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Showing results 21 to 23 of 23
   Thermoelectric properties of Mexican-hat band structures; ; et al in Advances in Natural Sciences: Nanoscience and Nanotechnology (2020), 11(1), 015012 Materials with Mexican-hat electronic energy dispersions emerging from heterostructures, substrate effects, or spin–orbit couplings are believed to exhibit excellent thermoelectric properties due to its ... [more ▼] Materials with Mexican-hat electronic energy dispersions emerging from heterostructures, substrate effects, or spin–orbit couplings are believed to exhibit excellent thermoelectric properties due to its van Hove singularity of density of states in two-dimension. However, within a constant relaxation time approximation, we disprove this belief and we find that the singularity effect is cancelled down by the group velocity contribution in the thermoelectric transport distribution. Nevertheless, the band parameters can still be optimised to reach thermoelectric figure of merit larger than 2 in a wide bandwidth, thus keeping the potential of materials with Mexican-hat bands for thermoelectric applications. [less ▲] Detailed reference viewed: 36 (0 UL)Modulation of coherent phonon amplitudes in low-dimensional materials by ultrafast laser pulse trains; ; et al in AIP Conference Proceedings (2020), 2256(1), 020005 We theoretically investigate how coherent phonon amplitudes in low dimensional materials can be modulated by ultrafast laser pulse trains. Important laser parameters for the modulation of coherent phonon ... [more ▼] We theoretically investigate how coherent phonon amplitudes in low dimensional materials can be modulated by ultrafast laser pulse trains. Important laser parameters for the modulation of coherent phonon amplitudes are the pulse width, repetition period, and number of pulses in the pulse train. We find that it is possible to switch on or switch off the radial breathing mode (RBM) and the G-band phonons in a single wall carbon nanotube (SWNT), as a typical model of low-dimensional materials. In particular, if the repetition period matches with integer multiple of the RBM phonon period, the RBM phonon could be switched on, while the other modes are switched off. On the other hand, for the G-band, which has a higher frequency (shorter period) than the RBM, the number of pulses in the pulse train also affects the switching process. The ratios of the G-band and RBM amplitudes are found to be significantly enhanced at certain integer multiples of pulse number as a function of SWNT diameter. Such a “magic number” phenomenon in ultrafast spectroscopy can be extended to other low-dimensional materials, in which we may realize a phonon switch in the future. [less ▲] Detailed reference viewed: 74 (2 UL)Origin of the Flat Band in Heavily Cs-Doped Graphene; ; et al in ACS Nano (2020), 14(1), 1055 A flat energy dispersion of electrons at the Fermi level of a material leads to instabilities in the electronic system and can drive phase transitions. Here we show that the flat band in graphene can be ... [more ▼] A flat energy dispersion of electrons at the Fermi level of a material leads to instabilities in the electronic system and can drive phase transitions. Here we show that the flat band in graphene can be achieved by sandwiching a graphene monolayer by two cesium (Cs) layers. We investigate the flat band by a combination of angle-resolved photoemission spectroscopy experiment and the calculations. Our work highlights that charge transfer, zone folding of graphene bands, and the covalent bonding between C and Cs atoms are the origin of the flat energy band formation. Analysis of the Stoner criterion for the flat band suggests the presence of a ferromagnetic instability. The presented approach is an alternative route for obtaining flat band materials to twisting bilayer graphene which yields thermodynamically stable flat band materials in large areas. [less ▲] Detailed reference viewed: 68 (1 UL)
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