Observation of an unconventional metal-insulator transition in overdoped CuO_2 compounds

TL;DR

This study reveals an unconventional quantum-critical metal-insulator transition in overdoped cuprate superconductors, characterized by anisotropic electron relaxation and selective insulating behavior of certain quasiparticles.

Contribution

It provides the first evidence of a transition where antinodal quasiparticles become insulating while nodal quasiparticles stay metallic, linking single- and many-particle properties.

Findings

Anisotropic electron relaxation in Bi$_2$Sr$_2$CaCu$_2$O$_{8+eta}$

Evidence of a quantum-critical transition in overdoped cuprates

Selective insulating behavior of antinodal quasiparticles

Abstract

The electron dynamics in the normal state of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is studied by inelastic light scattering over a wide range of doping. A strong anisotropy of the electron relaxation is found which cannot be explained by single-particle properties alone. The results strongly indicate the presence of an unconventional quantum-critical metal-insulator transition where "hot" (antinodal) quasiparticles become insulating while "cold" (nodal) quasiparticles remain metallic. A phenomenology is developed which allows a quantitative understanding of the Raman results and provides a scenario which links single- and many-particle properties.