Showing papers on "Electric field published in 2018"

Electric-field switching of two-dimensional van der Waals magnets.

Abstract: Controlling magnetism by purely electrical means is a key challenge to better information technology 1 . A variety of material systems, including ferromagnetic (FM) metals2-4, FM semiconductors 5 , multiferroics6-8 and magnetoelectric (ME) materials9,10, have been explored for the electric-field control of magnetism. The recent discovery of two-dimensional (2D) van der Waals magnets11,12 has opened a new door for the electrical control of magnetism at the nanometre scale through a van der Waals heterostructure device platform 13 . Here we demonstrate the control of magnetism in bilayer CrI3, an antiferromagnetic (AFM) semiconductor in its ground state 12 , by the application of small gate voltages in field-effect devices and the detection of magnetization using magnetic circular dichroism (MCD) microscopy. The applied electric field creates an interlayer potential difference, which results in a large linear ME effect, whose sign depends on the interlayer AFM order. We also achieve a complete and reversible electrical switching between the interlayer AFM and FM states in the vicinity of the interlayer spin-flip transition. The effect originates from the electric-field dependence of the interlayer exchange bias.

Electrical Control of 2D Magnetism in Bilayer CrI3

Abstract: The challenge of controlling magnetism using electric fields raises fundamental questions and addresses technological needs such as low-dissipation magnetic memory. The recently reported two-dimensional (2D) magnets provide a new system for studying this problem owing to their unique magnetic properties. For instance, bilayer chromium triiodide (CrI3) behaves as a layered antiferromagnet with a magnetic field-driven metamagnetic transition. Here, we demonstrate electrostatic gate control of magnetism in CrI3 bilayers, probed by magneto-optical Kerr effect (MOKE) microscopy. At fixed magnetic fields near the metamagnetic transition, we realize voltage-controlled switching between antiferromagnetic and ferromagnetic states. At zero magnetic field, we demonstrate a time-reversal pair of layered antiferromagnetic states which exhibit spin-layer locking, leading to a remarkable linear dependence of their MOKE signals on gate voltage with opposite slopes. Our results pave the way for exploring new magnetoelectric phenomena and van der Waals spintronics based on 2D materials.

Ferroelectric switching of a two-dimensional metal

Abstract: A ferroelectric is a material with a polar structure whose polarity can be reversed (switched) by applying an electric field1,2. In metals, itinerant electrons screen electrostatic forces between ions, which explains in part why polar metals are very rare3–7. Screening also excludes external electric fields, apparently ruling out the possibility of ferroelectric switching. However, in principle, a thin enough polar metal could be sufficiently penetrated by an electric field to have its polarity switched. Here we show that the topological semimetal WTe2 provides an embodiment of this principle. Although monolayer WTe2 is centro-symmetric and thus non-polar, the stacked bulk structure is polar. We find that two- or three-layer WTe2 exhibits spontaneous out-of-plane electric polarization that can be switched using gate electrodes. We directly detect and quantify the polarization using graphene as an electric-field sensor8. Moreover, the polarization states can be differentiated by conductivity and the carrier density can be varied to modify the properties. The temperature at which polarization vanishes is above 350 kelvin, and even when WTe2 is sandwiched between graphene layers it retains its switching capability at room temperature, demonstrating a robustness suitable for applications in combination with other two-dimensional materials9–12. Two- and three-layer WTe2 exhibits spontaneous out-of-plane electric polarization that can be switched electrically at room temperature and is sufficiently robust for use in applications with other two-dimensional materials.

