Pressure-Resistant Intermediate Valence in the Kondo Insulator<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>SmB</mml:mi></mml:mrow><mml:mrow><mml:mn>6</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Butch, Nicholas P.; Paglione, Johnpierre; Chow, Paul; Xiao, Yuming; Marianetti, Chris A.; Booth, C. H.; Jeffries, J. R.

doi:10.1103/physrevlett.116.156401

Cited by 43 publications

(87 citation statements)

References 51 publications

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“…At T = 8 K, a quick enhancement of the valence was observed under pressure from ν = 2.55 at 0.6 GPa to ν = 2.70 at P c = ∼8 GPa, followed by a slow valence increase to ν = 2.78 at 26 GPa, across the level of the surface valence value of ν = 2.73. SmB 6 becomes magnetically ordered below 12 K [31,43] once the insulating gap closes by 5-10 GPa [44,45], with a Sm mean valence of ν = ∼2.69(3) [17] (marked as the grey area in Fig. 3).…”

Section: Resultsmentioning

confidence: 99%

“…The strong hybridization also leads to a mixture of the Sm 2+ (4f 6 ) and Sm 3+ (4f 5 ) configurations, with the electronic structure described by the Hund's rule ground states with total orbital momenta of J = 0 and 5/2, respectively. The bulk and surface electronic properties have been investigated using a wide range of experimental methods, highpressure x-ray-absorption spectroscopy experiments [17,18], scanning tunneling spectroscopy [19][20][21], angle-resolved photoelectron spectroscopy [22][23][24], hard x-ray photoelectron spectroscopy [25,26], and resonant soft x-ray reflectometry [27] providing additional confirmation of surface states in SmB 6 .…”

Section: Introductionmentioning

confidence: 99%

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Surface- and pressure-induced bulk Kondo breakdown in SmB6

et al. 2018

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Motivated by the prediction of surface Kondo breakdown in topological Kondo insulators, we investigated the valence and magnetism of SmB 6 with x-ray absorption and magnetic circular dichroism at the Sm M 4,5 and L 2 edges with surface and bulk sensitivity, respectively. A higher Sm valence state at the surface and in the bulk under pressure indicates the surface-and pressure-induced bulk Kondo breakdown. We confirmed the different magnetization origin from the surface (f electron) to the bulk (d electron) and ascertained the direct relationship between the disappearance of the Sm L 2 -edge x-ray magnetic circular dichroism signal and the closure of the d-f hybridization gap in SmB 6 bulk under pressure, paving the way for further investigations of the Kondo insulators. Above P c = 8.5 GPa, a more localized 4f state with higher valence and the disappearing of the 5d magnetism are observed, suggesting the closure of the hybridization gap in the bulk.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Surface- and pressure-induced bulk Kondo breakdown in SmB6

et al. 2018

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“…To cure the inadequacy of mean-field and recover an insulator with an indirect gap, ad hoc dispersion of f electrons is frequently assumed [23,24], whose minimum in the Brillouin zone is shifted by (π, π) from that of conduction electrons. However, suchan additional ingredient is not truly justified, e.g., in SmB 6 , where the large separation between 4f elements [29], hence their negligible mutual overlap, implies that the main source of f itineracy remains the c-f hybridization. We mention that spin-polarized local density approximation (LSDA)+U calculations [54] suggest a sizable f -f hopping mediated by the hybridization with boron p states.…”

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confidence: 99%

“…The emergence of an indirect gap [27] or its closure [28] from a model of nondispersive f orbitals, in accordance with their large mutual distance in actual materials [29,30], is relevant to candidate TKIs, e.g., SmB 6 , but also to other 4f compounds not yet excluded to host topologically nontrivial states, which show bulk insulating behavior (Ce 3 Bi 4 Pt 3 [31], YbB 12 [32], CeRhAs [33]) as well as metallic one (CeNiSn [28],CeRhSb [34], CeIrSb [35]). Moreover, assuming that increasing pressure roughly corresponds to reducing the interaction strength, we can qualitatively account for the nonuniversal behavior of the gap as observed in several Kondo semiconductors [33,[36][37][38][39][40].…”

