Interlayer Exciton Diode and Transistor

Abstract

Controlling the flow of charge neutral interlayer exciton (IX) quasiparticles can potentially lead to low loss excitonic circuits. Here, we report unidirectional transport of IXs along nanoscale electrostatically defined channels in an MoSe2–WSe2 heterostructure. These results are enabled by a lithographically defined triangular etch in a graphene gate to create a potential energy “slide”. By performing spatially and temporally resolved photoluminescence measurements, we measure smoothly varying IX energy along the structure and high speed exciton flow with a drift velocity up to 2 × 106 cm/s, an order of magnitude larger than previous experiments. Furthermore, exciton flow can be controlled by saturating exciton population in the channel using a second laser pulse, demonstrating an optically gated excitonic transistor. Our work paves the way toward low loss excitonic circuits, the study of bosonic transport in one-dimensional channels, and custom potential energy landscapes for excitons in van der Waals heterostructures.

Signatures of Electric Field and Layer Separation Effects on the Spin-Valley Physics of MoSe2/WSe2 Heterobilayers: From Energy Bands to Dipolar Excitons

“…In particular, our g-factor calculations for the band edges ( Figure 6 ) suggest that intralayer excitons could also provide valuable information on the interlayer hybridization via the valley Zeeman as a function of the electric field. Gated devices based on MoSe /WSe heterostructures are within experimental reach [ 18 , 42 , 46 ], and could be used to test our hypothesis. We note that, in order to properly evaluate the intralayer exciton physics, it would be desirable to go beyond DFT calculations, and to employ the GW + Bethe–Salpeter formalism [ 45 , 65 , 97 , 125 ], which is beyond the scope of this work.…”

“…We now turn to the behavior of the different dipolar excitons as a function of the electric field. Motivated by the experimentally accessible regime [ 42 , 43 , 44 , 45 , 46 ], in which there is no indication of any crossings in the top valence band or lower conduction bands, we restrict ourselves to electric field values ≳−0.75 V/nm, ensuring that the conduction band of MoSe is always below the conduction band of WSe . For positive values of electric field, there are no visible band crossings, so we can extend our analysis towards electric field values of ∼2 V/nm.…”

“…In particular, for the TMDC-based van der Waals heterostructures, one relevant system of great interest is the MoSe /WSe heterobilayer: in this system, the type-II band alignment favors the appearance of interlayer excitons, also known as dipolar excitons, with electrons and holes localized in different layers [ 36 , 37 , 38 ]. Interestingly, dipolar excitons exhibit long recombination times [ 39 , 40 , 41 ], robust out-of-plane electric dipole moments [ 42 , 43 , 44 , 45 , 46 ], and giant valley Zeeman signatures that are dependent on the twist angle and atomic registry [ 20 , 43 , 47 , 48 , 49 , 50 , 51 ]: these are attractive features that could be exploited in exciton-based opto-spintronics devices [ 17 , 18 ], such as dipolar excitons quantum emitters [ 43 ] and diode transistors [ 46 ]. Furthermore, these MoSe /WSe are suitable platforms on which to study the optical signatures of moiré superlattices [ 19 , 20 , 52 , 53 ] and atomic reconstruction [ 54 , 55 , 56 , 57 ].…”

“…In these systems, the type-II band alignment favors the appear-ance of interlayer excitons, also known as dipolar excitons, with electrons and holes localized in different layers [36][37][38] . Interestingly, dipolar excitons exhibit long recombination times [39][40][41] , robust out-of-plane electric dipole moments [42][43][44][45][46] , and giant valley Zeeman signatures that are dependent on the twist angle and atomic registry 20,43,[47][48][49][50][51] .…”

Surface acoustic wave induced phenomena in two-dimensional materials

“…For example, a biaxial strain pattern could be generated by either using orthogonal SAWs or selecting crystal cuts and propagation directions. 91 To control the directional transport of the charge neutral exciton flux, spatial tunings of exciton potential by mechanical strain 160,165 or an electric field [139][140][141][142]166 were realized and are summarized in Table 2. Travelling SAWs can dynamically utilize both strain fields and piezo-electric fields to manipulate and transport excitons in 2D semiconducting materials.…”