Browsing by Author "Kitagawa, S."

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    Charge-neutral fermions and magnetic field-driven instability in insulating YbIr3Si7
    (Springer Nature, 2022) 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.
    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.