Quantum materials, which often exhibit collective orders such as magnetism or superconductivity, tend to respond sensitively to small changes of temperature, magnetic field, composition or crystal lattice parameters. The use of such parameters thus permits control and tuning of the materials’ properties. Lattice deformations, or strain, are special tuning parameters because of their selectivity.

An exemplary class of quantum materials, that responds sensitively to strain, are the iron-based superconductors. Notably, their electronic nematicity, which breaks rotational symmetry, makes them extremely sensitive to the anisotropic strain.

I will show how strain can be used to study nematicity and its interplay with magnetis and superconductivity. This includes high-resolution dilatometry measurements of the thermal strain and the elastic modulus. We have used the elastic modulus to infer the nematic susceptibility in a wide range of iron-based materials.

Finally, I will discuss recent examples of strain as a powerful control parameter. I will show how a change of the tetragonal unit-cell aspect ratio may be used to dramatically modify correlated phases.