I went for a jog today and thought back to an insight that I had in graduate school. During my phD, I studied frustrated magnetism. In frustrated magnets, you consider a material where the atoms are arranged in triangular motifs. If these atoms have unpaired spins on them and only nearest neighbor antiferromagnetic interactions, then the interactions will be unable to be simultaneously satisfied and the material will never order, despite having strong interactions. However, in practice, I found that Nature is tricky and that a number of these materials would order. In some cases, thermal or quantum fluctuations would result in ordering. In other cases, order in the system could be stabilized by a structural phase transition which would favor some interactions over others. However, one thing that gradually became clear was that there were interesting phases near such frustrated magnets and the interesting question is how a small perturbation might result in interesting physics.
I think this could be a general strategy for searching for switchable phenomena. Find a phase which is subject to an instability through some type of perturbation. For example, pressure, electric field, etc. If you can move the system towards the instability using one control parameter you’re half way there. The next challenge is whether you can use another perturbation to move it back across the boundary using another control parameter. If so, then you have a chance to build something interesting…
