We report the successful growth of sizable crystals of the cuprate superconductors HgBa 2 CaCu 2 O 6 +δ and HgBa 2 Ca 2 Cu 3 O 8 +δ. These compounds are well known for their high optimal superconducting critical temperatures of Tc=128 K and 134 K at ambient pressure, respectively, and for their challenging synthesis. Using a conventional quartz-tube encapsulation method and a two-layer encapsulation method that utilizes custom-built high-pressure furnaces, we are able to grow single crystals with linear dimensions up to several millimeters parallel to the CuO2 planes. Extended postgrowth annealing is shown to lead to sharp superconducting transitions, indicative of high macroscopic homogeneity. X-ray diffraction and polarized Raman spectroscopy are identified as viable nondestructive methods to help separate the two compounds from synthesis products, as the latter often contain intergrowths of the former. Our work helps to remove obstacles toward the study of these model cuprate systems with experimental probes that require sizable high-quality crystals.
Bibliographical noteFunding Information:
We wish to thank Weiliang Yao, Hongjie Chen, and Yiqi Xie for their help with the synthesis and characterization, and D. Pelc and A. Sacuto for comments on the paper. The work at Peking University was supported by the National Natural Science Foundation of China (Grant No. 11522429 and No. 11874069) and Ministry of Science and Technology of China (Grant No. 2018YFA0305602 and No. 2015CB921302). The work at the University of Minnesota was funded by the Department of Energy through the University of Minnesota Center for Quantum Materials under DE-SC-0016371.
© 2018 American Physical Society.