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Fermi-Surface Topological Phase Transition and Horizontal Order-Parameter Nodes in CaFe2As2 Under Pressure
R S Gonnelli1, D Daghero1, M Tortello1
1Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 10129 Torino, Italy.
Scientific Reports
|May 25, 2016
Summary
Superconducting properties in iron-based compounds like CaFe2As2 are highly sensitive to lattice structure. Applying pressure induces a topological transition in the Fermi surface, leading to superconductivity with a specific order parameter symmetry.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Solid-State Physics
Background:
- Iron-based compounds exhibit diverse superconducting properties.
- Superconductivity in these materials is strongly linked to lattice structure details.
- CaFe2As2 becomes superconducting under pressure, making it a system of interest.
Purpose of the Study:
- Investigate the superconducting properties of CaFe2As2 under pressure.
- Understand the relationship between lattice structure, Fermi surface topology, and superconductivity.
- Determine the symmetry of the superconducting order parameter.
Main Methods:
- Directional point-contact Andreev-reflection spectroscopy (PCARS) under quasi-hydrostatic pressure.
- 3D modeling of Andreev reflection.
- Ab-initio calculations using density functional theory (DFT) for Fermi surface.
- Random-phase-approximation (RPA) in a ten-orbital model for order parameter symmetry.
Main Results:
- PCARS measurements reveal changes in superconducting properties under pressure.
- Theoretical predictions show excellent agreement with experimental PCARS data.
- A topological transition in the holelike Fermi surface sheet was observed.
- An order parameter with a horizontal node line emerged on this sheet.
Conclusions:
- The study confirms a strong link between lattice structure modifications and superconducting behavior in CaFe2As2.
- Pressure-induced changes in the Fermi surface topology are directly related to the emergence of superconductivity.
- The observed order parameter symmetry provides crucial insight into the superconducting mechanism.
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