报告题目：Optical response of donor arrays in silicon: a time-dependent Hartree-Fock study
报告时间：2019-08-24 15:00 (星期六)
报告地点：天津大学新校区理学院218
报告人：武威 (University College London)

Abstract:

Donors in silicon provide a promising route to develop terahertzradiation, quantum technologies, topological states of artificially designednanostructures and other atomic-scale devices [1, 2]. Understanding theelectronic structure and excited states of donor clusters in silicon (the buildingblocks), is important for the aforementioned applications. Herein we present asystematic theoretical study for the excited states and optical responses ofdonor clusters in silicon. 

First, we haveadopted a spherical band approximation and use hydrogen atoms to representshallow donors. We have computed the electronic structure and optical propertiesof a series of donor lines with up to 10 donors [3] by using configurationinteraction, time-dependent Hartree Fock and time-dependent density-functionaltheory. Our calculations show charge-transfer excitations play an importantrole, dominating the transition for separation ~5nm and dropping down to 10meV. We have also computed the excited states of the finite alternating chainof donors to simulate the Su-Schrieffer-Heeger model but with strong electroncorrelation. We found the phase transition between the trivialantiferromagnetic state to topological state with spin-polarized edge statefrom the discontinuous optical spectra. 

Second, We havedeveloped a more realistic theoretical description for the excited states ofsilicon donors, by taking into account central-cell corrections, anisotropy ofthe effective-mass equation, and multi-valley effect [4]. We have included theappropriate central-cell correction to model the electric potential in siliconlattice environment. The anisotropic single-valley hamiltonians were solved byusing standard quantum-chemistry method, Gaussian expansion, for the donors’envelope function. We have calculated the band structure of silicon from firstprinciples using Quantum Espresso code, from which we extract theconduction-band wave functions to compute the multi-valley interactions. Thetime-dependent Hartree-Fock methods was used to compute the excited states. Wehave performed the single-valley and multi-valley calculations for a donorpair, which show distinct features in the excitation spectra arising from multi-valleyeffect. One interesting consequence is to open up a gap between the ionic stateand the 1s→2p intra-atom transition. Single-valley calculations can be usefulto understand the excited states of valley-polarized electrons [5]. Theexcitation energy drops down to ~12 meV. 

Our calculations show an interesting optical propertiesof donors in silicon, and would thus provide theoretical foundation to a broadrange of applications.  

报告人简介：

武威博士毕业于英国伦敦大学学院,先后在伦敦纳米中心和伦敦帝国理工学院做研究工作。他的学术贡献集中在国际半导体理论前沿领域的关键课题，主要包括无机半导体中的杂质团簇和有机半导体以及有机大分子的光磁和含时理论，以及这些材料在量子计算、量子模拟、自旋电子学中的应用。迄今为止，已发表SCI论文27篇，其中一些成果发表在Nature Communications、Advanced Materials、ACS Nano和Physics Review B上。武威博士的研究经历结合了光磁性理论计算模拟和含时理论计算，其先后曾与多名著名学者，包括Prof. Gabriel Aeppli、Prof. Andrew Fisher、 Prof. Nicholas Harrison等人。

[1] R. Drost, et. al., Nat. Mat. 13, 668 (2017). 

[2] J. Salfi, et. al., Nat. Commun. 7, 11342 (2016). 

[3] Wei Wu, et. al., Phys. Rev. B, 97, 035205 (2018). 

[4] Wei Wu, et. al., In preparation. 

[5] J. Salfi, et. al., Nat. Mat., 13, 605 (2014).