The 5f heavy fermion system of URu2Si2 is famous for an unconventional “hidden order” (HO) phase transition at T0=17.5K that has been a topic of study for 35 years. A new model is proposed for the underlying physics to be the existence of a van Hove singularity saddle-band dispersion at the Brillouin zone N-point that is only a few meV below the Fermi level, and thus thermally active at T0. The new model, based on temperature-dependent angle resolved photoemission (ARPES) measurements in comparison to DMFT electronic structure calculations [1], is further confirmed by additional ARPES observation of the N-point spectral and dichroic changes for various chemically doped phases with different ferromagnetic, antiferromagnetic or non-magnetic ground states.

[1] J. D. Denlinger et al., Electron. Struct. 4, 013001 (2022).