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 SnS2-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.
Highlights
Since the discovery of graphene, van der Waals materials are the subject of intensive research due to their fascinating optical, electrical, and mechanical properties
The scale bar is 10 mm. c scanning electron microscope (SEM) image of the cross-section of an individual cylindrite cylinder showing the crystals are formed by concentric layers of materials held by van der Waals (vdW) interactions
The vdW interaction, local atomic alignment, and lattice deformation while stacking of the constituent SnS2-like and PbS-like layers create small out-of-plane rippling on the crystal surface, resulting in strong inplane structural anisotropy in the crystal
Summary
Since the discovery of graphene, van der Waals (vdW) materials are the subject of intensive research due to their fascinating optical, electrical, and mechanical properties. Several exfoliated naturally occurring vdW heterostructure materials such as cylindrite[24], franckeite[25], and levyclaudite[26] have been reported, which belong to the sulfosalt mineral family with the vdW superlattices formed by alternate stacking of SnS2-like pseudo-hexagonal (H) layer and PbS-like pseudo-tetragonal (Q) layer. Out of these materials, the optical and electrical properties of bulk to single unit cell thick franckeite have been explored for optoelectronic applications in the linear optical regime[27,28]. To date, there is no study on the anisotropic optical responses of cylindrite yet
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