Two-dimensional nanoelectronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with ab initio calculations establish the large work function and narrow bands of α-RuCl 3 enable modulation doping of exfoliated single and bilayer graphene, chemical vapor deposition grown graphene and WSe 2 , and molecular beam epitaxy grown EuS. We further demonstrate proof of principle photovoltage devices, control via twist angle, and charge transfer through hexagonal boron nitride. Short-ranged lateral doping (≤65 nm) and high homogeneity are achieved in proximate materials with a single layer of α-RuCl 3 . This leads to the best-reported monolayer graphene mobilities (4900 cm 2 /(V s)) at these high hole densities (3 × 10 13 cm −2 ) and yields larger charge transfer to bilayer graphene (6 × 10 13 cm −2 ).

Since the discovery of Weyl semimetals (WSMs) 1,2 , there have been significant efforts to pursue ideal WSMs with all the Weyl nodes being symmetry related and not interfered with by any other bands. Although ideal WSM states have been realized in bosonic systems (i.e., photonic crystals 3 ), ideal fermionic WSMs are still lacking. In this Letter, we report transport evidence for a magnetic-field-induced ideal type-II Weyl state in the intrinsic antiferromagnetic topological insulator Mn(Bi,Sb)2Te4 4,5 . At an optimal sample composition, we minimize the carrier density, thus lowering the chemical potential and realizing the

Magnetic van der Waals (vdW) materials offer an opportunity to design heterostructures that will lead to exotic functionalities that arise from interfacial interaction. In addition to coupling to different vdW materials, the naturally oxidized surface layer of a vdW material also forms a heterostructure with its bulk film, giving rise to intriguing phenomena. Here, we directly observe the impact of oxidation on the magnetic domains, namely, magnetic stripe domain and skyrmions, in a nanoscale Fe3GeTe2 flake using cryo Lorentz transmission electron microscopy. After the Fe3GeTe2 is exposed to ambient conditions, partial oxidation leads to an increase in the density of skyrmions even under zero magnetic field. Complete oxidation leads to a loss of the magnetic domain structure. We observe a gradual change in Fe3GeTe2 from single crystal to amorphous as the oxidation increases. The oxidized Fe3GeTe2 primarily consists of iron oxide, which could be antiferromagnetic in nature. We hypothesize that the interfacial interaction between these surface antiferromagnetic oxides and the bulk ferromagnetic Fe3GeTe2, as well as the effect of interfacial roughness, leads to the increase in Néel skyrmion creation. This work opens a path to harness controlled oxidation as a build block to create dense skyrmion lattices without the need for an external magnetic field, leading to potential future applications in spintronic devices.

Topological magnetism typically appear in non-centrosymmetric compounds or compounds with geometric frustration. Here, we report the effective tuning of magnetism in centrosymmetric tetragonal Mn 2−x Zn x Sb by Zn substitution. The magnetism is found to be closely coupled to the transport properties, giving rise to a very large topological hall effect with fine tuning of Zn content, which even persists to high temperature (∼ 250 K). The further magnetoentropic analysis suggests that the topological hall effect is possibly associated with topological magnetism. Our finding suggests Mn 2−x Zn x Sb is a candidate material for centrosymmetric tetragonal topological magnetic system, offers opportunities for studying and tuning spin textures and developing near room temperature spin-based devices.

We report the fabrication, characterization, and modeling of photoconductive antennas (PCAs) using 40 nm thin-film flakes of black phosphorus (BP) as the photoconductor and hexagonal boron nitride (hBN) as a capping layer to prevent oxidation of BP. Dipole antennas were fabricated on oxidized high-resistivity Si substrates, and BP and hBN flakes were picked up and transferred onto the antenna inside a nitrogen glovebox. The transfer matrix technique was used to optimize the thickness of BP and hBN for maximum absorption. BP flakes were aligned with the armchair axis along the anode–cathode gap of the antenna, with crystal orientation measured using reflection anisotropy. Photocurrent imaging under illumination with 100 fs pulses at 780 and 1560 nm showed a bias-dependent maximum photocurrent localized to the antenna gap with a peak photoconductivity of 1 (2) S/cm in the linear regime of bias for excitation at 780 (1560) nm. Photocurrent saturation in bias (pump fluence) occurred at approximately 1 V (0.25mJ/cm2). Device performance was modeled numerically by solving Maxwell’s equations and the drift–diffusion equation to obtain the photocurrent density in response to pulsed laser excitation, which was largely in qualitative agreement with the experimental observations. THz output computed from surface current density suggests that BP THz PCA performance is at least comparable to more traditional devices based on low-temperature-grown GaAs. These devices represent a step toward high-performance THz photoconductive antennas using BP.