R-3 Repository :: Browsing by Author "Paschen, Silke"

Browsing by Author "Paschen, Silke"

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Emergent flat band and topological Kondo semimetal driven by orbital-selective correlations
(Springer Nature, 2024) Chen, Lei; Xie, Fang; Sur, Shouvik; Hu, Haoyu; Paschen, Silke; Cano, Jennifer; Si, Qimiao
Flat electronic bands are expected to show proportionally enhanced electron correlations, which may generate a plethora of novel quantum phases and unusual low-energy excitations. They are increasingly being pursued in d-electron-based systems with crystalline lattices that feature destructive electronic interference, where they are often topological. Such flat bands, though, are generically located far away from the Fermi energy, which limits their capacity to partake in the low-energy physics. Here we show that electron correlations produce emergent flat bands that are pinned to the Fermi energy. We demonstrate this effect within a Hubbard model, in the regime described by Wannier orbitals where an effective Kondo description arises through orbital-selective Mott correlations. Moreover, the correlation effect cooperates with symmetry constraints to produce a topological Kondo semimetal. Our results motivate a novel design principle for Weyl Kondo semimetals in a new setting, viz. d-electron-based materials on suitable crystal lattices, and uncover interconnections among seemingly disparate systems that may inspire fresh understandings and realizations of correlated topological effects in quantum materials and beyond.
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.
Global phase diagram and momentum distribution of single-particle excitations in Kondo insulators
(American Physical Society, 2018) Pixley, J.H.; Yu, Rong; Paschen, Silke; Si, Qimiao
Kondo insulators are emerging as a simplified setting to study both magnetic and insulator-to-metal quantum phase transitions. Here, we study the half-filled Anderson lattice model defined on a magnetically frustrated Shastry-Sutherland geometry. We determine a “global” phase diagram that applies to both the local-moment and intermediate-valence regimes. This provides the theoretical basis for understanding how tuning a Kondo insulator by external parameters can close its hybridization gap, liberate the local-moment spins from the conduction electrons, and lead to a magnetically correlated metal. We also calculate the momentum distribution of the single-particle excitations in the Kondo insulating state, and show how Fermi-surface-like features emerge as a precursor to the actual Fermi surfaces of the Kondo-destroyed metals. The implications for an incipient Fermi surface and quantum phase transitions of Kondo insulators including SmB6 are discussed.
Low-carrier density and fragile magnetism in a Kondo lattice system
(American Physical Society, 2019) Rai, Binod K.; Oswald, Iain W.H.; Ban, Wenjing; Huang, C.-L.; Loganathan, V.; Hallas, A.M.; Wilson, M.N.; Luke, G.M.; Harriger, L.; Huang, Q.; Li, Y.; Dzsaber, Sami; Chan, Julia Y.; Wang, N.L.; Paschen, Silke; Lynn, J.W.; Nevidomskyy, Andriy H.; Dai, Pengcheng; Si, Q.; Morosan, E.; Rice Center for Quantum Materials
Kondo-based semimetals and semiconductors are of extensive current interest as a viable platform for strongly correlated states in the dilute carrier limit. It is thus important to explore the routes to understand such systems. One established pathway is through the Kondo effect in metallic nonmagnetic analogs, in the so called half-filling case of one conduction electron and oneﾠ4fﾠelectron per site. Here, we demonstrate that Kondo-based semimetals develop out of conduction electrons with a low-carrier density in the presence of an even number of rare-earth sites. We do so by studying the Kondo materialﾠYb3Ir4Ge13ﾠalong with its closed-4f-shell counterpart,ﾠLu3Ir4Ge13. Through magnetotransport, optical conductivity, and thermodynamic measurements, we establish that the correlated semimetallic state ofﾠYb3Ir4Ge13ﾠbelow its Kondo temperature originates from the Kondo effect of a low-carrier conduction-electron background. In addition, it displays fragile magnetism at very low temperatures, which in turn, can be tuned to a Griffiths-phase-like regime through Lu-for-Yb substitution. These findings are connected with recent theoretical studies in simplified models. Our results can pave the way to exploring strong correlation physics in a semimetallic environment.
