1,791 research outputs found
Structural Fluctuations in the Spin Liquid State of Tb2Ti2O7
High resolution X-ray scattering measurements on single crystal Tb2Ti2O7
reveal finite structural correlations at low temperatures. This geometrically
frustrated pyrochlore is known to exhibit a spin liquid, or cooperative
paramagnetic state, at temperatures below ~ 20 K. Parametric studies of
structural Bragg peaks appropriate to the Fdm space group of Tb2Ti2O7
reveal substantial broadening and peak intensity reduction in the temperature
regime 20 K to 300 mK. We also observe a small, anomalous lattice expansion on
cooling below a density maximum at ~ 18 K. These measurements are consistent
with the development of fluctuations above a cooperative Jahn-Teller,
cubic-tetragonal phase transition at very low temperatures.Comment: 5 pages, 4 figures, submitted for publicatio
Interplay of Spin-Orbit Interactions, Dimensionality, and Octahedral Rotations in Semimetallic SrIrO
We employ reactive molecular-beam epitaxy to synthesize the metastable
perovskite SrIrO and utilize {\it in situ} angle-resolved photoemission
to reveal its electronic structure as an exotic narrow-band semimetal. We
discover remarkably narrow bands which originate from a confluence of strong
spin-orbit interactions, dimensionality, and both in- and out-of-plane IrO
octahedral rotations. The partial occupation of numerous bands with strongly
mixed orbital characters signals the breakdown of the single-band Mott picture
that characterizes its insulating two-dimensional counterpart,
SrIrO, illustrating the power of structure-property relations for
manipulating the subtle balance between spin-orbit interactions and
electron-electron interactions
High resolution X-ray scattering studies of structural phase transitions in underdoped LaBaCuO
We have studied structural phase transitions in high quality underdoped
LaBaCuO single crystals using high resolution x-ray scattering
techniques. Critical properties associated with the continuous High Temperature
Tetragonal (HTT, ) to Middle Temperature Orthorhombic (MTO, )
phase transition were investigated in single crystal samples with x=0.125,
0.095, and 0.08 and we find that all behavior is consistent with three
dimensional XY criticality, as expected from theory. Power law behavior in the
orthorhombic strain, 2(a-b)/(a+b), is observed over a remarkably wide
temperature range, spanning most of the MTO regime in the phase diagram. Low
temperature measurements investigating the Low Temperature Tetragonal (LTT,
) phase, below the strongly discontinuous MTOLTT phase
transition, in x=0.125 and x=0.095 samples show that the LTT phase is
characterized by relatively broad Bragg scattering, compared with that observed
at related wavevectors in the HTT phase. This shows that the LTT phase is
either an admixture of tetragonal and orthorhombic phases, or that it is
orthorhombic with very small orthorhombic strain, consistent with the ``less
orthorhombic" low temperature structure previously reported in mixed
LaSrBaCuO single crystals. We compare the complex
temperature-composition phase diagram for the location of structural and
superconducting phase transitions in underdoped LaBaCuO and
find good agreement with results obtained on polycrystalline samples.Comment: 8 pages, 7 figures, 1 tabl
Ordering of the pyrochlore Ising model with the long-range RKKY interaction
The ordering of the Ising model on a pyrochlore lattice interacting via the
long-range RKKY interaction, which models a metallic pyrochlore magnet such as
Pr_2Ir_2O_7, is studied by Monte Carlo simulations. Depending on the parameter
k_F representing the Fermi wavevector, the model exhibits rich ordering
behaviors
Revisiting Static and Dynamic Spin Ice Correlations in Ho2Ti2O7
Elastic and inelastic neutron scattering studies have been carried out on the
pyrochlore magnet Ho2Ti2O7. Measurements in zero applied magnetic field show
that the disordered spin ice ground state of Ho2Ti2O7 is characterized by a
pattern of rectangular diffuse elastic scattering within the [HHL] plane of
reciprocal space, which closely resembles the zone boundary scattering seen in
its sister compound Dy2Ti2O7. Well-defined peaks in the zone boundary
scattering develop only within the spin ice ground state below ~ 2 K. In
contrast, the overall diffuse scattering pattern evolves on a much higher
temperature scale of ~ 17 K. The diffuse scattering at small wavevectors below
[001] is found to vanish on going to Q=0, an explicit signature of expectations
for dipolar spin ice. Very high energy-resolution inelastic measurements reveal
that the spin ice ground state below ~ 2 K is also characterized by a
transition from dynamic to static spin correlations on the time scale of
10^{-9} seconds. Measurements in a magnetic field applied along the
[10] direction in zero-field cooled conditions show that the system
can be broken up into orthogonal sets of polarized alpha chains along
[10] and quasi-one-dimensional beta chains along [110]. Three
dimensional correlations between beta chains are shown to be very sensitive to
the precise alignment of the [10] externally applied magnetic field.Comment: 11 pages, 10 figures. Submitted for publicatio
The chiral phase transition in charge ordered 1T-TiSe2
It was recently discovered that the low temperature, charge ordered phase of
1T-TiSe2 has a chiral character. This unexpected chirality in a system
described by a scalar order parameter could be explained in a model where the
emergence of relative phase shifts between three charge density wave components
breaks the inversion symmetry of the lattice. Here, we present experimental
evidence for the sequence of phase transitions predicted by that theory, going
from disorder to non-chiral and finally to chiral charge order. Employing X-ray
diffraction, specific heat, and electrical transport measurements, we find that
a novel phase transition occurs ~7 K below the main charge ordering transition
in TiSe2, in agreement with the predicted hierarchy of charge ordered phases.Comment: 5 pages, 3 figures; includes additional experimental and theoretical
results; fixed typo
A novel approach for x-ray scattering experiments in magnetic fields utilizing trapped flux in type-II superconductors
We introduce a novel approach to x-ray scattering studies in applied magnetic fields by exploiting vortices in superconductors. This method is based on trapping magnetic flux in a small disk-shaped superconductor (known as a trapped field magnet, TFM) with a single-crystal sample mounted on or at close proximity to its surface. This opens an unrestricted optical access to the sample and allows magnetic fields to be applied precisely along the x-ray momentum transfer, facilitating polarization-sensitive experiments that have been impractical or impossible to perform to date. The TFMs used in our study remain stable and provide practically uniform magnetic fields for days, which are sufficient for comprehensive x-ray diffraction experiments, specifically x-ray resonance exchange scattering (XRES) to study field-induced phenomena at a modern synchrotron source. The TFM instrument has been used in a “proof-of-principle” XRES study of a meta-magnetic phase in a rare-earth compound, TbNi2Ge2, in order to demonstrate its potential
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