivity arises beyond the point of optimal doping
corresponding to the peak of the superconducting instability. For lower doping
levels, the condensation of particle-hole pairs due to the nesting of the
saddle points takes over, leading to the opening of a gap for quasiparticles in
the neighborhood of the singular points.Comment: 4 pages, 6 Postscript figures, the physical discussion of the results
has been clarifie
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