Crystal structure, lattice vibrations, and superconductivity of LaO1−xFxBiS2

Charge Fluctuations in the NdO1−xFxBiS2 Superconductors

“…The fitting of the diffraction pattern with the model calculated using The NOMAD is a medium-range resolution instrument ( ∆d d ∼0.8%) [19] and within this resolution, no Bragg peak broadening is observed unlike the case of high pressure annealed LaO 1−x F x BiS 2 in which (00l) peaks were severely compromised. [20,21] The diffraction pattern can be fit well with the P4/nmm symmetry for both superconducting and nonsuperconducting compositions. As a function of x, the c/a ratio decreases from c/a=3.4087 for x =0.2 and c/a=3.3813 for x =0.4 which is due to the a lattice constant expansion as shown in Fig.…”

Unconventional Superconductivity in the BiS2 -Based Layered Superconductor NdO0.71Ota1, Okazaki2, Yamamoto3 et al. 2017Phys. Rev. Lett.

“…However, recent neutron scattering experiments have indicated that the electron-phonon coupling is much weaker than expected from the above scenario [11], and suggested the importance of charge fluctuations to superconductivity in BiS 2 -based superconductors [12]. In addition, a large 2∆/k B T c suggests that the pairing mechanism is unconventional [13,14] and theoretical studies have suggested unconventional superconducting (SC) pairing mechanisms on the basis of calculations that assume superconductivity driven purely by electronelectron coupling [10,[15][16][17][18].…”

“Checkerboard Stripe” Electronic State on Cleaved Surface of NdO0.7F0.3BiS2 Probed by Scanning Tunneling Microscopy

“…Some of them have proposed that an unstable phonon at q = (q, q, 0) corresponding to the Fermi surface nesting vector causes a CDW instability 29,30 . How the SC is related to this Fermi surface nesting has been argued vigorously [28][29][30][31][32][33][34][35] . Meanwhile, the symmetry of the superconducting gap has also been investigated theoretically and experimentally.…”