801 research outputs found
Pressure-tuned First-order Phase Transition and Accompanying Resistivity Anomaly in CeZn_{1-\delta}Sb_{2}
The Kondo lattice system CeZn_{0.66}Sb_{2} is studied by the electrical
resistivity and ac magnetic susceptibility measurements at several pressures.
At P=0 kbar, ferromagnetic and antiferromagnetic transitions appear at 3.6 and
0.8 K, respectively. The electrical resistivity at T_N dramatically changes
from the Fisher-Langer type (ferromagnetic like) to the Suzaki-Mori type near
17 kbar, i.e., from a positive divergence to a negative divergence in the
temperature derivative of the resistivity. The pressure-induced SM type
anomaly, which shows thermal hysteresis, is easily suppressed by small magnetic
field (1.9 kOe for 19.8 kbar), indicating a weakly first-order nature of the
transition. By subtracting a low-pressure data set, we directly compare the
resistivity anomaly with the SM theory without any assumption on backgrounds,
where the negative divergence in d\rho/dT is ascribed to enhanced critical
fluctuations in the presence of superzone gaps.Comment: 5 pages, 4 figures; journal-ref adde
Orbital magnetization and its effect in antiferromagnets on the distorted fcc lattice
We study the intrinsic orbital magnetization (OM) in antiferromagnets on the
distorted face-centered-cubic lattice. The combined lattice distortion and spin
frustration induce nontrivial -space Chern invariant, which turns to result
in profound effects on the OM properties. We derive a specific relation between
the OM and the Hall conductivity, according to which it is found that the
intrinsic OM vanishes when the electron chemical potential lies in the Mott
gap. The distinct behavior of the intrinsic OM in the metallic and insulating
regions is shown. The Berry phase effects on the thermoelectric transport is
also discussed.Comment: 18 pages, 6 figure
Parisi States in a Heisenberg Spin-Glass Model in Three Dimensions
We have studied low-lying metastable states of the Heisenberg model
in two () and three () dimensions having developed a hybrid genetic
algorithm. We have found a strong evidence of the occurrence of the Parisi
states in but not in . That is, in lattices, there exist
metastable states with a finite excitation energy of for
, and energy barriers between the ground state and
those metastable states are with in
but with in . We have also found droplet-like
excitations, suggesting a mixed scenario of the replica-symmetry-breaking
picture and the droplet picture recently speculated in the Ising SG model.Comment: 4 pages, 6 figure
Electronic Structure of Cu_(1-x)Ni_xRh_2S_4 and CuRh_2Se_4: Band Structure Calculations, X-ray Photoemission and Fluorescence Measurements
The electronic structure of spinel-type Cu_(1-x)Ni_xRh_2S_4 (x = 0.0, 0.1,
0.3, 0.5, 1.0) and CuRh_2Se_4 compounds has been studied by means of X-ray
photoelectron and fluorescent spectroscopy. Cu L_3, Ni L_3, S L_(2,3) and Se
M_(2,3) X-ray emission spectra (XES) were measured near thresholds at Beamline
8.0 of the Lawrence Berkeley Laboratory's Advanced Light Source. XES
measurements of the constituent atoms of these compounds, reduced to the same
binding energy scale, are found to be in excellent agreement with XPS valence
bands. The calculated XES spectra which include dipole matrix elements show
that the partial density of states reproduce experimental spectra quite well.
States near the Fermi level (E_F) have strong Rh d and S(Se) p character in all
compounds. In NiRh_2S_4 the Ni 3d states contribute strongly at E_F, whereas in
both Cu compounds the Cu 3d bands are only ~1 eV wide and centered ~2.5 eV
below E_F, leaving very little 3d character at E_F. The density of states at
the Fermi level is less in NiRh_2S_4 than in CuRh_2S_4. This difference may
contribute to the observed decrease, as a function of Ni concentration, in the
superconducting transition temperature in Cu_(1-x)Ni_xRh_2S_4. The density of
states of the ordered alloy Cu_(1/2)Ni_(1/2)Rh_2S_4 shows behavior that is more
``split-band''-like than ``rigid band''-like.Comment: 7 pages of text, 11 trailing figures, updated to fix faulty
postscript in Fig.
Dispersion of Magnetic Excitations in Superconducting Optimally Doped YBa_2Cu_3O_6.95
Detailed neutron scattering measurements of YBa_2Cu_3O_6.95 found that the
resonance peak and incommensurate magnetic scattering induced by
superconductivity represent the same physical phenomenon: two dispersive
branches that converge near 41 meV and the in-plane wave-vector q_af=(pi/a,
pi/a) to form the resonance peak. One branch has a circular symmetry around
q_af and quadratic downward dispersion from ~41 meV to the spin gap of
33+-1meV. The other, of lower intensity, disperses from ~41 meV to at least 55
meV. Our results exclude a quartet of vertical incommensurate rods in q-w space
expected from spin waves produced by dynamical charge stripes as an origin of
the observed incommensurate scattering in optimally-doped YBCO.Comment: Version 3: Author change. Changes made throughout the text and minor
changes in figures, Model parameters slightly changed after a small error in
the calculation was discovere
Universality of the helimagnetic transition in cubic chiral magnets: Small angle neutron scattering and neutron spin echo spectroscopy studies of FeCoSi
We present a comprehensive Small Angle Neutron Scattering (SANS) and Neutron
Spin Echo Spectroscopy (NSE) study of the structural and dynamical aspects of
the helimagnetic transition in FeCoSi with = 0.30. In contrast
to the sharp transition observed in the archetype chiral magnet MnSi, the
transition in FeCoSi is gradual and long-range helimagnetic
ordering coexists with short-range correlations over a wide temperature range.
The dynamics are more complex than in MnSi and involve long relaxation times
with a stretched exponential relaxation which persists even under magnetic
field. These results in conjunction with an analysis of the hierarchy of the
relevant length scales show that the helimagnetic transition in
FeCoSi differs substantially from the transition in MnSi and
question the validity of a universal approach to the helimagnetic transition in
chiral magnets
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