Chirality-Induced Quantum and Topological Properties in 2D Tellurium

Chirality is increasingly recognized as a critical property in various aspects of human life, spanning fields such as biological chemistry and physics. The disruption of chiral symmetry significantly influences the properties of matter, particularly in pharmaceuticals, biochemistry, and materials science. Thus, a comprehensive understanding and manipulation of chiral materials are crucial for advancing cutting-edge technologies, including chirality-based sensors, optical devices, and electronic systems.<br/>Trigonal Tellurium (Te) possesses one of the simplest crystal structures, consisting of a unit cell where three Te atoms form a covalently bonded spiral chain. The chirality of the Te crystal is determined by the helicity of these atomic Te chains, classified into different space groups: P3₁21 (right-handed) and P3₂21 (left-handed). Recently, hydrothermally grown two-dimensional (2D) Tellurium (Te) with a thickness of about 10 nanometers has attracted considerable attention due to its excellent electrical, thermal, and optical properties. The chemical potential of 2D Te can be electrostatically tuned by applying a gate voltage, enabling systematic studies of the quantum and topological properties induced by chirality.<br/>Under ambient pressure, the conduction band minimum and valence band maximum of Te are located at the H(H') point in the first Brillouin zone. Due to Te atoms' strong spin-orbit interaction and the unique chiral crystal structure characterized by three-fold screw symmetry, the conduction bands split and cross at the H(H') point, leading to a Weyl node. This node produces a radial-like spin texture in k-space, where spin polarization aligns parallel to the direction of electron momentum. This characteristic distinguishes it from the spin texture observed in Rashba semiconductors or the surface states of topological insulators, where the spin polarization is perpendicular to the electron momentum direction. Importantly, the spin polarization and charge of the Weyl nodes reverse in different enantiomers, a consequence of the mirror symmetry of left- and right-handed Te crystals.<br/>Our investigations of the chirality-induced properties in 2D Te involved electrical and photoelectric responses. The chirality of 2D Te flakes was determined and verified using hot sulfuric acid etch pits and high-angle tilted high-resolution scanning transmission electron microscopy (HR-STEM). At low temperatures (0.3 K), we observed gate-tunable nonlinear electrical responses in 2D Te, including nonreciprocal electrical transport along the longitudinal direction and a nonlinear planar Hall effect along the transverse direction when subjected to a magnetic field. At room temperature, we discovered tunable chirality-dependent circular photogalvanic and photovoltaic effects, stemming from the interaction between circular-polarized light and the chiral crystal structure of 2D Te. These findings highlight the ability to control and manipulate the degree of chirality in materials.