Paramagnonlike excitations and spin diffusion in magnetic resonance studies of copper oxide superconductors

TL;DR

This paper develops a relaxation function theory for doped 2D Heisenberg antiferromagnets in the paramagnetic state, analyzing spin excitations and diffusion in high-$T_c$ copper oxide superconductors across temperature and doping levels.

Contribution

It introduces a comprehensive theoretical framework for understanding paramagnonlike excitations and spin diffusion in cuprates, connecting experimental relaxation data with spin dynamics regimes.

Findings

Identification of long lifetime paramagnon regimes below 400 K.

Detection of overdamped excitations above 700 K.

Mapping of spin excitation regimes in the temperature-doping phase diagram.

Abstract

The relaxation function theory for a doped two-dimensional Heisenberg antiferromagnetic system in the paramagnetic state for all wave vectors through the Brillouin zone is presented in view of low frequency response of high-$T_c$ copper oxide superconductors. We deduced the regions of long lifetime [$T \lesssim 400(1-4x)$ K] and "overdamped" [$T \gtrsim 700(1-4x)$ K] paramagnonlike excitations in the temperature ($T$)-doping index ($x$) phase diagram from plane oxygen nuclear spin-lattice relaxation rate $^{17}(1/T_1)$ data in up to optimally doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ thus providing the regimes for the spin wave concept and the ''overdamped'' mode.