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Spin-coupled valley-dependent dichroic photocurrent in monolayer MoS2. (a) Photocurrent (PC) as a function of angle of photon polarization ϕ when illuminated by 2.33 eV (off-resonance with the excitons) laser is shown. The PC data are collected by rotating a quarter-wave plate which changes polarization of a linearly polarized laser from 0° linear (↔) to 45° left circular (σ−), back to 90° linear (↔) to 135° right circular (σ+), and then back to 180° linear (↔) polarization, and so on. The (cyan) curve is the fitting function based on the phenomenological PC formula for monolayer MoS2, yielding negligible polarization between σ+ and σ− excitations. (b) PC as a function of ϕ when illuminated by 1.96 eV (on-resonance) laser. The (magenta) curve is the fitting function based on the phenomenological PC formula for monolayer MoS2, yielding a polarization of ~60% between σ+ and σ− excitations, which control the valley currents in K (linked with hole spin up) and −K (linked with hole spin down) valleys, respectively.
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The aim of valleytronics is to exploit confinement of charge carriers in local valleys of the energy bands of semiconductors as an additional degree of freedom in optoelectronic devices. Thanks to strong direct excitonic transitions in spin-coupled K valleys, monolayer molybdenum disulphide is a rapidly emerging valleytronic material, with high val...
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Citations
... As mentioned before, TMDs have degenerate energy levels with antiparallel spin in the K and K valleys, resulting in different responses of two valleys to external excitations with opposite rotations. [52,59,[66][67][68][69][70] The valley emission of TMDs in different valleys can be separated into opposite directions by plasmonic nanowires through near-field interactions. For example, Gong et al. established a system of plasmonic nanowires and monolayered TMDs, which was published on Science in 2018. ...
Nano-optics is an emergent research field in physics that appeared in the 1980s, which deals with light–matter optical interactions at the nanometer scale. In early studies of nano-optics, the main concern focus is to obtain higher optical resolution over the diffraction limit. The researches of near-field imaging and spectroscopy based on scanning near-field optical microscopy (SNOM) are developed. The exploration of improving SNOM probe for near-field detection leads to the emergence of surface plasmons. In the sense of resolution and wider application, there has been a significant transition from seeking higher resolution microscopy to plasmonic near-field modulations in the nano-optics community during the nano-optic development. Nowadays, studies of nano-optics prefer the investigation of plasmonics in different material systems. In this article, the history of the development of near-field optics is briefly reviewed. The difficulties of conventional SNOM to achieve higher resolution are discussed. As an alternative solution, surface plasmons have shown the advantages of higher resolution, wider application, and flexible nano-optical modulation for new devices. The typical studies in different periods are introduced and characteristics of nano-optics in each stage are analyzed. In this way, the evolution progress from near-field optics to plasmonics of nano-optics research is presented. The future development of nano-optics is discussed then.
... Additionally, h-TMDs have fascinating optical properties, including its strong band gap photoluminescence at the edge, and surface-sensitive luminescence. and strain-controlled optical band gap [30][31][32][33][34][35][36] . However, most of the intrinsic TMDs are nonmagnetic at ambient condition. ...
Two-dimensional semiconductors, including transition metal dichalcogenides (TMDs), are of interest in electronics and photonics but remain nonmagnetic in their intrinsic form. Atomic modulation using physical and chemical ways is an effective means to control the physical properties such as magnetic and electrical properties of two-dimensional materials which can be controlled by irradiation. Here we treat mechanically exfoliated MoS 2 with a helium ion beam, which exhibits semiconducting and ferromagnetic ordering at room temperature, while Monte Carlo simulations and theoretical calculations confirmed that the control of nanoholes result in the presence of magnetism. In addition, the irradiation results of multilayer MoS 2 show that the magnetic moment increases with the increase of 10 layers. The conductivity remains virtually unchanged before and after being treated by a helium ion beam. The treated MoS 2 spintronic device displays the switch of ‘on/off” under the light, magnetic field, and/or electric field, which means 2D photosensitive ferromagnetic semiconductor functions are successfully demonstrated at room temperature.
... Our study provides experimental demonstration of the generation of a photocurrent in monolayer and bilayer TMDCA samples. Earlier experimental studies [9][10][11][12][13] were focused on monolayer/bilayer/bulk TMDC materials with no study reported so far on the Janus material MoSSe or the related class of TMDCA materials. ...
... In our experiment, we detect only the charge photocurrent, and the data enable us to obtain a quantitative estimate of the polarization degree of the photocurrent. More generally, different microscopic mechanisms contribute to a photocurrent generated by polarized light with polarization ranging from linear to circular [9][10][11]. The experimental setup for the generation of a photocurrent in response to polarized light is shown in Fig. 4(a). ...
... The generated photocurrent is measured in the y direction. The photocurrent density is, in general, described by the phenomenological equation [9,11,12], j PC = C sin 2ϕ + L 1 sin 4ϕ + L 2 cos 4ϕ + D. ...