How the formation of interfacial charge causes hysteresis in perovskite solar cells

Abstract: In this study, we discuss the underlying mechanism of the current–voltage hysteresis in a hybrid lead-halide perovskite solar cell. We have developed a method based on Kelvin probe force microscopy that enables mapping charge redistribution in an operating device upon a voltage- or light pulse with sub-millisecond resolution. We observed the formation of a localized interfacial charge at the anode interface, which screened most of the electric field in the cell. The formation of this charge happened within 10 ms after applying a forward voltage to the device. After switching off the forward voltage, however, these interfacial charges were stable for over 500 ms and created a reverse electric field in the cell. This reverse electric field directly explains higher photocurrents during reverse bias scans by electric field-assisted charge carrier extraction. Although we found evidence for the presence of mobile ions in the perovskite layer during the voltage pulse, the corresponding ionic field contributed only less than 10% to the screening. Our observation of a time-dependent ion concentration in the perovskite layer suggests that iodide ions adsorbed and became neutralized at the hole-selective spiro-OMeTAD electrode. We thereby show that instead of the slow migration of mobile ions, the formation and the release of interfacial charges is the dominating factor for current–voltage hysteresis.

Designing lead-free bismuth ferrite-based ceramics learning from relaxor ferroelectric behavior for simultaneous high energy density and efficiency under low electric field

Abstract: Bismuth ferrite (BiFeO3, BFO) possesses very large spontaneous polarization, which provides a great potential in dielectric energy-storage capacitors. However, the presence of large remanent polarization heavily restricts the achievement of excellent performance in the energy storage field. Herein we designed local compositional disorder and constructed quenched random fields to maximize the discrepancy between the maximum polarization and the remanent polarization by means of introducing Zn2+ and Ta5+ at B-sites together in BiFeO3-based solution. Interestingly, pinched-hysteresis loops were observed in this Ba(Zn1/2Ta2/3)O3-modified BFO-based solution. Ultrahigh recoverable energy density (2.56 J cm−3) was first reported under low electric field (16 kV mm−1), which is much superior to the previous results regarding BFO-based bulk ceramics. In addition, an excellent recoverable energy density (>2 J cm−3) and a high efficiency (>80%) were obtained simultaneously in this BZT-modified BFO-based bulk material under low electric field (<20 kV mm−1). These results demonstrate that the strategy of constructing weakly coupled polar structures is feasible and effective to boost the energy density and efficiency for BiFeO3-based bulk ceramics, which may pave a significant step towards utilizing energy-storage applications for BiFeO3-based materials.

Large-Voltage Tuning of Dzyaloshinskii-Moriya Interactions: A Route toward Dynamic Control of Skyrmion Chirality.

Abstract: Electric control of magnetism is a prerequisite for efficient and low-power spintronic devices. More specifically, in heavy metal–ferromagnet–insulator heterostructures, voltage gating has been shown to locally and dynamically tune magnetic properties such as interface anisotropy and saturation magnetization. However, its effect on interfacial Dzyaloshinskii–Moriya Interaction (DMI), which is crucial for the stability of magnetic skyrmions, has been challenging to achieve and has not been reported yet for ultrathin films. Here, we demonstrate a 130% variation of DMI with electric field in Ta/FeCoB/TaOx trilayer through Brillouin Light Spectroscopy (BLS). Using polar magneto-optical Kerr-effect microscopy, we further show a monotonic variation of DMI and skyrmionic bubble size with electric field with an unprecedented efficiency. We anticipate through our observations that a sign reversal of DMI with an electric field is possible, leading to a chirality switch. This dynamic manipulation of DMI establishes ...

Heteroatomic interface engineering in MOF-derived carbon heterostructures with built-in electric-field effects for high performance Al-ion batteries

Abstract: Confronted with challenges in promoting fast AlxCly− anion diffusion and intercalation for aluminum ion batteries (AIBs), it is of vital importance to rationally design gradient hetero-interfaces with an ideal built-in interfacial electric potential to enhance charge diffusion and transfer kinetics. Herein, we demonstrate an effective strategy to realize accurate tuning gradient heteroatom N and P doping in MOF-derived porous carbon in C@N-C@N,P-C graded heterostructures. Importantly, gradient N and P doping could modify the electronic structure of MOF-derived carbon as certified by DFT calculations, and lead to charge redistribution to induce graded energy levels and a built-in electric field in the C@N-C@N,P-C graded heteroatomic interface, thus boosting interfacial charge transfer and accelerating reaction kinetics. Furthermore, the large surface area and high porosity of C@N-C@N,P-C graded heterostructures could efficiently absorb electrolyte and enhance anion transport kinetics. As expected, the designed gradiently N,P-doped C@N-C@N,P-C heterostructure with a built-in interfacial electric field could facilitate electron and AlCl4− anion transfer spontaneously between N,P-C, N-C and C gradient components, exhibiting a superior capacity of 98 mA h g−1 at a high current density of 5 A g−1 after 2500 cycles. This strategy reveals new insights about the gradient energy band for designing high-performance electrochemical energy storage devices.

