A resolution to doping asymmetry puzzle in high Tc cuprates

TL;DR

This paper proposes a microscopic model explaining doping asymmetry in high Tc cuprates, revealing that Ce atoms quench local spins and induce a first-order transition from Mott insulator to superconductor, with equal electron and hole carriers.

Contribution

It introduces a novel microscopic explanation for doping asymmetry, emphasizing the role of Ce atoms in spin quenching and site dilution, and predicts a first-order transition line in the phase diagram.

Findings

Ce atoms quench Cu spins, acting as site diluters.

A first-order Mott insulator to superconductor transition is induced by chemical pressure.

Equal number of positive and negative carriers in the metallic state.

Abstract

We present a microscopic model for `electron doped' $Nd_{2-x}Ce_xCuO_4$ family and offer a resolution to a long standing doping asymmetry puzzle. Here, i) Ce atoms do not dope free electrons, instead a Ce atom effectively quenches a $Cu^{2+}$ spin moment at an adjacent site, at an energy scale > superexchange J of $CuO_2$ plane and `site dilutes' the Mott insulator. ii) Effective chemical pressure, caused by increased Ce substitution, induces a {\em first order Mott insulator to superconductor transition} in the $CuO_2$ plane. We predict, i) {\em equal number of +e and -e carriers} in metallic state and ii) a line of first order transition ending at a critical point in normal state. Phenomenology gets organized.