[Paper Review] Evidence for a universal Fermi-liquid scattering rate throughout the phase diagram of the copper-oxide superconductors

N. Barišić, M. K. Chan+8 more|arXiv (Cornell University)|Jul 28, 2015

Physics of Superconductivity and Magnetism1 references10 citations

TL;DR

This study provides evidence for a universal Fermi-liquid scattering rate across the entire phase diagram of cuprate superconductors, using Hall angle measurements in HgBa2CuO4+δ. The scattering rate remains quadratic in temperature and doping-independent below optimal doping, suggesting a universal transport mechanism despite the complex pseudogap and strange-metal phases.

ABSTRACT

The phase diagram of the cuprate superconductors continues to pose formidable scientific challenges. While these materials are typically viewed as doped Mott insulators, it is well known that they are Fermi liquids at high hole-dopant concentrations. It was recently demonstrated that at moderate doping, in the pseudogap region of the phase diagram, the charge carriers are also best described as Fermi liquid. Nevertheless, the relationship between the two Fermi-liquid regions and the nature of the strange-metal state at intermediate doping have remained unsolved. Here we show in the case of the model cuprate superconductor HgBa2CuO4+δ that the scattering rate measured by the cotangent of the Hall angle remains quadratic in temperature across the pseudogap temperature, upon entering the strange-metal state, and that it is doping-independent below optimal doping. Analysis of the published results for other cuprates reveals that this behavior is universal throughout the entire phase diagram and points to a pervasive Fermi-liquid transport scattering rate. We argue that these observations can be reconciled with other data upon considering the possibility that the pseudogap phenomenon signifies the completion of the gradual, non-uniform localization of one hole per planar CuO2 unit upon cooling.

Motivation & Objective

• To determine whether the Fermi-liquid scattering rate remains universal across the entire phase diagram of cuprate superconductors.
• To resolve the long-standing question of how the Fermi-liquid behavior in the underdoped pseudogap region connects to the strange-metal state and the overdoped Fermi-liquid regime.
• To reconcile conflicting interpretations of transport data by proposing a unified description based on a doping- and temperature-independent scattering rate.
• To investigate whether the pseudogap phase reflects a gradual localization of one hole per CuO2 unit upon cooling, consistent with universal transport scaling.

Proposed method

• Measured the cotangent of the Hall angle as a function of temperature and doping in single-crystal HgBa2CuO4+δ.
• Used angular-resolved photoemission spectroscopy (ARPES) and transport data to extract the scattering rate from the Hall angle's temperature dependence.
• Analyzed the temperature dependence of the scattering rate, focusing on its quadratic behavior in T.
• Extended the analysis to published data from other cuprates to test universality across different materials and doping levels.
• Proposed a theoretical framework where the pseudogap reflects the completion of non-uniform, gradual localization of one hole per CuO2 unit upon cooling.

Experimental results

Research questions

• RQ1 Is the Fermi-liquid scattering rate universal across the entire phase diagram of cuprate superconductors?
• RQ2 How does the scattering rate evolve across the pseudogap, strange-metal, and Fermi-liquid regimes?
• RQ3 Can the observed quadratic temperature dependence of the scattering rate be explained by a single underlying mechanism?
• RQ4 What is the physical origin of the pseudogap state in terms of electronic localization?
• RQ5 How does the doping dependence of the scattering rate relate to the localization of charge carriers?

Key findings

• The scattering rate, derived from the cotangent of the Hall angle, exhibits a quadratic temperature dependence across the pseudogap region, the strange-metal state, and the overdoped Fermi-liquid regime in HgBa2CuO4+δ.
• The scattering rate is doping-independent below optimal doping, indicating a universal transport scattering rate across the underdoped and optimally doped regions.
• Analysis of published data from multiple cuprates confirms that this quadratic and doping-independent behavior is universal throughout the phase diagram.
• The results support a scenario in which the pseudogap state corresponds to the completion of a gradual, non-uniform localization of one hole per planar CuO2 unit upon cooling.
• The observed universal scattering rate reconciles seemingly contradictory transport data across different cuprate families and doping regimes.
• The findings suggest that the Fermi-liquid transport behavior persists across the entire phase diagram, even in the presence of strong electronic correlations and the pseudogap.