Two-channel Kondo physics from arsenic bond oscillations in zirconium arsenide selenide

The two-channel Kondo effect is a fascinating but extremely fragile many-body state that has been theoretically discussed extensively. we address metallic compounds of a specific (PbFCl) structure for which a $-AT^{1/2}$ term to $\rho(T)$ is frequently observed, in line with the two-channel Kondo effect. The origin of this anomalous behavior has remained enigmatic since here, solely the interaction between electrons may account for this behavior, and the two-channel Kondo state is not expected to occur. By combining chemical and structural investigations with various physical property measurements we show that the magnetic field-independent $-AT^{1/2}$ term to the low-T resistivity observed over two decades in ZrAs$_x$Se$_y$ with 1.90 $\leq x+y \leq$ 1.99 originates from vacancies in the layer exclusively built up by As. Furthermore, we can trace back the two-channel Kondo effect in this material to a dynamic Jahn-Teller effect operating at these vacancies. All physical properties of the investigated compounds support this conclusion. Our findings will be relevant also for other metallic systems with pnictogen-pnictogen bondings, e.g., cage-forming compounds like the skutterudites.