Conventional and Valley-Polarized Quantum Anomalous Hall Phases in Ti-Cr-C MXenes

Quantum anomalous Hall (QAH) and valley-polarized QAH (VP-QAH) effects offer dissipationless edge transport, which is essential for low-power electronics and valleytronics devices. However, finding both phenomena in a single material remains significantly challenging. Herein, we develop a first-principles screening approach to identify QAH and VP-QAH effects in functionalized Ti-Cr-C MXenes due to their intrinsic magnetism and strong spin-orbit coupling. Out of 100 noncentrosymmetric MXenes, 28 are found to be dynamically stable, among which 14 (13) exhibit in-plane (out-of-plane) ferromagnetism and one shows out-of-plane stripy antiferromagnetism in the respective ground states. Ferromagnetic Ti-Cr-C-H-OCN MXene shows the QAH effect, while Ti-Cr-C-CN-Cl and Ti-Cr-C-SCN-O exhibit the strain-induced VP-QAH effect. To further enrich the search space, we explore heterostructuring and, notably, find that compressed Ti-Cr-C-H-OCN MXene/2H-CrS₂ van der Waals heterostructure hosts the VP-QAH effect. Importantly, electric-field-induced topological phase transitions in the Ti-Cr-C-H-OCN MXene/2H-CrS₂ heterostructure and pronounced valley polarization (∼33.7-35.3 meV) in Ti-Cr-C-SCN-O MXene are observed under an applied field, demonstrating strong potential for valleytronics applications.