Surface Kondo effect and non-trivial metallic state of the Kondo insulator YbB12

Hagiwara, Kenta; Ohtsubo, Yoshiyuki; Matsunami, Masaharu; Ideta, S.; Tanaka, Kiyohisa; Miyazaki, Hitoshi; Rault, Julien; Fèvre, P. Le; Bertran, F.; Taleb‐Ibrahimi, A.; Yukawa, Ryu; Kobayashi, Masaki; Horiba, Koji; Kumigashira, Hiroshi; Sumida, Kazuki; Okuda, Takashi; Iga, Fumitoshi; Kimura, S.

doi:10.1038/ncomms12690

Cited by 53 publications

(43 citation statements)

References 27 publications

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“…The ubiquitous low-temperature resistivity plateau led to proposals of surface-dominated conductivity and observations of nonlocal transport (3)(4)(5). Surface states have been found in angle-resolved photoemission spectroscopy (ARPES) measurements (6)(7)(8)(9)(10), but the topological origin of these states is under debate (11). Furthermore, discovery of anomalous quantum oscillations (QOs) (12)(13)(14)(15) in the insulating state suggests the existence of exotic ground states, and questions the traditional dichotomy between insulators and metals.…”

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confidence: 99%

Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb ₂

Chen

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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The resistance of a conventional insulator diverges as temperature approaches zero. The peculiar low-temperature resistivity saturation in the 4f Kondo insulator (KI) SmB6has spurred proposals of a correlation-driven topological Kondo insulator (TKI) with exotic ground states. However, the scarcity of model TKI material families leaves difficulties in disentangling key ingredients from irrelevant details. Here we use angle-resolved photoemission spectroscopy (ARPES) to study FeSb2, a correlated d-electron KI candidate that also exhibits a low-temperature resistivity saturation. On the (010) surface, we find a rich assemblage of metallic states with two-dimensional dispersion. Measurements of the bulk band structure reveal band renormalization, a large temperature-dependent band shift, and flat spectral features along certain high-symmetry directions, providing spectroscopic evidence for strong correlations. Our observations suggest that exotic insulating states resembling those in SmB6and YbB12may also exist in systems with d instead of f electrons.

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confidence: 99%

Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb ₂

Chen

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…The surface states in SmB 6 are protected by time reversal and inversion symmetries, while those in YbB 12 are protected by crystal symmetry. In both compounds, the metallic surface states have been established using a number of experimental techniques, including angle-resolved photoemission spectroscopy (ARPES) [12,13]. In particular, in SmB 6 , spin-resolved ARPES has shown the spinmomentum locked surface, which is a characteristic feature of a topological insulator.…”

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confidence: 99%

Unconventional thermal metallic state of charge-neutral fermions in an insulator

et al. 2019

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Quantum oscillations (QOs) in transport and thermodynamic parameters at high magnetic fields are an unambiguous signature of the Fermi surface, the defining characteristic of a metal. Therefore, recent observations of QOs in insulating SmB 6 [1-4] and YbB 12 , in particular the QOs of the resistivity ρ xx in YbB 12 [5], have been a big surprise, pointing to the formation of a novel state of quantum matter. Despite the large charge gap inferred from the insulating behaviour of ρ xx , these compounds seemingly host a Fermi surface at high magnetic fields. However, the nature of the ground state in zero field has been little explored. Here we report the use of low-temperature heat-transport measurements to discover gapless, itinerant, charge-neutral excitations in the ground state of YbB 12 . At zero field, despite ρ xx being far larger than that of conventional metals, a sizable linear temperature dependent term in the thermal conductivity is clearly resolved in the zero-temperature limit (κ xx /T (T → 0) = κ 0 xx /T = 0), analogous to normal metallic behaviour. Such a residual κ 0 xx /T term at zero field, which is absent in SmB 6 [3, 6, 7], leads to a spectacular violation of the Wiedemann-Franz law: the Lorenz ratio L = κ xx ρ xx /T is 10 4 -10 5 times larger than that expected in conventional metals. These data indicate that YbB 12 is a charge insulator but a thermal metal, suggesting the presence of itinerant neutral fermions. Remarkably, more insulating crystals with larger activation energies exhibit a larger amplitude of the resistive QOs as well as a larger κ 0 xx /T , in stark contrast to conventional metals. Moreover, we find that these fermions couple to magnetic field, despite their charge neutrality. Our findings expose novel gapless and highly itinerant, charge-neutral quasiparticles in this unconventional quantum state.In intermetallic 4f and 5f compounds, strong hybridization between itinerant and predominately localized electrons often opens an insulating gap [8,9]. Among

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“…Following the methods shown in Sec. II A, we numerically calculate the renormalization factor b and the energy shift of the f -electron level λ self-consistently for the effective models (33) and (41). Then, based on the results, we discuss the effect of laser light on the Kondo effect.…”

Section: Linearly Polarized Laser Lightmentioning

confidence: 99%

“…Some kinds of Kondo insulators show topological phases thanks to their peculiar hybridization structures. They are called topological Kondo insulators 18,19,33 , which are gathering the great attention as the analogue of topological insulators in strongly correlated electron systems. In this section, we demonstrate that the laser light changes the topological properties of the topological Kondo insulators.…”

Section: A Model Of Topological Kondo Insulatorsmentioning

confidence: 99%

Laser-irradiated Kondo insulators: Controlling the Kondo effect and topological phases

2017

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We theoretically investigate the nature of laser-irradiated Kondo insulators. Using Floquet theory and slave boson approach, we study a periodic Anderson model and derive an effective model which describes the laser-irradiated Kondo insulators. In this model, we find two generic effects induced by laser light. One is the dynamical localization, which suppresses hopping and hybridization. The other is the laser-induced hopping and hybridization, which can be interpreted as a synthetic spinorbit coupling or magnetic field. The first effect drastically changes the behavior of the Kondo effect. Especially, the Kondo effect under laser light qualitatively changes its character depending on whether the hybridization is on-site or off-site. The second effect triggers topological phase transitions. In topological Kondo insulators, linearly polarized laser light realizes phase transitions between trivial, weak topological, and strong topological Kondo insulators. Moreover, circularly polarized laser light breaks time-reversal symmetry and induces Weyl semimetallic phases. Our results pave the new way to dynamically control the Kondo effect and topological phases in heavy fermion systems. We also discuss experimental setups to detect the signatures.

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Surface Kondo effect and non-trivial metallic state of the Kondo insulator YbB12

Cited by 53 publications

References 27 publications

Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb ₂

Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb ₂

Unconventional thermal metallic state of charge-neutral fermions in an insulator

Laser-irradiated Kondo insulators: Controlling the Kondo effect and topological phases

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Surface Kondo effect and non-trivial metallic state of the Kondo insulator YbB12

Cited by 53 publications

References 27 publications

Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb 2

Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb 2

Unconventional thermal metallic state of charge-neutral fermions in an insulator

Laser-irradiated Kondo insulators: Controlling the Kondo effect and topological phases

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Product

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Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb ₂

Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb ₂