Evolution of Magnetic and Superconducting Fluctuations with Doping of High-Tc Superconductors

TL;DR

This study investigates how magnetic and superconducting fluctuations evolve with doping in high-Tc cuprate superconductors using electronic Raman scattering, revealing persistent antiferromagnetic correlations and the emergence of coherence leading to superconductivity.

Contribution

It provides new insights into the evolution of magnetic and superconducting fluctuations with doping, highlighting the role of incoherent quasiparticles and the formation of a coherent state.

Findings

Persistent antiferromagnetic correlations in underdoped samples

Observation of a sharp Raman resonance above T_c

Development of a coherent state with cooling leading to superconductivity

Abstract

Electronic Raman scattering from high- and low-energy excitations was studied as a function of temperature, extent of hole doping, and energy of the incident photons in Bi_2Sr_2CaCu_2O_{8 \pm \delta} superconductors. For underdoped superconductors, short range antiferromagnetic (AF) correlations were found to persist with hole doping, and doped single holes were found to be incoherent in the AF environment. Above the superconducting (SC) transition temperature T_c, the system exhibits a sharp Raman resonance of B_{1g} symmetry and energy of 75 meV and a pseudogap for electron-hole excitations below 75 meV, a manifestation of a partially coherent state forming from doped incoherent quasi particles. The occupancy of the coherent state increases with cooling until phase ordering at T_c produces a global SC state.