Impurity resonances in the mixed state of high-Tc superconductors

TL;DR

This paper investigates how strong impurities affect quasiparticle resonance states in high-Tc d-wave superconductors under magnetic fields, revealing field-dependent behaviors of zero-bias peaks observed in STM experiments.

Contribution

It introduces a model for impurity resonance states in the mixed state, accounting for Doppler shifts and field orientation effects, providing new insights into the magnetic field dependence of these states.

Findings

Zero-bias peaks scale as rac{rac{rac{Hc2}{H}}

Field orientation significantly influences peak response

Impurity resonance hybridizes with nodal quasiparticles, causing broadening

Abstract

We study the quasiparticle resonance states near strong impurities in the mixed state of a d-wave superconductor. These states give rise to zero-bias peaks in the local density of states, observed in scanning tunneling microscopy experiments. The field dependence of the peaks is obtained by averaging with respect to the spatially non-uniform Doppler shifts in the energy of excitations. The hybridization of the magnetic field-induced nodal quasiparticles with the impurity resonances results in the suppression and broadening of the zero-bias peaks. The height of the peaks is found to scale as \sqrt{Hc2/H}. The magnetic field response of the peaks is shown to be strongly dependent on the field orientation.