From weak- to strong-coupling superconductivity in the AlB₂-type solid solution SrGa_1-AlGe with honeycomb layers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid-State Chemistry

Background:

• 9-electron 111 compounds with honeycomb layers are of interest for their unique electronic and structural properties.
• Understanding the relationship between crystal structure and superconductivity is crucial for designing new materials.

Purpose of the Study:

• To investigate the crystal structure and superconducting properties of SrGaGe, SrAlGe, and their solid solution.
• To elucidate the correlation between structural order/disorder in honeycomb layers and the transition between weak- and strong-coupling superconductivity.

Main Methods:

• Single-crystal X-ray diffraction for structural analysis.
• Magnetization and specific heat measurements to determine superconducting properties.
• Synthesis and characterization of SrGa1-xAlxGe solid solutions.

Main Results:

• SrGaGe crystallizes in a centrosymmetric space group (P6/mmm) with disordered honeycomb layers and exhibits weak-coupling superconductivity (Tc = 2.6 K).
• SrAlGe crystallizes in a non-centrosymmetric space group (P6-m2) with ordered honeycomb layers and shows strong-coupling superconductivity (Tc = 6.7 K).
• The SrGa1-xAlxGe solid solution demonstrates a transition from weak- to strong-coupling superconductivity linked to the order-disorder transition in honeycomb layers and loss of inversion symmetry.

Conclusions:

• The crystal structure, particularly the order of honeycomb layers and the presence/absence of an inversion center, significantly influences the superconducting properties of these 111 compounds.
• A transition from disordered to ordered honeycomb layers correlates with a shift from weak- to strong-coupling superconductivity.