436 research outputs found
Parity-broken ground state for the spin-1 pyrochlore antiferromagnet
The ground-state properties of the spin-1 pyrochlore antiferromagnet are
studied by applying the VBS-like tetrahedron-unit decomposition to the original
spin system. The symmetrization required on every vertex is taken into account
by introducing a ferromagnetic coupling. The pairwise effective Hamiltonian
between the adjacent tetrahedrons is obtained by considering the next nearest
neighbor and the third neighbor exchange interactions. We find that the
transverse component of the spin chirality exhibits a long-range order,
breaking the parity symmetry of the tetrahedral group, while the chirality
itself is not broken.Comment: 4 pages, 3 figures, REVTeX(ver.3.1
Berry phase in Magnetic Superconductors
In magnetic systems, electronic bands often acquire nontrivial topological
structure characterized by gauge flux distribution in momentum (k)-space. It
sometimes follows that the phase of the wavefunctions cannot be defined
uniquely over the whole Brillouin zone. In this Letter we develop a theory of
superconductivity in the presence of this gauge flux both in two- and
three-dimensional systems. It is found that the superconducting gap has "nodes"
as a function of k where the Fermi surface is penetrated by a gauge string.Comment: 4 pages, 3 figures, substantial changes in the presentation, to be
published in Phys. Rev. Let
Quantized Anomalous Hall Effect in Two-Dimensional Ferromagnets - Quantum Hall Effect from Metal -
We study the effect of disorder on the anomalous Hall effect (AHE) in
two-dimensional ferromagnets. The topological nature of AHE leads to the
integer quantum Hall effect from a metal, i.e., the quantization of
induced by the localization except for the few extended states
carrying Chern number. Extensive numerical study on a model reveals that
Pruisken's two-parameter scaling theory holds even when the system has no gap
with the overlapping multibands and without the uniform magnetic field.
Therefore the condition for the quantized AHE is given only by the Hall
conductivity without the quantum correction, i.e., .Comment: 5 pages, 4 figures, REVTe
Anomalous Hall effect as a probe of the chiral order in spin glasses
Anomalous Hall effect arising from the noncoplanar spin configuration
(chirality) is discussed as a probe of the chiral order in spin glasses. It is
shown that the Hall coefficient yields direct information about the linear and
nonlinear chiral susceptibilities of the spin sector, which has been hard to
obtain experimentally from the standard magnetic measurements. Based on the
chirality scenario of spin-glass transition, predictions are given on the
behavior of the Hall resistivity of canonical spin glasses.Comment: Order estimate of the effect given, one reference added. To appear in
Phys. Rev. Letter
Orbital-dependent modifications of electronic structure across magneto-structural transition in BaFe2As2
Laser angle-resolved photoemission spectroscopy (ARPES) is employed to
investigate the temperature (T) dependence of the electronic structure in
BaFe2As2 across the magneto-structural transition at TN ~ 140 K. A drastic
transformation in Fermi surface (FS) shape across TN is observed, as expected
by first-principles band calculations. Polarization-dependent ARPES and band
calculations consistently indicate that the observed FSs at kz ~ pi in the
low-T antiferromagnetic (AF) state are dominated by the Fe3dzx orbital, leading
to the two-fold electronic structure. These results indicate that
magneto-structural transition in BaFe2As2 accompanies orbital-dependent
modifications in the electronic structure.Comment: 13 pages, 4 figures. accepted by Physical Review Letter
Anomalous Hall Effect and Skyrmion Number in Real- and Momentum-space
We study the anomalous Hall effect (AHE) for the double exchange model with
the exchange coupling being smaller than the bandwidth for the
purpose of clarifying the following unresolved and confusing issues: (i) the
effect of the underlying lattice structure, (ii) the relation between AHE and
the skyrmion number, (iii) the duality between real and momentum spaces, and
(iv) the role of the disorder scatterings; which is more essential,
(Hall conductivity) or (Hall resistivity)? Starting from a generic
expression for , we resolve all these issues and classify the regimes
in the parameter space of (: elastic-scattering time), and
(length scale of spin texture). There are two distinct mechanisms
of AHE; one is characterized by the real-space skyrmion-number, and the other
by momentum-space skyrmion-density at the Fermi level, which work in different
regimes of the parameter space.Comment: 4 pages, 1 figure, REVTe
Observation of Giant Band Splitting in Altermagnetic MnTe
We performed angle-resolved photoemission spectroscopy (ARPES) on hexagonal
MnTe, a candidate for an altermagnet with a high critical temperature
(TN=307K). By utilizing photon-energy-tunable ARPES in combination with
first-principles calculations, we found that the band structure in the
antiferromagnetic phase exhibits a strongly anisotropic band-splitting
associated with the time-reversal-symmetry breaking, providing the first direct
experimental evidence for the altermagnetic band-splitting. The magnitude of
the splitting reaches 0.8 eV at non-high-symmetry momentum points, which is
much larger than the spin-orbit gap of ~0.3 eV along the GammaK high-symmetry
cut. The present result paves the pathway toward realizing exotic physical
properties associated with the altermagnetic spin-splitting.Comment: 17 pages, 6 figure
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