2,238 research outputs found
Transport through superconductor/magnetic dot/superconductor structures
The coupling of two s-wave superconductors through a small magnetic dot is
discussed. Assuming that the dot charging energy is small compared to the
superconducting gap, , and that the moment of the dot is
classical, we develop a simple theory of transport through the dot. The
presence of the magnetic dot will position Andreev bound states within the
superconducting gap at energies tunable with the magnetic properties of the
dot. Studying the Josephson coupling it is shown that the constructed junction
can be tuned from a "0" to a ""-junction via a degenerate two-level state
either by changing the magnetic moment of the dot or by changing temperature.
Furthermore, it is shown that details of the magnetic dot can be extracted from
the sub-harmonic structure in the current-voltage characteristics of the
junction.Comment: 5 pages, 4 figures, paper presented at the conference SDP 2001 in
Tokyo on June 2
Suppressed Coherence due to Orbital Correlations in the Ferromagnetically Ordered Metallic Phase of Mn Compounds
Small Drude weight together with small specific heat coefficient
observed in the ferromagnetic phase of RAMnO (R=La, Pr, Nd, Sm;
A=Ca, Sr, Ba) are analyzed in terms of a proximity effect of the Mott
insulator. The scaling theory for the metal-insulator transition with the
critical enhancement of orbital correlations toward the staggered ordering of
two orbitals such as and symmetries may lead to the
critical exponents of and with
and . The result agrees with the experimental indications.Comment: 4 pages LaTeX using jpsj.sty. To appear in J. Phys. Soc. Jpn.
67(1998)No.
Entanglement Entropy of Two Spheres
We study the entanglement entropy S_{AB} of a massless free scalar field on
two spheres A and B whose radii are R_1 and R_2, respectively, and the distance
between the centers of them is r. The state of the massless free scalar field
is the vacuum state. We obtain the result that the mutual information
S_{A;B}:=S_A+S_B-S_{AB} is independent of the ultraviolet cutoff and
proportional to the product of the areas of the two spheres when r>>R_1,R_2,
where S_A and S_B are the entanglement entropy on the inside region of A and B,
respectively. We discuss possible connections of this result with the physics
of black holes.Comment: 17 pages, 9 figures; v4, added references, revised argument in
section V, a typo in eq.(25) corrected, published versio
Beyond the Medial Regions of Prefrontal Cortex in the Regulation of Fear and Anxiety.
Fear and anxiety are adaptive responses but if left unregulated, or inappropriately regulated, they become biologically and socially maladaptive. Dysregulated emotions are manifest in a wide variety of psychiatric and neurological conditions but the external expression gives little indication of the underlying causes, which are inevitably multi-determined. To go beyond the overt phenotype and begin to understand the causal mechanisms leading to conditions characterized by anxiety and disorders of mood, it is necessary to identify the base psychological processes that have become dysregulated, and map them on to their associated neural substrates. So far, attention has been focused primarily on the medial regions of prefrontal cortex (PFC) and in particular their contribution to the expression and extinction of conditioned fear. However, functional neuroimaging studies have shown that the sphere of influence within the PFC is not restricted to its medial regions, but extends into dorsal, ventrolateral (vlPFC) and orbitofrontal (OFC) regions too; although the causal role of these other areas in the regulation of fear and anxiety remains to be determined and in the case of the OFC, existing findings are conflicting. Here, we review the evidence for the contribution of these other regions in negative emotion regulation in rodents and old world and new world monkeys. We consider a variety of different contexts, including conditioned and innate fear, learned and unlearned anxiety and cost-benefit decision-making, and a range of physiological and behavioral measures of emotion. It is proposed that both the OFC and vlPFC contribute to emotion regulation via their involvement, respectively, in the prediction of future outcomes and higher-order attentional control. The fractionation of these neurocognitive and neurobehavioral systems that regulate fear and anxiety opens up new opportunities for diagnostic stratification and personalized treatment strategies.This research was supported by a Medical Research Programme Grant (G0901884) from the Medical Research Council (MRC), UK to ACR and carried out within the Behavioral and Clinical Neurosciences Institute supported by a consortium award from the Wellcome Trust and the MRC.This is the final version of the article. It first appeared from Frontiers via http://dx.doi.org/10.3389/fnsys.2016.0001
Variational Monte Carlo Study of the Kondo Necklace Model with Geometrical Frustration
We investigate the ground state of the Kondo necklace model on
geometrically-frustrated lattices by the variational Monte Carlo simulation. To
explore the possibility of a partially-ordered phase, we employ an extension of
the Yosida-type wave function as a variational state, which can describe a
coexistence of spin-singlet formation due to the Kondo coupling and magnetic
ordering by the Ruderman-Kittel-Kasuya-Yosida interaction. We show the
benchmark of the numerical simulation to demonstrate the high precision brought
by the optimization of a large number of variational parameters. We discuss the
ground-state phase diagram for the model on the kagome lattice in comparison
with that for the triangular-lattice case.Comment: 3 pages, proceedings for ICHE201
Phase Diagram of Lattice-Spin System RbCoBr
We study the lattice-spin model of RbCoBr which is proposed by Shirahata
and Nakamura, by mean field approximation. This model is an Ising spin system
on a distorted triangular lattice. There are two kinds of frustrated variables,
that is, the lattice and spin. We obtain a phase diagram of which phase
boundary is drawn continuously in a whole region. Intermediate phases that
include a partial disordered state appear. The model has the first-order phase
transitions in addition to the second-order phase transitions. We find a
three-sublattice ferrimagnetic state in the phase diagram. The three-sublattice
ferrimagnetic state does not appear when the lattice is not distorted.Comment: 5 pages, 4 figures, jpsj2.cls, to be published in J. Phys. Soc. Jpn.
Vol.75 (2006) No.
Broken particle-hole symmetry at atomically flat a-axis YBa2Cu3O7-d interfaces
We have studied quasiparticle tunneling into atomically flat a-axis films of
YBa2Cu3O7-d and DyBa2Cu3O7-d through epitaxial CaTiO3 barriers. The junction
heterostructures were grown by oxide molecular beam epitaxy and were carefully
optimized using in-situ monitoring techniques, resulting in unprecedented
crystalline perfection of the superconductor/insulator interface. Below Tc, the
tunneling conductance shows the evolution of a large unexpected asymmetrical
feature near zero bias. This is evidence that superconducting YBCO crystals,
atomically truncated along the lobe direction with a titanate layer, have
intrinsically broken particle-hole symmetry over macroscopically large areas.Comment: 15 pages, 4 figures; v2 includes minor changes in concluding
paragraph to match PRL versio
Resonant Impurity States in the D-Density-Wave Phase
We study the electronic structure near impurities in the d-density-wave (DDW)
state, a possible candidate phase for the pseudo-gap region of the
high-temperature superconductors. We show that the local DOS near a
non-magnetic impurity in the DDW state is {\it qualitatively} different from
that in a superconductor with -symmetry. Since this result is a
robust feature of the DDW phase, it can help to identify the nature of the two
different phases recently observed by scanning tunneling microscopy experiments
in the superconducting state of underdoped Bi-2212 compounds
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