Strain-Driven Approach to Quantum Criticality in AFe_{2}As_{2} with A=K, Rb, and Cs

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Iron-based superconductors (AFe2As2) display large Sommerfeld coefficients, similar to heavy-fermion systems.
• Unusual electronic properties necessitate further investigation into their underlying mechanisms.

Purpose of the Study:

• To elucidate the origin of the heavy-fermion-like behavior in AFe2As2 superconductors.
• To understand the relationship between electronic correlations, volume effects, and superconductivity in this class of materials.

Main Methods:

• Magnetostriction and thermal expansion measurements were performed on the AFe2As2 series (A=K, Rb, Cs).
• Quantum oscillations in magnetostriction were analyzed to determine band-specific quasiparticle masses.
• Grüneisen ratio was derived from thermal expansion data to probe volume dependencies.

Main Results:

• Band-specific quasiparticle masses significantly exceed those predicted by band structure calculations.
• Thermal expansion data shows a diverging Grüneisen ratio, indicating proximity to a quantum critical point with increasing volume.
• Critical fluctuations associated with enhanced quasiparticle masses appear to suppress superconductivity.

Conclusions:

• The heavy-fermion-like behavior in AFe2As2 is linked to enhanced quasiparticle masses driven by proximity to a quantum critical point.
• Critical fluctuations play a dual role, enhancing electronic correlations while simultaneously weakening the superconducting state.