Higher superconducting transition temperature by breaking the universal pressure relation

• Published in: Proceedings of the National Academy of Sciences - PNAS 2019-02, Vol.116 (6), p.2004-2008
• Main Authors: Deng, Liangzi, Zheng, Yongping, Wu, Zheng, Huyan, Shuyuan, Wu, Hung-Cheng, Nie, Yifan, Cho, Kyeongjae, Chu, Ching-Wu
• Format: Article
• Language: English
• Subjects: Bilayers; BSCCO; Charge transfer; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Copper; cuprate; Density functional theory; high pressure; High temperature superconductors; high-Tc superconductivity; Physical Sciences; Pressure; Saturation; Superconductivity; Tc resurgence; Transition temperature; Transition temperatures
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1819512116

By investigating the bulk superconducting state via dc magnetization measurements, we have discovered a common resurgence of the superconducting transition temperatures (Tcs) of the monolayer Bi₂Sr₂CuO6+δ (Bi2201) and bilayer Bi₂Sr₂CaCu₂O8+δ (Bi2212) to beyond the maximum Tcs (Tc-maxs) predicted by the universal relation between Tc and doping (p) or pressure (P) at higher pressures. The Tc of underdoped Bi2201 initially increases from 9.6 K at ambient to a peak at 23 K at 26 GPa and then drops as expected from the universal Tc-P relation. However, at pressures above 40 GPa, Tc rises rapidly without any sign of saturation up to 30 K at 51 GPa. Similarly, the Tc for the slightly overdoped Bi2212 increases after passing a broad valley between 20 and 36 GPa and reaches 90 K without any sign of saturation at 56 GPa. We have, therefore, attributed this Tc resurgence to a possible pressure-induced electronic transition in the cuprate compounds due to a charge transfer between the Cu 3 d x 2 − y 2 and the O 2p bands projected from a hybrid bonding state, leading to an increase of the density of states at the Fermi level, in agreement with our density functional theory calculations. Similar Tc-P behavior has also been reported in the trilayer Br₂Sr₂Ca₂Cu₃O10+δ (Bi2223). These observations suggest that higher Tcs than those previously reported for the layered cuprate high-temperature superconductors can be achieved by breaking away from the universal Tc-P relation through the application of higher pressures.