124 research outputs found
Anisotropic magnetotransport properties coupled with spiral spin modulation in a triangular-lattice magnet EuZnGe
We investigate the thermodynamic, magnetic, and electrical transport
properties of a triangular-lattice antiferromagnet EuZnGe using single crystals
grown from Eu-Zn flux in sealed tantalum tubes. Magnetic properties are found
to be isotropic in the paramagnetic state while we observe an enhancement of
in-plane magnetic susceptibility at the temperature near T* =11.3 K, suggesting
an easy-plane anisotropy at low temperatures. Magnetic transition temperature
is lower than T* as specific heat shows a peak at TN =7.6 K. We reveal the
magnetic modulation along the c axis by resonant x-ray scattering at Eu L2
edge, which suggests competing magnetic interaction among Eu triangular-lattice
layers. We observe a double-peak structure in the intensity profile along (0,
0, L) below TN, which is mainly composed of a dominant helical modulation with
q ~ (0, 0, 0.4) coexisting with a secondary contribution from q ~ (0, 0, 0.5).
We reproduce the intensity profile with a random mixture of five- and
four-sublattice helices with spin rotation skipping due to hexagonal in-plane
anisotropy. The metallic conductivity is highly anisotropic with the ratio
rho_zz/rho_xx exceeding 10 over the entire temperature range and additionally
exhibits a sharp enhancement of rho_zz at TN giving rise to rho_zz/rho_xx ~ 50,
suggesting a coupling between out-of-plane electron conduction and the spiral
magnetic modulations. In-plane magnetic field induces a spin-flop like
transition, where the q = 0.4 peak disappears and an incommensurate peak of
approximately qICM ~ 0.47 emerges, while the q = 0.5 modulation retains a
finite intensity. This transition correlates with non-monotonic
magnetoresistance and Hall resistivity, suggesting a significant interplay
between electrons and spin structures through Ruderman-Kittel-Kasuya-Yosida
(RKKY) interaction.Comment: 9 pages, 6 figure
Real-Space Observation of Ligand Hole State in Cubic Perovskite SrFeO
An anomalously high valence state sometimes shows up in transition-metal
oxide compounds. In such systems, holes tend to occupy mainly the ligand
orbitals, giving rise to interesting physical properties such as
superconductivity in cuprates and rich magnetic phases in ferrates. However, no
one has ever observed the distribution of ligand holes in real space. Here, we
report a successful observation of the spatial distribution of valence
electrons in cubic perovskite SrFeO by high-energy X-ray diffraction
experiments and precise electron density analysis using a core differential
Fourier synthesis method. A real-space picture of ligand holes formed by the
orbital hybridization of Fe 3 and O 2 is revealed. The anomalous valence
state in Fe is attributed to the considerable contribution of the ligand hole,
which is related to the metallic nature and the absence of Jahn-Teller
distortions in this system.Comment: 14 pages, 4 figure
Single crystal growths and magnetic properties of hexagonal polar semimetals RAuGe (R = Y, Gd-Tm, and Lu)
We study structural and magnetic properties of rare-earth based semimetals
RAuGe (R = Y, Gd-Tm, and Lu) using flux-grown single crystals. These compounds
belong to the noncentrosymmetric polar space group P63mc. We confirm the
systematic structural evolution at room temperature as a function of ionic
radius of rare earths to clarify the isopointal crossover between two polar
structures: three-dimensional LiGaGe-type and quasi-two-dimensional
NdPtSb-type. Magnetism shows a characteristic anisotropy in reasonable
agreement with the crystal electric field (CEF) theory; the easy-plane-type
anisotropy for R = Tb and Dy turns into the Ising-type anisotropy for R = Er
and Tm. We evaluate the CEF parameters based on the Stevens operators to
reasonably reproduce the temperature dependence of magnetic susceptibilities
and specific heat for RAuGe (R = Tb-Tm). The estimated energy scale of the
Ising gap (~ 11 meV) in TmAuGe is consistent with an excitation observed in an
inelastic neutron scattering experiment. These findings suggest an opportunity
for interplay between conduction electrons and nontrivial spin structures in
the family of magnetic polar semimetals RAuGe.Comment: 10 pages, 7 figures, 1 tabl
MgZnO/ZnO heterostructures with electron mobility exceeding 1 × 10⁶ cm²/Vs
The inherently complex chemical and crystallographic nature of oxide materials has suppressed the purities achievable in laboratory environments, obscuring the rich physical degrees of freedom these systems host. In this manuscript we provide a systematic approach to defect identification and management in oxide molecular beam epitaxy grown MgZnO/ZnO heterostructures which host two-dimensional electron systems. We achieve samples displaying electron mobilities in excess of 1 × 10⁶ cm²/Vs. This data set for the MgZnO/ZnO system firmly establishes that the crystalline quality has become comparable to traditional semiconductor materials
The pi N -> pi pi N reaction around the N(1440) energy
We study the pi N -> pi pi N reaction around the N(1440) mass-shell energy.
Considering the total cross sections and invariant mass distributions, we
discuss the role of N(1440) and its decay processes. The calculation is
performed by extending our previous approach [Phys. Rev. C 69, 025206 (2004)]
to this reaction, in which only the nucleon and Delta(1232) were considered as
intermediate baryon states. The characteristics observed in the recent data for
the pi- p -> pi0 pi0 n reaction obtained by Crystal Ball Collaboration (CBC),
can be understood as a strong interference between the two decay processes:
N(1440) -> pi Delta(1232) and N(1440) -> N(pi pi)_S. It is also found that the
scalar-isoscalar pi pi rescattering effect in the NN*(pi pi)_S vertex, which
corresponds to the propagation of sigma meson, seems to be necessary for
explain ing the several observables of the pi N -> pi pi N reaction: the large
asymmetric shape in the pi0-pi0 invariant mass distributions of the pi- p ->
pi0 pi0 n reaction and the pi+ p -> pi+ pi+ n total cross section.Comment: 28 pages, 13 figures. Version to appear in Phys. Rev.
Coherent Pair State of Pion in Constituent Quark Model
A coherent state of pions is introduced to the nonrelativistic quark model.
The coherent pair approximation is employed for the pion field in order to
maintain the spin-isospin symmetry. In this approximation the pion is localized
in the momentum space, and the vertex form factor in the pion-quark interaction
is derived from this localization. The nucleon masses and wave functions are
calculated using this model, and our results are compared to those of the quark
model with the one pion exchange potential. Similar result is obtained for the
mass spectrum, but there exists a clear difference in the internal structure of
nucleon resonances.Comment: 17 pages, 2 figures, revtex, submitted to Phys. Rev.
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