Antiferromagnetic Excitations and Van Hove Singularities in YBa$_2$Cu$_3$O$_{6+x}$

TL;DR

This paper investigates how Van Hove singularities influence magnetic excitations in YBa2Cu3O6+x, revealing new quasi-particle behaviors and challenging existing assumptions about gap and coupling values.

Contribution

It demonstrates the impact of Van Hove singularities on magnetic excitations in quasi-2D d-wave superconductors, aligning theoretical predictions with experimental data.

Findings

Van Hove singularities induce novel magnetic excitations.

Calculated susceptibility matches neutron scattering results.

Gap and antiferromagnetic coupling are smaller than previously thought.

Abstract

We show that in quasi-two-dimensional $d$-wave superconductors Van Hove singularities close to the Fermi surface lead to novel magnetic quasi-particle excitations. We calculate the temperature and doping dependence of dynamical magnetic susceptibility for YBCO and show that the proposed excitations are in agreement with inelastic neutron scattering experiments. In addition, the values of the gap parameter and in-plane antiferromagnetic coupling are much smaller than usually believed.