Piezotronic spin and valley transistors based on monolayer. Concepts of ferrovalley material and anomalous valley hall effect. Technologically, singlelayer mos 2 is relevant due to a direct optical gap at 1. Spinpolarized valley hall effect in ultrathin silicon. Quantum parity hall effect in bernalstacked trilayer. A scheme to realize the quantum spinvalley hall effect in. Here, we show that the valley hall effect in bilayer mos2 transistors can be controlled with a gate voltage. The electrons from different valleys moved in opposite directions across the sample, with one valley being overrepresented. Mechanisms of photoconductivity in atomically thin mos2. Valley magnetization in singlelayer mos2 is demonstrated by breaking the threefold rotational symmetry via uniaxial stress. Highfield transport and velocity saturation in synthetic monolayer mos2. Dichroic spinvalley photocurrent in monolayer molybdenum.
In this talk i will talk about our recent results on optical generation of valley polarization, based on which a novel hall effect associated with the new degree of freedom is demonstrated. The circularly polarized photoluminescence correspond to the emission from the k and k. Enhancing and controlling valley magnetic response in mos2ws2. The electrons from different valleys moved in opposite directions across the sample, with one valley being overrepresented with respect to the other. Mak k f, mcgill k l, park j and mceuen p l 2014 the valley hall effect in mos2 transistors science 344 148992. This class of materials has been studied extensively since 1960s in bulk, fewlayer, or fullerenelike nanoparticle or nanotube, forms, mostly in the context of lowfriction coatings and catalysis. Pdf works title dynamics of symmetrybreaking stacking. Highperformance silicon transistors can have gate lengths as short as 5 nm before sourcedrain tunneling and loss of electrostatic control lead to unacceptable leakage current when the device is off. Extrinsic origin of persistent photoconductivity in. The mechanisms responsible for driving the new valley hall effect will be discussed. Optical imaging of the valley hall effect in mos2 transistors. Here we present a systematic study of scaling mos2 devices and contacts with varying electrode metals and controlled deposition conditions, over a wide range of temperatures 80 to 500 k, carrier densities 1012 to 10 cm2, and contact dimensions 20 to 500 nm.
Thickness dependent charge transport in fewlayer mos2 field effect transistors. Aug 02, 2016 the performances of devices based on transition metal dichalcogenides tmds are far from their intrinsic limits, presumably due to various disorders in these 2d crystals. May 21, 2019 the quantum hall effect, which is characterized by an insulating bulk and chiral edge states, has recently been generalized from transport of charges to transport of other degrees of freedom, leading to quantum spin hall and quantum valley hall effects. Mos2 and semiconductors in the flatland sciencedirect. Direct observation of valleycoupled topological current in mos2. Nanophotonics with 2d transition metal dichalcogenides alex krasnok,1 sergey lepeshov,2 and andrea alu 1 1 department of electrical and computer engineering, the university of texas at austin, tx 78712, usa 2 itmo university, st. Jan 25, 2016 the valley hall effect in bilayer mos2 transistors can be controlled using a gate voltage and the induced valley polarization imaged with kerr microscopy.
However, the valley hall conductivity in monolayer mos2, a noncentrosymmetric crystal, cannot be easily tuned, which presents a challenge for the development of valley based applications. Low variability in synthetic monolayer mos2 devices acs nano. Electrical control of the valley hall effect in bilayer. The electronic structure of the twodimensional material mos2 has two distinct valleys of energy that may help to carry information in future electronic devices. We demonstrate analytically that this valley dependent band gap results in the emergence of a quantum spin hall effect, the reduction of the quantum valley hall effect, and enhancement. It was the thinning down to single layers and the availability of a wide range of techniques developed for graphenerelated research that opened new perspectives for the study of 2d. The valley hall conductivity in monolayer mos2, a noncentrosymmetric crystal, however, cannot be easily tuned, presenting a challenge for valley based applications. The noncentrosymmetric structure of monolayer transition metal dichalcogenides tmdcs, such as molybdenum disulfide mos2, has allowed for valley. As a result, not only optical control of the valley dof is allowed, but each valley is also predicted to exhibit an anomalous hall effect whose sign depends on the valley index. Thickness dependent charge transport in fewlayer mos2. Microscopic origin of the valley hall effect in transition. We investigate circularly polarized photoluminescence pl in the mos2 moo3 heterostructure, which was fabricated by transferring mos2 monolayer to cover the moo3 few layers on the sio2si substrate. Here, we report the first observation of intrinsic valley hall transport without any extrinsic symmetry breaking in the noncentrosymmetric monolayer and trilayer mos2, evidenced by.
