Growth and electronic structure of epitaxial single-layer<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>WS</mml:mtext><mml:mn>2</mml:mn></mml:msub></mml:math>on Au(111)

Dendzik, Maciej; Michiardi, Matteo; Sanders, Charlotte E.; Bianchi, Marco; Miwa, Jill A.; Grønborg, Signe S.; Lauritsen, Jeppe V.; Bruix, Albert; Hammer, Bjørk; Hofmann, Philip

doi:10.1103/physrevb.92.245442

Cited by 81 publications

(106 citation statements)

References 57 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The upper valence band of single-layer WS 2 is located inside the bandgap of h-BN and the single-layer WS 2 VBM is characterized by a spin-orbit splitting of 430 meV (see Fig. 1j), in agreement with theoretical predictions 12 and previous experiments 23,24 . The clear electronic states and lack of band hybridization reveal a weak interlayer interaction between the two materials.…”

supporting

confidence: 77%

Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures

et al. 2018

View full text Add to dashboard Cite

In two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), new electronic phenomena such as tunable bandgaps 1-3 and strongly bound excitons and trions emerge from strong many-body effects [4][5][6] , beyond the spin and valley degrees of freedom induced by spin-orbit coupling and by lattice symmetry 7 . Combining single-layer TMDs with other 2D materials in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these many-body effects, by means of engineered interlayer interactions [8][9][10] . Here, we use micro-focused angle-resolved photoemission spectroscopy (microARPES) and in situ surface doping to manipulate the electronic structure of single-layer WS 2 on hexagonal boron nitride (WS 2 /h-BN). Upon electron doping, we observe an unexpected giant renormalization of the spin-orbit splitting of the single-layer WS 2 valence band, from 430 meV to 660 meV, together with a bandgap reduction of at least 325 meV, attributed to the formation of trionic quasiparticles. These findings suggest that the electronic, spintronic and excitonic properties are widely tunable in 2D TMD/h-BN heterostructures, as these are intimately linked to the quasiparticle dynamics of the materials [11][12][13] . Coulomb interactions in 2D materials are several times stronger than in their 3D counterparts. In 2D TMDs, this is most directly evidenced by the presence of excitons with binding energies an order of magnitude higher than in the bulk 4 . Although the excitons in these 2D materials have been widely studied by optical techniques 13 , the impact of strong electron-electron interactions on the quasiparticle band structure remains unclear. Theory predicts that many-body effects will influence the spin-orbit splitting around the valenceband maximum (VBM) and conduction-band minimum (CBM) 14 . Although these should be observable by ARPES, a direct probe of many-body effects 15 , measurements so far have mainly focused on the layer-dependence of the single-particle spectrum and the direct bandgap transition in 2D TMD systems, including epitaxial single- . Unfortunately, the lateral size of mechanically assembled heterostructures is usually of the order of 10 μ m, much smaller than the beam spot of typical ARPES setups (≳ 100 μ m). Furthermore, sample charging on insulating bulk h-BN substrates would complicate ARPES experiments.We overcome these challenges as follows. We realize a high-quality 2D semiconductor-insulator interface by mechanically transferring a relatively large (~100 μ m) single-layer WS 2 crystal onto a thin flake of h-BN that has itself been transferred onto a degenerately doped TiO 2 substrate, as depicted in Fig. 1a. Sample charging is avoided because there is electrical contact from the continuous single-layer WS 2 flake to both the h-BN and the conductive TiO 2 . Figure 1b is an optical microscope image of the sample, including a flake of h-BN, approximately 100 μ m wide, surrounded by several transferred flakes of single-layer WS 2 on the Ti...

show abstract

supporting

confidence: 77%

Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures

et al. 2018

View full text Add to dashboard Cite

show abstract

“…We therefore use epitaxial SL WS 2 grown on Ag(111). WS 2 is characterized by a strong spin-splitting on the order of 420 meV at the valence band maximum (VBM) [22]. Intriguingly, our experiments reveal excited electron and hole populations that are strongly peaked for a resonant excitation between the upper VB spin state and the conduction band (CB).…”

mentioning

confidence: 72%

“…The growth on Ag(111) is similar to the growth described for SL WS 2 on Au(111) in Ref. [22]. The sample was transported to the Artemis TR-ARPES end-station at the Central Laser Facility at the Harwell Campus in the United Kingdom [23] in an evacuated tube and cleaned by annealing to 500 K in the UHV chamber.…”

mentioning

confidence: 99%

Spin and valley control of free carriers in single-layer WS2

et al. 2017

Self Cite

View full text Add to dashboard Cite

The semiconducting single-layer transition metal dichalcogenides have been identified as ideal materials for accessing and manipulating spin-and valley-quantum numbers due to a set of favorable optical selection rules in these materials. Here, we apply time-and angle-resolved photoemission spectroscopy to directly probe optically excited free carriers in the electronic band structure of a high quality single layer of WS2. We observe that the optically generated free hole density in a single valley can be increased by a factor of 2 using a circularly polarized optical excitation. Moreover, we find that by varying the photon energy of the excitation we can tune the free carrier density in a given spin-split state around the valence band maximum of the material. The control of the photon energy and polarization of the excitation thus permits us to selectively excite free electron-hole pairs with a given spin and within a single valley.In two-dimensional (2D) materials, control of the spinand valley-degrees of freedom has been suggested as a new type of tuning knob for carrier dynamics [1]. Singlelayer (SL) transition metal dichalcogenides (TMDCs) such as SL MoS 2 and WS 2 are particularly promising candidates for new spin-and valley-tronic device paradigms, owing to the broken inversion symmetry of their crystal lattices, a strong spin-orbit coupling and a direct band gap at theK andK ′ valleys in the electronic structure of the materials [2-4]. These properties have been indirectly verified in SL TMDCs through selective excitation of bound electron-hole pairs with circularly polarized light, leading to the observation of valley polarized excitons [5][6][7][8], which could be coherently manipulated [9]. Device measurements have shown indications of spin-and valley-coupled photocurrents [10] and Hall effects [11,12]. Direct measurements of the electronic structure and associated quasiparticles have been carried out for the bulk TMDC material WSe 2 using photoemission spectroscopies with spin [13] and time resolution [14]. Such measurements can, to some degree, even give information about the situation in a single layer, due to the surface sensitivity of photoemission spectroscopy. However, there is a need for experimental evidence and quantification of these properties for free carriers in the electronic structure of actual SL TMDCs, which are truly non-inversion symmetric materials.Time-and angle-resolved photoemission spectroscopy (TR-ARPES) is a powerful experimental approach for detecting optically excited free carriers with time-, energyand momentum-resolution with extremely high sensitivity towards 2D materials [15,16]. In this technique, a pump pulse with tuneable photon energy and polarization optically excites the material in question. The excited state is then probed by ARPES with an ultraviolet pulse, produced via high harmonic generation (HHG), which can provide sufficiently high photon energies to reach theK valleys at the corner of the SL TMDC's Brillouin zone (BZ). Since the two pulses are time-delaye...

show abstract

“…However, the hybridization in the possible final states for scattering processes might still affect the quantitative results. The Au(111) surface state is found to be energetically well above the VB maximum and should thus not play a role here [22].…”

mentioning

confidence: 99%

“…[20][21][22]. Angle-resolved photoemission spectroscopy data were collected on the SGM-3 beamline of ASTRID2 [23].…”

mentioning

confidence: 99%