Demonstrating the model nature of the high-temperature superconductor HgBa$_2$CuO$_{4+\Delta}$

TL;DR

This paper reports the successful growth and characterization of high-quality HgBa$_2$CuO$_{4+\Delta}$ crystals, enabling systematic studies of its superconducting properties across a wide doping range, establishing it as a model high-temperature superconductor.

Contribution

It demonstrates controlled doping of Hg1201 crystals and provides comprehensive magnetic, transport, and surface analyses, establishing a foundation for future research on this superconductor.

Findings

Achieved uniform doping over a wide range of hole concentrations.

High-quality crystals exhibit clear magnetic and transport properties.

Large, good-quality surfaces confirmed by XPS.

Abstract

The compound HgBa$_2$CuO$_{4+\Delta}$ (Hg1201) exhibits a simple tetragonal crystal structure and the highest superconducting transition temperature (T$_c$) among all single Cu-O layer cuprates, with T$_c$ = 97 K (onset) at optimal doping. Due to a lack of sizable single crystals, experimental work on this very attractive system has been significantly limited. Thanks to a recent breakthrough in crystal growth, such crystals have now become available. Here, we demonstrate that it is possible to identify suitable heat treatment conditions to systematically and uniformly tune the hole concentration of Hg1201 crystals over a wide range, from very underdoped (T$_c$ = 47 K, hole concentration p ~ 0.08) to overdoped (T$_c$ = 64 K, p ~ 0.22). We then present quantitative magnetic susceptibility and DC charge transport results that reveal the very high-quality nature of the studied crystals. Using XPS on cleaved samples, we furthermore demonstrate that it is possible to obtain large surfaces of good quality. These characterization measurements demonstrate that Hg1201 should be viewed as a model high-temperature superconductor, and they provide the foundation for extensive future experimental work.