Here we provide the first clear evidence of Fermi-liquid breakdown in an intermediate valence system. We employ high precision magnetization measurements of the valence fluctuating superconductor beta-YbAlB4 to probe the quantum critical free energy down to temperatures far below the characteristic energy scale of the valence fluctuations. The observed T/B scaling in the magnetization over three decades not only indicates unconventional quantum criticality, but places an upper bound on the critical magnetic field |B_c| < 0.2 mT, a value comparable with the Earth's magnetic field and six orders of magnitude smaller than the valence fluctuation scale. This tiny value of the upper bound on B_c, well inside the superconducting dome, raises the fascinating possibility that valence fluctuating beta-YbAlB4 is intrinsically quantum critical, without tuning the magnetic field, pressure, or composition: the first known example of such a phenomenon in a metal.
@article{arxiv.1210.7279,
title = {T/B scaling of magnetization in the mixed valent compound \beta-YbAlB4},
author = {Yosuke Matsumoto and S. Nakatsuji and K. Kuga and Y. Karaki and Y. Shimura and T. Sakakibara and A. H. Nevidomskyy and P. Coleman},
journal= {arXiv preprint arXiv:1210.7279},
year = {2014}
}