Electric-field control of anomalous and topological Hall effects in oxide bilayer thin films.

Abstract: One of the key goals in spintronics is to tame the spin-orbit coupling (SOC) that links spin and motion of electrons, giving rise to intriguing magneto-transport properties in itinerant magnets. Prominent examples of such SOC-based phenomena are the anomalous and topological Hall effects. However, controlling them with electric fields has remained unachieved since an electric field tends to be screened in itinerant magnets. Here we demonstrate that both anomalous and topological Hall effects can be modulated by electric fields in oxide heterostructures consisting of ferromagnetic SrRuO3 and nonmagnetic SrIrO3. We observe a clear electric field effect only when SrIrO3 is inserted between SrRuO3 and a gate dielectric. Our results establish that strong SOC of nonmagnetic materials such as SrIrO3 is essential in electrical tuning of these Hall effects and possibly other SOC-related phenomena.

Ferroelectric switching of a two-dimensional metal

Abstract: A ferroelectric is a material with a polar structure whose polarity can be reversed by applying an electric field. In metals, the itinerant electrons tend to screen electrostatic forces between ions, helping to explain why polar metals are very rare. Screening also excludes external electric fields, apparently ruling out the possibility of polarity reversal and thus ferroelectric switching. In principle, however, a thin enough polar metal could be penetrated by an electric field sufficiently to be switched. Here we show that the layered topological semimetal WTe2 provides the first embodiment of this principle. Although monolayer WTe2 is centrosymmetric and thus nonpolar, the stacked bulk structure is polar. We find that two- or three-layer WTe2 exhibits a spontaneous out-of-plane electric polarization which can be switched using gate electrodes. We directly detect and quantify the polarization using graphene as an electric field sensor. Moreover, the polarization states can be differentiated by conductivity, and the carrier density can be varied to modify the properties. The critical temperature is above 350 K, and even when WTe2 is sandwiched in graphene it retains its switching capability at room temperature, demonstrating a robustness suitable for applications in combination with other two-dimensional materials.

A state of art on magneto-rheological materials and their potential applications:

Abstract: Smart materials are kinds of designed materials whose properties are controllable with the application of external stimuli such as the magnetic field, electric field, stress, and heat. Smart materials whose rheological properties are controlled by externally applied magnetic field are known as magneto-rheological materials. Magneto-rheological materials actively used for engineering applications include fluids, foams, grease, elastomers, and plastomers. In the last two decades, magneto-rheological materials have gained great attention of researchers significantly because of their salient controllable properties and potential applications to various fields such as automotive industry, civil environment, and military sector. This article offers a recent progressive review on the magneto-rheological materials technology, especially focusing on numerous application devices and systems utilizing magneto-rheological materials. Conceivable limitations, challenges, and comparable advantages of applying these magn...

Electric-field-tuned topological phase transition in ultrathin Na3Bi.

