133 research outputs found
Origin of charge density wave formation in insulators from a high resolution photoemission study of BaIrO3
We investigate the origin of charge density wave (CDW) formation in
insulators by studying BaIrO3 using high resolution (1.4 meV) photoemission
spectroscopy. The spectra reveal the existence of localized density of states
at the Fermi level in the vicinity of room temperature. These localized states
are found to vanish as the temperature is lowered thereby, opening a soft gap
at the Fermi level, as a consequence of CDW transition. In addition, the energy
dependence of the spectral density of states reveals the importance of magnetic
interactions, rather than well-known Coulomb repulsion effect, in determining
the electronic structure thereby implying a close relationship between
ferromagnetism and CDW observed in this compound. Also, Ba core level spectra
surprisingly exhibit an unusual behavior prior to CDW transition.Comment: 4 pages, 4 figures. To appear in Physical Review Letter
Observation of pseudogap in MgB2
Pseudogap phase in superconductors continues to be an outstanding puzzle that
differentiates unconventional superconductors from the conventional ones
(BCS-superconductors). Employing high resolution photoemission spectroscopy on
a highly dense conventional superconductor, MgB2, we discover an interesting
scenario. While the spectral evolution close to the Fermi energy is
commensurate to BCS descriptions as expected, the spectra in the wider energy
range reveal emergence of a pseudogap much above the superconducting transition
temperature indicating apparent departure from the BCS scenario. The energy
scale of the pseudogap is comparable to the energy of E2g phonon mode
responsible for superconductivity in MgB2 and the pseudogap can be attributed
to the effect of electron-phonon coupling on the electronic structure. These
results reveal a scenario of the emergence of the superconducting gap within an
electron-phonon coupling induced pseudogap.Comment: 4 figure
Importance of conduction electron correlation in a Kondo lattice, Ce2CoSi3
Kondo systems are usually described by the interaction of strong correlation
induced local moment with the highly itinerant conduction electrons. Here, we
study the role of electron correlations among conduction electrons in the
electronic structure of a Kondo lattice compound, CeCoSi, using high
resolution photoemission spectroscopy and {\it ab initio} band structure
calculations, where Co 3 electrons contribute in the conduction band. High
energy resolution employed in the measurements helped to reveal signature of Ce
4 states derived Kondo resonance feature at the Fermi level and dominance of
Co 3 contributions at higher binding energies in the conduction band. The
line shape of the experimental Co 3 band is found to be significantly
different from that obtained from the band structure calculations within the
local density approximations, LDA. Consideration of electron-electron Coulomb
repulsion, among Co 3 electrons within the LDA+ method leads to a
better representation of experimental results. Signature of electron
correlation induced satellite feature is also observed in the Co 2 core
level spectrum. These results clearly demonstrate the importance of the
electron correlation among conduction electrons in deriving the microscopic
description of such Kondo systems.Comment: 6 figure
Observation of particle hole asymmetry and phonon excitations in non-Fermi liquid systems: A high-resolution photoemission study of ruthenates
We investigate the temperature evolution of the electronic states in the
vicinity of the Fermi level of a non-Fermi liquid (NFL) system, CaRuO3 using
ultra high-resolution photoemission spectroscopy; isostructural SrRuO3
exhibiting Fermi liquid behavior despite similar electron interaction
parameters as that of CaRuO3, is used as a reference. High-energy resolution in
this study helps to reveal particle-hole asymmetry in the excitation spectra of
CaRuO3 in contrast to that in SrRuO3. In addition, we observe signature of
phonon excitations in the photoemission spectra of CaRuO3 at finite
temperatures while these are weak in SrRuO3.Comment: 4 pages including 3 figure
Evolution of the Kondo resonance feature and its relationship to spin-orbit coupling across the quantum critical point in Ce2Rh{1-x}CoxSi3
We investigate the evolution of the electronic structure of Ce2Rh{1-x}CoxSi3
as a function of x employing high resolution photoemission spectroscopy. Co
substitution at the Rh sites in antiferromagnetic Ce2RhSi3 leads to a
transition from an antiferromagnetic system to a Kondo system, Ce2CoSi3 via the
Quantum Critical Point (QCP). High resolution photoemission spectra reveal
distinct signature of the Kondo resonance feature (KRF) and its spin orbit
split component (SOC) in the whole composition range indicating finite Kondo
temperature scale at the quantum critical point. We observe that the intensity
ratio of the Kondo resonance feature and its spin orbit split component,
KRF/SOC gradually increases with the decrease in temperature in the strong
hybridization limit. The scenario gets reversed if the Kondo temperature
becomes lower than the magnetic ordering temperature. While finite Kondo
temperature within the magnetically ordered phase indicates applicability of
the spin density wave picture at the approach to QCP, the dominant temperature
dependence of the spin-orbit coupled feature suggests importance of spin-orbit
interactions in this regime.Comment: 6 figure
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