Browsing by Subject "Electronic bandstructure"

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Open Access
Geometric band properties in strained monolayer transition metal dichalcogenides using simple band structures
(American Institute of Physics, 2019) Aas, Shahnaz; Bulutay, Ceyhun
Monolayer transition metal dichalcogenides (TMDs) bare large Berry curvature hotspots readily exploitable for geometric band effects. Tailoring and enhancement of these features via strain is an active research direction. Here, we consider spinless two- and three-band and spinful four-band models capable to quantify the Berry curvature and the orbital magnetic moment of strained TMDs. First, we provide a k⋅p parameter set for MoS2, MoSe2, WS2, and WSe2 in the light of the recently released ab initio and experimental band properties. Its validity range extends from the K valley edge to about one hundred millielectron volts into valence and conduction bands for these TMDs. To expand this over a larger part of the Brillouin zone, we incorporate strain to an available three-band tight-binding Hamiltonian. With these techniques, we demonstrate that both the Berry curvature and the orbital magnetic moment can be doubled compared to their intrinsic values by applying typically a 2.5% biaxial tensile strain. These simple band structure tools can find application in the quantitative device modeling of the geometric band effects in strained monolayer TMDs.
Open Access
Photonic band gaps with layer-by-layer double-etched structures
(A I P Publishing LLC, 1996-09-03) Biswas, R.; Özbay, Ekmel; Ho, K. M.
Periodic layer‐by‐layer dielectric structures with full three‐dimensional photonic band gaps have been designed and fabricated. In contrast to previous layer‐by‐layer structures the rods in each successive layer are at an angle of 70.5° to each other, achieved by etching both sides of a silicon wafer. Photonic band‐structure calculations are utilized to optimize the photonic band gap by varying the structural geometry. The structure has been fabricated by double etching Si wafers producing millimeter wavephotonic band gaps between 300 and 500 GHz, in excellent agreement with band calculations. Overetching this structure produces a multiply connected geometry and increases both the size and frequency of the photonic band gap, in very good agreement with experimental measurements. This new robust double‐etched structure doubles the frequency possible from a single Si wafer, and can be scaled to produced band gaps at higher frequencies. © 1996 American Institute of Physics