Valley-polarized exciton currents in a van der Waals heterostructure

Abstract

Valleytronics is an appealing alternative to conventional charge-based electronics which aims at encoding data in the valley degree of freedom, i.e. the information over which extreme of the conduction or valence band carriers are occupying. The ability to create and control valleycurrents in solid state devices could therefore enable new paradigms for information processing. Transition metal dichalcogenides (TMDCs) are a promising platform for valleytronics, due to the presence of two inequivalent valleys with spin-valley locking 1 and a direct band gap 2,3 , which allows optical initialization and readout of the valley-state 4,5. Recent progresses on the control of interlayer excitons in these materials 6-8 could offer an effective way to realize optoelectronic devices based on the valley degree of freedom. Here, we show the generation and transport over mesoscopic distances of valley-polarized excitons in a device based on a type-II TMDC heterostructure. Engineering of the interlayer coupling results in enhanced diffusion of valleypolarized excitons, which can be controlled and switched electrically. Furthermore, using electrostatic traps, we can increase exciton concentration by an order of magnitude, reaching densities in the order of 10 12 cm-2 , opening the route to achieving a coherent quantum state of valley-polarized excitons via Bose-Einstein condensation. Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Moiré potential impedes interlayer exciton diffusion in van der Waals heterostructures

“…The diffusion and mobility of various carriers including electrons, holes, and IXs are important properties because they determine the charge and energy transport processes in hBLs, which, in turn, are critical for building transistors and photovoltaic devices. Several experiments performed on WS 2 /WSe 2 , MoS 2 /WSe 2 , and MoSe 2 /WSe 2 hBLs have reported long free carrier and IX diffusion length and electric field control of this transport ( 16 , 17 , 20 – 22 ). Other recent experiments, on the other hand, suggest that IXs may be localized by the moiré potential on the order of 100 to 200 meV ( 18 , 19 , 23 ).…”

Thermomechanical Nanocutting of 2D Materials

“…[ 34 ] A possible solution to reduce the effect of PPA on the sheet resistance of the 2D material is to engineer the interface by adding an ultrathin dangling‐bond‐free material such as a monolayer or a few layers of h‐BN between the PPA and the 2D film. [ 35–39 ] Depending of the mechanical properties and thickness of separating layer, the cutting might not be possible with the maximum indentation force of the specific commercial t‐SPL cantilever used in this work, but it is within the reach of dedicated t‐SPL cantilevers with larger spring constants.…”

Gate-tunable trion switch for excitonic device applications

“…The monolayer semiconducting transition metal dichalcogenides (MoS 2 , WS 2 , MoSe 2 , and WSe 2 ) exhibit strongly bound two-dimensional excitons with a binding energy on the order of few hundreds of meV, making these ultra-thin monolayers an excellent test bed for excitonic manipulation even at room temperature [1][2][3][4][5]. The neutral excitons (X 0 ) show excellent valley polarization and valley coherence properties that can be readily probed through initialization by circularly and linearly polarized photons, respectively, followed by detection through a circular or linear analyzer [6][7][8][9][10][11].…”

“…Recently, this problem has been addressed by creating inter-layer exciton [20][21][22][23][24] to suppress the fast radiative decay, and exciton transport over several micrometer in the plane of the layered material has been demonstrated [4]. An external gate control has also been achieved by modulating the binding energy of the neutral exciton [4,5].…”

“…In addition, transport of the exciton also remains challenging due to the ultra-fast radiative recombination of exciton [12][13][14][15][16] resulting from the high oscillator strength [17][18][19] -limiting the application of excitonic devices.Recently, this problem has been addressed by creating inter-layer exciton [20][21][22][23][24] to suppress the fast radiative decay, and exciton transport over several micrometer in the plane of the layered material has been demonstrated [4]. An external gate control has also been achieved by modulating the binding energy of the neutral exciton [4,5].In this regard, the charged exciton or trion (X − ) is promising since its intensity can be readily controlled electrically by modulating the doping density using a gate voltage. In addition, the trion, while being optically initiated, can be electrically detected in a spatially nonlocal manner through measuring a charge current [25].…”