Fermi surfaces in Kondo insulators

Liu, Hsu; Hartstein, M.; Wallace, Gregory J.; Davies, Alexander J.; Hatnean, Monica Ciomaga; Johannes, M. D.; Shitsevalova, N. Yu.; Balakrishnan, G.; Sebastian, Suchitra E.

doi:10.1088/1361-648x/aaa522

Cited by 49 publications

(58 citation statements)

References 47 publications

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“…Our findings bring to the fore the question of how such bulk quantum oscillations can arise in a bulk insulator given that thus far they have been considered the preserve of metals. This striking phenomenon first observed in SmB 6 ( Tan et al., 2015 ), now extends across a growing class of unconventional insulators including YbB 12 ( Xiang et al., 2018 ; Liu et al., 2018 ), and overturns the previously held belief that quantum oscillations are a property unique to metals. A theoretical challenge is thus posed that requires an understanding beyond our current interpretation of quantum oscillations that occur only in metals.…”

Section: Discussionsupporting

confidence: 57%

Intrinsic Bulk Quantum Oscillations in a Bulk Unconventional Insulator SmB6

et al. 2020

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Summary The finding of bulk quantum oscillations in the Kondo insulator SmB 6 proved a considerable surprise. Subsequent measurements of bulk quantum oscillations in other correlated insulators including YbB 12 lent support to our discovery of a class of bulk unconventional insulators that host bulk quantum oscillations. Here we perform a series of experiments to examine evidence for the intrinsic character of bulk quantum oscillations in floating zone-grown single crystals of SmB 6 that have been the subject of our quantum oscillation studies. We present results of thermodynamic, transport, and composition analysis experiments on pristine floating zone-grown single crystals of SmB 6 and compare quantum oscillations with metallic LaB 6 and elemental aluminum. These results establish the intrinsic origin of quantum oscillations from the insulating bulk of floating zone-grown SmB 6 . The similarity of the Fermi surface in insulating SmB 6 with the conduction-electron Fermi surface in metallic hexaborides is at the heart of a theoretical mystery.

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Section: Discussionsupporting

confidence: 57%

Intrinsic Bulk Quantum Oscillations in a Bulk Unconventional Insulator SmB6

et al. 2020

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Section: Introductionmentioning

confidence: 99%

“…The origin of bulk quantum oscillations in bulk insulating unconventional insulators, first discovered in SmB 6 [1], has been the subject of much debate [1][2][3][4][5][6][7][8]. Another recently discovered unconventional insulator is the Kondo insulator YbB 12 [4,6], in which high magnetic fields dramatically reduce the electrical resistivity, causing the metallic ground state to be realised beyond 𝜇 0 𝐻 ≈ 47 T [9,10]. Quantum oscillation measurements in metallic YbB 12 accessed in high magnetic fields thus uniquely enable us to make a comparison between quantum oscillations in the unconventional insulating state and the field-induced metallic state.…”

Section: Introductionmentioning

confidence: 99%

$f$-electron hybridised metallic Fermi surface in magnetic field-induced metallic YbB$_{12}$

Liu,

Hickey,

Hartstein

et al. 2021

Preprint

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The nature of the Fermi surface observed in the recently discovered family of unconventional insulators starting with SmB 6 and subsequently YbB 12 is a subject of intense inquiry. Here we shed light on this question by comparing quantum oscillations between the high magnetic field-induced metallic regime in YbB 12 and the unconventional insulating regime. In the field-induced metallic regime beyond 47 T, we find prominent quantum oscillations in the contactless resistivity characterised by multiple frequencies up to at least 3000 T and heavy effective masses up to at least 17 𝑚 e , characteristic of an 𝑓 -electron hybridised metallic Fermi surface. The growth of quantum oscillation amplitude at low temperatures in electrical transport and magnetic torque in insulating YbB 12 is closely similar to the Lifshitz-Kosevich low temperature growth of quantum oscillation amplitude in field-induced metallic YbB 12 , pointing to an origin of quantum oscillations in insulating YbB 12 from in-gap neutral low energy excitations. The field-induced metallic regime of YbB 12 is characterised by more Fermi surface sheets of heavy quasiparticle effective mass that emerge in addition to the heavy Fermi surface sheets yielding multiple quantum oscillation frequencies below 1000 T observed in both insulating and metallic regimes. We thus observe a heavy multi-component Fermi surface in which 𝑓electron hybridisation persists from the unconventional insulating to the fieldinduced metallic regime of YbB 12 , which is in distinct contrast to the unhybridised conduction electron Fermi surface observed in the case of the unconventional insulator SmB 6 . Our findings require a different theoretical model of neutral in-gap low energy excitations in which the 𝑓 -electron hybridisation is retained in the case of the unconventional insulator YbB 12 .

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“…[1,2] In some mixed-valence compounds, however, electron-electron interactions lead to the opening of a charge gap at low temperature, resulting in an insulating state which can be called a mixed-valence insulator (MVI). The nature of this insulating state has attracted much attention in recent years, following a proposal that some MVIs could host an interaction-induced three-dimensional topological insulator state [3][4][5], and the subsequent experimental observation of quantum oscillations coexisting with the insulating state in the MVIs SmB 6 [6,7] and YbB 12 [8,9].…”

Section: Introductionmentioning

confidence: 99%

Properties of the donor impurity band in mixed valence insulators

Skinner

2019

Phys. Rev. Materials

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In traditional semiconductors with large effective Bohr radius, an electron donor creates a hydrogen-like bound state just below the conduction band edge. The properties of the impurity band arising from such hydrogenic impurities have been studied extensively during the last 70 years. In this paper we consider whether a similar bound state and a similar impurity band can exist in mixed-valence insulators, where the gap arises at low temperature due to strong electron-electron interactions. We find that the structure of the hybridized conduction band leads to an unusual bound state that can be described using the physics of the one-dimensional hydrogen atom. The properties of the resulting impurity band are also modified in a number of ways relative to the traditional semiconductor case; most notably, the impurity band can hold a much larger concentration without inducing an insulator-to-metal transition. We estimate the critical doping associated with this transition, and then proceed to calculate the dc and ac conductivities and the specific heat. We discuss our results in light of recent measurements on the mixed-valence insulator SmB 6 , and find them to be consistent with the experiments.

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Fermi surfaces in Kondo insulators

Cited by 49 publications

References 47 publications

Intrinsic Bulk Quantum Oscillations in a Bulk Unconventional Insulator SmB6

Intrinsic Bulk Quantum Oscillations in a Bulk Unconventional Insulator SmB6

$f$-electron hybridised metallic Fermi surface in magnetic field-induced metallic YbB$_{12}$

Properties of the donor impurity band in mixed valence insulators

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