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

In the series R2PdSi3, Nd2PdSi3 is 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 4f localization. Here, we have studied the electronic structure of single crystalline Nd2PdSi3 employing high resolution photoemission spectroscopy and ab initio band 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 4f hybridization, the states near the Fermi level are found to be dominated by hybridized Nd 4f-Si 3p states, which is possibly responsible for the ferromagnetism in Nd compound. Nd 3d core 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 4f states with the conduction electrons possibly responsible for the exoticity of this compound.

Complex spectral evolution in a BCS superconductor, ZrB12.

We investigate the electronic structure of a complex conventional superconductor, ZrB12 employing high resolution photoemission spectroscopy and ab initio band structure calculations. The experimental valence band spectra could be described reasonably well within the local density approximation. Energy bands close to the Fermi level possess t2g symmetry and the Fermi level is found to be in the proximity of quantum fluctuation regime. The spectral lineshape in the high resolution spectra is complex exhibiting signature of a deviation from Fermi liquid behavior. A dip at the Fermi level emerges above the superconducting transition temperature that gradually grows with the decrease in temperature. The spectral simulation of the dip and spectral lineshape based on a phenomenological self energy suggests finite electron pair lifetime and a pseudogap above the superconducting transition temperature.

Electronic structure of EuFe2As2.

Employing high resolution photoemission spectroscopy, we studied the temperature evolution of the electronic structure of EuFe2As2, a unique pnictide, where antiferromagnetism of the Eu layer survives within the superconducting phase due to 'FeAs' layers, achieved via substitution and/or pressure. High energy and angle resolution helped to reveal the signature of peak-dip features, having significant p orbital character and spin density wave transition induced band folding in the electronic structure. A significant spectral weight redistribution is observed below 20 K manifesting the influence of antiferromagnetic order on the conduction electrons.