Mixed-Valent Regime of the two-channel Anderson impurity as a model for U1xThxBe13

In recent years, a new class of f-electron materials has emerged featuring log(T) enhancements of the specific heat and susceptibility, and a low-temperature resistivity that varies either linearly or as the square root of the temperature. Such behaviors are incompatible with Landau's Fermi-liquid picture of metals. One primary example is UITThTBel3, in which uranium ions fluctuate between two different charge configurations. In this talk I will show that the non-Fermi-liquid behavior of UITThTBel3 is best understood in terms of a novel mixed-valent state in which the ionic fluctuations undergo an exotic many-body screening. By considering realistic crystalline electric field splittings, this scenario successfully explains the linear and nonlinear susceptibility data for UBe13 which thus far appeared incompatible, and accounts for their variation upon doping with thorium. It also supports a small many-body energy scale, as found in U1TThTBe13. These results were obtained using extensive Monte Carlo, non-crossing approximation, and numerical renormalization-group calculations