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1. ZrTe2/CrTe2: an epitaxial van der Waals platform for spintronics

   https://doi.org/10.1038/s41467-022-30738-1  

   Ou, Yongxi; Yanez, Wilson; Xiao, Run; Stanley, Max; Ghosh, Supriya; Zheng, Boyang; Jiang, Wei; Huang, Yu-Sheng; Pillsbury, Timothy; Richardella, Anthony; et al (December 2022, Nature Communications)

   Abstract The rapid discovery of two-dimensional (2D) van der Waals (vdW) quantum materials has led to heterostructures that integrate diverse quantum functionalities such as topological phases, magnetism, and superconductivity. In this context, the epitaxial synthesis of vdW heterostructures with well-controlled interfaces is an attractive route towards wafer-scale platforms for systematically exploring fundamental properties and fashioning proof-of-concept devices. Here, we use molecular beam epitaxy to synthesize a vdW heterostructure that interfaces two material systems of contemporary interest: a 2D ferromagnet (1T-CrTe 2 ) and a topological semimetal (ZrTe 2 ). We find that one unit-cell (u.c.) thick 1T-CrTe 2 grown epitaxially on ZrTe 2 is a 2D ferromagnet with a clear anomalous Hall effect. In thicker samples (12 u.c. thick CrTe 2 ), the anomalous Hall effect has characteristics that may arise from real-space Berry curvature. Finally, in ultrathin CrTe 2 (3 u.c. thickness), we demonstrate current-driven magnetization switching in a full vdW topological semimetal/2D ferromagnet heterostructure device. 

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2. Natural van der Waals heterostructure cylindrite with highly anisotropic optical responses

   https://doi.org/10.1038/s41699-021-00254-9  

   Dasgupta, Arindam; Gao, Jie; Yang, Xiaodong (December 2021, npj 2D Materials and Applications)

   Abstract The mechanical exfoliation of naturally occurring layered materials has emerged as an easy and effective method for achieving ultrathin van der Waals (vdW) heterostructures with well-defined lattice orientations of the constituent two-dimensional (2D) material layers. Cylindrite is one such naturally occurring vdW heterostructure, where the superlattice is composed of alternating stacks of SnS 2 -like and PbS-like layers. Although the constituent 2D lattices are isotropic, inhomogeneous strain occurring from local atomic alignment for forcing the commensuration makes the cylindrite superlattice structurally anisotropic. Here, we demonstrate the highly anisotropic optical responses of cylindrite thin flakes induced by the anisotropic crystal structure, including angle-resolved polarized Raman scattering, linear dichroism, and polarization-dependent anisotropic third-harmonic generation. Our results provide a promising approach for identifying various natural vdW heterostructure-based 2D materials with tailored optical properties and can be harnessed for realizing anisotropic optical devices for on-chip photonic circuits and optical information processing. 

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3. Large in-plane vibrational and optical anisotropy in natural 2D heterostructure abramovite

   https://doi.org/10.1038/s41598-022-21042-5  

   Dasgupta, Arindam; Belakovskiy, Dmitriy I.; Chaplygin, Ilya V.; Gao, Jie; Yang, Xiaodong (December 2022, Scientific Reports)

   Abstract The design and formation of van der Waals (vdW) heterostructures with different two-dimensional (2D) materials provide an opportunity to create materials with extraordinary physical properties tailored toward specific applications. Mechanical exfoliation of natural vdW materials has been recognized as an effective way for producing high-quality ultrathin vdW heterostructures. Abramovite is one of such naturally occurring vdW materials, where the superlattice is composed of alternating Pb 2 BiS 3 and SnInS 4 2D material lattices. The forced commensuration between the two incommensurate constituent 2D material lattices induces in-plane structural anisotropy in the formed vdW heterostructure of abramovite, even though the individual 2D material lattices are isotropic in nature. Here, we show that ultrathin layers of vdW heterostructures of abramovite can be achieved by mechanical exfoliation of the natural mineral. Furthermore, the structural anisotropy induced highly anisotropic vibrational and optical responses of abramovite thin flakes are demonstrated by angle-resolved polarized Raman scattering, linear dichroism, and polarization-dependent third-harmonic generation. Our results not only establish abramovite as a promising natural vdW material with tailored linear and nonlinear optical properties for building future anisotropic integrated photonic devices, but also provide a deeper understanding of the origin of structural, vibrational and optical anisotropy in vdW heterostructures. 

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4. Van der Waals heterostructures: a promising platform to design high-performance optoelectronics

   https://doi.org/10.1088/2399-1984/ae236b  

   Wu, Judy; Ghopry, Samar (December 2025, Nano Futures)

   Abstract Two-dimensional (2D) atomic materials regard a large family of monolayer or few layers atomic sheets that can stand alone. While there are no dangling chemical bonds in the direction normal to the sheets, stacking different kinds of 2D atomic materials into so-called van der Waals (vdW) heterostructures enables a platform for designing high-performance quantum devices that can have unique and unprecedented physical properties and device functionalities in conventional semiconductors. Following the discovery of the first 2D atomic material of graphene in 2004, the progress in exploration of new 2D atomic materials and their vdW heterostructures has been explosive during the past two decades. This perspective aims to highlight some recent progress in the research of vdW heterostructures, particularly in transition-metal dichalcogenide/graphene optoelectronics, enabled by the quantum physics in constituent components and their interfaces. New approaches in layer by layer synthesizing these vdW heterostructures are promising for wafer-size fabrication of high-performance, low-cost optoelectronic devices for practical applications. 

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5. Natural 2D layered mineral cannizzarite with anisotropic optical responses

   https://doi.org/10.1038/s41598-022-14046-8  

   Dasgupta, Arindam; Yang, Xiaodong; Gao, Jie (December 2022, Scientific Reports)

   Abstract Cannizzarite is a naturally occurring mineral formed by van der Waals (vdW) stacking of alternating layers of PbS-like and Bi 2 S 3 -like two-dimensional (2D) materials. Although the PbS-type and Bi 2 S 3 -type 2D material layers are structurally isotropic individually, the forced commensuration between these two types of layers while forming the heterostructure of cannizzarite induces strong structural anisotropy. Here we demonstrate the mechanical exfoliation of natural cannizzarite mineral to obtain thin vdW heterostructures of PbS-type and Bi 2 S 3 -type atomic layers. The structural anisotropy induced anisotropic optical properties of thin cannizzarite flakes are explored through angle-resolved polarized Raman scattering, linear dichroism, and polarization-dependent anisotropic third-harmonic generation. Our study establishes cannizzarite as a new natural vdW heterostructure-based 2D material with highly anisotropic optical properties for realizing polarization-sensitive linear and nonlinear photonic devices for future on-chip optical computing and optical information processing. 

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