Interplay between antiferromagnetic order and spin polarization in ferromagnetic metal/electron-doped cuprate superconductor junctions

TL;DR

This paper extends a theory of point-contact spectroscopy to ferromagnetic metal/electron-doped cuprate superconductor junctions, exploring how antiferromagnetic order and spin polarization influence conductance and proposing a method to determine spin polarization.

Contribution

It introduces an extended theoretical model for FM/EDSC junctions considering AF order, spin polarization, Fermi-wave vector mismatch, and barriers, providing new insights into conductance behavior.

Findings

Midgap surface state contributes to conductance modifications.

Low-energy conductance enhancement indicates AF order presence.

Proposes a more accurate formula for spin polarization measurement.

Abstract

Recently we proposed a theory of point-contact spectroscopy and argued that the splitting of zero-bias conductance peak (ZBCP) in electron-doped cuprate superconductor point-contact spectroscopy is due to the coexistence of antiferromagnetic (AF) and d-wave superconducting orders [Phys. Rev. B {\bf 76}, 220504(R) (2007)]. Here we extend the theory to study the tunneling in the ferromagnetic metal/electron-doped cuprate superconductor (FM/EDSC) junctions. In addition to the AF order, the effects of spin polarization, Fermi-wave vector mismatch (FWM) between the FM and EDSC regions, and effective barrier are investigated. It is shown that there exits midgap surface state (MSS) contribution to the conductance to which Andreev reflections are largely modified due to the interplay between the exchange field of ferromagnetic metal and the AF order in EDSC. Low-energy anomalous conductance enhancement can occur which could further test the existence of AF order in EDSC. Finally, we propose a more accurate formula in determining the spin polarization value in combination with the point-contact conductance data.