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Two dimensional topological insulators in bilayer BiB
摘要： With the help of ?rst-principles calculations, we propose a new type of two dimensional (2D) topological insulator BiB with bilayer hexagonal lattice. Its dynamic stability was con?rmed by the phonon spectrum. When spin-orbit coupling (SOC) e?ect is not considered, the low energy electronic states around the Fermi level show metallic characteristics. However, the SOC will induce a global band gap and turn this 2D material into topological insulators with nontrivial edge states. Surprisingly, two mechanisms, including crystal ?eld and strong SOC, induce two band inversions and manipulate the low energy electronic states simultaneously. The BiB provides a fertile platform for studying the interactions between the two di?erent mechanisms in the same topological insulator. Moreover, the sizable global nontrivial band gap indicates its high working temperature.
关键词： Topological insulator,Edge states,Z2,Spin-orbit coupling (SOC)
更新于2025-09-23 15:22:29
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Osmium sensitizer with enhanced spin-orbit coupling for panchromatic dye-sensitized solar cells
摘要： Low-lying triplet metal-to-ligand charge transfer (3MLCT) transitions of osmium complexes induced by spin-orbit coupling (SOC) is promising to extend photocurrent response when applied to dye-sensitized solar cells. In this study, we present a newly designed osmium complex (coded CYC-33O), incorporating a 2-thiohexyl-3,4-ethylenedioxythiophene functionalized bipyridyl ancillary ligand to red-shift the absorption and enhance the absorbance of both singlet and triplet MLCT transitions. Time-dependent density functional theory (TDDFT) calculations clearly signify the reinforced 1MLCT and 3MLCT transitions of CYC-33O mainly originate from osmium to 4,4',4"-tricarboxy-2,2':6',2"-terpyridine anchoring ligand, advantaging the heterogeneous electron transfer between CYC-33O and TiO2. The device sensitized with CYC-33O exhibits the panchromatic conversion beyond 1000 nm, yielding the photocurrent density of 19.38 mA cm–2 which is much higher than those of the cells based on the ruthenium analogue (CYC-33R) and model osmium complex (Os-3) sensitizers.
关键词： dye-sensitized solar cell,triplet metal-to-ligand charge transfer (3MLCT),ruthenium complex,spin-orbit coupling (SOC),osmium complex,time-dependent density functional theory (TDDFT)
更新于2025-09-23 15:21:01
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Weak Antilocalization at the Atomic-Scale Limit of Metal Film Thickness
摘要： Creation of the 2D metallic layers with the thickness as small as a few atomic layers and investigation of their properties are interesting and challenging tasks of the modern condensed-matter physics. One of the possible ways to grow such layers resides in the synthesis of the so-called metal-induced reconstructions on silicon (i.e., silicon substrates covered with ordered metal ?lms of monolayer or submonolayer thickness). The 2D Au?Tl compound on Si(111) surface having 7×7 periodicity belongs to the family of the reconstructions incorporating heavy-metal atoms with a strong spin?orbit coupling (SOC). In such systems, strong SOC results in the spin-splitting of surface-state bands due to the Rashba e?ect, the occurrence of which was experimentally proved. Another remarkable consequence of a strong SOC that manifests itself in the transport properties is a weak antilocalization (WAL) e?ect, which has never been explored in the metal layers of atomic thickness. In the present study, the transport and magnetotransport properties of the 2D Au?Tl compound on Si(111) surface were investigated at low temperatures down to ～2.0 K. The compound was proved to show behavior of the 2D nearly free electron gas system with metallic conduction, as indicated by Io?e?Regel criterion. It demonstrates the WAL e?ect which is interpreted in the framework of Hikami?Larkin?Nagaoka theory, and possible mechanisms of the electron decoherence are discussed. Bearing in mind that besides the (Au, Tl)/Si(111) 7×7 system, there are many other ordered atomic-layer metal ?lms on silicon di?ering by composition, structure, strength of SOC, and spin texture, which provide a promising area for prospective investigations of the WAL e?ect at the atomic-scale limit when the ?lm thickness is less than the electron wavelength.
关键词： weak antilocalization (WAL),2D compounds,transport measurements,magnetoresistance,strong spin?orbit coupling (SOC)
更新于2025-09-09 09:28:46