No abstract

Polarized high resolution absorption spectra at 4-2 K are reported for single crystals of CszU(Np)O2C1 a and CsU(Np)O,,(NOz)s.Five transitions of the charge-transfer type are observed in both complexes. Zeeman effect measurements give values of g~ in every case. MCD measurements in the nitrate complex permit the unambiguous assignment of a number of excited state symmetries.It is shown by evaluation of the electron-electron repulsion integrals that the excited states are best described as originating from euy),', as opposed to rru s yy', configurations. These configurations are analogous to those describing the charge-transfer states of the uranyl(VI) ion and in some cases the parentage of the neptunyl transitions can be recognized from the polarization of their vibronic structure.

Anderson localisation —the inhibition of wave propagation in disordered media— is a surprising interference phenomenon which is particularly intriguing in two-dimensional (2D) systems. While an ideal, non-interacting 2D system of infinite size is always localised, the localisation length-scale may be too large to be unambiguously observed in an experiment. In this sense, 2D is a marginal dimension between one-dimension, where all states are strongly localised, and three-dimensions, where a well-defined phase transition between localisation and delocalisation exists as the energy is increased. Here, we report the results of an experiment measuring the 2D transport of ultracold atoms between two reservoirs, which are connected by a channel containing pointlike disorder. The design overcomes many of the technical challenges that have hampered observation of localisation in previous works. We experimentally observe exponential localisation in a 2D ultracold atom system.