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Manipulating the strength of the interlayer coupling is an effective strategy to induce intriguing properties in layered materials. Recently, enhanced superconductivity has been reported in Weyl semimetal MoTe2 and WTe2 via ionic liquid (IL) cation intercalation. However, how the superconductivity enhancement depends on the interlayer interaction still remains elusive. Here by inserting IL cations with different sizes into MoTe2 through this strategy, we are able to tune the interlayer spacing of the intercalated MoTe2 samples and reveal the dependence of superconducting transition temperature T c on the interlayer spacing. Our results show that T c increases with the interlayer spacing, suggesting that the weakened interlayer coupling plays an important role in the superconductivity. Interestingly, the intercalation induced superconductivity shows a high Ginzburg–Landau anisotropy, which suggests a quasi-two-dimensional nature of the superconductivity where the adjacent superconducting layers are coupled through Josephson tunnelling.

The two-dimensional layered material MoTe2 has aroused extensive research interests in its rich optoelectronic properties in various phases. One property of particular interest is the circular photogalvanic effect (CPGE): a conventional second order nonlinear optical effect that is related to the chirality of materials. It has been demonstrated in Td-MoTe2, a type-II topological Weyl semimetal candidate, while it has been unclear so far whether it exists in the semimetallic 1T’ phase, another interesting phase that hosts a quantum spin hall state. In this article, we report a clear experimental observation of in-plane CPGE in 1T’-MoTe2. The observation is confirmed under various experimental designs with excitation by normally incident mid-infrared laser, and we find it to be related to an in-plane internal DC electric field. We attribute the circular photogalvanic response to a third-order nonlinear optical effect involving this DC electric field, which is consistent with the crystal symmetry of the lattices and present in both the 1T’ and Td phases of the material.

Artificially constructed van der Waals heterostructures (vdWHs) provide an ideal platform for realizing emerging quantum phenomena in condensed matter physics. Two methods for building vdWHs have been developed: stacking two-dimensional (2D) materials into a bilayer structure with different lattice constants, or with different orientations. The interlayer coupling stemming from commensurate or incommensurate superlattice pattern plays an important role in vdWHs for modulating the band structures and generating new electronic states. In this article, we review a series of novel quantum states discovered in two model vdWH systems -- graphene/hexagonal boron nitride (hBN) hetero-bilayer and twisted bilayer graphene (tBLG), and discuss how the electronic structures are modified by such stacking and twisting. We also provide perspectives for future studies on hetero-bilayer materials, from which an expansion of 2D material phase library is expected., Comment: Submitted to Chin. Phys. B for Topical Review

The weak van der Waals interaction between adjacent layers of quasi-two-dimensional materials provides opportunities for inserting intercalants to induce novel properties distinct from the host materials. Here we report induced superconductivity in an intercalated SnSe2 crystal by using a new type of intercalants—organic cations from ionic liquids, [C2MIm]+ and [DEMB]+. The intercalation of both cations increases the interlayer spacing and leads to induced superconductivity with T c of 7.1 and 6.9 K and a large superconducting anisotropy. Angle-resolved photoemission spectroscopy and Hall measurements reveal the importance of electron doping by the cations in the induced superconductivity, and the interlayer expansion and electric polarization of the cations in the large anisotropy. Our work reports induced superconductivity in an intercalated material with new intercalants which contribute both charge carriers and interlayer expansion, and provides a new pathway to the manipulation of superconductivity in layered materials.

In this paper, near infrared (NIR) absorbing dye and fluorane dye (FD) was successfully encapsulated into microcapsules with NIR light responsive performance. The NIR responsive microcapsules are able to be utilized in information recording and anti-counterfeiting fields. Specifically, the factors effecting on synthesis of NIR responsive microcapsules were studied in detail. Microcapsules with an average particle size of 0.2 ∼ 0.5 μm were prepared by adjusting the mass ratio of shell/core material, the viscosity of oil phase and the mass ratio of water/oil (W/O) phase. It was found that the preferred reaction condition was the feeding mass ratio of shell/core materiel at 1:2 and the W/O phase mass ratio of 2:1. When the feeding mass ratio of NIR absorbing dye and FD is 1/10, the NIR responsive microcapsules have the best coloration performance. Then the NIR responsive microcapsules were coated on aluminum substrate and scanned by 808 nm near-infrared laser, the image precision reached 20 μm.

Recently, topological semimetals have attracted extensive research interests in optoelectronics properties, especially along the direction for high performance photodetection for low energy photons. Among various topological semimetals, the photocurrent response of type-II Dirac semimetals with tilted cones that breaks Lorentz invariance is seldom studied. In this work, we report the photocurrent response studies of a lateral field effect device based on type-II Dirac semimetal PtTe2 over broad wavelength range from 532 nm to 4 μm. A moderate responsivity of 34 μA W-1 is obtained at 633 nm without applying any external bias. Further excitation power and temperature dependent measurements are performed to reveal the photocurrent response mechanism of PtTe2. The measurement results show clear anisotropic photocurrent response through polarization-dependent measurement and a response time of 34 μs can be extracted from chopping frequency-dependent measurement. Our results provide comprehensive studies of photocurrent response of type-II Dirac semi-metallic PtTe2.

Atomically thin transition metal dichalcogenide films with distorted trigonal (1T$^\prime$) phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1T$^\prime$ film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1T$^\prime$-MoTe$_2$ films grown by molecular beam epitaxy (MBE). Growth of the 1T$^\prime$-MoTe$_2$ film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction and sharp diffraction spots in low energy electron diffraction. Angle-resolved photoemission spectroscopy measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1T$^\prime$-MoTe$_2$ films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect., Comment: 13 pages,5 figures

Hexagonal boron nitride nanosheets (h-BNNSs) with unique properties, including wide band gap, excellent thermal conductivity and thermal stability, are among the most promising 2D inorganic nanomaterials in recent years. Functionalization of h-BNNSs is necessary to prevent them from strong tendency to agglomeration and to improve their dispersity and interfacial properties in solvents and polymer composites. In this work, amino and silane functionalized h-BNNSs were obtained, respectively. The chemical-bonding amino and silane functionalization of h-BNNSs were verified by FTIR, XPS and TG-MS analyses. The functionalized h-BNNSs show higher concentration, improved compatibility and dispersity in solvents and gel matrices after doping them into organically-modified silicate gel glasses using a sol-gel method. The functionalized h-BNNSs have broadband absorption and their doped glasses show high transmittances in the visible and near-infrared regions. The nonlinear optical properties of the functionalized h-BNNSs and their doped glasses were measured using Nd:YAG laser system and the doped glasses show broadband optical limiting responses at 532–1570 nm with the lowest onset threshold of 9 mJ cm−2. The optical limiting mechanisms investigated through Z-scan technique were nonlinear absorption. This work indicates that the functionalized h-BNNSs and their doped glasses are promising candidates for nonlinear optical, optical limiting and other optoelectronic materials and devices.

Atomically thin PtSe2 films have attracted extensive research interests for potential applications in high-speed electronics, spintronics and photodetectors. Obtaining high quality, single crystalline thin films with large size is critical. Here we report the first successful layer-by-layer growth of high quality PtSe2 films by molecular beam epitaxy. Atomically thin films from 1 ML to 22 ML have been grown and characterized by low-energy electron diffraction, Raman spectroscopy and X-ray photoemission spectroscopy. Moreover, a systematic thickness dependent study of the electronic structure is revealed by angle-resolved photoemission spectroscopy (ARPES), and helical spin texture is revealed by spin-ARPES. Our work provides new opportunities for growing large size single crystalline films for investigating the physical properties and potential applications of PtSe2.