Evolution of Cr's charge and spin density waves under GPa pressures

We trace the development of Cr's charge density wave (intensity 10$^{-4}$ $\times $ Bragg peak) and spin density wave (intensity 10$^{-8} \quad \times $ Bragg peak!) at GPa pressures at the Advanced Photon Source. Using a diamond anvil cell combined with a newly developed chemical filtering technique, we find a previously unknown incommensurate to commensurate transition at 2 GPa. We analyze the incommensurate Q-vector and intensity changes at the approach to the transition. At much higher pressures ($>$ 7 GPa), Cr's antiferromagnetism is completely suppressed and the evolution of the line shape at the approach to the quantum critical point directly reveals the role played by quantum fluctuations.