Electronic structure of single-crystallineNdO0.5F0.5BiS2studied by angle-resolved photoemission spectroscopy

Abstract

BiS 2 is a new layered superconductor. We have studied the low-lying electronic structure of a single crystalline NdO 0.5 F 0.5 BiS 2 superconductor, whose superconducting transition temperature is 4.87K, with angle-resolved photoemission spectroscopy. The Fermi surface consists of two small electron pockets around the X point and shows little warping along the k z direction. Our results demonstrate the multi-band and twodimensional nature of the electronic structure. The good agreement between the photoemission data and the band calculations gives the renormalization factor of 1, indicating the rather weak electron correlations in this material. Moreover, we found that the actual electron doping level and Fermi surface size are much smaller than what are expected from the nominal composition, which could be largely explained by the bismuth dificiency. The small Fermi pocket size and the weak electron correlations found here put strong constraints on theory, and suggest that the BiS 2 -based superconductors could be conventional BCS superconductors mediated by the electron-phonon coupling.

Pressure-tuned enhancement of superconductivity and change of ground state properties inLaO0.5F0.5BiSe2single crystals

“…In addition, possible triplet paring and weak topological superconductivity were suggested based on renormalization-group numerical calculation [16], but this mechanism is still much debated. Moreover, the experiments on the NdO 0.5 F 0.5 BiS 2 single crystals also reveal interesting discoveries concerning the SC mechanisms in this new system [17][18][19][20][21].…”

Electronic structure ofLaO1−xFxBiSe2(x=Saini1, Ootsuki2, Paris3 et al. 2014Phys. Rev. B160130View full textAdd to dashboardCite

“…Very recently, an x-ray photoemission spectroscopy (XPS) study on LaO 1−x F x BiS 2 [24] and angle-resolved photoemission spectroscopy (ARPES) studies on NdO 1−x F x BiS 2 [25,26] have revealed that there is an overall agreement between the band-structure calculations and the experimental band dispersions and Fermi surfaces. However, the XPS spectral weight near the Fermi level (E F ) appears to disagree with the calculations, and the disagreement emphasizes the importance of the electron-electron and/or electron-phonon interactions [24].…”

“…The possible polaron correlation effect is also suggested by the peculiar temperature dependence reported in the ARPES study by Zeng et al [25]. On the other hand, the ARPES study by Ye et al indicates rather weak electron correlations [26]. In addition, an optical spectroscopy study by Wang et al excludes strong electron/polaron correlations [27].…”

“…Interestingly, nanoscale stripe patterns have been observed at the cleaved surface of NdO 1−x F x BiS 2 by means of scanning tunneling microscopy [28], indicating that the cleaved surface of REO 1−x F x BiS 2 may suffer from structural and electronic reconstructions. The disagreement between the two ARPES studies [25,26] would be related to a kind of microscale phase separation (or microscale coexisting domains) between two phases, with and without the nanoscale reconstruction of the cleaved surfaces. Another serious problem is that the area of the observed Fermi surfaces is much smaller than that expected from the amount of the F substitution in the previous works on the BiS 2 system [25,26].…”

The Role of Nanoscale Atomic Fluctuations in the Superconducting Mechanism of the BiS2 Superconductors

“…The maximum T c that can be achieved in the weak coupling limit is ∼20 K. [6,14] The BiS 2 systems are phononic superconductors [15,16] with an electron-phonon coupling constant ∼0.8 indicating strong coupling. [17,18] The experimental results from magnetic penetration depth, muon spin rotation spectroscopy and angle-resolved photoemission spectroscopy (ARPES) also support conventional BCS superconductivity mediated by electron phonon coupling [19][20][21]. However, scanning tunneling spectroscopy (STS) measurements show two superconducting gaps exist in NdO 1−x F x BiS 2 .…”