Abstract: The electric-field-induced quantum phase transition from topological to conventional insulator has been proposed as the basis of a topological field effect transistor1-4. In this scheme, 'on' is the ballistic flow of charge and spin along dissipationless edges of a two-dimensional quantum spin Hall insulator5-9, and 'off' is produced by applying an electric field that converts the exotic insulator to a conventional insulator with no conductive channels. Such a topological transistor is promising for low-energy logic circuits4, which would necessitate electric-field-switched materials with conventional and topological bandgaps much greater than the thermal energy at room temperature, substantially greater than proposed so far6-8. Topological Dirac semimetals are promising systems in which to look for topological field-effect switching, as they lie at the boundary between conventional and topological phases3,10-16. Here we use scanning tunnelling microscopy and spectroscopy and angle-resolved photoelectron spectroscopy to show that mono- and bilayer films of the topological Dirac semimetal3,17 Na3Bi are two-dimensional topological insulators with bulk bandgaps greater than 300 millielectronvolts owing to quantum confinement in the absence of electric field. On application of electric field by doping with potassium or by close approach of the scanning tunnelling microscope tip, the Stark effect completely closes the bandgap and re-opens it as a conventional gap of 90 millielectronvolts. The large bandgaps in both the conventional and quantum spin Hall phases, much greater than the thermal energy at room temperature (25 millielectronvolts), suggest that ultrathin Na3Bi is suitable for room-temperature topological transistor operation.

High Discharge Energy Density at Low Electric Field Using an Aligned Titanium Dioxide/Lead Zirconate Titanate Nanowire Array.

Abstract: Polymer-based capacitors with high energy density have attracted significant attention in recent years due to their wide range of potential applications in electronic devices. However, the obtained high energy density is predominantly dependent on high applied electric field, e.g., 400-600 kV mm-1, which may bring more challenges relating to the failure probability. Here, a simple two-step method for synthesizing titanium dioxide/lead zirconate titanate nanowire arrays is exploited and a demonstration of their ability to achieve high discharge energy density capacitors for low operating voltage applications is provided. A high discharge energy density of 6.9 J cm-3 is achieved at low electric fields, i.e., 143 kV mm-1, which is attributed to the high relative permittivity of 218.9 at 1 kHz and high polarization of 23.35 µC cm-2 at this electric field. The discharge energy density obtained in this work is the highest known for a ceramic/polymer nanocomposite at such a low electric field. The novel nanowire arrays used in this work are applicable to a wide range of fields, such as energy harvesting, energy storage, and photocatalysis.

Controlling Dzyaloshinskii-Moriya Interaction via Chirality Dependent Atomic-Layer Stacking, Insulator Capping and Electric Field.

Abstract: Using first-principles calculations, we demonstrate several approaches to control Dzyaloshinskii-Moriya Interaction (DMI) in ultrathin films with perpendicular magnetic anisotropy. First, we find that DMI is significantly enhanced when the ferromagnetic (FM) layer is sandwiched between nonmagnetic (NM) layers inducing additive DMI in NM1/FM/NM2 structures. For instance, when two NM layers are chosen to induce DMI of opposite chirality in Co, e.g. NM1 representing Au, Ir, Al or Pb, and NM2 being Pt, the resulting DMI in NM1/Co/Pt trilayers is enhanced compared to Co/Pt bilayers. Moreover, DMI can be significantly enhanced further in case of using FM layer comprising Fe and Co layers. Namely, it is found that the DMI in Ir/Fe/Co/Pt structure can be enhanced by 80% compared to that of Co/Pt bilayers reaching a very large DMI amplitude of 5.59 meV/atom. Our second approach for enhancing DMI is to use oxide capping layer. We show that DMI is enhanced by 60% in Oxide/Co/Pt structures compared to Co/Pt bilayers. Moreover, we unveiled the DMI mechanism at Oxide/Co interface due to Rashba effect, which is different to Fert-Levy DMI at FM/NM interfaces. Finally, we demonstrate that DMI amplitude can be modulated using an electric field with an efficiency factor comparable to that of the electric field control of perpendicular magnetic anisotropy in transition metal/oxide interfaces. These approaches of DMI controlling pave the way for skyrmion and domain wall motion-based spintronic applications.