Monolayer transition metal dichalcogenides (TMDCs) constitute the core group of materials in the emerging semiconductor technology of valleytronics. While the coupled spin-valley physics of pristine TMDC materials and their heterostructures has been extensively investigated, less attention has been given to TMDC alloys,
which could be useful in optoelectronic applications due to the tunability of their band gaps. The experimental investigations presented herein focus on the exploration of the spin-valley physics of the monolayer and bilayer TMDC alloy MoS2xSe2(1−x) in terms of valley polarization and the generation as well as electrical control of a photocurrent utilizing the circular photogalvanic effect. Piezoelectric force microscopy provides evidence for an internal electric field perpendicular to the alloy layer, thus breaking the out-of-plane mirror symmetry. The experimental observation is supported by first-principles calculations based on the density functional theory. A comparison of the photocurrent device, based on the alloy material, is made with similar devices involving other TMDC materials.
... where represents the rotation angle of QWP, C is the coefficient of CPGE current, and L is related to the linear photocurrent. [35,36] As shown in Figure S10a (Supporting Information), theoretically, with the variation of , the photocurrent variation of an individual Stokes detector is the combined results of simultaneously recognizing CPL and LPL. It was found that after fully imprinting the nanowire array, although a large linear polarization ratio L can be obtained, the recognition effect of CPL was greatly reduced. ...
Polarization detection plays an essential role in a wide range of fields, including target identification, 3D reconstruction, and robotic vision. Self‐driven on‐chip full‐Stokes photodetectors are urgently required to meet the trend of miniaturization and integration. Nevertheless, how to fulfill efficient circular and linear polarimetry simultaneously with sufficient recognition effectiveness in a compact device is a great challenge. Herein, a patterned chiral perovskite film is fabricated by imprinting strategy, and vertically‐structured self‐driven Stokes photodetector is demonstrated, which can recognize various polarization states at 0 V. Through patterned design of the chiral perovskite film by integrating circle and nanowire structure, flexible tuning of circular and linear polarization components within the detector is achieved, enabling the detector to strike a balance between circular and linear polarization detection ability when recognizing arbitrary polarization light. The maximum circular polarization sensitivity factor and linear polarization ratio can reach 0.125 and 1.5, respectively. By optimizing well‐defined patterned shape, the resultant detector can recognize polarized light with an average recognition error <7%. This work opens an avenue toward the fabrication of self‐driven filterless Stokes detectors based on patterned chiral perovskite film for accurate detection of arbitrary polarization states.
... [17][18][19][20][21][22][23][24][25] Eginligil et al. demonstrated that large photocurrent dichroism can be achieved in high-quality MoS 2 monolayers grown by chemical vapor deposition (CVD). 26 Yuan et al. conducted a study showcasing the generation of the spin and valley polarized photocurrent in the WSe 2 electric double-layer transistors as well as the control of this current by the helicity of the circularly polarized light and the magnitude of the breaking of the inversion symmetry of the perpendicular electric field at the surface of WSe 2 . 23 However, the photocurrent produced by the PGE is typically constrained, which imposes limitations on its practical utility. ...
The photogalvanic effect (PGE) in two-dimensional materials has emerged as a fascinating mechanism for generating photocurrent in non-centrosymmetric crystals without semiconductor p–n junction or bias voltage. In this paper, the impact of grain boundaries (GBs) on the performance of photogalvanic device with Janus MoSSe monolayer is theoretically investigated by quantum transport simulations. Two 4|8 GBs along armchair direction are taken into consideration. Under the illumination of linearly polarized light, we observe a significant enhancement of the PGE photocurrent in the visible light region, which can be attributed to the reduction of device's symmetry. The averaged enhancement ratios reach around 20 and 13 for two 4|8 GBs, respectively.
... Transition metal dichalcogenides (TMDs), such as MoS 2 , WS 2 , and MoSe 2 , have garnered significant attention due to their unique electronic, optical, and mechanical properties [1][2][3][4][5][6][7]. TMDs consist of atomically thin layers held together by weak van der Waals forces. ...
We investigate the interaction between a monolayer of WS2 and a chiral plasmonic metasurface. WS2 possesses valley excitons that selectively couple with one-handed circularly polarized light. At the same time, the chiral plasmonic metasurface exhibits spin-momentum locking, leading to a robust polarization response in the far field. Using a scattering formalism based on the coupled mode method, we analyze various optical properties of the WS2 monolayer. Specifically, we demonstrate the generation of circular dichroism in the transition metal dichalcogenide (TMD) by harnessing the excitation of surface plasmon polaritons (SPPs) in the metasurface. Moreover, we observe the emergence of other guided modes, opening up exciting possibilities for further exploration in TMD-based devices.
... Our study provides the first experimental demonstration of the generation of a photocurrent in monolayer and bilayer TMDCA samples. Earlier experimental studies [9][10][11][12][13] were focused on monolayer/bilayer/bulk TMDC materials with no study reported so far on the Janus material MoSSe or the related class of TMDCA materials. ...
... The generated photocurrent is measured in the y-direction. The phenomenological expression for the photocurrent density is given by [9], ...
