Browsing by Author "Nakatsuji, Satoru"

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    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, Satoru
    Intermetallic 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.
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    Inhomogeneous Kondo-lattice in geometrically frustrated Pr2Ir2O7
    (Springer Nature, 2021) Kavai, Mariam; Friedman, Joel; Sherman, Kyle; Gong, Mingda; Giannakis, Ioannis; Hajinazar, Samad; Hu, Haoyu; Grefe, Sarah E.; Leshen, Justin; Yang, Qiu; Nakatsuji, Satoru; Kolmogorov, Aleksey N.; Si, Qimiao; Lawler, Michael; Aynajian, Pegor; Rice Center for Quantum Materials
    Magnetic fluctuations induced by geometric frustration of local Ir-spins disturb the formation of long-range magnetic order in the family of pyrochlore iridates. As a consequence, Pr2Ir2O7 lies at a tuning-free antiferromagnetic-to-paramagnetic quantum critical point and exhibits an array of complex phenomena including the Kondo effect, biquadratic band structure, and metallic spin liquid. Using spectroscopic imaging with the scanning tunneling microscope, complemented with machine learning, density functional theory and theoretical modeling, we probe the local electronic states in Pr2Ir2O7 and find an electronic phase separation. Nanoscale regions with a well-defined Kondo resonance are interweaved with a non-magnetic metallic phase with Kondo-destruction. These spatial nanoscale patterns display a fractal geometry with power-law behavior extended over two decades, consistent with being in proximity to a critical point. Our discovery reveals a nanoscale tuning route, viz. using a spatial variation of the electronic potential as a means of adjusting the balance between Kondo entanglement and geometric frustration.
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    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 Materials
    We 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.