247 research outputs found
Interplay between phase defects and spin polarization in the specific heat of the spin density wave compound (TMTTF)_2Br in a magnetic field
Equilibrium heat relaxation experiments provide evidence that the ground
state of the commensurate spin density wave (SDW) compound (TMTTF)Br after
the application of a sufficient magnetic field is different from the
conventional ground state. The experiments are interpreted on the basis of the
local model of strong pinning as the deconfinement of soliton-antisoliton pairs
triggered by the Zeeman coupling to spin degrees of freedom, resulting in a
magnetic field induced density wave glass for the spin carrying phase
configuration.Comment: 4 pages, 5 figure
Renormalization Group Technique Applied to the Pairing Interaction of the Quasi-One-Dimensional Superconductivity
A mechanism of the quasi-one-dimensional (q1d) superconductivity is
investigated by applying the renormalization group techniques to the pairing
interaction. With the obtained renormalized pairing interaction, the transition
temperature Tc and corresponding gap function are calculated by solving the
linearized gap equation. For reasonable sets of parameters, Tc of p-wave
triplet pairing is higher than that of d-wave singlet pairing due to the
one-dimensionality of interaction. These results can qualitatively explain the
superconducting properties of q1d organic conductor (TMTSF)2PF6 and the ladder
compound Sr2Ca12Cu24O41.Comment: 18 pages, 9 figures, submitted to J. Phys. Soc. Jp
Structure of the Fulde-Ferrell-Larkin-Ovchinnikov state in two-dimensional superconductors
Nonuniform superconducting state due to strong spin magnetism is studied in
two-dimensional type-II superconductors near the second order phase transition
line between the normal and the superconducting states. The optimum spatial
structure of the orderparameter is examined in systems with cylindrical
symmetric Fermi surfaces. It is found that states with two-dimensional
structures have lower free energies than the traditional one-dimensional
solutions, at low temperatures and high magnetic fields. For s-wave pairing,
triangular, square, hexagonal states are favored depending on the temperature,
while square states are favored at low temperatures for d-wave pairing. In
these states, orderparameters have two-dimensional structures such as square
and triangular lattices.Comment: 11 pages (LaTeX, revtex.sty), 3 figures; added reference
Weak-Coupling Approach to Hole-Doped S=1 Haldane Systems
As a weak-coupling analogue of hole-doped Haldane systems, we study two
models for coupled chains via Hund coupling; coupled Hubbard chains, and a
Hubbard chain coupled with an Heisenberg chain. The fixed point
properties of these models are investigated by using bosonization and
renormalization group methods. The effect of randomness on these fixed points
is also studied. It is found that the presence of the disorder parameter
inherent in the Haldane state in the former model suppresses the Anderson
localization for weak randomness, and stabilizes the Tomonaga-Luttinger liquid
state with the spin gap.Comment: 4 pages, RevTex, 1 postscript figure (uuencoded and compressed), to
appear in Phys. Rev.
Anomalous Spin and Charge Dynamics of the 2D t-J Model at low doping
We present an exact diagonalization study of the dynamical spin and density
correlation function of the 2D t-J model for hole doping < 25%. Both
correlation functions show a remarkably regular, but completely different
scaling behaviour with both hole concentration and parameter values: the
density correlation function is consistent with that of bosons corresponding to
the doped holes and condensed into the lowest state of the noninteracting band
of width 8t, the spin correlation function is consistent with Fermions in a
band of width J. We show that the spin bag picture gives a natural explanation
for this unusual behaviour.Comment: Revtex-file, 4 PRB pages + 5 figures attached as uu-encoded ps-files
Hardcopies of figures (or the entire manuscript) can also be obtained by
e-mailing to: [email protected]
Superconductivity of Quasi-One and Quasi-Two Dimensional Tight-Binding Electrons in Magnetic Field
The upper critical field of the tight-binding electrons in the
three-dimensional lattice is investigated.
The electrons make Cooper pairs between the eigenstates with the same energy
in the strong magnetic field. The transition lines in the quasi-one dimensional
case are shown to deviate from the previously obtained results where the
hopping matrix elements along the magnetic field are neglected. In the absence
of the Pauli pair breaking the transition temperature of the quasi-two
dimensional electrons is obtained to oscillationally increase as the magnetic
field becomes large and reaches to in the strong field as in the
quasi-one dimensional case.Comment: 4pages,4figures,to be published in J.Phys.Soc.Jp
Effect of spin-orbit impurity scattering in the superconducting state of t-J model
We study the effect of magnetic impurities in the d_{x^2-y^2}-wave
superconducting (SC) state of the two dimensional t-J model.The spin-orbit and
the spin-exchange interactions are examined by treating the impurity as a
classical spin. The Bogoliubov de Gennes equation derived within a slave-boson
mean-field approximation is solved numerically at T = 0. The spin-exchange
scattering induces spin-triplet p-wave SC order parameters near the impurity,
while a SC state with broken time-reversal symmetry and a spontaneous current
appears in the presence of the spin-orbit interaction. When both interactions
coexist, it turns out that a state which carries a spontaneous spin current
occurs.Comment: 4 pages, 7 figure
Impurity-induced spin polarization and NMR line broadening in underdoped cuprates
We present a theory of magnetic (S=1) Ni and nonmagnetic Zn impurities in
underdoped cuprates. Both types of impurities are shown to induce S=1/2 moments
on Cu sites in the proximity of the impurity, a process which is intimately
related to the spin gap phenomenon in cuprates. Below a characteristic Kondo
temperature, the Ni spin is partially screened by the Cu moments, resulting in
an effective impurity spin S=1/2. We further analyze the
Ruderman-Kittel-Kasiya-Yosida-type response of planar Cu spins to a
polarization of the effective impurity moments and derive expressions for the
corresponding ^{17}O NMR line broadening. The peculiar aspects of recent
experimental NMR data can be traced back to different spatial characteristics
of Ni and Zn moments as well as to an inherent temperature dependence of local
antiferromagnetic correlations.Comment: PRB B1 01June9
Nontrivial behavior of the Fermi arc in the staggered-flux ordered phase
The doping and temperature dependences of the Fermi arc in the
staggered-flux, or the d-density wave, ordered phase of the t-J model are
analyzed by the U(1) slave boson theory. Nontrivial behavior is revealed by the
self-consistent calculation. At low doped and finite-temperature region, both
the length of the Fermi arc and the width of the Fermi pocket are proportional
to and the area of the Fermi pocket is proportional to .
This behavior is completely different from that at the zero temperature, where
the area of the Fermi pocket becomes . This behavior should be
observed by detailed experiments of angle-resolved photoemission spectroscopy
in the pseudogap phase of high-T_c cuprates if the pseudogap phase is the
staggered-flux ordered phase.Comment: 4 pages, 4 figure
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