Magnetic Excitations and their energy change available to Superconducting Condensation in Optimally Doped YBa$_2$Cu$_3$O$_{6.95}$

TL;DR

This study maps magnetic excitations in optimally doped YBa2Cu3O6.95 and finds that the change in magnetic exchange energy significantly exceeds the superconducting condensation energy, suggesting a magnetic origin for high-Tc superconductivity.

Contribution

It provides a comprehensive measurement of magnetic excitations and quantifies the magnetic exchange energy change, supporting its role as the driving force for superconductivity in YBa2Cu3O6.95.

Findings

Magnetic exchange energy change is about 15 times the condensation energy.

Magnetic excitations were extensively mapped across the full spectrum.

Results support magnetic interactions as the key mechanism for high-Tc superconductivity.

Abstract

Understanding the magnetic excitations in high-transition temperature (high-$T_c$) copper oxides is important because they may mediate the electron pairing for superconductivity. By determining the wavevector ({\bf Q}) and energy ($\hbar\omega$) dependence of the magnetic excitations, one can calculate the change in the exchange energy available to the superconducting condensation energy. For the high-$T_c$ superconductor YBa$_2$Cu$_3$O$_{6+x}$, the most prominent feature in the magnetic excitations is the resonance. Although the resonance has been suggested to contribute a major part of the superconducting condensation, the accuracy of such an estimation has been in doubt because the resonance is only a small portion of the total magnetic scattering. Here we report an extensive mapping of magnetic excitations for YBa$_2$Cu$_3$O$_{6.95}$ ($T_c\approx 93$ K). Using the absolute intensity measurements of the full spectra, we estimate the change in the magnetic exchange energy between the normal and superconducting states and find it to be about 15 times larger than the superconducting condensation energy. Our results thus indicate that the change in the magnetic exchange energy is large enough to provide the driving force for high-$T_c$ superconductivity in YBa$_2$Cu$_3$O$_{6.95}$.