Browsing by Author "Grefe, Sarah E."

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    Giant spontaneous Hall effect in a nonmagnetic Weyl–Kondo semimetal
    (PNAS, 2021) Dzsaber, Sami; Yan, Xinlin; Taupin, Mathieu; Eguchi, Gaku; Prokofiev, Andrey; Shiroka, Toni; Blaha, Peter; Rubel, Oleg; Grefe, Sarah E.; Lai, Hsin-Hua; Si, Qimiao; Paschen, Silke; Rice Center for Quantum Materials
    Nontrivial topology in condensed-matter systems enriches quantum states of matter to go beyond either the classification into metals and insulators in terms of conventional band theory or that of symmetry-broken phases by Landau’s order parameter framework. So far, focus has been on weakly interacting systems, and little is known about the limit of strong electron correlations. Heavy fermion systems are a highly versatile platform to explore this regime. Here we report the discovery of a giant spontaneous Hall effect in the Kondo semimetal Ce3Bi4Pd3 that is noncentrosymmetric but preserves time-reversal symmetry. We attribute this finding to Weyl nodes—singularities of the Berry curvature—that emerge in the immediate vicinity of the Fermi level due to the Kondo interaction. We stress that this phenomenon is distinct from the previously detected anomalous Hall effect in materials with broken time-reversal symmetry; instead, it manifests an extreme topological response that requires a beyond-perturbation-theory description of the previously proposed nonlinear Hall effect. The large magnitude of the effect in even tiny electric and zero magnetic fields as well as its robust bulk nature may aid the exploitation in topological quantum devices.
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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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    Weyl–Kondo semimetal in heavy-fermion systems
    (National Academy of Sciences, 2018) Lai, Hsin-Hua; Grefe, Sarah E.; Paschen, Silke; Si, Qimiao; Rice Center for Quantum Materials
    While electronic states with nontrivial topology have traditionally been known in insulators, they have been evidenced in metals during the past 2 years. Such Weyl semimetals show topological protection while conducting electricity both in the bulk and on the surface. An outstanding question is whether topological protection can happen in metals with strong correlations. Here, we report theoretical work on a strongly correlated lattice model to demonstrate the emergence of a Weyl–Kondo semimetal. We identify Weyl fermions in the bulk and Fermi arcs on the surface, both of which are associated with the many-body phenomenon called the Kondo effect. We determine a key signature of this Weyl–Kondo semimetal, which is realized in a recently discovered heavy-fermion compound.