Patrick Vora1,Jaydeep Joshi1,Benedikt Scharf2,Igor Mazin1,Sergiy Krylyuk3,Daniel Campbell4,Johnpierre Paglione4,5,Albert Davydov3,1,4,Igor Zutic6
George Mason University1,University of Wurzburg2,National Institute of Standards and Technology3,University of Maryland4,Canadian Institute for Advanced Research5,University at Buffalo, The State University of New York6
Patrick Vora1,Jaydeep Joshi1,Benedikt Scharf2,Igor Mazin1,Sergiy Krylyuk3,Daniel Campbell4,Johnpierre Paglione4,5,Albert Davydov3,1,4,Igor Zutic6
George Mason University1,University of Wurzburg2,National Institute of Standards and Technology3,University of Maryland4,Canadian Institute for Advanced Research5,University at Buffalo, The State University of New York6
Two-dimensional (2D) materials allow for the construction of heterostructures without the constraint of lattice matching. This increased flexibility enables novel proximity effects through the stacking of strongly correlated 2D materials on 2D semiconductors. Here we use temperature-dependent photoluminescence (PL) microscopy to reveal a new proximity effect where excitons in monolayer MoSe<sub>2</sub> interact with the commensurate charge density wave (CDW) in bulk TiSe<sub>2 </sub>[1]. Below the CDW ordering temperature we observe a new PL emission line (H1) on the TiSe<sub>2</sub>-MoSe<sub>2</sub> interface that is 30 meV higher in energy than the neutral exciton. This observation is unique compared to other examinations of 2D heterostructures where additional spectral features appear at lower energies compared to the neutral exciton. Power and temperature-dependent measurements show that H1 behaves as a free exciton, therefore excluding interface trapping or localization as an explanation. Most interestingly, we find that H1 disappears above the TiSe<sub>2</sub> CDW ordering temperature, which suggests that the CDW plays a vital role in activating this previously unobserved exciton. We discuss possible CDW-based origins of H1 and outline future opportunities for using proximity effects to engineer novel excitonic states.<br/><br/>[1] J. Joshi, B. Scharf, I. Mazin, S. Krylyuk, D. J. Campbell, J.Paglione, A. Davydov, I. Zutić, and P. M. Vora, APL Materials, 10 (2022) 011103.<br/><br/>*Co-authors acknowledge support from the National Science Foundation under DMR-1748650 and DMR-1847782; the US DOE, Office of Science BES under Award No. DE-SC0004890; and the Gordon and Betty Moore Foundation's EPiQS Initiative through Grant No. GBMF9071.