1,432 research outputs found
Origin of the Heavy Fermion Behavior in Ca_{2-x}Sr_{x}RuO_{4}: Roles of Coulomb Interaction and the Rotation of RuO_{6} octahedra
We study the electronic states for Ca_{2-x}Sr_{x}RuO_{4} in within the Gutzwiller approximation (GA) on the basis of the three-orbital
Hubbard model for the Ru t_{2g} orbitals. The main effects of the Ca
substitution are taken account as the changes of the hybridizations
between the Ru 4d and O 2p orbitals. Using the numerical minimization of the
energy obtained in the GA, we obtain the renormalization factor (RF) of the
kinetic energy and total RF, which estimates the inverse of the mass
enhancement, for three cases with the effective models of x=2 and 0.5 and a
special model. We find that the inverse of the total RF becomes the largest for
the case of x=0.5, and that the van Hove singularity, which is located on
(below) the Fermi level for the special model (the effective model of x=0.5),
plays a secondary role in enhancing the effective mass. Our calculation
suggests that the heavy fermion behavior around x=0.5 comes from the
cooperative effects between moderately strong Coulomb interaction compared to
the total bandwidth and the modification of the electronic structures due to
the rotation of RuO_{6} octahedra (i.e., the variation of the
hybridizations and the downward shift for the orbital). We propose
that moderately strong electron correlation and the orbital-dependent
modifications of the electronic structures due to the lattice distortions play
important roles in the electronic states for Ca_{2-x}Sr_{x}RuO_{4}.Comment: 16 pages, 13 figures, 1 table, accepted for publication in Physical
Review B; added the discussions both about the validity of the present
treatment and about Hund's metal in this allo
Search for Effect of Influence from Future in Large Hadron Collider
We propose an experiment which consists of drawing a card and using it to
decide restrictions on the running of Large Hadron Collider (LHC for short) at
CERN, such as luminosity, and beam energy. There may potentially occur total
shut down. The purpose of such an experiment is to search for influence from
the future, that is, backward causation. Since LHC will produce particles of a
mathematically new type of fundamental scalars, i.e., the Higgs particles,
there is potentially a chance to find unseen effects, such as on influence
going from future to past, which we suggest in the present paper.Comment: 18pp, comments added, change of title and corrections of main text;
v4:minor typos correcte
Quantum Melting of Charge Order due to Frustration in Two-Dimensional Quarter-Filled Systems
The effect of geometrical frustration in a two-dimensional 1/4-filled
strongly correlated electron system is studied theoretically, motivated by
layered organic molecular crystals. An extended Hubbard model on the square
lattice is considered, with competing nearest neighbor Coulomb interaction, V,
and that of next-nearest neighbor along one of the diagonals, V', which favor
different charge ordered states. Based on exact diagonalization calculations,
we find a metallic phase stabilized over a broad window at V' ~ V even for
large Coulomb repulsion strengths as a result of frustrating the charge ordered
states. Slightly modifying the lattice geometry relevant to the actual organic
compounds does not alter the results, suggesting that this `quantum melting' of
charge order is a robust feature of frustrated strongly correlated 1/4-filled
systems.Comment: 5 pages, 4 figures, to be published in Phys. Rev.
Spectroscopy of the Clock Transition of Sr in an Optical Lattice
We report on the spectroscopy of the clock transition of atoms (natural linewidth of 1
mHz) trapped in a one-dimensional optical lattice. Recoilless transitions with
a linewidth of 0.7 kHz as well as the vibrational structure of the lattice
potential were observed. By investigating the wavelength dependence of the
carrier linewidth, we determined the magic wavelength, where the light shift in
the clock transition vanishes, to be nm.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Lett. (09/May/2003
Effects of Fermi surface and superconducting gap structure in the field-rotational experiments: A possible explanation of the cusp-like singularity in YNiBC
We have studied the field-orientational dependence of zero-energy density of
states (FODOS) for a series of systems with different Fermi surface and
superconducting gap structures. Instead of phenomenological Doppler-shift
method, we use an approximate analytical solution of Eilenberger equation
together with self-consistent determination of order parameter and a
variational treatment of vortex lattice. First, we compare zero-energy density
of states (ZEDOS) when a magnetic field is applied in the nodal direction
() and in the antinodal direction (), by taking
account of the field-angle dependence of order parameter. As a result, we found
that there exists a crossover magnetic field so that for for , consistent with our previous analyses. Next, we showed that and the
shape of FODOS are determined by contribution from the small part of Fermi
surface where Fermi velocity is parallel to field-rotational plane. In
particular, we found that is lowered and FODOS has broader minima, when a
superconducting gap has point nodes, in contrast to the result of the
Doppler-shift method. We also studied the effects of in-plane anisotropy of
Fermi surface. We found that in-plane anisotropy of quasi-two dimensional Fermi
surface sometimes becomes larger than the effects of Doppler-shift and can
destroy the Doppler-shift predominant region. In particular, this tendency is
strong in a multi-band system where superconducting coherence lengths are
isotropic. Finally, we addressed the problem of cusp-like singularity in
YNiBC and present a possible explanation of this phenomenon.Comment: 13pages, 23figure
Ultrastable Optical Clock with Neutral Atoms in an Engineered Light Shift Trap
An ultrastable optical clock based on neutral atoms trapped in an optical
lattice is proposed. Complete control over the light shift is achieved by
employing the transition of
atoms as a "clock transition". Calculations of ac multipole polarizabilities
and dipole hyperpolarizabilities for the clock transition indicate that the
contribution of the higher-order light shifts can be reduced to less than 1
mHz, allowing for a projected accuracy of better than .Comment: 4 pages, 2 figures, accepted for publication in Phys. Rev. Let
Scaling Behavior of Ricci Curvature at Short Distance near Two Dimensions
We study the renormalization of the Ricci curvature as an example of
generally covariant operators in quantum gravity near two dimensions. We find
that it scales with a definite scaling dimension at short distance. The Ricci
curvature singularity at the big bang can be viewed as such a scaling
phenomenon. The problem of the spacetime singularity may be resolved by the
scale invariance of the spacetime at short distance.Comment: 9pages, LaTe
Magnetic-Field Dependences of Thermodynamic Quantities in the Vortex State of Type-II Superconductors
We develop an alternative method to solve the Eilenberger equations
numerically for the vortex-lattice states of type-II superconductors. Using it,
we clarify the magnetic-field and impurity-concentration dependences of the
magnetization, the entropy, the Pauli paramagnetism, and the mixing of higher
Landau levels in the pair potential for two-dimensional - and
-wave superconductors with the cylindrical Fermi surface.Comment: 8 pages, 6 figure
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