9 research outputs found
Preparation, Characterization and electronic structure of Ti-doped BiSe
We report the preparation of high-quality single crystal of BiSe, a
well-known topological insulator and its Ti-doped compositions using Bridgeman
technique. Prepared single crystals were characterized by x-ray diffraction
(XRD) to check the crystalline structure and energy dispersive analysis of
x-rays for composition analysis. The XRD data of Ti-doped compounds show a
small shift with respect to normal BiSe indicating changes in the
lattice parameters while the structure type remained unchanged; this also
establishes that Ti goes to the intended substitution sites. All the above
analysis establishes successful preparation of these crystals with high quality
using Bridgman technique. We carried out x-ray photo-emission spectroscopy to
study the composition via investigating the core level spectra. BiSe
spectra exhibit sharp and distinct features for the core levels and absence of
impurity features. The core level spectra of the Ti-doped sample exhibit
distinct signal due to Ti core levels. The analysis of the spectral features
reveal signature of plasmon excitation and final state satellites; a signature
of finite electron correlation effect in the electronic structure.Comment: Proceedings of DAE SSPS 201
Layer-resolved electronic behavior in a Kondo lattice system, CeAgAs2
We investigate the electronic structure of an antiferromagnetic Kondo lattice
system CeAgAs2 employing hard x-ray photoemission spectroscopy. CeAgAs2, an
orthorhombic variant of HfCuSi2 structure, exhibits antiferromagnetic ground
state, Kondo like resistivity upturn and compensation of magnetic moments at
low temperatures. The photoemission spectra obtained at different photon
energies suggest termination of the cleaved surface at cis-trans-As layers. The
depth-resolved data show significant surface-bulk differences in the As and Ce
core level spectra. The As 2p bulk spectrum shows distinct two peaks
corresponding to two different As layers. The peak at higher binding energy
correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce
layers. The As layers between Ce and Ag-layers possess close to trivalent
configuration due to strong hybridization with the neighboring atoms and the
corresponding feature appear at lower binding energy. Ce 3d core level spectra
show multiple features reflecting strong Ce-As hybridization and strong
correlation. Intense f0 peak is observed in the surface spectrum while it is
insignificant in the bulk. In addition, we observe a features at binding energy
lower than the well-screened feature indicating the presence of additional
interactions. This feature becomes more intense in the bulk spectra suggesting
it to be a bulk property. Increase in temperature leads to a spectral weight
transfer to higher binding energies in the core level spectra and a depletion
of spectral intensity at the Fermi level as expected in a Kondo material. These
results reveal interesting surface-bulk differences, complex interplay of
intra- and inter-layer covalency, and electron correlation in the electronic
structure of this novel Kondo lattice system
Complexity in the hybridization physics revealed by depth-resolved photoemission spectroscopy of single crystalline novel Kondo lattice systems, CeCuX (X = As/Sb)
We investigate the electronic structure of a novel Kondo lattice system
CeCuX2 (X = As/Sb) employing high resolution depth-resolved photoemission
spectroscopy of high quality single crystalline materials. CeCuSb2 and CeCuAs2
represent different regimes of the Doniach phase diagram exhibiting Kondo-like
transport properties and CeCuSb2 is antiferromagnetic (TN ~ 6.9 K) while
CeCuAs does not show long-range magnetic order down to the lowest
temperature studied. In this study, samples were cleaved in ultrahigh vacuum
before the photoemission measurements and the spectra at different surface
sensitivity establish the pnictogen layer having squarenet structure as the
terminated surface which is weakly bound to the other layers. Cu 2p and As 2p
spectra show spin-orbit split sharp peaks along with features due to plasmon
excitations. Ce 3d spectra exhibit multiple features due to the hybridization
of the Ce 4f/5d states with the valence states. While overall lineshape of the
bulk spectral functions look similar in both the cases, the surface spectra are
very different; the surface-bulk difference is significantly weaker in CeCuAs2
compared to that observed in CeCuSb2. A distinct low binding energy peak is
observed in the Ce 3d spectra akin to the scenario observed in cuprates and
manganites due to the Zhang-Rice singlets and/or high degree of itineracy of
the conduction holes. The valence band spectra of CeCuSb manifest highly
metallic phase. In CeCuAs2, intensity at the Fermi level is significantly small
suggesting a pseudogap-type behavior. These results bring out an interesting
scenario emphasizing the importance and subtlety of hybridization physics
underlying the exoticity of this novel Kondo system
Electronic structure of a Kondo lattice system CeCuAs
