Electrical Control of Quantum Emitters in a Van der Waals Heterostructure

Controlling and manipulating individual quantum systems in solids underpins the growing interest in development of scalable quantum technologies1, 2. Recently, hexagonal boron nitride (hBN) has garnered significant attention in quantum photonic applications due to its ability to host optically stable quantum emitters3-7. However, the large band gap of hBN and the lack of efficient doping inhibits electrical triggering and limits opportunities to study electrical control of emitters. Here, we show an approach to electrically modulate quantum emitters in an hBN–graphene van der Waals heterostructure. We show that quantum emitters in hBN can be reversibly activated and modulated by applying a bias across the device. Notably, a significant number of quantum emitters are intrinsically dark, and become optically active at non-zero voltages. To explain the results, we provide a heuristic electrostatic model of this unique behaviour. Finally, employing these devices we demonstrate a nearly-coherent source with linewidths of ~ 160 MHz. Our results enhance the potential of hBN for tunable solid state quantum emitters for the growing field of quantum information science.

Electrostatic charge distribution in armchair and zigzag carbon nanotubes: a numerical comparison of CNT charge models

In engineering—especially in mechanics, lightweight engineering, aerospace engineering, electrical engineering as well as bioengineering—there is a desire of developing materials enabling an excellent performance with respect to mechanical, thermal, and electrical properties. One of the most promising materials are carbon nanotubes (CNTs), as they show excellent mechanical and electrical properties. To improve the understanding of the electrical behavior, i.e., the charge distribution in single-walled carbon nanotubes, both open ended armchair and zigzag types are investigated. In the present research, three different modeling approaches, a classic electrostatic model, the model by Li and Chou and the model by Mayer, are analyzed and compared with respect to their further applicability. In the numerical investigations, different test cases are performed: (i) the carbon nanotubes are charged with an overall charge, (ii) the CNTs are exposed to an external electric field, and (iii) the test cases (i) and (ii) are combined. Furthermore, the influence of different geometric parameters is investigated. It is shown that the charge applied to the CNTs distributes over the whole CNT having maxima at the ends of the tubes. These maxima can be influenced by both, the geometric parameters and the electric field strength.

The Electrostatic Model of Homeopathy: The Mechanism of Physicochemical Activities of Homeopathic Medicines

This paper attempts to propose a model, called the electrostatic model of homeopathy, to explain a mechanism for the physicochemical activities of highly diluted homeopathic medicines (HMs). According to this proposed model, the source of HMs' action is dipole orientations as electrostatic imprints of the original molecules carried by diluent molecules (such as sugar molecules) or potentization-induced aqueous nanostructures. The nanoscale domains' contact charging and dielectric hysteresis play critical roles in the aqueous nanostructures' or sugar molecules' acquisition of the original molecules' dipole orientations. The mechanical stress induced by dynamization (vigorous agitation or trituration) is a crucial factor that facilitates these phenomena. After dynamization is completed, the transferred charges revert to their previous positions but, due to dielectric hysteresis, they leave a remnant polarization on the aqueous nanostructures or sugar molecules' nanoscale domains. This causes some nanoscale domains of the aqueous nanostructures or sugar molecules to obtain the original substance molecules' dipole orientations. A highly diluted HM may have no molecule of the original substance, but the aqueous nanostructures or sugar molecules may contain the original substance's dipole orientations. Therefore, HMs can precisely aim at the biological targets of the original substance molecules and electrostatically interact with them as mild stimuli.

Improvement of the Gaussian Electrostatic Model by Separate Fitting of Coulomb and Exchange-Repulsion Densities and Implementation of a new Dispersion term

The description of each separable contribution of the intermolecular interaction is a useful approach to develop polarizable force fields (polFF). The Gaussian Electrostatic Model (GEM) is based on this approach, coupled with the use of density fitting techniques. In this work, we present the implementation and testing of two improvements of GEM: the Coulomb and Exchange-Repulsion energies are now computed with separate frozen molecular densities, and a new dispersion formulation inspired by the SIBFA polFF, which has been implemented to describe the dispersion and charge–transfer interactions. Thanks to the combination of GEM characteristics and these new features, we demonstrate a better agreement of the computed structural and condensed properties for water with experimental results, as well as binding energies in the gas phase with the ab initio reference compared with the previous GEM* potential. This work provides further improvements to GEM and the items that remain to be improved, and the importance of the accurate reproduction for each separate contribution.

Electrostatic model of dielectric elastomer generator based on finite element

When dielectric elastomer materials are used for power generation, bias voltage is applied at both ends of dielectric elastomer film, and there are equal amounts of heterogeneous charges on both sides of the film, so Maxwell electrostatic force is always coupled in the process of power generation. In order to investigate the distribution of Maxwell stress in dielectric elastomer material under electric field, the electrostatic model of dielectric elastomer generator is established in COMSOL finite element simulation software environment in this paper. The distribution of electrostatic force is studied from two aspects of theoretical derivation and simulation, and the magnitude and direction of electrostatic force are determined. The simulation results show that the Maxwell electrostatic force can be equivalent to the tensile force along the film plane and the extrusion force perpendicular to the plane, and they are the same.

Achieving high carrier density and high mobility in graphene using monolayer tungsten oxyselenide

Highly doped graphene holds promise for next-generation electronic and photonic devices. However, chemical doping cannot be precisely controlled, and introduces external disorder that significantly diminishes the carrier mobility and therefore the graphene conductivity. Here, we show that monolayer tungsten oxyselenide (TOS) created by oxidation of WSe2 acts as an efficient and low-disorder hole-dopant for graphene. When the TOS is directly in contact with graphene, the induced hole density is 3 × 1013 cm-2 , and the room-temperature mobility is 2,000 cm2 /V·s, far exceeding that of chemically-doped graphene. Inserting WSe2 layers between the TOS and graphene tunes the induced hole density as well as reduces charge disorder such that the mobility exceeds 20,000 cm2 /V·s and reaches the limit set by acoustic phonon scattering, resulting in sheet resistance below 50 Ω/□. An electrostatic model based on work-function mismatch accurately describes the tuning of the carrier density with WSe2 interlayer thickness. These films show unparalleled performance as transparent conductors at telecommunication wavelengths, as shown by measurements of transmittance in thin films and insertion loss in photonic ring resonators. This work opens up new avenues in optoelectronics incorporating two-dimensional heterostructures including infrared transparent conductors, electro-phase modulators, and various junction devices.