Electrical control of the valley hall effect in bilayer mos2 transistors. Temperaturedependent excitonic effects in the optical. We investigate the valley hall effect vhe in monolayer wse2 field effect transistors using optical kerr rotation measurements at 20 k. Dopant introduced valley polarization, spin, and valley. Thicknessdependent charge transport in fewlayer mos 2. However, generation and detection of pure valley current without relying on optical selection have not yet been demonstrated in these materials.
Here we report the control of the valley hall effect in bilayer mos2 transistors through a gate. This socalled valley hall effect vhe has been used by mak et al. Mos2 transistors with 1nanometer gate lengths science. The valley hall effect in bilayer mos2 transistors can be controlled using a gate voltage and the induced valley polarization imaged with kerr microscopy. Monolayer mos2 transistors are illuminated with circularly polarized light, which preferentially excites electrons into. A team of researchers from purdue university, sematech and suny college of. Spatial separation of carrier spin by the valley hall. Cornell chronicle feature 50 strongly bound excitons in gapless twodimensional structures. Twodimensional semiconducting transitionmetal dichalcogenides have attracted considerable interest owing to their unique physical properties and future device applications. For this work, we fabricated wse2 fieldeffect transistors. The results are consistent with a theoretical model of valley. Here we report the properties of fieldeffect transistors based on a few layers of chemical vapor transport grown.
We further demonstrate an experimental strategy, based on wavelength dependent spatial mapping of the hall voltage, which allows the exciton and trion contributions to the valley hall effect to be discriminated in the measurement. The valley hall effect in mos2 transistors science. Characterization of photoinduced anomalous hall effect in. Spatial separation of carrier spin by the valley hall e. Spatial separation of carrier spin by the valley hall effect in monolayer wse2 transistors. Therefore, the spin and valley hall conductivity is expected to increase with dopant introduced exchange field for state in the vicinity of valleys. It is shown that the pl with the same helicity as the excitation light is dominant due to the inherent chiral optical selectivity, which allows exciting one of the valleys in mos2 monolayer.
Uncovering edge states and electrical inhomogeneity in mos2. Imaging grains and grain boundaries in singlelayer graphene. In dirty samples the intrinsic valley hall conductivity receives gatingdependent corrections that are only weakly dependent on the impurity concentration, consistent with. Here, we report a class of quantum hall effect, the quantum parity hall qph effect, in which boundary channels are distinguished by even or. Magnetoelectric effects and valleycontrolled spin quantum gates in transition metal dichalcogenide bilayers. Monolayer mos2 transistors are illuminated by circularly polarized light which preferentially excites electrons into a specific valley, and a finite anomalous hall.
Detecting spin valley hall effects using polar kerr effect measurements. The valley hall effect in mos 2 transistors kin fai mak1,2, kathryn l. We have measured circularly polarization resolved photoluminescence in monolayer mose 2 under magnetic fields up to 10 t in the faraday geometry. Here we report the first observation of this new valley hall effect vhe.
Here, we report the observation of this socalled valley hall effect vhe. Hall effect in the absence of a magnetic field whose sign depends on the valley index, but to date this effect has not been observed. Second, spin and valley relaxation are suppressed at the valenceband edges, as flip of each index alone is forbidden by the valleycontrasting spin splitting 0. In contrast to both mos2 and mose2, our mote2 fieldeffect transistors are observed to be holedoped. We performed fieldeffect and hall mobility measurements, as well as raman scattering and transmission electron microscopy. From 2002 2014, she was an assistant and associate professor in physics at case western reserve university. Tremendous progress has been made in exploring the valley pseudospin of two dimensional 2d tmds, ranging from optical generation and detection of valley polarization 79 to manipulation of valley pseudospin state with optical and magnetic field 1014 and observation of the valley hall effect. Crystal symmetry of twodimensional 2d materials plays an important role in their electronic and optical properties. Monolayer mos2 possess a new valley pseudospin degree of freedom besides electronic charge and spin.
