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1. Weyl-Kondo semimetals in nonsymmorphic systems

   https://doi.org/10.1103/PhysRevB.101.075138  

   Grefe, Sarah E.; Lai, Hsin-Hua; Paschen, Silke; Si, Qimiao (February 2020, Physical Review B)
2. Kondo-Induced Giant Isotropic Negative Thermal Expansion

   https://doi.org/10.1103/PhysRevLett.124.125701  

   Mazzone, D. G.; Dzero, M.; Abeykoon, AM. M.; Yamaoka, H.; Ishii, H.; Hiraoka, N.; Rueff, J.-P.; Ablett, J. M.; Imura, K.; Suzuki, H. S.; et al (March 2020, Physical Review Letters)
3. Pristine quantum criticality in a Kondo semimetal

   https://doi.org/10.1126/sciadv.abf9134  

   Fuhrman, Wesley T.; Sidorenko, Andrey; Hänel, Jonathan; Winkler, Hannes; Prokofiev, Andrey; Rodriguez-Rivera, Jose A.; Qiu, Yiming; Blaha, Peter; Si, Qimiao; Broholm, Collin L.; et al (May 2021, Science Advances)

   The observation of quantum criticality in diverse classes of strongly correlated electron systems has been instrumental in establishing ordering principles, discovering new phases, and identifying the relevant degrees of freedom and interactions. At focus so far have been insulators and metals. Semimetals, which are of great current interest as candidate phases with nontrivial topology, are much less explored in experiments. Here, we study the Kondo semimetal CeRu 4 Sn 6 by magnetic susceptibility, specific heat, and inelastic neutron scattering experiments. The power-law divergence of the magnetic Grünesien ratio reveals that, unexpectedly, this compound is quantum critical without tuning. The dynamical energy over temperature scaling in the neutron response throughout the Brillouin zone and the temperature dependence of the static uniform susceptibility, indicate that temperature is the only energy scale in the criticality. Such behavior, which has been associated with Kondo destruction quantum criticality in metallic systems, could be generic in the semimetal setting. 

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4. Migdal–Eliashberg superconductivity in a Kondo lattice

   https://doi.org/10.1088/1361-648X/ad43a5  

   Awelewa, Samuel; Dzero, Maxim (May 2024, Journal of Physics: Condensed Matter)

   Abstract We apply the Migdal–Eliashberg theory of superconductivity to heavy-fermion and mixed valence materials. Specifically, we extend the Anderson lattice model to a case when there exists a strong coupling between itinerant electrons and lattice vibrations. Using the saddle-point approximation, we derive a set of coupled nonlinear equations which describe competition between the crossover to a heavy-fermion or mixed-valence regimes and conventional superconductivity. We find that superconductivity at strong coupling emerges on par with the development of the many-body coherence in a Kondo lattice. Superconductivity is gradually suppressed with the onset of the Kondo screening and for strong electron-phonon coupling the Kondo screening exhibits a characteristic re-entrant behavior. Even though for both weak and strong coupling limits the suppression of superconductivity is weaker in the mixed-valence regime compared to the local moment one, superconducting critical temperature still remains nonzero. In the weak coupling limit the onset of the many body coherence develops gradually, in the strong coupling limit it emerges abruptly in the mixed valence regime while in the local moment regime thef-electrons remain effectively decoupled from the conduction electrons. Possibility of experimental realization of these effects in Ce-based compounds is also discussed. 

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5. Inhomogeneous Kondo-lattice in geometrically frustrated Pr2Ir2O7

   https://doi.org/s41467-021-21698-z  

   Kavai, Mariam; Friedman, Joel; Sherman, Kyle; Gong, Mingda; Giannakis, Ioannis; Hajinazar, Samad; Hu, Haoyu; Grefe, Sarah E; Leshen, Justin; Yang, Qiu; et al (March 2021, Nature communications)

   null (Ed.)

   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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