Polarity-Driven Surface Metallicity in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>SmB</mml:mi><mml:mn>6</mml:mn></mml:msub></mml:math>

Zhu, Zhiwei; Nicolaou, A.; Levy, G.; Butch, Nicholas P.; Syers, Paul; Wang, X. F.; Paglione, Johnpierre; Sawatzky, G. A.; Elfimov, I. S.; Damascelli, A.

doi:10.1103/physrevlett.111.216402

Cited by 138 publications

(170 citation statements)

References 40 publications

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“…Consequently, our locally resolved measurements show that the surface reconstruction alone cannot account for the surface conductance (51). The robustness of the measured conductance at V = 0 is consistent with an additional conductance channel, possibly at the surface.…”

Section: Discussionmentioning

confidence: 51%

Hybridization gap and Fano resonance in SmB₆

Rößler¹,

Jang

Kim

et al. 2014

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

127

160

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Hybridization between conduction electrons and the strongly interacting f-electrons in rare earth or actinide compounds may result in new states of matter. Depending on the exact location of the concomitant hybridization gap with respect to the Fermi energy, a heavy fermion or an insulating ground state ensues. To study this entanglement locally, we conducted scanning tunneling microscopy and spectroscopy (STS) measurements on the "Kondo insulator" SmB 6 . The vast majority of surface areas investigated were reconstructed, but infrequently, patches of varying sizes of nonreconstructed Smor B-terminated surfaces also were found. On the smallest patches, clear indications for the hybridization gap with logarithmic temperature dependence (as expected for a Kondo system) and for intermultiplet transitions were observed. On nonreconstructed surface areas large enough for coherent cotunneling, we were able to observe clear-cut Fano resonances. Our locally resolved STS indicated considerable finite conductance on all surfaces independent of their structure, not proving but leaving open the possibility of the existence of a topologically protected surface state.M aterials with strong electron correlations continue to draw enormous attention, not only because they may give rise to fundamentally new states of matter or new phenomena but also because of the hope for advanced technological applications. Heavy fermion (HF) materials, i.e., intermetallics of certain rare earths (REs), such as Ce, Sm, and Yb, are model systems to study strong electronic correlations (1). Here, the RE-derived localized 4f states are covalently mixed with the conduction-band states and, thus, acquire a finite lifetime. The associated decay rate in relation to the energy of the localized 4f state corresponds to the valency. In an Sm-based HF system, the valence lies between 3+ (4f 5 ) and 2+ (4f 6 ), which implies a considerable amount of charge fluctuations. This usually is referred to as intermediate valence (2). In addition to the abovementioned mixing of 4f states and the conduction band, which is well described within the framework of one-electron models, a manybody interaction is operating between the 4f and conduction electrons. This "Kondo effect" (3) eventually leads to a screening of the local moments as a result of particle-hole excitations that are manifested by a narrow Abrikosov-Suhl, or Kondo, resonance at E F , the width of which is given by the single-ion Kondo temperature T K .Because of the periodic arrangement of REs in an HF intermetallic, the Kondo resonances form a weakly dispersive HF or "coherent 4f−" band, resulting in a heavy Fermi liquid state well below T K . The band interaction between the renormalized 4f and the conduction band generates a so-called hybridization gap, which opens at around T K . Under certain conditions, E F may reside inside this gap, characterizing a so-called Kondo insulator (4).SmB 6 is such a Kondo insulator, with a valence ν ∼ 2:6 (5), ν being slightly temperature dependent (6, 7). A sharp de...

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Section: Discussionmentioning

confidence: 51%

Hybridization gap and Fano resonance in SmB₆

Rößler¹,

Jang

Kim

et al. 2014

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

127

160

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“…More specifically, while the layered structure of Bi 2 Se 3 allows an easy exposure of atomically smooth surfaces via cleavage, the 3D crystalline structure of SmB 6 makes it unfeasible. Also, it is known that the polar nature of the (001) surface, where the topological surface states are predicted to exist, causes various complex issues including surface reconstruction 37 and time-dependent evolution 41 . Quantum oscillation measurements have shown the existence of surface bands and their possible topological nature 42 but the nature of the bulk insulating state inferred from such measurements is currently under debate 43 .…”

Section: Introductionmentioning

confidence: 99%

Planar tunneling spectroscopy of the topological Kondo insulator SmB6

et al. 2017

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Several technical issues and challenges are identified and investigated for the planar tunneling spectroscopy of the topological Kondo insulator SmB6. Contrasting behaviors of the tunnel junctions prepared in two different ways are analyzed and explained in detail. The conventional approach based on an AlOx tunnel barrier results in unsatisfactory results due to the inter-diffusion between SmB6 and deposited Al. On the contrary, plasma oxidation of SmB6 crystals produces high-quality tunnel barriers on both (001) and (011) surfaces. Resultant conductance spectra are highly reproducible with clear signatures for the predicted surface Dirac fermions and the bulk hybridization gap as well. The surface states are identified to reside on two or one distinguishable Dirac cone(s) on the (001) and (011) surface, respectively, in good agreement with the recent literature. However, their topological protection is found to be limited within the low energy region due to their inevitable interaction with the bulk excitations, called spin excitons, consistent with a recent theoretical prediction. Implications of our findings on other physical properties in SmB6 and also other correlated topological materials are remarked.

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“…Although activated electrical transport is readily inferred from the dramatic temperature-dependent resistivity, at low temperatures the resistivity saturates at a finite value instead of diverging to infinity. This anomalous behavior is now linked to the presence of electrically conducting surface states [8], and many experiments have been directed at determining the topological classification of the material [9][10][11][12][13][14][15][16][17][18][19][20]. A full description of the underlying strongly correlated electron state is key to understanding nontrivial topology in f-electron materials.…”

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confidence: 99%

Pressure-Resistant Intermediate Valence in the Kondo InsulatorSmB6

et al. 2016

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Resonant x-ray emission spectroscopy (RXES) was used to determine the pressure dependence of the f-electron occupancy in the Kondo insulator SmB6. Applied pressure reduces the f-occupancy, but surprisingly, the material maintains a significant divalent character up to a pressure of at least 35 GPa. Thus, the closure of the resistive activation energy gap and onset of magnetic order are not driven by stabilization of an integer valent state. Over the entire pressure range, the material maintains a remarkably stable intermediate valence that can in principle support a nontrivial band structure.

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Polarity-Driven Surface Metallicity inSmB6

Cited by 138 publications

References 40 publications

Hybridization gap and Fano resonance in SmB₆

Hybridization gap and Fano resonance in SmB₆

Planar tunneling spectroscopy of the topological Kondo insulator SmB6

Pressure-Resistant Intermediate Valence in the Kondo InsulatorSmB6

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Polarity-Driven Surface Metallicity inSmB6

Cited by 138 publications

References 40 publications

Hybridization gap and Fano resonance in SmB6

Hybridization gap and Fano resonance in SmB6

Planar tunneling spectroscopy of the topological Kondo insulator SmB6

Pressure-Resistant Intermediate Valence in the Kondo InsulatorSmB6

Contact Info

Product

Resources

About

Hybridization gap and Fano resonance in SmB₆

Hybridization gap and Fano resonance in SmB₆