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Quantum wells constitute one of the most important classes of devices in the study of 2D systems. In a double layer QW, the additional "which-layer" degree of freedom gives rise to celebrated phenomena such as Coulomb drag, Hall drag and exciton condensation. Here we demonstrate facile formation of wide QWs in few-layer black phosphorus devices that host double layers of charge carriers. In contrast to tradition QWs, each 2D layer is ambipolar, and can be tuned into n-doped, p-doped or intrinsic regimes. Fully spin-polarized quantum Hall states are observed on each layer, with enhanced Lande g-factor that is attributed to exchange interactions. Our work opens the door for using 2D semiconductors as ambipolar single, double or wide QWs with unusual properties such as high anisotropy.

Few layer phosphorene(FLP) devices are extensively studied due to its unique electronic properties and potential applications on nano-electronics . Here we present magnetotransport studies which reveal electron-electron interactions as the dominant scattering mechanism in hexagonal boron nitride-encapsulated FLP devices. From weak localization measurements, we estimate the electron dephasing length to be 30 to 100 nm at low temperatures, which exhibits a strong dependence on carrier density n and a power-law dependence on temperature (~T-0.4). These results establish that the dominant scattering mechanism in FLP is electron-electron interactions., Comment: accepted by 2D Materials

As the only non-carbon elemental layered allotrope, few-layer black phosphorus or phosphorene has emerged as a novel two-dimensional (2D) semiconductor with both high bulk mobility and a band gap. Here we report fabrication and transport measurements of phosphorene-hexagonal BN (hBN) heterostructures with one-dimensional (1D) edge contacts. These transistors are stable in ambient conditions for >300 hours, and display ambipolar behavior, a gate-dependent metal-insulator transition, and mobility up to 4000 $cm^2$/Vs. At low temperatures, we observe gate-tunable Shubnikov de Haas (SdH) magneto-oscillations and Zeeman splitting in magnetic field with an estimated g-factor ~2. The cyclotron mass of few-layer phosphorene holes is determined to increase from 0.25 to 0.31 $m_e$ as the Fermi level moves towards the valence band edge. Our results underscore the potential of few-layer phosphorene (FLP) as both a platform for novel 2D physics and an electronic material for semiconductor applications., Comment: minor correction of typos, equations and references

Using transport measurements, we investigate multicomponent quantum Hall (QH) ferromagnetism in dual-gated rhombohedral trilayer graphene (r-TLG), in which the real spin, orbital pseudospin and layer pseudospins of the lowest Landau level form spontaneous ordering. We observe intermediate quantum Hall plateaus, indicating a complete lifting of the degeneracy of the zeroth Landau level (LL) in the hole-doped regime. In charge neutral r-TLG, the orbital degeneracy is broken first, and the layer degeneracy is broken last and only the in presence of an interlayer potential U. In the phase space of U and filling factor, we observe an intriguing hexagon pattern, which is accounted for by a model based on crossings between symmetry-broken LLs.

Due to their unique electron dispersion and lack of a Fermi surface, Coulomb interactions in undoped two-dimensional Dirac systems, such as single, bi- and tri-layer graphene, can be marginal or relevant. Relevant interactions can result in spontaneous symmetry breaking, which is responsible for a large class of physical phenomena ranging from mass generation in high energy physics to correlated states such as superconductivity and magnetism in condensed matter. Here, using transport measurements, we show that rhombohedral-stacked trilayer graphene (r-TLG) offers a simple, yet novel and tunable, platform for study of various phases with spontaneous or field-induced broken symmetries. Here, we show that, contrary to predictions by tight-binding calculations, rhombohedral-stacked trilayer graphene (r-TLG) is an intrinsic insulator, with a giant interaction-induced gap {\Delta}~42meV. This insulating state is a spontaneous layer antiferromagnetic with broken time reversal symmetry, and can be suppressed by increasing charge density n, an interlayer potential, a parallel magnetic field, or a critical temperature Tc~38K. This gapped collective state can be explored for switches with low input power and high on/off ratio.