LaB6 and SmB6 (001) surfaces studied by angle-resolved XPS, LEED and ISS

Aono, Masakazu; Nishitani, Ryusuke; Oshima, C.; Tanaka, Takaho; Bannai, E.; Kawai, Shichio

doi:10.1016/0039-6028(79)90443-6

Cited by 49 publications

(38 citation statements)

References 15 publications

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“…However, many of the surfaces (we estimate more than 90% of the surface areas investigated so far) exhibited much more complex topographies, as exemplified in otherwise flat B terraces; we refer to these as chain-like disordered reconstructions, in contrast to the ð2 × 1Þ ordered one. Both reconstructions are in good agreement with the proposal of a partly occupied Sm surface layer (38) and clearly attest the simplest solution to avoid the polarization catastrophe associated with polar surface termination planes (39). The presence of Sm and B 6 octahedra in equal amounts and their mixing on short length scales prevents the buildup of long-range electric fields from charged surface areas.…”

Section: Resultssupporting

confidence: 84%

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: Resultssupporting

confidence: 84%

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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“…They found that whereas the (100) and (111) surfaces yield (1 × 1) patterns, indicating that no reconstruction occurs, the (110) surface shows additional spots due to reconstruction. Subsequent studies have also shown LEED patterns of (100) [32][33][34][35][36] and (111) [36] surfaces of LaB 6 confirming the results of Oshima et al [25]. For the LaB 6 (110) surface, the reconstruction was confirmed by Bas et al [37] and Nishitani et al [36] who observed a c(2 × 2) pattern at room temperature, which changed into a (1 × 1) pattern at 860…”

Section: Hexaboride Surface Structuresupporting

confidence: 76%

“…A plot of the metal-to-boron peak-height ratio was well fit with a calculated ratio based on a La-terminated surface model. A similar approach was applied to the SmB 6 (100) surface, where the XPS data implied that the surface was only partly metal terminated [33]. Support for this interpretation of the XPS data for SmB 6 (100) was provided by ion scattering spectroscopy (ISS) data.…”

Section: Hexaboride Surface Structurementioning

confidence: 99%

Surface science studies of metal hexaborides

Trenary

2012

Science and Technology of Advanced Materials

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Over 30 years of surface science research on metal hexaborides are reviewed. Of this class of compounds, lanthanum hexaboride has been the subject of the majority of the studies because of its outstanding properties as a thermionic emitter. The use of LaB 6 cathodes as an electron source stems from the unusually low work function of ∼2.5 eV for the (100) surface combined with a low evaporation rate at high temperatures. Of particular interest has been the determination of the surface geometric and electronic structure responsible for the low work function and how the work function is affected by various adsorbates. The low-index faces of single crystals of LaB 6 and other hexaborides have been studied with a variety of ultrahigh vacuum surface science methods to gain a better understanding of the structure and properties of the clean surfaces as well as their interactions with gases such as O 2 , H 2 O and CO.

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“…A 2×1 surface reconstruction has been indeed observed on SmB 6 (001). This reconstruction has been found on UHV (ultra high vacuum) annealed samples by LEED [68,69] and on UHV cleaved samples by STM topographic imaging [19,20] and also in one ARPES study [57]. However, for UHV cleaved samples, neither LEED [24,25] nor the vast majority of ARPES studies [22][23][24][25][26] have found signs of a 2×1 reconstruction.…”

Section: Resultsmentioning

confidence: 99%

Comparative study of rare earth hexaborides using high resolution angle-resolved photoemission

Ramankutty

Jong

Huang

et al. 2016

Journal of Electron Spectroscopy and Related Phenomena

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Strong electron correlations in rare earth hexaborides can give rise to a variety of interesting phenomena like ferromagnetism, Kondo hybridization, mixed valence, superconductivity and possibly topological characteristics. The theoretical prediction of topological properties in SmB6 and YbB6, has rekindled the scientific interest in the rare earth hexaborides, and high-resolution ARPES has been playing a major role in the debate. The electronic band structure of the hexaborides contains the key to understand the origin of the different phenomena observed, and much can be learned by comparing the experimental data from different rare earth hexaborides. We have performed high-resolution ARPES on the (001) surfaces of YbB6, CeB6 and SmB6. On the most basic level, the data show that the differences in the valence of the rare earth element are reflected in the experimental electronic band structure primarily as a rigid shift of the energy position of the metal 5d states with respect to the Fermi level. Although the overall shape of the d-derived Fermi surface contours remains the same, we report differences in the dimensionality of these states between the compounds studied. Moreover, the spectroscopic fingerprint of the 4f states also reveals considerable differences that are related to their coherence and the strength of the d-f hybridization. For the SmB6 case, we use ARPES in combination with STM imaging and electron diffraction to reveal time dependent changes in the structural symmetry of the highly debated SmB6(001) surface. All in all, our study highlights the suitability of electron spectroscopies like high-resolution ARPES to provide links between electronic structure and function in complex and correlated materials such as the rare earth hexaborides.

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LaB6 and SmB6 (001) surfaces studied by angle-resolved XPS, LEED and ISS

Cited by 49 publications

References 15 publications

Hybridization gap and Fano resonance in SmB₆

Hybridization gap and Fano resonance in SmB₆

Surface science studies of metal hexaborides

Comparative study of rare earth hexaborides using high resolution angle-resolved photoemission

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LaB6 and SmB6 (001) surfaces studied by angle-resolved XPS, LEED and ISS

Cited by 49 publications

References 15 publications

Hybridization gap and Fano resonance in SmB6

Hybridization gap and Fano resonance in SmB6

Surface science studies of metal hexaborides

Comparative study of rare earth hexaborides using high resolution angle-resolved photoemission

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Product

Resources

About

Hybridization gap and Fano resonance in SmB₆

Hybridization gap and Fano resonance in SmB₆