By investigating the bulk superconducting state via dc magnetization measurements, we have discovered a common resurgence of the superconducting transition temperatures (T c s) of the mono-layer Bi 2 Sr 2 CuO 6 + δ (Bi2201) and bilayer Bi 2 Sr 2 CaCu 2 O 8 + δ (Bi2212) to beyond the maximum T c s (T c-max s) predicted by the universal relation between T c and doping (p) or pressure (P) at higher pressures. The T c 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 T c -P relation. However, at pressures above 40 GPa, T c rises rapidly without any sign of saturation up to 30 K at 51 GPa. Similarly, the T c 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 T c resurgence to a possible pressure-induced electronic transition in the cuprate compounds due to a charge transfer between the Cu 3d 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 T c -P behavior has also been reported in the trilayer Br 2 Sr 2 Ca 2 Cu 3 O 10 + δ (Bi2223). These observations suggest that higher T c s than those previously reported for the layered cuprate high-temperature superconductors can be achieved by breaking away from the universal T c -P relation through the application of higher pressures.
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Publication status||Published - 2019 Feb 5|
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