Jian Yun He

Electron correlation effects in resonant inelastic X-ray scattering of NaV2O5.

Element- and site-specific resonant inelastic x-ray scattering spectroscopy (RIXS) is employed to investigate electron correlation effects in NaV2O5. In contrast to single photon techniques, RIXS at the vanadium L3 edge is able to probe d-d* transitions between V d-bands. A sharp energy loss feature is observed at -1.56 eV, which is well reproduced by a model calculation including correlation effects. The calculation identifies the loss feature as excitation between the lower and upper Hubbard bands and permits an accurate determination of the Hubbard interaction term U = 3.0 +/- 0.2 eV.

Fluctuation effects on the physical properties of Cd2Re2O7 near 200 K

Experimental investigation of the resistivity ρ, susceptibility χ, specific heat Cp and Hall coefficient RH of the pyrochlore Cd2Re2O7 reveals the presence of a continuous phase transition of uncertain origin with critical temperature T* = 200 K. Electron and x-ray diffraction measurements indicate that a commensurate structural transformation accompanies the changes in the electronic properties, implying that lattice as well as electronic degrees of freedom are involved in the transition. Remarkable scaling relationships between ρ, χ and Cp are observed, indicating that fluctuations are crucial in the transition regime. Both spin and ionic density fluctuation scenarios are considered.

Quasi-One-Dimensional Magnons in an Intermetallic Marcasite

We present inelastic neutron scattering measurements and first principles calculations examining the intermetallic marcasite CrSb(2). The observed spin-wave dispersion implies that the magnetic interactions are strongly one-dimensional with antiferromagnetic chains parallel to the crystalline c axis. Such low-dimensional excitations are unexpected in a semiconducting intermetallic system. Moreover, we observe a clear anisotropic thermal conductivity indicating that the magnetic anisotropy enhances thermoelectric properties along particular crystallographic directions.