Anomalous High-Temperature Superconductivity in YH₆

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Pressure-stabilized hydrides represent a rapidly advancing field of high-temperature superconductors.
• These materials are generally understood through the conventional phonon-mediated coupling mechanism.

Purpose of the Study:

• To synthesize and characterize yttrium hexahydride (YH6), a prominent high-temperature superconductor.
• To investigate the superconducting properties of YH6, including its transition temperature, critical magnetic field, and critical current density.

Main Methods:

• High-pressure synthesis of yttrium hexahydride (YH6).
• Measurement of superconducting transition temperature (Tc) at approximately 224 K under 166 GPa.
• Extrapolation of the upper critical magnetic field (Bc2(0)).
• Isotope effect measurements using yttrium deuteride (YD6).
• Current-voltage measurements to determine critical current (Ic) and critical current density (Jc).
• Superconducting density functional theory (SCDFT) and anharmonic calculations.

Main Results:

• Superconducting transition observed at approximately 224 K under 166 GPa for YH6.
• Extrapolated upper critical magnetic field (Bc2(0)) of YH6 is significantly high (116-158 T), exceeding theoretical predictions.
• A notable isotope coefficient (0.4) in YD6 supports phonon-assisted superconductivity.
• Critical current density (Jc) exceeds 3500 A mm-2 at 4 K, surpassing commercial superconductors like NbTi and YBCO.

Conclusions:

• The observed properties of YH6, particularly its high critical magnetic field, deviate from conventional Migdal-Eliashberg and Bardeen-Cooper-Schrieffer theories.
• Evidence suggests the presence of an additional, non-conventional mechanism contributing to superconductivity in YH6.
• Further theoretical and experimental investigations are warranted to fully understand the superconductivity in this material.