High-temperature superconductors are the new wave of field-induced pair density

Superconductors are quantum materials, which are considered as the perfect transmitters of electricity and electronic information. Presently, cupates are the best candidate for highest temperature superconductivity at ambient pressure, operating at approximately -120°C. Improving this involves understanding competing phases, one of which has now been identified.

Although, the superconductors form the technological basis of solid-state quantum computing, they are also its key limiting factor because conventional superconductors only work at temperatures near -270 °C. This has motivated race to try to discover higher temperature superconductors.

At present, materials containing CuO2 crystal layers (cuprates) are the best candidate for highest temperature superconductivity, operating at approximately -120 °C. But, in these compounds, room temperature superconductivity appears to be frustrated by the existence of a competing electronic phase, and focus has recently been on identifying and controlling that mysterious second phase.

When pairs of opposite spin and opposite momentum are formed, it results in the superconductivity Eventually, these cooper pairs are condensed into a pair density wave. (PDW) state where the density of pairs modulates periodically in space. Intense theoretical interest has emerged in whether such a PDW is the competing phase in cuprates.

To search for evidence of such a PDW state, a team led by Professor JC Seamus Davis (University of Oxford) and Professor Andrew P. Mackenzie (Max Planck Institute CPfS, Dresden) with key collaborators Dr. Stephen Dr. Edkins and Dr. Mohammad Hamidian (Cornell University) and Dr. Kazuhiro Fujita (Brookhaven National Lab.), used high magnetic fields to suppress the homogeneous superconductivity in the cuprate superconductor Bi2Sr2Ca2CuO2. They then carried out atomic-scale visualization of the electronic structure of the new field-induced phase.

Under these circumstances, modulations in the density of electronic states containing multiple signatures of a PDW state were discovered. The phenomena are in detailed agreement with theoretical predictions for a field-induced PDW state, implying that it is a pair density wave which competes with superconductivity in cuprates. This discovery makes it clear that in order to understand the mechanism behind the enigmatic high-temperature superconductivity of the cuprates, this exotic PDW state needs to be taken into account, and therefore opens a new frontier in cuprate research.

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