Optical Anisotropy in van der Waals materials: Impact on Direct Excitation of Plasmons and Photons by Quantum Tunneling  

作　　者：Zhe Wang Vijith Kalathingal Thanh Xuan Hoang Hong-Son Chu Christian A.Nijhuis 

机构地区：[1]Department of Chemistry,National University of Singapore,3 Science Drive 3,Singapore 117543,Singapore [2]Centre for Advanced 2D Materials,National University of Singapore,6 Science Drive 2,Singapore 117564,Singapore [3]Department of Electrical and Computer Engineering,National University of Singapore,4 Engineering Drive 3,Singapore 117583,Singapore [4]Department of Electronics and Photonics,Institute of High Performance Computing,A*STAR(Agency for Science,Technology and Research),1 Fusionopolis Way,Singapore 138632,Singapore [5]Hybrid Materials for Opto-Electronics Group,Department of Molecules and Materials,MESA+Institute for Nanotechnology and Center for Brain-Inspired Nano Systems,Faculty of Science and Technology,University of Twente,7500 AE Enschede,The Netherlands

出　　处：《Light(Science & Applications)》2021年第12期2387-2398,共12页光（科学与应用)（英文版）

基　　金：The authors acknowledge the National Research Foundation(NRF)for supporting this research under the Prime Minister’s Office,Singapore,under its Medium Sized Centre Programme and the Competitive Research Programme(CRP)(NRF-CRP17-2017-08).

摘　　要：Inelastic quantum mechanical tunneling of electrons across plasmonic tunnel junctions can lead to surface plasmon polariton(SPP)and photon emission.So far,the optical properties of such junctions have been controlled by changing the shape,or the type of the material,of the electrodes,primarily with the aim to improve SPP or photon emission efficiencies.Here we show that by tuning the tunneling barrier itself,the efficiency of the inelastic tunneling rates can be improved by a factor of 3.We exploit the anisotropic nature of hexagonal boron nitride(hBN)as the tunneling barrier material in Au//hBN//graphene tunnel junctions where the Au electrode also serves as a plasmonic strip waveguide.As this junction constitutes an optically transparent hBN–graphene heterostructure on a glass substrate,it forms an open plasmonic system where the SPPs are directly coupled to the dedicated strip waveguide and photons outcouple to the far field.We experimentally and analytically show that the photon emission rate per tunneling electron is significantly improved(~×3)in Au//hBN//graphene tunnel junction due to the enhancement in the local density of optical states(LDOS)arising from the hBN anisotropy.With the dedicated strip waveguide,SPP outcoupling efficiency is quantified and is found to be∼80%stronger than the radiative outcoupling in Au//hBN//graphene due to the high LDOS of the SPP decay channel associated with the inelastic tunneling.The new insights elucidated here deepen our understanding of plasmonic tunnel junctions beyond the isotropic models with enhanced LDOS.

关 键 词：TUNNELING STRIP COUPLING 

分 类 号：TB34[一般工业技术—材料科学与工程]