Large-bipolaron liquids in cuprate superconductors

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Cuprate superconductors exhibit unusual properties not fully explained by conventional theories.
• The electronic structure and charge carrier behavior in these materials remain areas of active research.

Purpose of the Study:

• To elucidate the microscopic mechanism behind the unique properties of cuprate superconductors.
• To explain the role of large bipolarons and superoxygens in superconductivity.

Main Methods:

• Theoretical analysis of electronic structure and bonding in CuO2 planes.
• Investigation of molecular orbital symmetry and vibrational dynamics of superoxygens.
• Correlation of theoretical findings with experimental observations of cuprate properties.

Main Results:

• Identified large bipolarons where self-trapped holes occupy superoxygens (four oxygens, four coppers).
• Demonstrated oxygen relaxation inward and copper relaxation outward, leading to electron transfer and elimination of copper spins.
• Linked the d-symmetry of superoxygens' ground state molecular orbital to their radial vibrations.

Conclusions:

• The behavior of these large bipolarons explains cuprate superconductors' charge transport, absorption, magnetism, and local vibrations.
• Condensation of these large bipolarons into a liquid provides a mechanism for superconductivity.
• The findings align with and explain the long-established unusual properties of cuprate superconductors.