Discontinuous Lifshitz Transition Achieved by Band-Filling Control in NaxCoO2

TL;DR

This study demonstrates a rare, discontinuous Lifshitz transition in NaxCoO2 driven by precise Na content control, revealing abrupt changes in magnetic and thermodynamic properties, and expanding understanding of phase transitions in correlated electron systems.

Contribution

It reports the first observation of a discontinuous Lifshitz transition induced by band-filling control in a strongly correlated material.

Findings

Discovered a narrow phase boundary at 0.620 < x < 0.621.

Observed abrupt property changes across the transition.

Confirmed the transition as a discontinuous Lifshitz type.

Abstract

Precise band-filling control is performed on a strongly correlated electron system NaxCoO2, by changing the Na content, and the influence of this on the magnetic and thermodynamic properties is studied. It has been discovered that a phase boundary between a Pauli paramagnetic metal appearing at small x and a Curie-Weiss metal at large x is located within an extremely narrow range of 0.620 < x < 0.621. The transition between these is a Lifshitz transition of the pocket-vanishing type, exceptionally achieved by band-filling control. Abrupt changes in various properties across the boundary are remarkably observed, suggesting that the Lifshitz transition occurs discontinuously in NaxCoO2, differently from the conventional Lifshitz transition defined at T = 0.