BEGIN:VCALENDAR VERSION:2.0 PRODID:Data::ICal 0.22 BEGIN:VEVENT DESCRIPTION:Genya Kolomeisky\, University of Virginia\n\n
\n The field of charged impurities in narrow-band gap semiconductors and Weyl semimetals can create electron-hole pairs when the total charge $Ze$ of the impurity exceeds a value $Z_{c}e.$ The particles of one charge escape to infinity\, leaving a screening space charge. The result is that the observable dimen sionless impurity charge $Q_{\\infty}$ is less than $Z$ but greater than $ Z_{c}$. There is a corresponding effect for nuclei with $Z >\;Z_{c} \\ap prox 170$\, however in the condensed matter setting we find $Z_{c} \\simeq 10$. Thomas-Fermi theory indicates that $Q_{\\infty} = 0$ for the Weyl se mimetal\, but we argue that this is a defect of the theory. For the case o f a highly-charged recombination center in a narrow band-gap semiconductor (or of a supercharged nucleus)\, the observable charge takes on a nearly universal value. In Weyl semimetals the observable charge takes on the uni versal value $Q_{\\infty} = Z_{c}$ set by the reciprocal of material'\; s fine structure constant.
\n DTSTART:20141017T193000Z LOCATION:Physics Building\, Room 204 SUMMARY:Fermion space charge in narrow-band gap semiconductors\, Weyl semim etals and around highly charged nuclei END:VEVENT END:VCALENDAR