Independent Electrical Control Research Articles

Independent Electrical Control of Spin and Valley Degrees in 2D Breathing Kagome Ta3I8 with Intrinsic Triferroicity.

Independent electrical control of spin and valley degrees of freedom (DOFs) in 2D materials is difficult due to the coupling of spin and valley DOFs. Here we propose that spin-filter transport and valley polarization can be independently manipulated by an electric field in 2D breathing kagome Ta3I8 due to the possession of both triferroic (ferromagnetism, ferroelectric, and ferrovalley) and bipolar magnetic semiconducting characteristics. The spin-filter transport can be realized by applying a bias voltage without altering the semiconducting characteristic. The flip of valley polarization is fulfilled by switching the ferroelectric polarization with a gate voltage. Our results demonstrate the potential to control different DOFs independently by adjusting the direction of the electric field.

High-energy picosecond pulses with a single spatial mode from a passively mode-locked, broad-area semiconductor laser

We present a mode-locked semiconductor laser oscillator that emits few picosecond pulses (5-8ps at a repetition rate of 379MHz and wavelength of 1064nm) with record peak power (112W) and pulse energy (0.5nJ) directly out of the oscillator (with no amplifier). To achieve this high power performance we employ a high-current broad-area, spatially multi-mode diode amplifier (0.3×5mm), placed in an external cavity that enforces oscillation in a single spatial mode. Consequently, the brightness of the beam is near-ideal (M2 = 1.3). Mode locking is achieved by dividing the large diode chip (edge emitter) into two sections with independent electrical control: one large section for gain and another small section for a saturable absorber. Precise tuning of the reverse voltage on the absorber section allows to tune the saturation level and recovery time of the absorber, providing a convenient knob to optimize the mode-locking performance for various cavity conditions.

Flexible topographical design of light-emitting diodes realizing electrically controllable multi-wavelength spectra

Multi-wavelength visible light emitters play a crucial role in current solid-state lighting. Although they can be realized by combining semiconductor light-emitting diodes (LEDs) and phosphors or by assembling multiple LED chips with different wavelengths, these design approaches suffer from phosphor-related issues or complex assembly processes. These challenges are significant drawbacks for emerging applications such as visible light communication and micro-LED displays. Herein we present a platform for tailored emission wavelength integration on a single chip utilizing epitaxial growth on flexibly-designed three-dimensional topographies. This approach spontaneously arranges the local emission wavelengths of InGaN-based LED structures through the local In composition variations. As a result, we demonstrate monolithic integration of three different emission colors (violet, blue, and green) on a single chip. Furthermore, we achieve flexible spectral control via independent electrical control of each component. Our integration scheme opens the possibility for tailored spectral control in an arbitrary spectral range through monolithic multi-wavelength LEDs.

Independent Electrical Control of Two Quantum Dots Coupled through a Photonic-Crystal Waveguide.

Efficient light-matter interaction at the single-photon level is of fundamental importance in emerging photonic quantum technology. A fundamental challenge is addressing multiple quantum emitters at once, as intrinsic inhomogeneities of solid-state platforms require individual tuning of each emitter. We present the realization of two semiconductor quantum dot emitters that are efficiently coupled to a photonic-crystal waveguide and individually controllable by applying a local electric Stark field. We present resonant transmission and fluorescence spectra in order to probe the coupling of the two emitters to the waveguide. We exploit the single-photon stream from one quantum dot to perform spectroscopy on the second quantum dot positioned 16 μm away in the waveguide. Furthermore, power-dependent resonant transmission measurements reveal signatures of coherent coupling between the emitters. Our work provides a scalable route to realizing multiemitter collective coupling, which has inherently been missing for solid-state deterministic photon emitters.

Optimizing multistage reverse electrodialysis for enhanced energy recovery from river water and seawater: Experimental and modeling investigation

• Fair comparison between single-stage and multistage reverse electrodialysis. • New “saving the gradient” electrical control strategy improves process performance. • To harvest energy from river water and seawater, applying two stages is optimal. • Reducing stack pressure drops favors multistage application. Reverse electrodialysis has been established as a promising method to harvest salinity gradient energy. To achieve market viability, an optimum process configuration is needed, in addition to material and stack development, to increase energy efficiency without compromising power density. Multistage reverse electrodialysis is a practical strategy providing several degrees of freedom, such as independent electrical control of the stages, asymmetric staging, and different configurations. This study tests a two-stage configuration experimentally, using seawater and river water (NaCl only), at several residence times and changing the electrical control. Furthermore, the results are compared with a numerical model that is subsequently used to predict the behavior of alternative multistage configurations. The results show that multistage reverse electrodialysis yields higher gross power density and energy efficiency than a single-stage configuration fed with the same salinity gradient. A new strategy named “saving the gradient” (i.e., lowering the discharge current in the first stage) increased the gross overall performance of the two stages up to 17% relative to single-stage and up to 6% relative to a sequentially optimized two-stage system. Modeling different configurations revealed that only two stages are needed when feeding seawater and river water. When retrieving 40% net energy efficiency, the net power density for a single stage is 0.86 W∙m −2 and 0.94 W∙m −2 for a two-stage system, representing an improvement of 9%. Multistage reverse electrodialysis is therefore a viable concept to enhance power and energy efficiency, and benefits from optimization through electrical control.

