Book Description

Below I present two related studies on the dynamics of spin-/charge-density-waves (SDW/CDW) in chromium. In the first study we measured equilibrium fluctuations of antiferromagnetic SDW/CDW domains in a bulk sample by correlating speckle patterns obtained with partially coherent synchrotron x-rays. The autocorrelation functions follow a double compressing exponential decay similar to that observed in other `jammed' condensed matter systems. This hyper-diffusive behavior indicates the existence of collective relaxation modes which we interpret to arise from the coherent rotation of weakly coupled blocks of spins. Time scales for this collective process range from tens of seconds at 150 Kelvin to thousands of seconds at low temperatures. Even near absolute zero, we observed fluctuations of the magnetic structure which can most directly be interpreted as arising from quantum mechanical zero-point motion. Because microscopic domains of energetically similar spin/charge ordered states are quantum mechanically linked, there exists a dynamic competition between alternate ground states that provides insight into the free energy landscape of domain wall configurations. We obtain estimates of the effective soliton mass of a domain wall and the Arrhenius activation energy.