57 research outputs found
Field-direction Dependence of Majorana-mediated Spin Transport
We study the field-direction dependence of the Majorana-mediated spin
transport in the Kitaev clusters with zigzag and armchair edges, applying a
static magnetic field to one of the edges and a magnetic pulsed field to the
other edges. By means of the exact diagonalization method, we calculate the
time-evolution of the spin moments in both edge regions to clarify how the
directions of two fields and shape of the edges affect the Majorana-mediated
spin transport.Comment: 6 pages, 3 figures, to be published in JPS Conference Proceedings
(LT29
Local density of states around a magnetic impurity in high-Tc superconductors based on the t-J model
The local density of states (LDOS) around a magnetic impurity in high-Tc
superconductors is studied using the two-dimensional t-J model with a realistic
band structure. The order parameters are determined in a self-consistent way
within the Gutzwiller approximation and the Bogoliubov-de Gennes theory. In
sharp contrast with the nonmagnetic impurity case, the LDOS near the magnetic
impurity shows two resonance peaks reflecting the presence of spin-dependent
resonance states. It is also shown that these resonance states are
approximately localized around the impurity. The present results have an large
implication on the scanning tunneling spectroscopy observation of
Bi_{2}Sr_{2}Ca(Cu_{1-x}Ni[Zn]_{x})_{2}O_{8+delta}.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
The Energy-dependent Checkerboard Patterns in Cuprate Superconductors
Motivated by the recent scanning tunneling microscopy (STM) experiments [J.
E. Hoffman {\it et al.}, Science {\bf 297}, 1148 (2002); K. McElroy {\it et
al.}, Nature (to be published)], we investigate the real space local density of
states (LDOS) induced by weak disorder in a d-wave superconductor. We first
present the energy dependent LDOS images around a single weak defect at several
energies, and then point out that the experimentally observed checkerboard
pattern in the LDOS could be understood as a result of quasiparticle
interferences by randomly distributed defects. It is also shown that the
checkerboard pattern oriented along to the Cu-O bonds at low energies
would transform to that oriented parallel to the Cu-O bonds at higher energies.
This result is consistent with the experiments.Comment: 3 pages, 3 figure
The effects of Zn Impurity on the Properties of Doped Cuprates in the Normal State
We study the interplay of quantum impurity, and collective spinon and holon
dynamics in Zn doped high-T cuprates in the normal state. The
two-dimensional t-t-J models with one and a small amount of Zn
impurity are investigated within a numerical method based on the double-time
Green function theory. We study the inhomogeneities of holon density and
antiferromagnetic correlation background in cases with different Zn
concentrations, and obtain that doped holes tend to assemble around the Zn
impurity with their mobility being reduced. Therefore a bound state of holon is
formed around the nonmagnetic Zn impurity with the effect helping Zn to
introduce local antiferromagnetism around itself. The incommensurate peaks we
obtained in the spin structure factor indicate that Zn impurities have effects
on mixing the q=(, ) and q=0 components in spin excitations.Comment: 5 pages, 3 figure
Electronic states around a vortex core in high-Tc superconductors based on the t-J model
Electronic states around vortex cores in high-Tc superconductors are studied
using the two-dimensional t-J model in order to treat the d-wave
superconductivity with short coherence length and the antiferromagnetic (AF)
instability within the same framework. We focus on the disappearance of the
large zero-energy peak in the local density of states observed in high-Tc
superconductors. When the system is near the optimum doping, we find that the
local AF correlation develops inside the vortex cores. However, the detailed
doping dependence calculations confirm that the experimentally observed
reduction of the zero-energy peak is more reasonably attributed to the
smallness of the core size rather than to the AF correlation developed inside
the core. The correlation between the spatial dependence of the core states and
the core radius is discussed.Comment: 4 pages, 4 figure
Zeeman effects on the impurity-induced resonances in d-wave superconductors
It is shown how the resonant states induced by a single spinless impurity in
a d-wave superconductor evolve under the effect of an applied Zeeman magnetic
field. Moreover, it is demonstrated that the spin-orbit coupling to the
impurity potential can have important and characteristic effects on the
resonant states and their response to the Zeeman field, especially when the
impurity is close to the unitary limit. For zero or very small spin-orbit
interaction, the resonant states becomes Zeeman splitted by the magnetic field
while when the spin-orbit coupling is important, new low-lying resonances arise
which do not show any Zeeman splitting.Comment: 5 pages with 5 eps figures embedded. To appear on Phys. Rev.
Impurity in a d-wave superconductor: Kondo effect and STM spectra
We present a theory for recent STM studies of Zn impurities in the
superconductor BSCCO, using insights from NMR experiments which show that there
is a net S=1/2 moment on the Cu ions near the Zn. We argue that the Kondo spin
dynamics of this moment is the origin of the low bias peak in the differential
conductance, rather than a resonance in a purely potential scattering model.
The spatial and energy dependence of the STM spectra of our model can also fit
the experiments.Comment: 4 pages, 2 color figures. Found improved saddle-point with d-wave
correlations near the impurity; onset of Kondo screening now occurs at a
significantly smaller coupling, but there is little qualitative change in
other features. Noted connection to STM of Kondo impurities in normal metals.
Final version as publishe
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
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