Pristine quantum criticality in a Kondo semimetal
(AAAS, 2021) Fuhrman, Wesley T.; Sidorenko, Andrey; Hänel, Jonathan; Winkler, Hannes; Prokofiev, Andrey; Rodriguez-Rivera, Jose A.; Qiu, Yiming; Blaha, Peter; Si, Qimiao; Broholm, Collin L.; Paschen, Silke; Rice Center for Quantum Materials
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 CeRu4Sn6 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. Thermodynamic and inelastic neutron scattering data evidence dynamical scaling in quantum critical candidate Weyl-Kondo semimetal. Thermodynamic and inelastic neutron scattering data evidence dynamical scaling in quantum critical candidate Weyl-Kondo semimetal.
Quantum criticality enabled by intertwined degrees of freedom
(National Academy of Sciences, 2023) Liu, Chia-Chuan; Paschen, Silke; Si, Qimiao; Rice Center for Quantum Materials
Strange metals appear in a wide range of correlated materials. Electronic localization–delocalization and the expected loss of quasiparticles characterize beyond-Landau metallic quantum critical points and the associated strange metals. Typical settings involve local spins. Systems that contain entwined degrees of freedom offer new platforms to realize unusual forms of quantum criticality. Here, we study the fate of an SU(4) spin–orbital Kondo state in a multipolar Bose–Fermi Kondo model, which provides an effective description of a multipolar Kondo lattice, using a renormalization-group method. We show that at zero temperature, a generic trajectory in the model’s parameter space contains two quantum critical points, which are associated with the destruction of Kondo entanglement in the orbital and spin channels, respectively. Our asymptotically exact results reveal an overall phase diagram, provide the theoretical basis to understand puzzling recent experiments of a multipolar heavy fermion metal, and point to a means of designing different forms of quantum criticality and strange metallicity in a variety of strongly correlated systems.
Sequential localization of a complex electron fluid
(National Academy of Sciences, 2019) Martelli, Valentina; Cai, Ang; Nica, Emilian M.; Taupin, Mathieu; Prokofiev, Andrey; Liu, Chia-Chuan; Lai, Hsin-Hua; Yu, Rong; Ingersent, Kevin; Küchler, Robert; Strydom, André M.; Geiger, Diana; Haenel, Jonathan; Larrea, Julio; Si, Qimiao; Paschen, Silke
Complex and correlated quantum systems with promise for new functionality often involve entwined electronic degrees of freedom. In such materials, highly unusual properties emerge and could be the result of electron localization. Here, a cubic heavy fermion metal governed by spins and orbitals is chosen as a model system for this physics. Its properties are found to originate from surprisingly simple low-energy behavior, with 2 distinct localization transitions driven by a single degree of freedom at a time. This result is unexpected, but we are able to understand it by advancing the notion of sequential destruction of an SU(4) spin–orbital-coupled Kondo entanglement. Our results implicate electron localization as a unified framework for strongly correlated materials and suggest ways to exploit multiple degrees of freedom for quantum engineering.
Symmetry constraints and spectral crossing in a Mott insulator with Green's function zeros
(American Physical Society, 2024) Setty, Chandan; Sur, Shouvik; Chen, Lei; Xie, Fang; Hu, Haoyu; Paschen, Silke; Cano, Jennifer; Si, Qimiao; Rice Center for Quantum Materials
Lattice symmetries are central to the characterization of electronic topology. Recently, it was shown that Green's function eigenvectors form a representation of the space group. This formulation has allowed the identification of gapless topological states even when quasiparticles are absent. Here we demonstrate the profundity of the framework in the extreme case, when interactions lead to a Mott insulator, through a solvable model with long-range interactions. We find that both Mott poles and zeros are subject to the symmetry constraints, and relate the symmetry-enforced spectral crossings to degeneracies of the original noninteracting eigenstates. Our results lead to new understandings of topological quantum materials and highlight the utility of interacting Green's functions toward their symmetry-based design.
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.

Browsing by Author "Paschen, Silke"

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