The determination of the concentration of the charge carriers n or p. Osa manipulating the valley pseudospin in mos2 transistors. Quantum spin valley hall effect qsvh is defined as one valley carries a current of only spin up spin down and the other valley carries a current of spin down spin up with same magnitude but in exactly opposite direction. The structure of a monolayer mos2 fieldeffect transistor is sketched in fig.
Engineering symmetry in 2d materials has recently emerged as a promising way to achieve novel properties and functions. Pdf in gated transitionmetal dichalcogenides tmds, electrons near the kvalleys experience. In this paper, strong mesoscopic submicrometer electrical inhomogeneity in mos2. Pdf valley polarization of trions and magnetoresistance in. Quantum wells based on twodimensional 2d layerstructured tmds have unique optical features of intersubband transition.
These systems are predicted to exhibit an anomalous hall effect whose sign depends on the valley index. Valley splitting and polarization by zeeman effect in. Jie shan received her diploma in mathematics and physics from moscow state university, russia in 1996 and ph. Pdf electrical control of the valley hall effect in. Spinpolarized valley hall effect in ultrathin silicon nanomembrane via interlayer antiferromagnetic coupling jiatao sun 1,2, zhengfei wang 2,3, s meng 1, shixuan du 1, f liu 2 and hj gao 1. Tahir department of physics, concordia university, 7141 sherbrooke ouest, montr. You are using an old browser, click here to download pdf. First, the valley hall effect is accompanied by a spin hall effect in both electrondoped and holedoped systems. Here, we report that valley current can be electrically induced and detected through the valley hall effect and inverse valley hall effect, respectively, in monolayer molybdenum disulfide. Dopant introduced valley polarization, spin, and valley hall.
The inversion symmetry present in bilayer mos2 was broken by the gate applied electric field. Improved contacts to mos2 transistors by ultrahigh vacuum. The valley hall effect in mos2 transistors mceuen group. Now, valley polarized excitonpolaritons in monolayers of. Trion induced negative photoconductivity in monolayer mos2. The valley hall effect in mos 2 transistors kagimura journal club 2017628 arxiv. Mceuen1,2 electrons in twodimensional crystals with a honeycomb lattice structure possess a valley degree of freedom dof in addition to charge and spin. Valley magnetoelectricity in singlelayer mos 2 nature.
Laboratory of atomic and solid state physics, cornell university. Monolayer mos 2 transistors are illuminated by circularly polarized light which preferentially excites electrons into a specific valley. Bandgap broadening at grain boundaries in singlelayer mos 2. Spin and valleypolarized transport in a monolayer of mos2. Twodimensional transition metal dichalcogenides tmdcs have recently become. While studies of the vhe have so far focused on ndoped mos2, we observe the vhe in wse2 in both the n and pdoping regimes. Valley hall effect in disordered monolayer mos2 from first. Exploitation of the valley electronic structure of transition metal dichalcogenides with excitonpolaritons is an elusive challenge. Sep 14, 2011 recently, field effect transistors have been demonstrated experimentally using a mechanically exfoliated mos2 monolayer, showing promising potential for next generation electronics. The scaling of transistors to sub10 nm dimensions is strongly limited by their contact resistance rc. The symmetry and strong spinorbit coupling of tmds can obtain spin and valley polarization 19,20. This ahe, which is generated by the optical effect, is also called valley hall effect vhe. The valley hall effect in mos2 transistors request pdf. Valley hall transport induced nonlocal resistance in monolayer mos 2.
