1. Charge-neutral fermions and magnetic field-driven instability in insulating YbIr₃Si₇
- Author
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Sato, Y., Suetsugu, S., Tominaga, T., Kasahara, Y., Kasahara, S., Kobayashi, T., Kitagawa, S., Ishida, K., Peters, R., Shibauchi, T., Nevidomskyy, A. H., Qian, L., Morosan, E., Matsuda, Y., Sato, Y., Suetsugu, S., Tominaga, T., Kasahara, Y., Kasahara, S., Kobayashi, T., Kitagawa, S., Ishida, K., Peters, R., Shibauchi, T., Nevidomskyy, A. H., Qian, L., Morosan, E., and Matsuda, Y.
- Abstract
Kondo lattice materials, where localized magnetic moments couple to itinerant electrons, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, with a dramatic example being recent observations of quantum oscillations and metallic thermal conduction in insulators, implying the emergence of enigmatic charge-neutral fermions. Here, we show that thermal conductivity and specific heat measurements in insulating YbIr₃Si₇ reveal emergent neutral excitations, whose properties are sensitively changed by a field-driven transition between two antiferromagnetic phases. In the low-field phase, a significant violation of the Wiedemann-Franz law demonstrates that YbIr₃Si₇ is a charge insulator but a thermal metal. In the high-field phase, thermal conductivity exhibits a sharp drop below 300 mK, indicating a transition from a thermal metal into an insulator/semimetal driven by the magnetic transition. These results suggest that spin degrees of freedom directly couple to the neutral fermions, whose emergent Fermi surface undergoes a field-driven instability at low temperatures.
- Published
- 2022