... These results clearly demonstrate the successful generation of a substantial photocurrent polarization, achieved naturally without the need for any external manipulation or intervention. The figure of merit of photocurrent polarization can be defined as [9], The plot of F versus the angle of incidence of illumination light is shown in Supplementary Fig. 15b. It is observed that F reaches its maximum value for θ = 60 0 . ...
Monolayer transition metal dichalcogenides (TMDCs) constitute the core group of materials in the emerging semiconductor technology of valleytronics. While the coupled spin-valley physics of pristine TMDC materials and their heterstructures has been extensively investigated, less attention was given to TMDC alloys, which could be useful in optoelectronic applications due to the tunability of their band gaps. We report here our experimental investigations of the spin-valley physics of the monolayer and bilayer TMDC alloy, MoS2xSe2(1−x), in terms of valley polarization and the generation as well as electrical control of a photocurrent utilising the circular photogalvanic effect. Piezoelectric force microscopy provides evidence for an internal electric field perpendicular to the alloy layer, thus breaking the out-of-plane mirror symmetry. This feature allows for the generation of a photocurrent in the alloy bilayer even in the absence of an external electric field. A comparison of the photocurrent device, based on the alloy material, is made with similar devices involving other TMDC materials.
... The application of valleytronic devices strongly depends on the carrier population distribution polarized in +K and −K valleys, which is referred to as valley polarization. [4][5][6] It is preferable to have a high degree of valley polarization and a long valley-polarized lifetime. ...
In recent years, valleytronics research based on 2D semiconducting transition metal dichalcogenides have attracted considerable attention. On the one hand, strong spin-orbit interaction allows the presence of spin-valley coupling in this system, which provides spin addressable valley degrees of freedom for information storage and processing. On the other hand, large exciton binding energy up to hundreds of millieletronvolts enable excitons to be stable carriers of valley information. Valley polarization, marked by an imbalanced exciton population in two inequivalent valleys (+K and -K), is the core of valleytronics as it can be utilized to store binary information. Motivated by the potential applications, we present a thorough overview of the recent advancements in the generation, relaxation, manipulation, and transport of the valley polarization in nonmagnetic transition metal dichalcogenide layered semiconductors. We also discuss the development of valleytronic devices and future challenges in this field.
... As shown schematically in Fig. 1c, by shining circularly polarized light onto the heterointerface, a net spin photocurrent can be generated from the non-uniformly distributed interband Berry curvature in the band structure, since the photo-induced carriers are excited with a probability proportional to the interband Berry curvature and move according to a group velocity (reflecting the band dispersion) during photonelectron angular momentum transfer (for a detailed calculation of the optical transition probability between the two bands based on the interband matrix element of the position operator, see Supplementary Section 15). Such a spin photocurrent can thus reveal the detailed distribution of spin texture and interband Berry curvature in the band structure [29][30][31][32][33][34][35][36][37][38][39][40] , and the amplitude of this spin photocurrent is expected to be proportional to the magnitude of the interband BCD [3][4][5] . If the mirror symmetry exists at the symmetry-mismatched heterointerface (C 1v symmetry), the pseudo-tensor BCD will be forced to be perpendicular to the mirror plane. ...
The Berry curvature dipole (BCD) is a key parameter that describes the geometric nature of energy bands in solids. It defines the dipole-like distribution of Berry curvature in the band structure and plays a key role in emergent nonlinear phenomena. The theoretical rationale is that the BCD can be generated at certain symmetry-mismatched van der Waals heterointerfaces even though each material has no BCD in its band structure. However, experimental confirmation of such a BCD induced via breaking of the interfacial symmetry remains elusive. Here we demonstrate a universal strategy for BCD generation and observe BCD-induced gate-tunable spin-polarized photocurrent at WSe2/SiP interfaces. Although the rotational symmetry of each material prohibits the generation of spin photocurrent under normal incidence of light, we surprisingly observe a direction-selective spin photocurrent at the WSe2/SiP heterointerface with a twist angle of 0°, whose amplitude is electrically tunable with the BCD magnitude. Our results highlight a BCD–spin–valley correlation and provide a universal approach for engineering the geometric features of twisted heterointerfaces.
... Transition metal dichalcogenides (TMDs), such as MoS 2 , WS 2 , and MoSe 2 , have garnered significant attention due to their unique electronic, optical, and mechanical properties [1][2][3][4][5][6][7]. TMDs consist of atomically thin layers held together by weak van der Waals forces. ...
We investigate the interaction between a monolayer of WS2 and a chiral plasmonic metasurface. WS2 possesses valley excitons that selectively couple with one-handed circularly polarised light. At the same time, the chiral plasmonic metasurface exhibits spin-momentum locking, leading to a robust polarisation response in the far field. Using a scattering formalism based on the coupled mode method, we analyse various optical properties of the WS2 monolayer. Specifically, we demonstrate the generation of circular dichroism in the transition metal dichalcogenide (TMD) by harnessing the excitation of surface plasmon polaritons (SPPs) in the metasurface. Moreover, we observe the emergence of other guided modes, opening up exciting possibilities for further exploration in TMD-based devices.
