It has long been assumed that the inversion asymmetry-induced Rashba spin splitting in two-dimensional (2D) systems at zero magnetic field is proportional to the electric field that characterizes the inversion asymmetry of the confining potential. Here we demonstrate, both theoretically and experimentally, that 2D heavy hole systems in accumulation layer-like single heterostructures show the opposite behavior, i.e., a decreasing, but nonzero electric field results in an increasing Rashba coefficient.Comment: 4 pages, 3 figure

The development of low resistance contacts to 2D transition-metal dichalcogenides (TMDs) is still a big challenge for the future generation field effect transistors (FETs) and optoelectronic devices. Here, we report a chemical doping technique to achieve low contact resistance by keeping the intrinsic properties of few layers WS2. The transfer length method has been used to investigate the effect of chemical doping on contact resistance. After doping, the contact resistance (Rc) of multilayer (ML) WS2 has been reduced to 0.9 kΩ·μm. The significant reduction of the Rc is mainly due to the high electron doping density, thus a reduction in Schottky barrier height, which limits the device performance. The threshold voltage of ML-WS2 FETs confirms a negative shift upon the chemical doping, as further confirmed from the positions of E(1)2g and A1g peaks in Raman spectra. The n-doped samples possess a high drain current of 65 μA/μm, with an on/off ratio of 1.05 × 10(6) and a field effect mobility of 34.7 cm(2)/(V·s) at room temperature. Furthermore, the photoelectric properties of doped WS2 flakes were also measured under deep ultraviolet light. The potential of using LiF doping in contact engineering of TMDs opens new ways to improve the device performance.

The metallic conductivity of dilute two-dimensional holes in a GaAs HIGFET (Heterojunction Insulated-Gate Field-Effect Transistor) with extremely high mobility and large rs is found to have a linear dependence on temperature, consistent with the theory of interaction corrections in the ballistic regime. Phonon scattering contributions are negligible in the temperature range of our interest, allowing comparison between our measured data and theory without any phonon subtraction. The magnitude of the Fermi liquid interaction parameter F σ 0 determined from the experiment, however, decreases with increasing rs for rs > ∼ 22, a behavior unexpected from existing theoretical calculations valid for small rs.PACS numbers: 71.30.+h,73.40.Kp In two-dimensional (2D) charge carrier systems, it is well known that any amount of disorder in the absence of interactions between the carriers will localize the carriers, leading to an insulator with zero conductivity (σ) as the temperature (T ) is decreased to zero 1 . Recent experiments on high mobility dilute 2D systems, on the other hand, have shown a "metallic" behavior at low T , characterized by an increasing σ with decreasing T , and an apparent metal-insulator transition (MIT) as the carrier density is lowered 2 . There are three important energy scales in these systems. The first two are the Fermi energy and the interaction energy. Their ratio, which is r s , is around 10 or higher for the systems where the MIT is observed, implying that interaction must be playing a role. The other energy scale is related to the disorder in the system given byh/τ , where τ is the elastic scattering time. It has been found from more recent experiments that disorder is also playing a significant role. In particular, the critical density (n c for electrons and p c for holes), above which a system shows the metallic behavior, is found to decrease when disorder in the 2D system is decreased3 .An important question is whether this apparent metallic state is truly a new ground state of the 2D charge carriers or simply a novel finite temperature behavior of the 2D gas, since all experiments are done at finite T . What is measured in such experiment is the temperature coefficient, dσ/dT . The metallic behavior evinced by the observation of negative dσ/dT at finite T does not necessarily mean, however, a true metal with nonzero conductivity at T = 0. Recently, Zala et al.4 calculated the Fermi liquid interaction corrections to the conductivity in the asymptotic low temperature regime (T /T F ≪ 1 where T F is the Fermi temperature), and pointed out that the metallic behavior seen in the high mobility samples could be understood by taking into account of interaction corrections in the "high temperature" ballistic regime (k B T ≫h/τ ). They found that the conductivity of interacting 2D carriers changes linearly with T in the ballistic regime, T F ≫ T ≫h/k B τ , with the sign as well as the magnitude of dσ/dT depending on the strength of the interaction, while in the low temperature diffusive regime...

We report drag measurements on dilute double layer two-dimensional hole systems in the regime of r(s) = 19-39. We observed a strong enhancement of the drag over the simple Boltzmann calculations of Coulomb interaction, and deviations from the T2 dependence which cannot be explained by phonon-mediated, plasmon-enhanced, or disorder-related processes. We suggest that this deviation results from interaction effects in the dilute regime.

We present a van der Waals p-MoTe2/n-MoTe2 homojunction p–n diode with low resistance metal contacts.