Mottness at finite doping and charge-instabilities in cuprates

TL;DR

This paper investigates how Mott physics influences the doping-temperature phase diagram of cuprates, revealing a critical doping point where charge-transfer excitations transition from localized to delocalized, linked to charge instabilities.

Contribution

It demonstrates the evolution of charge-transfer excitations with doping and connects high-energy Mott physics to low-temperature charge instabilities in cuprates.

Findings

Charge-transfer excitations become coherent at critical doping p_{cr} ≈ 0.16.

The transition is well described by dynamical mean field theory.

Charge instabilities at low temperature are linked to underlying Mottness.

Abstract

The intrinsic instability of underdoped copper oxides towards inhomogeneous states is one of the central puzzles of the physics of correlated materials. The influence of the Mott physics on the doping-temperature phase diagram of copper oxides represents a major issue that is subject of intense theoretical and experimental effort. Here, we investigate the ultrafast electron dynamics in prototypical single-layer Bi-based cuprates at the energy scale of the O-2p$\rightarrow$Cu-3d charge-transfer (CT) process. We demonstrate a clear evolution of the CT excitations from incoherent and localized, as in a Mott insulator, to coherent and delocalized, as in a conventional metal. This reorganization of the high-energy degrees of freedom occurs at the critical doping p$_{cr}\simeq$0.16 irrespective of the temperature, and it can be well described by dynamical mean field theory calculations. We argue that the onset of the low-temperature charge instabilities is the low-energy manifestation of the underlying Mottness that characterizes the p<p$_{cr}$ region of the phase diagram. This discovery sets a new framework for theories of charge order and low-temperature phases in underdoped copper oxides.