Superconductivity at High Temperatures: Current Progress and Challenges

Abstract

High-temperature superconductivity (HTS), discovered in cuprates in 1986, revolutionized condensed matter physics by breaking the cryogenic barrier. Materials like YBa₂Cu₃O₇ (YBCO) with Tᶜ ≈ 93 K enabled practical cooling with liquid nitrogen, sparking widespread research and the so-called “Woodstock of Physics” in 1987 . Subsequent discoveries included Bi-, Tl-, and Hg-based cuprates reaching Tᶜ up to ≈ 133 K .

Experimental progress extended beyond cuprates. Interface-enhanced superconductivity in single-layer FeSe on SrTiO₃ showed possible Tᶜ above 100 K . Hydrogen-rich compounds under extreme pressure, such as H₂S superconducting at ≈ 203 K, demonstrated conventional electron-phonon coupling may also achieve high Tᶜ . Microscopic studies— including STM/STS—unveiled pseudogap behavior, vortex phenomena, and density modulations, enriching understanding of HTS mechanisms . High-field experiments revealed quantum critical points in cuprates that could underpin pairing .

However, challenges persist. The pairing mechanisms remain elusive due to complex normal-state properties like pseudogap, phase fluctuations, and interplay of competing orders. Practical application is hindered by brittleness, anisotropy, and fabrication difficulties of ceramic HTS—e.g., BSCCO tapes require careful grain alignment and mechanical processing .

This paper synthesizes these advances, offering a clear timeline of breakthroughs, examining methodologies from atomic-scale probes to high-pressure synthesis, summarizing prevailing theories (e.g., RVB, interface phonon coupling), and highlighting both the promise and limitations of HTS. Addressing the interplay between experimental innovation and theoretical ambiguity before 2020 provides a robust foundation for future exploration of roomtemperature superconductivity