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Register a new userSmB6 Photoemission: Past and Present
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Added by
Jonathan D. Denlinger
Publication date
2013
fields
Physics
and research's language is
English
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Recent renewed interest in the mixed valent insulator SmB6 comes from topological theory predictions and surface transport measurements of possible in-gap surface states whose existence is most directly probed by angle-resolved photoemission spectroscopy (ARPES). Early photoemission leading up to a recent flurry of ARPES studies of in-gap states is reviewed. Conflicting interpretations about the nature of the Sm 4f-5d hybridization gap and observed X-point bands between the f-states and the Fermi level are critically assessed using the important tools of photon polarization and spatial dependence which also provide additional insight into the origin of the more ambiguous {Gamma}-point in-gap states.
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The mixed valent compound SmB6 is of high current interest as the first candidate example of topologically protected surface states in a strongly correlated insulator and also as a possible host for an exotic bulk many-body state that would manifest properties of both an insulator and a metal. Two different de Haas van Alphen (dHvA) experiments have each supported one of these possibilities, while angle resolved photoemission spectroscopy (ARPES) for the (001) surface has supported the first, but without quantitative agreement to the dHvA results. We present new ARPES data for the (110) surface and a new analysis of all published dHvA data and thereby bring ARPES and dHvA into substantial consistency around the basic narrative of two dimensional surface states.
Specialized computational chemistry packages have permanently reshaped the landscape of chemical and materials science by providing tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties. In this regard, electronic structure packages have played a special role by using first-principledriven methodologies to model complex chemical and materials processes. Over the last few decades, the rapid development of computing technologies and the tremendous increase in computational power have offered a unique chance to study complex transformations using sophisticated and predictive many-body techniques that describe correlated behavior of electrons in molecular and condensed phase systems at different levels of theory. In enabling these simulations, novel parallel algorithms have been able to take advantage of computational resources to address the polynomial scaling of electronic structure methods. In this paper, we briefly review the NWChem computational chemistry suite, including its history, design principles, parallel tools, current capabilities, outreach and outlook.
Recent studies suggest that an exemplary Kondo insulator SmB6 belongs to a new class of topological insulators (TIs), in which non-trivial spin-polarized metallic states emerge on surface upon the formation of Kondo hybridization gap in the bulk. Remarkably, the bulk resistivity reaches more than 20 Ohm cm at 4 K, making SmB6 a candidate for a so-called bulk-insulating TI. We here investigate optical-pulse responses of SmB6 by pump-and-probe photoemission spectroscopy. Surface photovoltage effect is observed below ~90 K. This indicates that an optically-active band bending region develops beneath the novel metallic surface upon the bulk-gap evolution. The photovoltaic effect persists for >200 microsec, which is long enough to be detected by electronics devices, and could be utilized for optical gating of the novel metallic surface.
Samarium hexaboride (SmB6) has been presumed to show a topological Kondo insulating state consisting of fully occupied quasiparticle bands in the concept of a Fermi liquid. This gap emerging below a small coherence temperature is the ultimate sign of coherence for a many-body system, which in addition induces a non-trivial topology. Here, we demonstrate that just one energy scale governs the gap formation in SmB6, which supports the Fermi liquid description. The temperature dependence of the gap formation in the mixed valence regime is captured within the dynamical mean field (DMFT) approximation to the periodic Anderson model (PAM). The scaling property of the model with the topological coherence temperature provides a strong connection to the photoemission spectra of SmB6. Our results suggest a simple way to compare a model study and an experiment result for heavy fermion insulators.
Experimental contributors to the field of Superconducting Materials share their informal views on the subject.
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