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confidence: 99%

Many-body breakdown of indirect gap in topological Kondo insulators

Wysokiński

Fabrizio

2016

Phys. Rev. B

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We show that the inclusion of nonlocal correlation effects in a variational wave function for the ground state of a topological Anderson lattice Hamiltonian is capable of describing both topologically trivial insulating phases and nontrivial ones characterized by an indirect gap, as well as its closure at the transition into a metallic phase. The method, though applied to an oversimplified model, thus captures the metallic and insulating states that are indeed observed in a variety of Kondo semiconductors, while accounting for topologically nontrivial band structures. PACS numbers: 71.27.+a, 71.30.+h, 03.65.Vf Introduction. Phenomena at the crossroads of topological insulators and strongly correlated systems have recently gained a lot of attention, mainly stimulated by theoretical proposals that the inclusion of strong correlations in specific models with a nontrivial topological content may give rise to novel and interesting phenomena [1][2][3][4][5]. However, electronic correlations in most of the discovered topological insulators [6,7] seem to be relatively weak, and hence of minor importance. For that reason, the concept of topological Kondo insulators (TKIs) originally put forward in Refs.[8] and [9] is particularly appealing due to its possible realization in already known Kondo insulating compounds [10]. Notably, SmB 6 is convincingly confirmed to be a TKI [11][12][13][14][15][16][17][18][19] with strong evidence of the essential role played by many-body correlations [20,21].Theoretically, the main physical properties of TKI are frequently described in the framework of topological Anderson lattice models in which strong spin-orbit coupling is encoded into a spin-dependent hybridization with odd parity in momentum space [8,9,22]. Many-body correlations in these models have been mostly treated by the slave-boson approach or by the dynamical mean-field theory (DMFT), and predicted to induce quantum phase transitions between topologically distinct bulk insulating phases [22][23][24].The aim of this work is to demonstrate that accounting for nonlocal spatial correlations, beyond those already well captured by the mentioned techniques, plays an important role in modeling TKIs. Specifically, those nonlocal correlations supply the f electron self-energy with a momentum dependence, which is otherwise purely local within DMFT and at the saddle point of the slave-boson theory. Remarkably, such a momentum dependence allows one to describe, above a critical interaction strength, the emergence of a topological Kondo insulator with an indirect gap, and its subsequent closure at the transition into a metallic state, an intriguing result opposite to the conventional Mott phenomenon where increasing interaction instead favours the onset of an insulating state. We disclose this scenario in two dimensions by means of the diagrammatic expansion of the Gutzwiller wave function (GWF) technique [25,26]. CeIrSb [35]). Moreover, assuming that increasing pressure roughly corresponds to reducing the interaction strength, we can ...

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“…To provide the qualitative understanding of the observed phenomena, we recall that it has been well established experimentally 21,22 that SmB 6 belongs to a class of intermediate valence systems: the f -orbital electronic configuration of samarium ions fluctuates between the 4f 5 and 4f 6 states on a typical timescale τ ivc across a fairly wide temperature range. Experiments that probe the samarium valence on a timescale longer than τ ivc will observe an intermediate valence state 23,24 .…”

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confidence: 99%

Surface-dominated conduction up to 240 K in the Kondo insulator SmB6 under strain

et al. 2017

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SmB 6 is a strongly correlated mixed-valence Kondo insulator 1,2 with a newly discovered surface state 3,4 , proposed to be of non-trivial topological origin 5,6 . However, the surface state dominates electrical conduction only below T * ≈ 4 K (ref. 3), limiting its scientific investigation and device application. Here, we report the enhancement of T * in SmB 6 under the application of tensile strain. With 0.7% tensile strain we report surface-dominated conduction at up to a temperature of 240 K, persisting even after the strain has been removed. This can be explained in the framework of strain-tuned temporal and spatial fluctuations of f-electron configurations, which might be generally applied to other mixed-valence materials. We note that this amount of strain can be induced in epitaxial SmB 6 films via substrate in potential device applications.SmB 6 is a prototypical Kondo insulator, a material where the quantum mechanical hybridization between the conduction and f -electronic orbitals leads to an opening of a narrow Kondo gap near the Fermi energy 1,2 . Experimental observations of the robust surface conductivity on the background of the fully insulating bulk 3,4 and quantum oscillations from a two-dimensional surface 7 both contribute to the highly non-trivial nature of an insulating state in SmB 6 . SmB 6 has so far attracted much attention as a prominent candidate material for a strongly correlated topological insulator 5,6,8 . It is noteworthy to mention that the first application of SmB 6 as a radiofrequency micro-oscillator device 9 has been recently demonstrated, operating at cryogenic temperatures.Due to the small value of the bandgap ∆, scientific investigations and device applications of SmB 6 have thus far been limited to temperatures below the resistance saturation temperature T *

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Pressure-Resistant Intermediate Valence in the Kondo InsulatorSmB6

Cited by 43 publications

References 51 publications

Surface- and pressure-induced bulk Kondo breakdown in SmB6

Surface- and pressure-induced bulk Kondo breakdown in SmB6

Many-body breakdown of indirect gap in topological Kondo insulators

Surface-dominated conduction up to 240 K in the Kondo insulator SmB6 under strain

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