637 research outputs found
Electronic structure reconstruction by orbital symmetry breaking in IrTe2
We report an angle-resolved photoemission spectroscopy (ARPES) study on IrTe2
which exhibits an interesting lattice distortion below 270 K and becomes
triangular lattice superconductors by suppressing the distortion via chemical
substitution or intercalation. ARPES results at 300 K show multi-band Fermi
surfaces with six-fold symmetry which are basically consistent with band
structure calculations. At 20 K in the distorted phase, whereas the flower
shape of the outermost Fermi surface does not change from that at 300 K,
topology of the inner Fermi surfaces is strongly modified by the lattice
distortion. The Fermi surface reconstruction by the distortion depends on the
orbital character of the Fermi surfaces, suggesting importance of Ir 5d and/or
Te 5p orbital symmetry breaking.Comment: 4pages, 4figure
Spectromicroscopy of electronic phase separation in KFeSe superconductor
Structural phase separation in AFeSe system has been studied
by different experimental techniques, however, it should be important to know
how the electronic uniformity is influenced, on which length scale the
electronic phases coexist, and what is their spatial distribution. Here, we
have used novel scanning photoelectron microscopy (SPEM) to study the
electronic phase separation in KFeSe, providing a direct
measurement of the topological spatial distribution of the different electronic
phases. The SPEM results reveal a peculiar interconnected conducting
filamentary phase that is embedded in the insulating texture. The filamentary
structure with a particular topological geometry could be important for the
high T superconductivity in the presence of a phase with a large magnetic
moment in AFeSe materials.Comment: 14 pages,3 figure
Important Roles of Te 5p and Ir 5d Spin-orbit Interactions on the Multi-band Electronic Structure of Triangular Lattice Superconductor Ir1-xPtxTe2
We report an angle-resolved photoemission spectroscopy (ARPES) study on a
triangular lattice superconductor IrPtTe in which the Ir-Ir
or Te-Te bond formation, the band Jahn-Teller effect, and the spin-orbit
interaction are cooperating and competing with one another. The Fermi surfaces
of the substituted system are qualitatively similar to the band structure
calculations for the undistorted IrTe with an upward chemical potential
shift due to electron doping. A combination of the ARPES and the band structure
calculations indicates that the Te spin-orbit interaction removes the
orbital degeneracy and induces type spin-orbit
coupling near the A point. The inner and outer Fermi surfaces are entangled by
the Te and Ir spin-orbit interactions which may provide exotic
superconductivity with singlet-triplet mixing.Comment: 10 pages, 4 figure
Three-Dimensional Fermi Surface of Overdoped La-Based Cuprates
We present a soft x-ray angle-resolved photoemission spectroscopy study of
the overdoped high-temperature superconductors LaSrCuO and
LaEuSrCuO. In-plane and out-of-plane components of
the Fermi surface are mapped by varying the photoemission angle and the
incident photon energy. No dispersion is observed along the nodal
direction, whereas a significant antinodal dispersion is identified.
Based on a tight-binding parametrization, we discuss the implications for the
density of states near the van-Hove singularity. Our results suggest that the
large electronic specific heat found in overdoped LaSrCuO can
not be assigned to the van-Hove singularity alone. We therefore propose quantum
criticality induced by a collapsing pseudogap phase as a plausible explanation
for observed enhancement of electronic specific heat
Concomitant Xeroderma pigmentosum and disseminated small plaque psoriasis: first case of an antinomic association
We present the case of an eighteen-year-old Caucasian white boy who was diagnosed with xeroderma pigmentosum type A at age 5 and who experienced over the past year disseminated small plaque psoriasis confirmed with skin punch biopsy. The psoriatic lesions were successfully treated with multipotent topical corticosteroids and systemic retinoids. To our knowledge, the association between psoriasis and xeroderma pigmentosum has not been previously reported and may be regarded as unlikely when considering the pathogenesis of both diseases
Electrochemical titrations and reaction time courses monitored in situ by magnetic circular dichroism spectroscopy
Magnetic circular dichroism (MCD) spectra, at ultraviolet–visible or near-infrared wavelengths (185–2000 nm), contain the same transitions observed in conventional absorbance spectroscopy, but their bisignate nature and more stringent selection rules provide greatly enhanced resolution. Thus, they have proved to be invaluable in the study of many transition metal-containing proteins. For mainly technical reasons, MCD has been limited almost exclusively to the measurement of static samples. But the ability to employ the resolving power of MCD to follow changes at transition metal sites would be a potentially significant advance. We describe here the development of a cuvette holder that allows reagent injection and sample mixing within the 50-mm-diameter ambient temperature bore of an energized superconducting solenoid. This has allowed us, for the first time, to monitor time-resolved MCD resulting from in situ chemical manipulation of a metalloprotein sample. Furthermore, we report the parallel development of an electrochemical cell using a three-electrode configuration with physically separated working and counter electrodes, allowing true potentiometric titration to be performed within the bore of the MCD solenoid
Evidence for a Square-Square Vortex Lattice Transition in a High-Tc Cuprate Superconductor
Using sound velocity and attenuation measurements in high magnetic fields, we identify a new transition in the vortex lattice state of La2−xSrxCuO4. The transition, observed in magnetic fields exceeding 35 T and temperatures far below zero field Tc, is detected in the compression modulus of the vortex lattice, at a doping level of x=p=0.17. Our theoretical analysis based on Eilenberger’s theory of the vortex lattice shows that the transition corresponds to the long-sought 45° rotation of the square vortex lattice, predicted to occur in d-wave superconductors near a van Hove singularity
Decoupling of Lattice and Orbital Degrees of Freedom in an Iron-Pnictide Superconductor
The interplay of structural and electronic phases in iron-based
superconductors is a central theme in the search for the superconducting
pairing mechanism. While electronic nematicity, defined as the breaking of
four-fold symmetry triggered by electronic degrees of freedom, is competing
with superconductivity, the effect of purely structural orthorhombic order is
unexplored. Here, using x-ray diffraction (XRD), we reveal a new structural
orthorhombic phase with an exceptionally high onset temperature
( K), which coexists with superconductivity
( K), in an electron-doped iron-pnictide superconductor far
from the underdoped region. Furthermore, our angle-resolved photoemission
spectroscopy (ARPES) measurements demonstrate the absence of electronic nematic
order as the driving mechanism, in contrast to other underdoped iron pnictides
where nematicity is commonly found. Our results establish a new, high
temperature phase in the phase diagram of iron-pnictide superconductors and
impose strong constraints for the modeling of their superconducting pairing
mechanism.Comment: SI available upon reques
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