Nanophotonics with 2d transition metal dichalcogenides. Hole doping enables access to the large spinsplitting of the valence band of this material. Photoinduced quantum spin and valley hall effects, and. Pdf intrinsic valley hall transport in atomically thin mos2. Jun, 2014 highperformance mos2 field effect transistors. Gorantla s, bachmatiuk a and schmidt o g 20 rolledup nanomembranes as compact 3d architectures for field effect transistors and fluidic sensing applications nano lett. Intrinsic valley hall transport in atomically thin mos2. The spontaneous hall effect driven by the quantum berry phase which serves as an internal magnetic flux in momentum space manifests the topological nature. We show that the spin valley hall effect can be manifested in the gate dependence of the. We study valley polarization, spin, and valley hall conductivity in doped monolayer considering dopant introduced magnetic exchange field using low energy effective hamiltonian. Spinpolarized valley hall effect in ultrathin silicon nanomembrane via interlayer antiferromagnetic coupling. Electrically switchable chiral lightemitting transistor. Also mos 2 exhibits a lack of inversion symmetry and a valleysplit valence band, leading to a valley hall effect that is promising for valley or spintronic devices 20, 21. Spin and valleypolarized transport in a monolayer of mos 2 p.
The valley hall effect in mos2 transistors open access. A transistor with a 1nm physical gate was constructed. In particular, grain boundaries gbs have been often observed in singlelayer mos2 grown via chemical vapor deposition, which can significantly influence the material properties. Observation of ultralong valley lifetime in wse2mos2. Jun 27, 2014 the electronic structure of the twodimensional material mos2 has two distinct valleys of energy that may help to carry information in future electronic devices. To date, little is known about the magnitude and characteristic length scale of electrical inhomogeneity induced by the disorders in tmds. Pdf supplementary 51 the valley hall effect in mos2 transistors k. Monolayer mos2 transistors are illuminated by circularly polarized light which preferentially excites electrons into a specific valley, and a finite anomalous hall voltage is observed whose sign is controlled by the helicity of the light. Taking mos2 as an example, monolayer mos2 consists of a. Photoinduced exfoliation of monolayer transition metal. Monolayer mos2 transistors are illuminated with circularly polarized light. Kavli institute at cornell for nanoscale science, ithaca, ny 14853, usa 2. These results represent a significant step forward in our understanding. We investigate the valley hall effect vhe in monolayer.
Department of electrical engineering, stanford university, stanford, california 94305, united states department of electrical and computer. The trions exhibit a high circular polarization of. Spatial separation of carrier spin by the valley hall effect. Intrinsic valley hall transport in atomically thin mos 2 nature. Thickness dependent charge transport in fewlayer mos2 field. Direct observation of valleycoupled topological current. New transistor material tested 30 june 2014, by anne ju atoms of molybdenum gray and sulfur yellow are shown in a twodimensional crystal formation. Monolayer mos2 transistors are illuminated by circularly polarized light which preferentially excites electrons into a specific valley, and a finite anomalous hall voltage is observed whose. Work purpose the hall effect is one of the most important effects in the determination of the parameters that characterize from the electrical point of view the semiconductor materials. Muller these authors contributed equally to this work.
Mobility enhancement and highly efficient gating of monolayer mos2 transistors with polymer electrolyte. Namely, when the semiconductor channel is biased, electrons from different valleys move in opposite directions perpendicular to the drift current, a phenomenon. Electrical control of the valley hall effect in bilayer mos nature. We found that dopant introduced magnetic exchange field breaks the time inversion symmetry and decouples the energetically degenerated valleys into nondegenerate. On the other hand, berry curvature is related to both spin hall and valley hall through relation. Exciton hall effect in monolayer mos 2 nature materials. Piezotronic spin and valley transistors based on monolayer mos2. Here we project the ultimate performance limit of mos2 transistors by using nonequilibrium greens function based quantum transport simulations.
Electrical control of the valley hall effect in bilayer mos2. Osa asymmetric valley polarization and photoluminescence in. The spontaneous hall effect driven by the quantum berry phase which serves as an internal magnetic flux in momentum space manifests the topological nature of quasiparticles and can be used to. Kavli institute at cornell for nanoscale science, ithaca, ny 14853, usa. They are also suitable platforms for carrying out research on fundamental physics phenomena such as the valley hall effect 5, ultrafast charge transfer 6, or valley excitons in twodimensional materials 7. Pdf spin valley hall effects in transitionmetal dichalcogenides.
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