Universal quantum phase transition from superconducting to insulating-like states in pressurized Bi2Sr2CaCu2O8+δ superconductors

Copper oxide superconductors have been continually fascinating the communities of condensed matter physics and material sciences because they host the highest ambient-pressure superconducting transition temperature ( T c ) and mysterious physics 1–3. Searching for the universal correlation between the superconducting state and its normal state or neighboring ground state is believed to be an effective way for finding clues to elucidate the underlying mechanism of the superconductivity. One of the common pictures for the copper oxide superconductors is that a well-behaved metallic phase will present after the superconductivity is entirely suppressed by chemical doping 4–8 or application of the magnetic field 9. Here, we report the first observation of universal quantum phase transition from superconducting state to insulating-like state under pressure in the under-, optimally- and over-doped Bi2Sr2CaCu2O8+δ (Bi2212) superconductors with two CuO2 planes in a unit cell. The same phenomenon has also been found in the Bi2Sr1.63La0.37CuO6+δ (Bi2201) superconductor with one CuO2 plane and the Bi2.1Sr1.9Ca2Cu3O10+δ (Bi2223) superconductor with three CuO2 planes in a unit cell. These results not only provide fresh information on the cuprate superconductors but also pose a new challenge for achieving unified understandings on the mechanism of the high-Tc superconductivity.

Possible quantum critical behavior revealed by the critical current density of hole doped high-Tc cuprates in comparison to heavy fermion superconductors

The superconducting critical current density, Jc, in hole doped cuprates show strong dependence on the doped hole content, p, within the copper oxide plane(s). The doping dependent Jc mainly exhibits the variation of the intrinsic depairing critical current density as p is varied. Jc(p) tends to peak at p ~ 0.185 in copper oxide superconductors. This particular value of the hole content, often termed as the critical hole concentration, has several features putative to a quantum critical point (QCP). Very recently, the pressure dependences of the superconducting transition temperature (Tc) and the critical current (Ic) in pure CeRhIn5 and Sn doped CeRhIn5 heavy fermion compounds have been reported (Nature Communications (2018) 9:44, 10.1038/s41467-018-02899-5). The critical pressure demarcates an antiferromagnetic quantum critical point where both Tc and Ic are maximized. We have compared and contrasted this behavior with those found for Y1−xCaxBa2Cu3O7−δ in this brief communication. The resemblance of the systematic behavior of the critical current with pressure and hole content between heavy fermion systems and hole doped cuprates is significant. This adds to the circumstantial evidence that quantum critical physics probably plays a notable role behind the unconventional normal and superconducting state properties of copper oxide superconductors.

Tuning from failed superconductor to failed insulator with magnetic field

Do charge modulations compete with electron pairing in high-temperature copper oxide superconductors? We investigated this question by suppressing superconductivity in a stripe-ordered cuprate compound at low temperature with high magnetic fields. With increasing field, loss of three-dimensional superconducting order is followed by reentrant two-dimensional superconductivity and then an ultraquantum metal phase. Circumstantial evidence suggests that the latter state is bosonic and associated with the charge stripes. These results provide experimental support to the theoretical perspective that local segregation of doped holes and antiferromagnetic spin correlations underlies the electron-pairing mechanism in cuprates.

Progress in the research of copper-oxide superconductors

Since H·Carvalin·Onnesse discovered the superconductivity of mercury in 1911, we have made progress in the research of the superconductor and the superconductor have evolved from single element, alloy to complex compounds with multiple elements.With the development of the research about new superconducting materials, the research of iron based superconductors, copper-oxide superconductor and magnesium boride superconductor is the latest research trend. So far the proved highest superconducting transition temperature of copper-oxide superconductor is 130 K under normal pressure and could reach more than 160 K under high pressure. Based on the experience accumulated in past decades, we propose some general introduction about the main structure type, the superconducting principle and the application of copper-oxide superconductor.It is expected that a positive effect would be made in the research of copper-oxide superconductor. Background: Since H·Carvalin·Onnesse discovered the superconductivity of mercury in 1911, we have made progress in the research of the superconductor and the superconductor have evolved from single element, alloy to complex compounds with multiple elements. Aim: The purpose of this paper is to explain the differences between copper oxide superconductors and conventional superconductors and their superconducting mechanism. Methods: The superconducting mechanism and structure of copper oxide superconductors were analyzed by means of literature investigation, conceptual analysis and comparative study. Results: In this paper, the different structure forms of copper oxide are analyzed, and its superconducting mechanism is described in detail. The applications of several main copper oxide superconductors are introduced. Conclusion: Based on the experience accumulated in past decades, we propose some general introduction about the main structure type, the superconducting principle and the application of copper-oxide superconductor.It is expected that a positive effect would be made in the research of copper-oxide superconductor.