K-Λ crossover transition in the conduction band of monolayer MoS
            <sub>2</sub>
            under hydrostatic pressure

Fu, Lei; Wan, Yi; Tang, Ning; Ding, Yi-min; Gao, Jing; Yu, Jiachen; Guan, Haijing; Zhang, Kun; Wang, Weiying; Zhang, Caifeng; Shi, Junjie; Wu, Xiang; Shi, Su‐Fei; Ge, Weikun; Dai, Li‐Xin; Shen, Bo

doi:10.1126/sciadv.1700162

Cited by 65 publications

(97 citation statements)

References 47 publications

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“…One possible explanation for the observed change in the PL spectra and intensities of CrPS 4 under pressure might be the band gap crossover (direct to indirect band gap). Similar behavior in the PL spectra has been observed previously in several systems such as InP 45 , InSe 46 and monolayer MoS 2 47 , and has been attributed to the direct-indirect gap crossover induced by pressure. However, given that the PL signal of CrPS 4 arises from the parity forbidden d−d transition, which is sensitive to the CrS 6 octahedra, the anomalous behavior of PL data above 3 GPa could be related to a subtle change in the crystal structure, possibly a modification of the CrS 6 octahedra under pressure.…”

Section: Resultssupporting

confidence: 86%

Band gap crossover and insulator–metal transition in the compressed layered CrPS4

Susilo¹,

Jang²,

Feng³

et al. 2020

npj Quantum Mater.

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Two-dimensional van der Waals (vdW) magnetic materials have emerged as possible candidates for future ultrathin spintronic devices, and finding a way to tune their physical properties is desirable for wider applications. Owing to the sensitivity and tunability of the physical properties to the variation of interatomic separations, this class of materials is attractive to explore under pressure. Here, we present the observation of direct to indirect band gap crossover and an insulator-metal transition in the vdW antiferromagnetic insulator CrPS 4 under pressure through in-situ photoluminescence, optical absorption, and resistivity measurements. Raman spectroscopy experiments revealed no changes in the spectral feature during the band gap crossover whereas the insulator-metal transition is possibly driven by the formation of the high-pressure crystal structure. Theoretical calculations suggest that the band gap crossover is driven by the shrinkage and rearrangement of the CrS 6 octahedra under pressure. Such high tunability under pressure demonstrates an interesting interplay between structural, optical and magnetic degrees of freedom in CrPS 4 , and provides further opportunity for the development of devices based on tunable properties of 2D vdW magnetic materials.

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Section: Resultssupporting

confidence: 86%

Band gap crossover and insulator–metal transition in the compressed layered CrPS4

Susilo¹,

Jang²,

Feng³

et al. 2020

npj Quantum Mater.

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“…Whereas for the hBN/WSe 2 -ML/hBN heterostructure both exciton energies increase linearly with increasing pressure with a coefficient of 3.5-3.8 meV/GPa, for the bare WSe 2 ML the excitons decrease in energy with a slope of -3.1 and -1.3 meV/GPa for the A-and B-exciton, respectively. Comparing with the available literature data, the pressure coefficient of the A-exciton determined here for the encapsulated WSe 2 ML is roughly one order of magnitude smaller than the one reported for a single ML of MoS 2 (20 meV/GPa [14], 30 meV/GPa [15], 40 meV/GPa [16], 50 meV/GPa [17]), WSe 2 (32 meV/GPa [19]) and WS 2 (20 meV/GPa [20]). All these data were obtained for monolayers on Si/SiO 2 substrates, where the oxide layer was fairly thick, ranging between 200 and 300 nm.…”

Section: -3contrasting

confidence: 49%

“…Because the bands at different points of the Brillouin zone shift in energy with different pressure coefficients, high pressure experiments can be used to distinguish between k-space direct and indirect transitions. As far as truly two-dimensional (2D) TMD materials are concerned, there are already several reports on the dependence on hydrostatic pressure of the emission and vibrational properties of monolayers of MoS 2 [14][15][16][17][18], WSe 2 [19] and WS 2 [20]. The results, however, are surprisingly contradictory.…”

Section: Introductionmentioning

confidence: 99%

On the impact of the stress situation on the optical properties of $WSe_2$ monolayers under high pressure

et al. 2019

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We have studied the optical properties of $WSe_2$ monolayers (ML) by means of photoluminescence (PL), PL excitation (PLE) and Raman scattering spectroscopy at room temperature and as a function of hydrostatic pressure up to ca. 12 GPa. For comparison the study comprises two cases: A single $WSe_2$ ML directly transferred onto one of the diamonds of the diamond anvil cell and a $WSe_2$ ML encapsulated into hexagonal boron nitride (hBN) layers. The pressure dependence of the A and B exciton, as determined by PL and PLE, respectively, is very different for the case of the bare $WSe_2$ ML and the $hBN/WSe_2-ML/hBN$ heterostructure. Whereas for the latter the A and B exciton energy increases linearly with increasing pressure at a rate of 3.5 to 3.8 meV/GPa, for the bare $WSe_2$ ML the A and B exciton energy decreases with a coefficient of -3.1 and -1.3 meV/GPa, respectively. We interpret that this behavior is due to a different stress situation. For a single ML the stress tensor is essentially uniaxial with the compressive stress component in the direction perpendicular to the plane of the ML. In contrast, for the substantially thicker $hBN/WSe_2-ML/hBN$ heterostructure the compression is hydrostatic. The results from an analysis of the pressure dependence of the frequency of Raman active modes comply with the interpretation of having a different stress situation in each case. Reviewed by: A. San Miguel, Institut Lumière Matière, Université de Lyon, France; Edited by: J. S. Reparaz

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“…On the other hand, the indirect Q = 1/3 exciton is lower in energy if the material is compressed. This behaviour could be interesting for pressure/strain sensors and similar applications [34].…”

Section: Tmdc Monolayersmentioning

confidence: 92%

Finite-momentum exciton landscape in mono- and bilayer transition metal dichalcogenides

2019

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K-Λ crossover transition in the conduction band of monolayer MoS ₂ under hydrostatic pressure

Abstract: We experimentally demonstrate the direct-to-indirect bandgap transition of monolayer MoS2 under hydrostatic pressure.

Cited by 65 publications

References 47 publications

Band gap crossover and insulator–metal transition in the compressed layered CrPS4

Band gap crossover and insulator–metal transition in the compressed layered CrPS4

On the impact of the stress situation on the optical properties of $WSe_2$ monolayers under high pressure

Finite-momentum exciton landscape in mono- and bilayer transition metal dichalcogenides

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K-Λ crossover transition in the conduction band of monolayer MoS 2 under hydrostatic pressure

Abstract: We experimentally demonstrate the direct-to-indirect bandgap transition of monolayer MoS2 under hydrostatic pressure.

Cited by 65 publications

References 47 publications

Band gap crossover and insulator–metal transition in the compressed layered CrPS4

Band gap crossover and insulator–metal transition in the compressed layered CrPS4

On the impact of the stress situation on the optical properties of $WSe_2$ monolayers under high pressure

Finite-momentum exciton landscape in mono- and bilayer transition metal dichalcogenides

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Product

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K-Λ crossover transition in the conduction band of monolayer MoS ₂ under hydrostatic pressure