Superconductivity and lattice instability in compressed lithium from Fermi surface hot spots

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Superconductivity is a quantum mechanical phenomenon where a material exhibits zero electrical resistance below a critical temperature.
• Elemental lithium exhibits the highest superconducting temperature (Tc) among elemental metals, reaching approximately 18-20 K at high pressures (35-48 GPa).
• Understanding the mechanisms driving high-Tc superconductivity in elemental metals is crucial for developing new superconducting materials.

Purpose of the Study:

• To elucidate the microscopic origins of the high superconducting temperature (Tc) in elemental lithium.
• To investigate the role of electron-phonon coupling in lithium's superconductivity under pressure.
• To determine the influence of Kohn anomaly surfaces and Fermi surface topology on coupling strength.

Main Methods:

• First-principles linear response calculations were employed to determine the phonon spectrum.
• Calculations of the electron-phonon coupling spectral function, alpha2F(omega), were performed.
• Analysis focused on the momentum (Q) and phonon-polarization dependence of the coupling strength.

Main Results:

• The study reveals that electron-phonon coupling in lithium is highly concentrated at the intersections of Kohn anomaly surfaces with the Fermi surface.
• Calculated coupling strengths align with experimentally observed superconducting temperatures in the range of 18-20 K.
• A strong dependence of coupling strength on both momentum transfer (Q) and phonon polarization was identified.

Conclusions:

• The high superconducting temperature in lithium is directly linked to strong electron-phonon coupling localized at specific Fermi surface-Kohn anomaly intersections.
• The sharp momentum dependence of coupling necessitates a fine Q-mesh for accurate calculations of the electron-phonon coupling parameter (lambda).
• These findings provide fundamental insights into superconductivity mechanisms in elemental metals and guide future materials design.