1,138 research outputs found
Persistence of singlet fluctuations in the coupled spin tetrahedra system Cu2Te2O5Br2 revealed by high-field magnetization and 79Br NQR - 125Te NMR
We present high-field magnetization and Br nuclear quadrupole
resonance (NQR) and Te nuclear magnetic resonance (NMR) studies in the
weakly coupled Cu () tetrahedral system CuTeOBr.
The field-induced level crossing effects were observed by the magnetization
measurements in a long-ranged magnetically ordered state which was confirmed by
a strong divergence of the spin-lattice relaxation rate 1/T1 at T0=13.5 K. In
the paramagnetic state, 1/T1 reveals an effective singlet-triplet spin gap much
larger than that observed by static bulk measurements. Our results imply that
the inter- and the intra-tetrahedral interactions compete, but at the same time
they cooperate strengthening effectively the local intratetrahedral exchange
couplings. We discuss that the unusual feature originates from the frustrated
intertetrahedral interactions.Comment: 5 pages, 4 figures, accepted in Phys. Rev. B as a Rapid
Communication
Phonon Anomalies, Orbital-Ordering and Electronic Raman Scattering in iron-pnictide Ca(Fe0.97Co0.03)2As2: Temperature-dependent Raman Study
We report inelastic light scattering studies on Ca(Fe0.97Co0.03)2As2 in a
wide spectral range of 120-5200 cm-1 from 5K to 300K, covering the tetragonal
to orthorhombic structural transition as well as magnetic transition at Tsm ~
160K. The mode frequencies of two first-order Raman modes B1g and Eg, both
involving displacement of Fe atoms, show sharp increase below Tsm.
Concomitantly, the linewidths of all the first-order Raman modes show anomalous
broadening below Tsm, attributed to strong spin-phonon coupling. The high
frequency modes observed between 400-1200 cm-1 are attributed to the electronic
Raman scattering involving the crystal field levels of d-orbitals of Fe2+. The
splitting between xz and yz d-orbital levels is shown to be ~ 25 meV which
increases as temperature decreases below Tsm. A broad Raman band observed at ~
3200 cm-1 is assigned to two-magnon excitation of the itinerant Fe 3d
antiferromagnet.Comment: Accepted for Publication in JPC
Investigation of the relation between local diffusivity and local inherent structures in the Kob-Andersen Lennard-Jones model
We analyze one thousand independent equilibrium trajectories of a system of
155 Lennard Jones particles to separate in a model-free approach the role of
temperature and the role of the explored potential energy landscape basin depth
in the particle dynamics. We show that the diffusion coefficient can be
estimated as a sum over over contributions of the sampled basins, establishing
a connection between thermodynamics and dynamics in the potential energy
landscape framework. We provide evidence that the observed non-linearity in the
relation between local diffusion and basin depth is responsible for the
peculiar dynamic behavior observed in supercooled states and provide an
interpretation for the presence of dynamic heterogeneities.Comment: minor text changes, references adde
Local magnetic anisotropy in BaFeAs: a polarized inelastic neutron scattering study
The anisotropy of the magnetic excitations in BaFeAs was studied by
polarized inelastic neutron scattering which allows one to separate the
components of the magnetic response. Despite the in-plane orientation of the
static ordered moment we find the in-plane polarized magnons to exhibit a
larger gap than the out-of-plane polarized ones indicating very strong
single-ion anisotropy within the layers. It costs more energy to rotate a spin
within the orthorhombic {\it a-b} plane than rotating it perpendicular to the
FeAs layers.Comment: 4 pages, 4 figure
TaIrTe4 a ternary Type-II Weyl semi-metal
In metallic condensed matter systems two different types of Weyl fermions can
in principle emerge, with either a vanishing (type-I) or with a finite
(type-II) density of states at the Weyl node energy. So far only WTe2 and MoTe2
were predicted to be type-II Weyl semi-metals. Here we identify TaIrTe4 as a
third member of this family of topological semi-metals. TaIrTe4 has the
attractive feature that it hosts only four well-separated Weyl points, the
minimum imposed by symmetry. Moreover, the resulting topological surface states
- Fermi arcs connecting Weyl nodes of opposite chirality - extend to about 1/3
of the surface Brillouin zone. This large momentum-space separation is very
favorable for detecting the Fermi arcs spectroscopically and in transport
experiments
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