Quantum critical matter has already been studied in many systems, including cold atomic gases. We report the observation of a universal behaviour of ultracold quantum critical Bose gases in a one-dimensional optical lattice. In the quantum critical region above the Berezinskii-Kosterlitz-Thouless transition, the relative phase fluctuations between neighboring subcondensates and spatial phase fluctuations of quasi-2D subcondensates coexist. We study the density probability distribution function when both these two phase fluctuations are considered. A universal exponential density probability distribution is demonstrated experimentally, which agrees well with a simple theoretical model by considering these two phase fluctuations.
We present studies of the magnetic domain structure of UMn2Ge2 single crystals using a homebuilt low temperature magnetic force microscope. The material has two distinct magnetic ordering temperatures, originating from the Mn and U moments. At room temperature, where the Mn moments dominate, there are flower-like domain patterns similar to those observed in uniaxial ferromagnets. After exposing the sample to a one-tesla magnetic field near 40 K, the evolution of the magnetic domains are imaged through zero-field warming up to 210 K. Near the ordering temperature of the Uranium moments a clear change in the domain wall motion is observed. The domain size analysis of the flower-like pattern reveals that the domain structure is consistent with a model of branching domains. PACS numbers: May be entered using the \pacs{#1} command.
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