NMR evidence for Friedel-like oscillations in the CuO chains of ortho-II YBa$_2$Cu$_3$O$_{6.5}$

TL;DR

This study uses NMR to reveal that CuO chains in ortho-II YBa2Cu3O6.5 exhibit Friedel-like oscillations, indicating static spin and charge density variations linked to chain ends, differing from typical density wave transitions.

Contribution

It provides direct NMR evidence for Friedel-like oscillations in CuO chains, a novel insight into their static spin and charge density behavior in YBCO6.5.

Findings

Line broadening increases with cooling, indicating static oscillations.

Oscillations are linked to chain ends, not a conventional density wave.

Plane Cu NMR shows influence of chain phenomena.

Abstract

Nuclear magnetic resonance (NMR) measurements of CuO chains of detwinned Ortho-II YBa$_2$Cu$_3$O$_{6.5}$ (YBCO6.5) single crystals reveal unusual and remarkable properties. The chain Cu resonance broadens significantly, but gradually, on cooling from room temperature. The lineshape and its temperature dependence are substantially different from that of a conventional spin/charge density wave (S/CDW) phase transition. Instead, the line broadening is attributed to small amplitude static spin and charge density oscillations with spatially varying amplitudes connected with the ends of the finite length chains. The influence of this CuO chain phenomenon is also clearly manifested in the plane Cu NMR.