Both topology and strong electron correlations are crucial ingredients in quantum materials and have been extensively studied. However, their interplay remains largely elusive. A classic example of strongly correlated behavior is the Kondo effect, which originates from the coupling between the spins of conduction electrons and local magnetic moments. As local magnetic moments form a Kondo lattice, the Kondo effect develops coherence and leads to the Kondo insulator with a hybridization gap near the Fermi energy. Inclusion of topological order in Kondo insulators leads to topological Kondo insulators that have attracted significant attention. |
Very recently, we revealed the Kondo effect in epitaxial films of antiferromagnetic TKM Mn3+xSn1-x with greatly extended compositional range. As Sn atoms are replaced by magnetic Mn atoms which behave as magnetic impurities exchange coupled to the conduction band states, the Kondo effect emerges, as evidenced by a resistance upturn instead of a residue below the resistance minimum temperature Tm. The -lnT increase of resistance with decreasing temperature at T < Tm and the deviation of lnT scaling at TK are characteristics of Kondo effect. The resistance increases as a result of Kondo scattering of magnetic impurities. As temperature further decreases, the Kondo scattering is inhibited due to the formation of a singlet state between a localized Mn moment and a conduction electron, which screens the magnetic moments of the impurities. As x increases further, the Kondo effect develops coherence with opening of a Kondo gap. The Kondo gap opening leads to striking resonance-enhanced THz Faraday rotation , which was also recently observed in a magnetic topological insulator but not in SmB6, suggesting new topological states. In addition, the Kondo effect has profound impacts on the anomalous Hall effect induced by Berry curvature. Large negative Hall resistance presumably induced by Weyl nodes exists at x < 0.40. Significantly, driven by the Kondo effect with higher Mn doping, a gapped state (possibly a Kondo insulator) emerges at x > 0.40 and shows positive Hall resistance at T < 225 K.
Relevant publications
Kondo physics in antiferromagnetic Weyl semimetal Mn3+xSn1-x films, Durga Khadka, T. R. Thapaliya, Sebastian Hurtado Parra, Xingyue Han, Jiajia Wen, Ryan F. Need, Pravin Khanal, Weigang Wang, Jiadong Zang, James M. Kikkawa, Liang Wu, and S. X. Huang*, Science Advances 6, eabc1977 (2020).