Mixed-Valence-Driven Heavy-Fermion Behavior and Superconductivity in KNi${}_2$Se${}_2$

James R. Neilson, Anna Llobet, Andreas V. Stier +7

Based on specific heat and magnetoresistance measurements, we report that a "heavy" electronic state exists below $T\approx$ 20 K in KNi${}_2$Se${}_2$, with an increased carrier mobil…