Condensed Matter Seminar "Transport in undoped Weyl semimetals and a new type of spin glass"

Two topics will be discussed. The first addresses transport in undoped Weyl semimetals (WSMs). Despite their name and the behavior of most WSMs, these materials should exhibit "semiconducting" temperature dependent resistivity, drho/dT<0, when undoped. We show that this form is obeyed in the rare-earth iridate pyrochlores, R2Ir2O7, in stoichiometric samples. We also show that for R = Yttrium, rho~1/T^4, consistent with a theory of charged impurity scattering, but extending into a temperature range where k_F l << 1, suggesting behavior of a "bad" WSM. The second topic will address an unusual spin glass, pseudobrookite Fe2TiO5 in which an Ising anisotropy develops due to interactions. This presents a second example of "quasi-spin" glass.