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

摘要

The superconductor-to-insulator transition (SIT) induced by means such asexternal magnetic fields, disorder or spatial confinement is a vividillustration of a quantum phase transition dramatically affecting thesuperconducting order parameter. In pursuit of a new realization of the SIT byinterfacial charge transfer, we developed extremely thin superlattices composedof high $T_c$ superconductor YBa$_2$Cu$_3$O$_7$ (YBCO) and colossalmagnetoresistance ferromagnet La$_{0.67}$Ca$_{0.33}$MnO$_3$ (LCMO). By usinglinearly polarized resonant X-ray absorption spectroscopy and magnetic circulardichroism, combined with hard X-ray photoelectron spectroscopy, we derived acomplete picture of the interfacial carrier doping in cuprate and manganiteatomic layers, leading to the transition from superconducting to an unusualMott insulating state emerging with the increase of LCMO layer thickness. Inaddition, contrary to the common perception that only transition metal ions mayresponse to the charge transfer process, we found that charge is also activelycompensated by rare-earth and alkaline-earth metal ions of the interface. Suchdeterministic control of $T_c$ by pure electronic doping without any hinderingeffects of chemical substitution is another promising route to disentangle therole of disorder on the pseudo-gap and charge density wave phases of underdopedcuprates.