The dimpling in the CuO_2 planes of YBa_2Cu_3O_x (x=6.806-6.984, T=20-300 K) measured by yttrium EXAFS

TL;DR

This study measures the subtle variations in the CuO_2 plane structure of YBa_2Cu_3O_x across different doping levels and temperatures using yttrium EXAFS, revealing connections to doping regimes and a characteristic temperature.

Contribution

It provides the first detailed measurement of CuO_2 plane dimpling as a function of doping and temperature using yttrium EXAFS, highlighting its relation to electronic phase transitions.

Findings

Dimpling variations are weak and within 0.05 Å.

Dimpling correlates with the transition from underdoped to overdoped regimes.

A characteristic temperature T* of 150 K is identified in the normal state.

Abstract

The dimpling of the CuO_2 planes (spacing between the O2,3 and Cu2 layers) in YBa_2Cu_3O_x has been measured as a function of oxygen concentration and temperature by yttrium x-ray extended-fine-structure spectroscopy (EXAFS). The relative variations of the dimpling with doping (x=6.806-6.984) and temperature (20-300 K) are weak (within 0.05 AA), and arise mainly from displacements of the Cu2 atoms off the O2,3 plane towards Ba. The dimpling appears to be connected with the transition from the underdoped to the overdoped regimes at x=6.95, and with a characteristic temperature in the normal state, T*=150 K.