Emergence of orbital two-channel Kondo effect in epitaxial TiN thin films

Abstract

The continual scaledown and stringent defect control in electronic devices are opening up frontiers in Kondo effect-a powerful testbed for probing magnetic impurity coupling to a continuum of electronic states. In disordered ferromagnets, degenerate quantum states like two-level systems (TLS) with a pseudo-half spin can couple with the continuum to mimic Kondo physics, creating the orbital two-channel Kondo (2CK) effect below the characteristic Kondo temperature (TK). By employing vacuum-annealing to inject ∼12 at.% nitrogen vacancies (VN) in TiN1-x films, we generated room-temperature ferromagnetic ordering with 13.6 emu g−1 saturation magnetization. The transport characteristics exhibited non-Fermi-liquid (NFL) behavior below TK of 20.2 K. The orbital 2CK effect is signified by a clear transition from logarithmic (T < T0∼40 K), to square-root dependence (T < TK) and subsequent deviation from it (T < TD∼10 K) in resistivity upturn behavior in three distinct low-temperature regimes. By controlling VN, we establish the necessity of ferromagnetism and ultrafast tunneling centers for generating orbital 2CK effect and NFL behavior in disordered metallic systems, extending their scope in non-magnetic nanomaterials.