Digital communication with Rydberg atoms and amplitude-modulated microwave fields

Abstract: Rydberg atoms, with one highly excited, nearly ionized electron, have extreme sensitivity to electric fields, including microwave fields ranging from 100 MHz to over 1 THz. Here, we show that room-temperature Rydberg atoms can be used as sensitive, high bandwidth, microwave communication antennas. We demonstrate near photon-shot-noise limited readout of data encoded in amplitude-modulated 17 GHz microwaves, using an electromagnetically induced-transparency (EIT) probing scheme. We measure a photon-shot-noise limited channel capacity of up to 8.2 Mbit s−1 and implement an 8-state phase-shift-keying digital communication protocol. The bandwidth of the EIT probing scheme is found to be limited by the available coupling laser power and the natural linewidth of the rubidium D2 transition. We discuss how atomic communication receivers offer several opportunities to surpass the capabilities of classical antennas.

Berry curvature dipole current in the transition metal dichalcogenides family

Abstract: We study the quantum nonlinear Hall effect in two-dimensional (2D) materials with time-reversal symmetry. When only one mirror line exists, a transverse charge current occurs in the second-order response to an external electric field, as a result of the Berry curvature dipole in momentum space. Candidate 2D materials to observe this effect are two-dimensional transition metal dichalcogenides (TMDCs). First, we use an ab initio based tight-binding approach to demonstrate that monolayer ${T}_{d}$-structure TMDCs exhibit a finite Berry curvature dipole. In the $1H$ and $1{T}^{\ensuremath{'}}$ phase of TMDCs, we show the emergence of a finite Berry curvature dipole with the application of strain and an electrical displacement field, respectively.

Computational optimization of electric fields for better catalysis design

Abstract: Although the ubiquitous role that long-ranged electric fields play in catalysis has been recognized, it is seldom used as a primary design parameter in the discovery of new catalytic materials Here we illustrate how electric fields have been used to computationally optimize biocatalytic performance of a synthetic enzyme, and how they could be used as a unifying descriptor for catalytic design across a range of homogeneous and heterogeneous catalysts Although focusing on electrostatic environmental effects may open new routes toward the rational optimization of efficient catalysts, much more predictive capacity is required of theoretical methods to have a transformative impact in their computational design — and thus experimental relevance — when using electric field alignments in the reactive centres of complex catalytic systems

The Plasma Wave Experiment (PWE) on board the Arase (ERG) satellite

Abstract: The Exploration of energization and Radiation in Geospace (ERG) project aims to study acceleration and loss mechanisms of relativistic electrons around the Earth. The Arase (ERG) satellite was launched on December 20, 2016, to explore in the heart of the Earth’s radiation belt. In the present paper, we introduce the specifications of the Plasma Wave Experiment (PWE) on board the Arase satellite. In the inner magnetosphere, plasma waves, such as the whistler-mode chorus, electromagnetic ion cyclotron wave, and magnetosonic wave, are expected to interact with particles over a wide energy range and contribute to high-energy particle loss and/or acceleration processes. Thermal plasma density is another key parameter because it controls the dispersion relation of plasma waves, which affects wave–particle interaction conditions and wave propagation characteristics. The DC electric field also plays an important role in controlling the global dynamics of the inner magnetosphere. The PWE, which consists of an orthogonal electric field sensor (WPT; wire probe antenna), a triaxial magnetic sensor (MSC; magnetic search coil), and receivers named electric field detector (EFD), waveform capture and onboard frequency analyzer (WFC/OFA), and high-frequency analyzer (HFA), was developed to measure the DC electric field and plasma waves in the inner magnetosphere. Using these sensors and receivers, the PWE covers a wide frequency range from DC to 10 MHz for electric fields and from a few Hz to 100 kHz for magnetic fields. We produce continuous ELF/VLF/HF range wave spectra and ELF range waveforms for 24 h each day. We also produce spectral matrices as continuous data for wave direction finding. In addition, we intermittently produce two types of waveform burst data, “chorus burst” and “EMIC burst.” We also input raw waveform data into the software-type wave–particle interaction analyzer (S-WPIA), which derives direct correlation between waves and particles. Finally, we introduce our PWE observation strategy and provide some initial results.

