Charge-neutral fermions and magnetic field-driven instability in insulating YbIr3Si7

• Published in: Nature communications Vol. 13; no. 1; p. 394
• Main Authors: 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.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19-01-2022; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/995; 639/766/119/997; Antiferromagnetism; Degrees of freedom; electronic properties and materials; Excitation; Fermi surfaces; Fermions; Heat conductivity; Heat transfer; Humanities and Social Sciences; Insulation; Lorenz number; Low temperature; Magnetic fields; Magnetic moments; magnetic properties and materials; Magnetic transitions; Magnetism; MATERIALS SCIENCE; multidisciplinary; Oscillations; Science; Science (multidisciplinary); Specific heat; Surface stability; Thermal conductivity
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-021-27541-9

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 YbIr
3
Si
7
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 YbIr
3
Si
7
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.
Charge-neutral excitations have been proposed to explain metal-like thermal transport in Kondo insulators. Here, the authors demonstrate the coupling between charge-neutral excitations and spin degrees of freedom in a Kondo insulator YbIr
3
Si
7
, which puts restrictions on current theories.