Browsing by Author "Kasahara, Y."

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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.
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    Tuning the Magnetic Quantum Criticality of Artificial Kondo Superlattices CeRhIn5/YbRhIn5
    (American Physical Society, 2016) Ishii, T.; Toda, R.; Hanaoka, Y.; Tokiwa, Y.; Shimozawa, M.; Kasahara, Y.; Endo, R.; Terashima, T.; Nevidomskyy, A.H.; Shibauchi, T.; Matsuda, Y.
    The effects of reduced dimensions and the interfaces on antiferromagnetic quantum criticality are studied in epitaxial Kondo superlattices, with alternating n layers of heavy-fermion antiferromagnet CeRhIn5 and seven layers of normal metal YbRhIn5. As n is reduced, the Kondo coherence temperature is suppressed due to the reduction of effective Kondo screening. The Néel temperature is gradually suppressed as n decreases and the quasiparticle mass is strongly enhanced, implying dimensional control toward a quantum critical point. Magnetotransport measurements reveal that a quantum critical point is reached for the n=3 superlattice by applying small magnetic fields. Remarkably, the anisotropy of the quantum critical field is opposite to the expectations from the magnetic susceptibility in bulk CeRhIn5, suggesting that the Rashba spin-orbit interaction arising from the inversion symmetry breaking at the interface plays a key role for tuning the quantum criticality in the two-dimensional Kondo lattice.