Micro-Raman study of the role of pressure in mercury-based superconductors

Abstract

Understanding the role of pressure in increasing Tc is a crucial issue in mercury-based superconductors. We report on the effect of pressure on the Raman frequency () of the apical oxygen (OA) in Hg-OA-Cu bonds of HgBa2Can-1CunO2n+2+ superconductors. For both Hg-1201 and Hg-1223, (2/02)/P is found to be strongly correlated with Tc/P, where 0 is the frequency at ambient pressure. Together with our local-density approximation total-energy phonon study of the OA-A1g Raman mode, it is concluded that the change of the OA Raman frequency is due to the change in Hg-OA bond strength, which may be directly related to the charge transfer between the CuO2 planes and the Hg-O layers. © 1995 The American Physical Society.