Unusual spectral renormalization in hexaborides

Electronic structure studies on single crystalline Nd2PdSi3, an exotic Nd-based intermetallic: evidence for Nd 4fhybridization

In the series R2PdSi3, Nd2PdSi3is an anomalous compound in the sense that it exhibits ferromagnetic order unlike other members in this family. The magnetic ordering temperature is also unusually high compared to the expected value for a Nd-based system, assuming 4flocalization. Here, we have studied the electronic structure of single crystalline Nd2PdSi3employing high resolution photoemission spectroscopy andab initioband structure calculations. Theoretical results obtained for the effective on-site Coulomb energy of 6 eV corroborate well with the experimental valence band spectra. While there is significant Pd 4d-Nd 4fhybridization, the states near the Fermi level are found to be dominated by hybridized Nd 4f-Si 3pstates, which is possibly responsible for the ferromagnetism in Nd compound. Nd 3dcore level spectrum exhibits multiple features manifesting strong final state effects due to electron correlation, charge transfer and collective excitations. These results serve as one of the rare demonstrations of hybridization of Nd 4fstates with the conduction electrons possibly responsible for the exoticity of this compound.

Three-dimensional bulk electronic structure of the Kondo lattice CeIn3 revealed by photoemission

We show the three-dimensional electronic structure of the Kondo lattice CeIn₃ using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn₃ by photoemission. The Fermi surface has a complicated hole pocket centred at the Γ-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn₃, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical mean-field theory. Those results illustrate that the f electrons of CeIn₃, which is the parent material of CeMIn₅ compounds, are closer to the localized description than the layered CeMIn₅ compounds.

The unexpected absence of Kondo resonance in the photoemission spectrum of CeAl2

We study the temperature dependent Ce 4f spectral evolution of a well known Kondo system, CeAl2, for a range extending beyond 2 eV below the Fermi level, using photoemission spectroscopy. Interestingly, the spectral evolution is inconsistent with the predictions of the many-body spectral function calculations corresponding to the Kondo resonance interpretation of the screened Ce 4f photoemission features. In order to explain our spectral evolution we propose the phenomenon of collapse of the Kondo singlet wavefunction upon photoelectron kinetic energy measurement. Our proposal suggests that the screened final states in photoemission spectroscopy are not quantum states.