Manipulation of gap nodes by uniaxial strain in iron-based superconductors

TL;DR

This paper demonstrates that uniaxial strain can manipulate the gap nodes in iron-based superconductors by controlling orbital spectral weights, potentially enhancing superconductivity and enabling external tuning of their properties.

Contribution

It introduces a microscopic model showing how uniaxial strain can create or annihilate superconducting gap nodes, offering a new method to control superconducting states in iron-based materials.

Findings

Uniaxial strain can enhance $T_c$ in iron-based superconductors.

Strain can induce the creation or annihilation of accidental gap nodes.

Experimental detection via anisotropic penetration depth is feasible.

Abstract

In the iron pnictides and chalcogenides, multiple orbitals participate in the superconducting state, enabling different gap structures to be realized in distinct materials. Here we argue that the spectral weights of these orbitals can in principle be controlled by a tetragonal symmetry-breaking uniaxial strain, due to the enhanced nematic susceptibility of many iron-based superconductors. By investigating multi-orbital microscopic models in the presence of orbital order, we show that not only $T_{c}$ can be enhanced, but pairs of accidental gap nodes can be annihilated and created in the Fermi surface by an increasing external strain. We explain our results as a mixture of nearly-degenerate superconducting states promoted by strain, and show that the annihilation and creation of nodes can be detected experimentally via anisotropic penetration depth measurements. Our results provide a promising framework to externally control the superconducting properties of iron-based materials.