Ferroelectric domain architecture and poling of BaTiO3 on Si

We investigate the ferroelectric domain architecture and its operando response to an external electric field in ${\mathrm{BaTiO}}_{3}$-based electro-optic heterostructures integrated on silicon. By noninvasive optical second-harmonic generation, we identify the preexistence of in-plane ($a$-) domains dispersed within a predominantly out-of-plane- ($c$-) oriented matrix. Monitoring the poling behavior of the respective domain populations, we show that the spontaneous polarization of these $a$-domains lack a predominant orientation in the pristine state, yet can be selectively aligned with an in-plane electric field, leaving the $c$-domain population intact. Hence, domain reorientation of a ferroelastic $c$-to-$a$ type was directly excluded. Such independent electrical control of ferroelectric $a$-domains in a $c$-oriented ${\mathrm{BaTiO}}_{3}$ film on silicon is a valuable platform for engineering multidirectional electro-optic functionality in integrated photonic devices.

Stretchable Persistent Spin Helices in GaAs Quantum Wells

The Rashba and Dresselhaus spin-orbit (SO) interactions in 2D electron gases act as effective magnetic fields with momentum-dependent directions, which cause spin decay as the spins undergo arbitrary precessions about these randomly-oriented SO fields due to momentum scattering. Theoretically and experimentally, it has been established that by fine-tuning the Rashba $\alpha$ and Dresselhaus $\beta$ couplings to equal $\it{fixed}$ strengths $\alpha=\beta$, the total SO field becomes unidirectional thus rendering the electron spins immune to dephasing due to momentum scattering. A robust persistent spin helix (PSH) has already been experimentally realized at this singular point $\alpha=\beta$. Here we employ the suppression of weak antilocalization as a sensitive detector for matched SO fields together with a technique that allows for independent electrical control over the SO couplings via top gate voltage $V_T$ and back gate voltage $V_B$. We demonstrate for the first time the gate control of $\beta$ and the $\it{continuous\,locking}$ of the SO fields at $\alpha=\beta$, i.e., we are able to vary both $\alpha$ and $\beta$ controllably and continuously with $V_T$ and $V_B$, while keeping them locked at equal strengths. This makes possible a new concept: "stretchable PSHs", i.e., helical spin patterns with continuously variable pitches $P$ over a wide parameter range. The extracted spin-diffusion lengths and decay times as a function of $\alpha/\beta$ show a significant enhancement near $\alpha/\beta=1$. Since within the continuous-locking regime quantum transport is diffusive (2D) for charge while ballistic (1D) for spin and thus amenable to coherent spin control, stretchable PSHs could provide the platform for the much heralded long-distance communication $\sim 8 - 25$ $\mu$m between solid-state spin qubits.

Completely independent electrical control of spin and valley in a silicene field effect transistor

One-atom-thick silicene is a silicon-based hexagonal-lattice material with buckled structure, where an electron fuses multiple degrees of freedom including spin, sublattice pseudospin and valley. We here demonstrate that a valley-selective spin filter (VSSF) that supports single-valley and single-spin transport can be realized in a silicene field effect transistor constructed of an npn junction, where an antiferromagnetic exchange field and a perpendicular electric field are applied in the p-doped region. The nontrivial VSSF property benefits from an electrically controllable state of spin-polarized single-valley Dirac cone. By reversing the electric field direction, the device can operate as a spin-reversed but valley-unreversed filter due to the dependence of band gap on spin and valley. Further, we find that all the possible spin-valley configurations of VSSF can be achieved just by tuning the electric field. Our findings pave the way to the realization of completely independent electrical control of spin and valley in silicene circuits.

The design, fabrication, and acoustic calibration of a 1-3 piezoelectric polymer composite-based cylindrical array module for towed applications

A cylindrical transducer array module containing eight double-layered 1–3 piezocomposite elements was acoustically calibrated in the frequency range 10–100 kHz. Each wedge-shaped element, covering approximately one octant (45) of the cylindrical radiating aperture, was housed in a molded syntactic foam hub component with its outer surface conforming to a cylindrical aperture 12.7 mm in diameter. The construction approach described would allow one to connect several modules of similar (or varying) diameter along the axial direction for towed-array applications requiring directional transmit and receive performance. The double-layer element design provides two independent electrical control points for optimizing the spatial and spectral response in both transmit and receive modes. The cylindrical module fabrication approach, associated tooling, and measured acoustic results for a single module under various drive conditions will be presented to illustrate the utility of this new transducer technology. [Work sponsored by the U.S. Navy.]

A dual-wavelength indium gallium nitride quantum well light emitting diode

We have designed and implemented a monolithic, dual-wavelength blue/green light emitting diode (LED) consisting of two active indium gallium nitride/gallium nitride (InGaN/GaN) multiple-quantum-well segments. The segments are part of a single vertical epitaxial structure in which a p++/n++ InGaN/GaN tunnel junction is inserted between the LEDs, emitting in this proof-of-concept device at 470 nm and 535 nm, respectively. The device has been operated as a three-terminal device with independent electrical control of each LEDs to a nanosecond time scale.