1,674 research outputs found
Validity and failure of some entropy inequalities for CAR systems
Basic properties of von Neumann entropy such as the triangle inequality and
what we call MONO-SSA are studied for CAR systems.
We show that both inequalities hold for any even state. We construct a
certain class of noneven states giving counter examples of those inequalities.
It is not always possible to extend a set of prepared states on disjoint
regions to some joint state on the whole region for CAR systems.
However, for every even state, we have its `symmetric purification' by which
the validity of those inequalities is shown.
Some (realized) noneven states have peculiar state correlations among
subsystems and induce the failure of those inequalities.Comment: 14 pages, latex, to appear in JMP. Some typos are correcte
Schwinger Boson approach to the fully screened Kondo model
We apply the Schwinger boson scheme to the fully screened Kondo model and
generalize the method to include antiferromagnetic interactions between ions.
Our approach captures the Kondo crossover from local moment behavior to a Fermi
liquid with a non-trivial Wilson ratio. When applied to the two impurity model,
the mean-field theory describes the "Varma Jones" quantum phase transition
between a valence bond state and a heavy Fermi liquid.Comment: 4 pages, 4 figures. Changes to references and text in v
A factorization of a super-conformal map
A super-conformal map and a minimal surface are factored into a product of
two maps by modeling the Euclidean four-space and the complex Euclidean plane
on the set of all quaternions. One of these two maps is a holomorphic map or a
meromorphic map. These conformal maps adopt properties of a holomorphic
function or a meromorphic function. Analogs of the Liouville theorem, the
Schwarz lemma, the Schwarz-Pick theorem, the Weierstrass factorization theorem,
the Abel-Jacobi theorem, and a relation between zeros of a minimal surface and
branch points of a super-conformal map are obtained.Comment: 21 page
Correlated band theory of spin and orbital contributions to Dzyaloshinskii-Moriya interactions
A new approach for calculations of Dzyaloshinskii-Moriya interactions in
molecules and crystals is proposed. It is based on the exact perturbation
expansion of total energy of weak ferromagnets in the canting angle with the
only assumption of local Hubbard-type interactions. This scheme leads to a
simple and transparent analytical expression for Dzyaloshinskii-Moriya vector
with a natural separation into spin and orbital contributions. The main problem
was transferred to calculations of effective tight-binding parameters in the
properly chosen basis including spin-orbit coupling. Test calculations for
LaCuO give the value of canting angle in a good agreement with
experimental data.Comment: 4 pages, 1 figur
Magnetic response and quantum critical behavior in the doped two-leg extended Hubbard ladder
We have investigated quantum critical behavior in the doped two-leg extended
Hubbard ladder, by using a weak-coupling bosonization method. In the ground
state, the dominant fluctuation changes from the conventional d-wave-like
superconducting (SCd) state into density-wave states, with increasing
nearest-neighbor repulsions and/or decreasing doping rate. The competition
between the SCd state and the charge-density-wave state coexisting with the
p-density-wave state becomes noticeable on the critical point, at which the gap
for magnetic excitations vanishes. Based on the Majorana-fermion description of
the effective theory, we calculate the temperature dependence of the magnetic
response such as the spin susceptibility and the NMR relaxation rate, which
exhibit unusual properties due to two kinds of spin excitation modes. On the
quantum critical point, the spin susceptibility shows paramagnetic behavior
with logarithmic corrections and the NMR relaxation rate also exhibits
anomalous power-law behavior. We discuss the commensurability effect due to the
umklapp scattering and relevance to the two-leg ladder compounds
Sr_{14-x}Ca_xCu_{24}O_{41}.Comment: 18 pages, 9 figures, accepted for publication in Phys. Rev.
Nuclear Magnetic Relaxation in the Ferrimagnetic Chain Compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O: Three-Magnon Scattering?
Recent proton spin-lattice relaxation-time (T_1_) measurements on the
ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O are
explained by an elaborately modified spin-wave theory. We give a strong
evidence of the major contribution to 1/T_1_ being made by the three-magnon
scattering rather than the Raman one.Comment: J. Phys.: Condens. Matter 16, No. 49, 9023 (2004
Coexistence of Superconductivity and Antiferromagnetism in Heavy-Fermion Superconductor CeCu_{2}(Si_{1-x}Ge_{x})_{2} Probed by Cu-NQR --A Test Case for the SO(5) Theory--
We report on the basis of Cu-NQR measurements that superconductivity (SC) and
antiferromagnetism (AF) coexist on a microscopic level in
CeCu_{2}(Si_{1-x}Ge_{x})_{2}, once a tiny amount of 1%Ge (x = 0.01) is
substituted for Si. This coexistence arises because Ge substitution expands the
unit-cell volume in nearly homogeneous CeCu2Si2 where the SC coexists with
slowly fluctuating magnetic waves. We propose that the underlying exotic phases
of SC and AF in either nearly homogeneous or slightly Ge substituted CeCu2Si2
are accountable based on the SO(5) theory that unifies the SC and AF. We
suggest that the mechanism of the SC and AF is common in CeCu2Si2.Comment: 7 pages with 6 figures embedded in the text. To be published in J.
Phys. Condens. Matter, 200
A Phenomenological Description of the Non-Fermi-Liquid Phase of MnSi
In order to understand the non-Fermi-liquid behavior of MnSi under pressure
we propose a scenario on the basis of the multispiral state of the magnetic
moment.
This state can describe the recent critical experiment of the Bragg sphere in
the neutron scattering which is the key ingredient of the non-Fermi-liquid
behavior.Comment: 3 page
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