Browsing by Author "Matsumoto, Yosuke"
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Item Anisotropy-driven quantum criticality in an intermediate valence system(Springer Nature, 2022) Grbić, Mihael S.; O’Farrell, Eoin C. T.; Matsumoto, Yosuke; Kuga, Kentaro; Brando, Manuel; Küchler, Robert; Nevidomskyy, Andriy H.; Yoshida, Makoto; Sakakibara, Toshiro; Kono, Yohei; Shimura, Yasuyuki; Sutherland, Michael L.; Takigawa, Masashi; Nakatsuji, SatoruIntermetallic compounds containing f-electron elements have been prototypical materials for investigating strong electron correlations and quantum criticality (QC). Their heavy fermion ground state evoked by the magnetic f-electrons is susceptible to the onset of quantum phases, such as magnetism or superconductivity, due to the enhanced effective mass (m*) and a corresponding decrease of the Fermi temperature. However, the presence of f-electron valence fluctuations to a non-magnetic state is regarded an anathema to QC, as it usually generates a paramagnetic Fermi-liquid state with quasiparticles of moderate m*. Such systems are typically isotropic, with a characteristic energy scale T0 of the order of hundreds of kelvins that require large magnetic fields or pressures to promote a valence or magnetic instability. Here we show the discovery of a quantum critical behaviour and a Lifshitz transition under low magnetic field in an intermediate valence compound α-YbAlB4. The QC origin is attributed to the anisotropic hybridization between the conduction and localized f-electrons. These findings suggest a new route to bypass the large valence energy scale in developing the QC.Item Kondo hybridization and quantum criticality in β−YbAlB4 by laser ARPES(American Physical Society, 2018) Bareille, Cédric; Suzuki, Shintaro; Nakayama, Mitsuhiro; Kuroda, Kenta; Nevidomskyy, Andriy H.; Matsumoto, Yosuke; Nakatsuji, Satoru; Kondo, Takeshi; Shin, Shik; Center for Quantum MaterialsWe report an angle-resolved photoemission (ARPES) study of β−YbAlB4, which is known to harbor unconventional quantum criticality (QC) without any tuning. We directly observe a quasiparticle peak (QP) emerging from hybridization, characterized by a binding energy and an onset of coherence both at about 4 meV. This value conforms with a previously observed reduced Kondo scale at about 40 K. Consistency with an earlier study of carriers in β−YbAlB4 via the Hall effect strongly suggests that this QP is responsible for the QC in β−YbAlB4. A comparison with the sister polymorph α−YbAlB4, which is not quantum critical at ambient pressure, further supports this result. Indeed, within the limitation of our instrumental resolution, our ARPES measurements do not show tangible sign of hybridization in this locally isomorphic system, while the conduction band we observe is essentially the same as in β−YbAlB4. We therefore claim that we identified by ARPES the carriers responsible for the QC in β−YbAlB4. The observed dispersion and the underlying hybridization of this QP are discussed in the context of existing theoretical models.