Proximity induced metal/insulator transition in $Y Ba_2 Cu_3 O_7 / La_{2/3} Ca_{1/3} Mn O_3$ superlattices

TL;DR

This study investigates how proximity effects in YBCO/LCMO superlattices induce a metal/insulator transition, revealing a long-range charge transfer or coupling to magnetic correlations as key mechanisms.

Contribution

It demonstrates a proximity-induced metal/insulator transition in YBCO/LCMO superlattices with large critical length scales, highlighting long-range charge transfer or magnetic coupling as underlying causes.

Findings

Significant decrease in free carrier response in superlattices

Critical length scale of ~20 nm in YBCO and ~10 nm in LCMO

Absence of metallicity suppression when LCMO is replaced by LaNiO3

Abstract

The far-infrared dielectric response of superlattices (SL) composed of superconducting YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) and ferromagnetic La$_{0.67}$% Ca$_{0.33}$MnO$_{3}$ (LCMO) has been investigated by ellipsometry. A drastic decrease of the free carrier response is observed which involves an unusually large length scale of d$^{crit}\approx $20 nm in YBCO and d$^{crit}\approx $10 nm in LCMO. A corresponding suppression of metallicity is not observed in SLs where LCMO is replaced by the paramagnetic metal LaNiO$_{3}$. Our data suggest that either a long range charge transfer from the YBCO to the LCMO layers or alternatively a strong coupling of the charge carriers to the different and competitive kind of magnetic correlations in the LCMO and YBCO layers are at the heart of the observed metal/insulator transition. The low free carrier response observed in the far-infrared dielectric response of the magnetic superconductor RuSr$_{2}$GdCu$_{2}$O$_{8}$ is possibly related to this effect.