An electromagnetic calorimeter for the silicon detector concept

A silicon-tungsten calorimeter for silicon detector (SiD) at the International Linear Collider is under development. Recent progress is summarized.      

Structural tuning of unconventional superconductivity in PuMGa5 (M=Co,Rh)

The superconducting properties of the recently discovered PuMGa5 (M=Co,Rh) superconductors, including the power law behavior of the specific heat, the evolution of the superconducting transition T(c) temperature with pressure, and the linear relation between T(c) and ratio of tetragonal lattice parameters c/a, are compared to those of the heavy fermion CeMIn5 (M=Co,Rh,Ir) unconventional superconductors. The striking similarity of the properties between the two families of superconductors suggests a common physics and a common (magnetically mediated) mechanism of superconductivity.     

Element specific magnetism with resonant X-ray magnetic scattering

Beam line X29 of the National Synchrotron Light Source (NSLS) has been operating for a year for macromolecular crystallography (PX) research, employing a mini-gap, in-vacuum undulator as its X-ray source. Development of this facility involved a close collaboration among the groups of Mark Chance (Case Proteomics Center, Case Western Reserve Univ. [CWR]), Erik Johnson [NSLS], and Robert Sweet (Macromolecular Crystallography Research Resource [PXRR] of BNL's Biology Dept.).

There were several joint objectives and complexities to this project. Firstly, we hoped to provide an undulator-based beam line with the attractive features of high collimation and high flux for macromolecular crystallography at the NSLS.     

Triple-q(-->) octupolar ordering in NpO2

We report the results of resonant x-ray scattering experiments performed at the Np M(4,5) edges in NpO2. Below T(0)=25 K, the development of long-range order of Np electric quadrupoles is revealed by the growth of superlattice Bragg peaks. The polarization and azimuthal dependence of the intensity of the resonant peaks are well reproduced assuming anisotropic tensor susceptibility scattering from a triple-q(-->) longitudinal antiferroquadrupolar structure. Electric-quadrupole order in NpO2 could be driven by the ordering at T0 of magnetic octupoles of Gamma(5) symmetry, splitting the Np ground state quartet and leading to a singlet ground state with zero dipole-magnetic moment.     

Understanding the complex phase diagram of uranium: the role of electron-phonon coupling

We report an experimental determination of the dispersion of the soft phonon mode along [100] in uranium as a function of pressure. The energies of these phonons increase rapidly, with conventional behavior found by 20 GPa, as predicted by recent theory. New calculations demonstrate the strong pressure (and momentum) dependence of the electron-phonon coupling, whereas the Fermi-surface nesting is surprisingly independent of pressure. This allows a full understanding of the complex phase diagram of uranium and the interplay between the charge-density wave and superconductivity.