Electronic structure and excitonic-enhanced superconducting mechanism in YBa2Cu

First-Principles Simulation of Dielectric Function in Biomolecules

The dielectric spectra of complex biomolecules reflect the molecular heterogeneity of the proteins and are particularly important for the calculations of electrostatic (Coulomb) and electrodynamic (van der Waals) interactions in protein physics. The dielectric response of the proteins can be decomposed into different components depending on the size, structure, composition, locality, and environment of the protein in general. We present a new robust simulation method anchored in rigorous ab initio quantum mechanical calculations of explicit atomistic models, without any indeterminate parameters to compute and gain insight into the dielectric spectra of small proteins under different conditions. We implement this methodology to a polypeptide RGD-4C (1FUV) in different environments, and the SD1 domain in the spike protein of SARS-COV-2. Two peaks at 5.2-5.7 eV and 14.4-15.2 eV in the dielectric absorption spectra are observed for 1FUV and SD1 in vacuum as well as in their solvated and salted models.

Laser Raman evidence for enhanced electron–phonon coupling in a Y–Ba–Cu-oxide superconductor below T c : an application of the maximum entropy method of spectral estimation

This report discusses Raman spectra, recorded at various temperatures from 4.2 to 100 K, of the high-temperature oxidic superconducting material YBa 2 Cu 3 O 7 ( T c = 90 K). By utilizing the maximum entropy method (MEM) the Raman bands were separated from the luminescent background. Our results clearly demonstrate significant enhancement of Raman activity, indicative of strong electron–phonon coupling, below the superconducting transition temperature, together with low-temperature ordering of the copper ions in their lattice sites. Several bands may also be attributed to defects of the oxygen lattice, some of which disappear as the reordering occurs.