2,103 research outputs found
Temperature-dependent Raman scattering of DyScO3 and GdScO3 single crystals
We report a temperature-dependent Raman scattering investigation of DyScO3
and GdScO3 single crystals from room temperature up to 1200 {\deg}C. With
increasing temperature, all modes decrease monotonously in wavenumber without
anomaly, which attests the absence of a structural phase transition. The high
temperature spectral signature and extrapolation of band positions to higher
temperatures suggest a decreasing orthorhombic distortion towards the ideal
cubic structure. Our study indicates that this orthorhombic-to-cubic phase
transition is close to or higher than the melting point of both rare-earth
scandates (\approx 2100 {\deg}C), which might exclude the possibility of the
experimental observation of such a phase transition before melting. The
temperature-dependent shift of Raman phonons is also discussed in the context
of thermal expansion
Raman scattering of perovskite SmScO3 and NdScO3 single crystals
We report an investigation of perovskite-type SmScO3 and NdScO3 single
crystals by Raman scattering in various scattering configurations and at
different wavelengths. The reported Raman spectra, together with the phonon
mode assignment, set the basis for the use of Raman scattering for the
structural investigation of RE-scandates. Further to the phonon signature, a
fluorescence signal is observed for both scandates and is particularly intense
for NdScO3 when using a 488 or 514 nm excitation line. A comparison of Raman
spectra of RE-scandates with literature Raman data on orthorhombic perovskites
shows that the frequency of particular modes scales with the orthorhombic
distortion in terms of the rotation (or tilt) angle of the ScO6 octahedr
Phonon Raman scattering of perovskite LaNiO3 thin films
We report an investigation of perovskite-type LaNiO3 thin films by Raman
scattering in both various scattering configurations and as a function of
temperature. The room-temperature Raman spectra and the associated phonon mode
assignment provide reference data for phonon calculations and for the use of
Raman scattering for structural investigations of LaNiO3, namely the effect of
strain in thin films or heterostructures. The temperature-dependent Raman
spectra from 80 to 900 K are characterized by the softening of the rotational
A1g mode, which suggest a decreasing rhombohedral distortion towards the ideal
cubic structure with increasing temperature
Theoretical study of impurity-induced magnetism in FeSe
Experimental evidence suggests that FeSe is close to a magnetic instability,
and recent scanning tunneling microscopy (STM) measurements on FeSe multilayer
films have revealed stripe order locally pinned near defect sites. Motivated by
these findings, we perform a theoretical study of locally induced magnetic
order near nonmagnetic impurities in a model relevant for FeSe. We find that
relatively weak repulsive impurities indeed are capable of generating
short-range magnetism, and explain the driving mechanism for the local order by
resonant eg-orbital states. In addition, we investigate the importance of
orbital-selective self-energy effects relevant for Hund's metals, and show how
the structure of the induced magnetization cloud gets modified by orbital
selectivity. Finally, we make concrete connection to STM measurements of
iron-based superconductors by symmetry arguments of the induced magnetic order,
and the basic properties of the Fe Wannier functions relevant for tunneling
spectroscopy.Comment: 10 pages, 4 figure
Temperature-dependent Raman scattering of KTa1-xNbxO3 thin films
We report a Raman scattering investigation of KTa1-xNbxO3 (x = 0.35, 0.5)
thin films deposited on MgO and LaAlO3 as a function of temperature. The
observed phase sequence in the range from 90 K to 720 K is similar to the
structural phase transitions of the end-member material KNbO3. Although similar
in the phase sequence, the actual temperatures observed for phase transition
temperatures are significantly different from those observed in the literature
for bulk samples. Namely, the tetragonal (ferroelectric) to cubic
(paraelectric) phase transition is up to 50 K higher in the films when compared
to bulk samples. This enhanced ferroelectricity is attributed to biaxial strain
in the investigated thin films
Robustness of Quasiparticle Interference Test for Sign-changing Gaps in Multiband Superconductors
Recently, a test for a sign-changing gap function in a candidate multiband
unconventional superconductor involving quasiparticle interference data was
proposed. The test was based on the antisymmetric, Fourier transformed
conductance maps integrated over a range of momenta corresponding to
interband processes, which was argued to display a particular resonant form,
provided the gaps changed sign between the Fermi surface sheets connected by
. The calculation was performed for a single impurity, however, raising
the question of how robust this measure is as a test of sign-changing pairing
in a realistic system with many impurities. Here we reproduce the results of
the previous work within a model with two distinct Fermi surface sheets, and
show explicitly that the previous result, while exact for a single nonmagnetic
scatterer and also in the limit of a dense set of random impurities, can be
difficult to implement for a few dilute impurities. In this case, however,
appropriate isolation of a single impurity is sufficient to recover the
expected result, allowing a robust statement about the gap signs to be made.Comment: 9 pages, 12 figure
Model of Electronic Structure and Superconductivity in Orbitally Ordered FeSe
We provide a band structure with low-energy properties consistent with recent
photoemission and quantum oscillations measurements on FeSe, assuming
mean-field like s and/or d-wave orbital ordering at the structural transition.
We show how the resulting model provides a consistent explanation of the
temperature dependence of the measured Knight shift and the spin-relaxation
rate. Furthermore, the superconducting gap structure obtained from spin
fluctuation theory exhibits nodes on the electron pockets, consistent with the
'V'-shaped density of states obtained by tunneling spectroscopy on this
material, and the temperature dependence of the London penetration depth. Our
studies prove that the recent experimental observations of the electronic
properties of FeSe are consistent with orbital order, but leave open the
microscopic origin of the unusual band structure of this material.Comment: 12 pages, 15 figures, T.B hopping error corrected, d-wave orbital
order added, real space hoppings included in tex fil
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