Magnetic Dynamics in Underdoped YBCO: Direct Observation of a Superconducting Gap

TL;DR

This study uses spectrometry to observe spin excitations in underdoped YBCO, revealing a reduced resonance energy and a superconducting gap signature, advancing understanding of magnetic dynamics in high-temperature superconductors.

Contribution

It provides the first direct observation of a superconducting gap in underdoped YBCO through magnetic excitation measurements.

Findings

Resonance energy shifts from 41 meV to 34.8 meV in underdoped YBCO.

Superconducting gap signature observed in normal state spin excitations.

Magnetic fluctuations are suppressed at energies around the resonance.

Abstract

Polarized and unpolarized triple-axis spectrometry has been used to study an underdoped YBa_2Cu3O6.6. Our results indicate that spin excitations in the superconducting state are essentially the same as those in the fully doped material except that the unusual 41 meV resonance is observed at 34.8 meV. The normal state spin excitations are characterized by a weakly energy-dependent continuum whose temperature dependence shows the clear signature of a superconducting gap at Tc. The enhancement at the resonance is accompanied by a suppression of magnetic fluctuations at both higher and lower energies.