Dielectric Engineering of Electronic Correlations in a van der Waals Heterostructure

Abstract

Heterostructures of van der Waals bonded layered materials offer unique means to tailor dielectric screening with atomic-layer precision, opening a fertile field of fundamental research. The optical analyses used so far have relied on interband spectroscopy. Here we demonstrate how a capping layer of hexagonal boron nitride (hBN) renormalizes the internal structure of excitons in a WSe 2 monolayer using intraband transitions. Ultrabroadband terahertz probes sensitively map out the full complex-valued mid-infrared conductivity of the heterostructure after optical injection of 1s A excitons. This approach allows us to trace the energies and line widths of the atom-like 1s−2p transition of optically bright and dark excitons as well as the densities of these quasiparticles. The excitonic resonance red shifts and narrows in the WSe 2 /hBN heterostructure compared to the bare monolayer. Furthermore, the ultrafast temporal evolution of the mid-infrared response function evidences the formation of optically dark excitons from an initial bright population. Our results provide key insight into the effect of nonlocal screening on electron−hole correlations and open new possibilities of dielectric engineering of van der Waals heterostructures.

Band nesting and exciton spectrum in monolayer MoS2

“…The same magnetic moments result in shift of the energy levels of s -series 83 , for which exciton's angular quantum number L is 0. The p-states can be probed in pumpprobe experiments [84][85][86][87][88][89][90] , where 1s excitons are generated and transition from 1s to 2p states can be measured by a probe terahertz beam 77 .…”

Time‐Resolved Terahertz Spectroscopy Studies on 2D Van der Waals Materials

“…As presented in Figure 7b, the phase shift comparing to the reference of exactly π in the left column (resonant excitation) shows the hallmark of an absorptive response, whereas the relative phase shift that deviates strongly from π in the right column (nonresonant excitation) indicates the response of a plasma. [103] Copyright 2018, American Chemical Society. As shown in this figure, an electron-hole plasma-like response appears in the real parts of the measured complex photoconductivities and dielectric functions at a time delay of t pp = 0 fs.…”

“…[103] A schematic illustration of the heterostructure studied in ref. [103] A schematic illustration of the heterostructure studied in ref.…”

“…In addition to the measurements on the exciton formation processes of bare and covered single-layer WSe 2 , [42,103] the concept of optical pump-broad band THz probe spectroscopy has also been employed to explore the exciton formation processes in other 2D vdW materials. [102,104,105] …”

Efficient Band Gap Engineering and Enhanced Optical Absorption of Vertical Germanene/h‐AlN Bilayer Heterostructure: Potential New Electronics and Optoelectronics

“…During the past decade, featured by novel electronic and opto‐electronic properties, two‐dimensional (2D) heterostructures (HTSs) have attracted a great deal of attentions in the physical and chemical fields . This contributed to the superiority of 2D HTSs to their parent materials in many prospects, which played a significant role to overcome the disadvantages of traditional materials and expand the application potential . In pace with the further explorations, there raises an exploration upsurge of 2D materials to excite the development progress.…”