Theoretical aspects of the study on the new bismuth chalcogenide based superconductors

Abstract

We review theoretical aspects of the studies on the recently discovered BiCh 2 (Ch=chalcogen) based superconductors. We first focus on the electronic band structure, the Fermi surface and their correlation with the lattice structure. We then discuss the phonon features and the issue of the lattice instability. Finally, we survey the phonon-mediated as well as the unconventional pairing mechanisms that have been proposed so far.

Intrinsic Phase Diagram of Superconductivity in the BiCh2-Based System Without In-Plane Disorder

“…These results suggest that the metallic conductivity can be induced by electron doping in BiCh2-based compounds with less in-plane disorder, as expected from the band structure [7,8].…”

“…For typical REO1-xFxBiS2 [2,[16][17][18][19]35], a metallic behavior is not observed in resistivity-temperature (-T) characteristics, and a semiconducting-like behavior is observed, in spite of carrier doping by F substitutions. In contrast, for LaO1-xFxBiSSe, a metallic behavior is observed in the -T measurements for all electron-doped samples (x = 0.05-0.5).These results suggest that the metallic conductivity can be induced by electron doping in BiCh2-based compounds with less in-plane disorder, as expected from the band structure [7,8].For all electron doped samples, a sharp superconducting transition was observed. On the transition temperature, we estimated Tc zero as the temperature where resistivity becomes zero.…”

“…On the transition temperature, we estimated Tc zero as the temperature where resistivity becomes zero. [7,8]. In addition, it has been experimentally confirmed by angle-resolved photoemisison spectroscopy (ARPES) [36][37][38].…”

“…Recently, Morice et al proposed that a 2 weak-coupling electron-phonon mechanism cannot explain the emerging Tc, as high as 11 K, in the BiCh2-based systems, from first principle calculations [6]. Therefore, full understandings of the basic characteristics of the superconductivity in the BiCh2-based system are crucial.The parent phase of the BiCh2-based superconductor is a band insulator [1,7,8]. On the basis of the calculated band structure, electrons carriers are doped into the bands mainly composed of Bi-6px and Bi-6py components.…”

“…The parent phase of the BiCh2-based superconductor is a band insulator [1,7,8]. On the basis of the calculated band structure, electrons carriers are doped into the bands mainly composed of Bi-6px and Bi-6py components.…”