Observation of Giant Surface Second-Harmonic Generation Coupled to Nematic Orders in the van der Waals Antiferromagnet FePS.

Second-harmonic generation has been applied to study lattice, electronic, and magnetic proprieties in atomically thin materials. However, inversion symmetry breaking is usually required for the materials to generate a large signal. In this work, we report a giant second-harmonic generation that arises below the Néel temperature in few-layer centrosymmetric FePS.

Direct Imaging of Antiferromagnetic Domains and Anomalous Layer-Dependent Mirror Symmetry Breaking in Atomically Thin MnPS_{3}.

We have developed a sensitive cryogenic second-harmonic generation microscopy to study a van der Waals antiferromagnet MnPS_{3}. We find that long-range Néel antiferromagnetic order develops from the bulk crystal down to the bilayer, while it is absent in the monolayer. Before entering the long-range antiferromagnetic ordered phase in all samples, an upturn of the second harmonic generation below 200 K indicates the formation of the short-range order and magnetoelastic coupling.

Defect-Mediated Phase Transformation in Anisotropic Two-Dimensional PdSe Crystals for Seamless Electrical Contacts.

The failure to achieve stable Ohmic contacts in two-dimensional material devices currently limits their promised performance and integration. Here we demonstrate that a phase transformation in a region of a layered semiconductor, PdSe, can form a contiguous metallic PdSe phase, leading to the formation of seamless Ohmic contacts for field-effect transistors. This phase transition is driven by defects created by exposure to an argon plasma.

Ion Migration Studies in Exfoliated 2D Molybdenum Oxide via Ionic Liquid Gating for Neuromorphic Device Applications.

The formation of an electric double layer in ionic liquid (IL) can electrostatically induce charge carriers and/or intercalate ions in and out of the lattice which can trigger a large change of the electronic, optical, and magnetic properties of materials and even modify the crystal structure. We present a systematic study of ionic liquid gating of exfoliated 2D molybdenum trioxide (MoO) devices and correlate the resultant electrical properties to the electrochemical doping via ion migration during the IL biasing process. A nearly 9 orders of magnitude modulation of the MoO conductivity is obtained for the two types of ionic liquids that are investigated.