Superconductor to Mott insulator transition in YBa$_2$Cu$_3$O$_7$/LaCaMnO$_3$ heterostructures

TL;DR

This study demonstrates a superconductor-to-Mott insulator transition in YBa₂Cu₃O₇/LaCaMnO₃ heterostructures driven by interfacial charge transfer, revealing new insights into electronic doping effects without chemical substitution.

Contribution

The paper introduces a novel interfacial charge transfer method to induce a superconductor-to-Mott insulator transition in cuprate heterostructures, avoiding chemical doping.

Findings

Transition from superconducting to Mott insulating state with increased LCMO layer thickness.

Charge transfer involves not only transition metals but also rare-earth and alkaline-earth ions.

Electronic doping controls $T_c$ without chemical substitution effects.

Abstract

The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high $T_c$ superconductor YBa$_2$Cu$_3$O$_7$ (YBCO) and colossal magnetoresistance ferromagnet La$_{0.67}$Ca$_{0.33}$MnO$_3$ (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may response to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of $T_c$ by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.