Douglas J. Scalapino

TL;DR: In this paper, a t x-t y-J x-J y model was proposed to describe stripe formation and orientation in LTT-phase cuprates, where the tilt pattern of the CuO6 octahedra in the low-temperature tetragonal phase of the cuprate superconductors leads to planar anisotropies for the exchange coupling and hopping integrals.

TL;DR: In this paper, a two-band model that reproduces the topology of the LDA Fermi surface and exhibits both ferromagnetic and spin-density wave fluctuations is presented.

TL;DR: In this article, the energy and temperature dependence of the on-shell nodal quasiparticle scattering rate in superconducting state was studied, which determined the momentum width of the angular-resolved photoemission spectroscopy (ARPES) momentum distribution curves.

Abstract: We present an analysis of the Raman spectra of optimally doped ${\rm Ba_{0.6}K_{0.4}Fe_2As_2}$ based on LDA band structure calculations and the subsequent estimation of effective Raman vertices. Experimentally a narrow, emergent mode appears in the $B_{1g}$ ($d_{x^2-y^2}$) Raman spectra only below $T_c$, well into the superconducting state and at an energy below twice the energy gap on the electron Fermi surface sheets. The Raman spectra can be reproduced quantitatively with estimates for the magnitude and momentum space structure of the s$_{+-}$ pairing gap on different Fermi surface sheets, as well as the identification of the emergent sharp feature as a Bardasis-Schrieffer exciton, formed as a Cooper pair bound state in a subdominant $d_{x^2-y^2}$ channel. The binding energy of the exciton relative to the gap edge shows that the coupling strength in this subdominant $d_{x^2-y^2}$ channel is as strong as 60% of that in the dominant $s_{+-}$ channel. This result suggests that $d_{x^2-y^2}$ may be the dominant pairing symmetry in Fe-based sperconductors which lack central hole bands.

TL;DR: In this paper, the authors investigated the nature of the mathematical singularities in the tunnel characteristic associated with the Van Hove and Phillips singularities, using the Eliashberg gap equation.