Local Built‐In Electric Field Enabled in Carbon‐Doped Co3O4 Nanocrystals for Superior Lithium‐Ion Storage

Abstract: In this work, a novel concept of introducing a local built-in electric field to facilitate lithium-ion transport and storage within interstitial carbon (C-) doped nanoarchitectured Co3O4 electrodes for greatly improved lithium-ion storage properties is demonstrated. The imbalanced charge distribution emerging from the C-dopant can induce a local electric field, to greatly facilitate charge transfer. Via the mechanism of “surface locking” effect and in situ topotactic conversion, unique sub-10 nm nanocrystal-assembled Co3O4 hollow nanotubes (HNTs) are formed, exhibiting excellent structural stability. The resulting C-doped Co3O4 HNT-based electrodes demonstrate an excellent reversible capacity ≈950 mA h g−1 after 300 cycles at 0.5 A g−1 and superior rate performance with ≈853 mA h g−1 at 10 A g−1.

Six-Plate Capacitive Coupler to Reduce Electric Field Emission in Large Air-Gap Capacitive Power Transfer

Abstract: This paper proposes a six-plate capacitive coupler for large air-gap capacitive power transfer to reduce electric field emissions to the surrounding environment. Compared to the conventional four-plate horizontal structure, the six-plate coupler contains two additional plates above and below the inner four-plate coupler to provide a shielding effect. Since there is a capacitive coupling between every two plates, the six-plate coupler results in a circuit model consisting of 15 coupling capacitors. This complex model is first simplified to an equivalent three-port circuit model, and then to a two-port circuit model which is used in circuit analysis and parameter design. This six-plate coupler can eliminate the external parallel capacitor in the previous LCLC topology, which results in the LCL compensation and reduces the system cost. Due to the symmetry of the coupler structure, the voltage between shielding plates is limited, which reduces electric field emissions. Finite element analysis by Maxwell is used to simulate the coupling capacitors and electric field distribution. Compared to the four-plate horizontal and vertical structures, the six-plate coupler can significantly reduce electric field emissions and expand the safety area from 0.9 to 0.1 m away from the coupler in the well-aligned case. A 1.97 kW prototype is implemented to validate the six-plate coupler, which achieves a power density of 1.95 kW/m2 and a dc–dc efficiency of 91.6% at an air-gap of 150 mm. Experiments also show that the output power maintains 65% of the well-aligned value at 300 mm X misalignment, and 49% at 300 mm Y misalignment.

Quantum-Limited Atomic Receiver in the Electrically Small Regime.

Abstract: We use a quantum sensor based on thermal Rydberg atoms to receive data encoded in electromagnetic fields in the extreme electrically small regime, with a sensing volume over $1{0}^{7}$ times smaller than the cube of the electric field wavelength. We introduce the standard quantum limit for data capacity, and experimentally observe quantum-limited data reception for bandwidths from 10 kHz up to 30 MHz. In doing this, we provide a useful alternative to classical communication antennas, which become increasingly ineffective when the size of the antenna is significantly smaller than the wavelength of the electromagnetic field.

Order enables efficient electron-hole separation at an organic heterojunction with a small energy loss.

Abstract: Donor–acceptor organic solar cells often show low open-circuit voltages (V OC) relative to their optical energy gap (E g) that limit power conversion efficiencies to ~12%. This energy loss is partly attributed to the offset between E g and that of intermolecular charge transfer (CT) states at the donor–acceptor interface. Here we study charge generation occurring in PIPCP:PC61BM, a system with a very low driving energy for initial charge separation (E g−E CT ~ 50 meV) and a high internal quantum efficiency (η IQE ~ 80%). We track the strength of the electric field generated between the separating electron-hole pair by following the transient electroabsorption optical response, and find that while localised CT states are formed rapidly (<100 fs) after photoexcitation, free charges are not generated until 5 ps after photogeneration. In PIPCP:PC61BM, electronic disorder is low (Urbach energy <27 meV) and we consider that free charge separation is able to outcompete trap-assisted non-radiative recombination of the CT state. Achieving charge separation in low energy loss organic heterojunctions is crucial to the efficiency of donor-acceptor solar cells, whilst the timescale of the process remains largely unknown. Here, Menke et al. observe slow charge separation up to 5 ps in a system with small energy offset of 50 meV.