We study the electronic properties of a Ce-based Kondo material, CeCuAs employing high-resolution hard x-ray photoemission spectroscopy. The measurements were done with different photon energies to probe the surface-bulk differences of the electronic structure. Experimental results show significant difference in the hybridization physics for the surface and bulk electronic structures indicating different Ce valency at the surface compared to the bulk. Surface termination appears to play an important role in the correlation physics of this system. In addition, the experimental spectra show loss features due to plasmon excitations. These results bring out complexity of this novel Kondo lattice system that does not show magnetic order down to the lowest temperature studied and have significantly different surface-bulk properties
Giant spectral renormalization and complex hybridization physics in the Kondo lattice system CeCuSb
We investigate the electronic structure of a Kondo lattice system, CeCuSb exhibiting significant mass enhancement and Kondo-type behavior. We observe multiple features in the hard x-ray photoemission spectra of Ce core levels due to strong final-state effects. The depth-resolved data exhibit a significant change in relative intensity of the features with the surface sensitivity of the probe. The extracted surface and bulk spectral functions are different and exhibit a Kondo-like feature at higher binding energies in addition to the well and poorly screened features. The core-level spectra of Sb exhibit huge and complex changes as a function of the surface sensitivity of the technique. The analysis of the experimental data suggests that the two nonequivalent Sb sites possess different electronic structures and in each category, the Sb layers close to the surface are different from the bulk ones. An increase in temperature influences the Ce-Sb hybridization significantly. The plasmon–excitation-induced loss features are also observed in all core-level spectra. All these results reveal the importance of Ce-Sb hybridizations and indicate that the complex renormalization of Ce-Sb hybridization may be the reason for the exotic electronic properties of this system
Layer-resolved electronic behavior in a Kondo lattice system, CeAgAs
We investigate the electronic structure of an antiferromagnetic Kondo lattice system CeAgAs employing hard x-ray photoemission spectroscopy. CeAgAs, an orthorhombic variant of HfCuSi structure, exhibits antiferromagnetic ground state, Kondo like resistivity upturn and compensation of magnetic moments at low temperatures. The photoemission spectra obtained at different photon energies suggest termination of the cleaved surface at cis-trans-As layers. The depth-resolved data show significant surface-bulk differences in the As and Ce core level spectra. The As 2p bulk spectrum shows distinct two peaks corresponding to two different As layers. The peak at higher binding energy correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce layers. The As layers between Ce and Ag-layers possess close to trivalent configuration due to strong hybridization with the neighboring atoms and the corresponding feature appear at lower binding energy. Ce 3d core level spectra show multiple features reflecting strong Ce-As hybridization and strong correlation. Intense f peak is observed in the surface spectrum while it is insignificant in the bulk. In addition, we observe a features at binding energy lower than the well-screened feature indicating the presence of additional interactions. This feature becomes more intense in the bulk spectra suggesting it to be a bulk property. Increase in temperature leads to a spectral weight transfer to higher binding energies in the core level spectra and a depletion of spectral intensity at the Fermi level as expected in a Kondo material. These results reveal interesting surface-bulk differences, complex interplay of intra- and inter-layer covalency, and electron correlation in the electronic structure of this novel Kondo lattice system
Emergence of well-screened states in a superconducting material of the family
Coupling among conduction electrons (e.g., Zhang-Rice singlet) are often manifested in the core level spectra of exotic materials such as cuprate superconductors, manganites, etc. These states are believed to play key roles in the ground state properties and appear as low binding energy features. To explore such possibilities in the Fe-based systems, we study the core level spectra of a superconductor CaFeCoAs (CaCo122) in the CaFeAs (Ca122) family employing high-resolution hard x-ray photoemission spectroscopy. While As core levels show almost no change with doping and cooling, the Ca 2p peak of CaCo122 shows reduced surface contribution relative to Ca122 and a gradual shift of the peak position towards lower binding energies with cooling. In addition, we discover the emergence of a feature at the lower binding energy side of the well-screened Fe 2p signal in CaCo122. The intensity of this feature grows with cooling and indicates additional channels to screen the core holes. The evolution of this feature in the superconducting composition and its absence in the parent compound suggests relevance of the underlying interactions in the ground state properties of this class of materials. These results reveal another dimension in the studies of Fe-based superconductors and the importance of such states in the unconventional superconductivity in general