Coexistence of Polaronic States and Superconductivity in Iron-Pnictide Compound Ba_2Ti_2Fe_2As_4O

The electronic structure of iron-pnictide compound superconductor Ba_2Ti_2Fe_2As_4O, which has metallic intermediate Ti_2O layers, is studied using angle-resolved photoemission spectroscopy. The Ti-related bands show a‘peak-dip-hump' line shape with two branches of dispersion associated with the polaronic states at temperatures below around 120 K. This change in the spectra occurs along with the resistivity anomaly that was not clearly understood in a previous study. Moreover, an energy gap induced by the superconducting proximity effect opens in the polaronic bands at temperatures below T_c(~21 K). Our study provides the spectroscopic evidence that superconductivity coexists with polarons in the same bands near the Fermi level, which provides a suitable platform to study interactions between charge, lattice and spin freedoms in a correlated system.     

Hybridization Effects Revealed by Angle-Resolved Photoemission Spectroscopy in Heavy-Fermion Ce_2IrIn_8

We utilize high-resolution resonant angle-resolved photoemission spectroscopy(ARPES)to study the band structure and hybridization effect of the heavy-fermion compound Ce_2 IrIn_8.We observe a nearly flat band at the binding energy of 7 meV below the coherent temperature T_(coh)～40 K,which characterizes the electrical resistance maximum and indicates the onset temperature of hybridization.However,the Fermi vector and the Fermi surface volume have little change around T_(coh),which challenges the widely believed evolution from a hightemperature small Fermi surface to a low-temperature large Fermi surface.Our experimental results of the band structure fit well with the density functional theory plus dynamic mean-field theory calculations.     

Electronic Structure of the Weak Topological Insulator Candidate Zintl Ba3Cd2Sb4

One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology.The existence of topological protected dissipationless surface state makes topological insulators great potential for applications and hotly studied.However,compared with the prosperity of strong topological insulators,theoretical predicted candidate materials and experimental confirmation of weak topological insulators(WTIs) are both extremely rare.By com...