A transistor based on spin rather than charge—a spin transistor—could potentially offer non-volatile data storage and improved performance compared with traditional transistors. Many approaches have been explored to realize spin transistors, but their development remains a considerable challenge. The recent discovery of two-dimensional magnetic insulators such as chromium triiodide (CrI 3 ), which offer electrically switchable magnetic order and an effective spin filtering effect, can provide new operating principles for spin transistors.

The Hall effect occurs only in systems with broken time-reversal symmetry, such as materials under an external magnetic field in the ordinary Hall effect and magnetic materials in the anomalous Hall effect (AHE) 1 . Here we show a nonlinear AHE in a non-magnetic material under zero magnetic field, in which the Hall voltage depends quadratically on the longitudinal current 2–6 . We observe the effect in few-layer T d -WTe 2 , a two-dimensional semimetal with broken inversion symmetry and only one mirror line in the crystal plane.

Many-body interactions in monolayer transition-metal dichalcogenides are strongly affected by their unique band structure. We study these interactions by measuring the energy shift of neutral excitons (bound electron-hole pairs) in gated WSe2 and MoSe2. Surprisingly, while the blueshift of the neutral exciton X0 in electron-doped samples can be more than 10 meV, the blueshift in hole-doped samples is nearly absent.

Advances in van der Waals heterostructures allow the control of interlayer excitons by electrical and other means, promising exciting opportunities for high-temperature exciton condensation and valley–spin optoelectronics. © 2018, Springer Nature Limited.

The emergence of two-dimensional Dirac materials, particularly transition metal dichalcogenides (TMDs), has reinvigorated interest in valleytronics, which utilizes the electronic valley degree of freedom for information storage and processing. Here, we review the basic valley-dependent properties and their experimental demonstrations in single-layer semiconductor TMDs with an emphasis on the effects of band topology and light–valley interactions.

The atomic thickness of two-dimensional materials provides a unique opportunity to control their electrical 1 and optical 2 properties as well as to drive the electronic phase transitions 3 by electrostatic doping. The discovery of two-dimensional magnetic materials 4-10 has opened up the prospect of the electrical control of magnetism and the realization of new functional devices 11 . A recent experiment based on the linear magneto-electric effect has demonstrated control of the magnetic order in bilayer CrI3 by electric fields 12 .

Time reversal and spatial inversion are two key symmetries for conventional Bardeen-Cooper-Schrieffer (BCS) superconductivity1. Breaking inversion symmetry can lead to mixed-parity Cooper pairing and unconventional superconducting properties1-5. Two-dimensional (2D) NbSe2 has emerged as a new non-centrosymmetric superconductor with the unique out-of-plane or Ising spin-orbit coupling (SOC)6-9. Here we report the observation of an unusual continuous paramagnetic-limited superconductor-normal metal transition in 2D NbSe2.

We demonstrate robust optical bistability, the phenomenon of two well-discriminated stable states depending upon the history of the optical input, in fully suspended monolayers of WSe2 at low temperatures near the exciton resonance. Optical bistability has been achieved under continuous-wave optical excitation that is red-detuned from the exciton resonance at an intensity level of 103 W/cm2. The observed bistability is originated from a photothermal mechanism, which provides both optical nonlinearity and passive feedback, two essential elements for optical bistability.

Controlling magnetism by purely electrical means is a key challenge to better information technology 1 . A variety of material systems, including ferromagnetic (FM) metals 2-4, FM semiconductors 5, multiferroics 6-8 and magnetoelectric (ME) materials 9,10, have been explored for the electric-field control of magnetism. The recent discovery of two-dimensional (2D) van der Waals magnets 11,12 has opened a new door for the electrical control of magnetism at the nanometre scale through a van der Waals heterostructure device platform 13 .