A comparison of the hidden order transition in URu${}_2$Si${}_2$ to the $\lambda$-transition in ${}^4$He

W. Montfrooij, J. A. Mydosh

The low-temperature states of ambient URu${}_2$Si${}_2$ and superfluid ${}^4$He are both characterized by momentum-dependent energy gaps between the ground and excited states. This behav…