Thomas F. Rosenbaum, Sonja and William Davidow Presidential Chair and Professor of Physics
We use hydrostatic pressure to suppress the magnetism in elemental chromium, a simple cubic metal that demonstrates a subtle form of itinerant antiferromagnetism, formally equivalent to the Bardeen-Cooper-Schrieffer (BCS) state in superconductors. By directly measuring the associated charge order with x-rays in a diamond anvil cell at low temperature, we reveal a phase transition at pressures ~ 10 GPa that destroys the BCS-like state while preserving the strong magnetic interaction between itinerant electrons and holes. Complementary transport results on both Cr and Cr doped with V expose a crossover to a narrow, fluctuation-dominated quantum critical regime. Cr is unique among stoichiometric magnetic metals studied to date in that its quantum phase transition is continuous in nature. This opens up experimental access to the naked quantum singularity, and a direct probe of the competition between conventional and exotic order in a theoretically tractable material.