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Landau Theory for Pair Density Modulation in Fe(Te,Se) Flakes
Po-Jui Chen1, Piers Coleman1,2
1Rutgers University, Department of Physics and Astronomy, Piscataway, New Jersey 08854, USA.
Physical Review Letters
|July 23, 2026
Summary
A new Landau theory explains pair-density modulation (PDM) in FeTe0.55Se0.45 flakes. This suggests local pairing on iron atoms in iron-based superconductors, driven by Hunds coupling.
Area of Science:
- Condensed Matter Physics
- Superconductivity Theory
Background:
- Recent scanning tunneling microscopy (STM) experiments observed pair-density modulation (PDM) in FeTe0.55Se0.45 flakes.
- The physical origin of PDM in these iron-based superconductors remains unclear.
Purpose of the Study:
- To develop a Landau theory explaining the origin of PDM in FeTe0.55Se0.45 flakes.
- To interpret PDM in terms of screw and glide symmetries and order parameter hybridization.
- To elucidate the pairing mechanism in iron-based superconductors.
Main Methods:
- Development of a Landau theory.
- Symmetry analysis of PDM using screw and glide symmetries.
- Interpretation of PDM as a hybridized state of two order parameters.
Main Results:
- PDM is interpreted as a hybridized state of two order parameters with opposite glide and screw parity.
- The absence of PDM in bulk is attributed to glide symmetry breaking at the surface, enabling nematic order to stabilize PDM in flakes.
- The symmetry constraints favor a site-based, rather than bond-based, pairing mechanism.
Conclusions:
- The PDM discovery in superconducting flakes suggests local pairing on iron atoms, potentially driven by Hunds coupling.
- A mismatch in Knight shift predicts magnetic-field enhancement of PDM at low fields and a reentrant triplet phase at high fields.
- These predictions are experimentally testable using STM.