Ge hole spin qubit

Abstract: Holes confined in quantum dots have gained considerable interest in the past few years due to their potential as spin qubits. Here we demonstrate double quantum dot devices in Ge hut wires. Low temperature transport measurements reveal Pauli spin blockade. We demonstrate electric-dipole spin resonance by applying a radio frequency electric field to one of the electrodes defining the double quantum dot. Next, we induce coherent hole spin oscillations by varying the duration of the microwave burst. Rabi oscillations with frequencies reaching 140MHz are observed. Finally, Ramsey experiments reveal dephasing times of 130ns. The reported results emphasize the potential of Ge as a platform for fast and scalable hole spin qubit devices.

Collective responses in electrical activities of neurons under field coupling.

Abstract: Synapse coupling can benefit signal exchange between neurons and information encoding for neurons, and the collective behaviors such as synchronization and pattern selection in neuronal network are often discussed under chemical or electric synapse coupling. Electromagnetic induction is considered at molecular level when ion currents flow across the membrane and the ion concentration is fluctuated. Magnetic flux describes the effect of time-varying electromagnetic field, and memristor bridges the membrane potential and magnetic flux according to the dimensionalization requirement. Indeed, field coupling can contribute to the signal exchange between neurons by triggering superposition of electric field when synapse coupling is not available. A chain network is designed to investigate the modulation of field coupling on the collective behaviors in neuronal network connected by electric synapse between adjacent neurons. In the chain network, the contribution of field coupling from each neuron is described by introducing appropriate weight dependent on the position distance between two neurons. Statistical factor of synchronization is calculated by changing the external stimulus and weight of field coupling. It is found that the synchronization degree is dependent on the coupling intensity and weight, the synchronization, pattern selection of network connected with gap junction can be modulated by field coupling.

High breakdown electric field in β-Ga2O3/graphene vertical barristor heterostructure

Abstract: In this work, we study the high critical breakdown field in β-Ga2O3 perpendicular to its (100) crystal plane using a β-Ga2O3/graphene vertical heterostructure. Measurements indicate a record breakdown field of 5.2 MV/cm perpendicular to the (100) plane that is significantly larger than the previously reported values on lateral β-Ga2O3 field-effect-transistors (FETs). This result is compared with the critical field typically measured within the (100) crystal plane, and the observed anisotropy is explained through a combined theoretical and experimental analysis.

Optical control of polarization in ferroelectric heterostructures

Abstract: In the ferroelectric devices, polarization control is usually accomplished by application of an electric field. In this paper, we demonstrate optically induced polarization switching in BaTiO3-based ferroelectric heterostructures utilizing a two-dimensional narrow-gap semiconductor MoS2 as a top electrode. This effect is attributed to the redistribution of the photo-generated carriers and screening charges at the MoS2/BaTiO3 interface. Specifically, a two-step process, which involves formation of intra-layer excitons during light absorption followed by their decay into inter-layer excitons, results in the positive charge accumulation at the interface forcing the polarization reversal from the upward to the downward direction. Theoretical modeling of the MoS2 optical absorption spectra with and without the applied electric field provides quantitative support for the proposed mechanism. It is suggested that the discovered effect is of general nature and should be observable in any heterostructure comprising a ferroelectric and a narrow gap semiconductor.

Imaging the Local Charge Environment of Nitrogen-Vacancy Centers in Diamond.

Abstract: Characterizing the local internal environment surrounding solid-state spin defects is crucial to harnessing them as nanoscale sensors of external fields. This is especially germane to the case of defect ensembles which can exhibit a complex interplay between interactions, internal fields, and lattice strain. Working with the nitrogen-vacancy (NV) center in diamond, we demonstrate that local electric fields dominate the magnetic resonance behavior of NV ensembles at a low magnetic field. We introduce a simple microscopic model that quantitatively captures the observed spectra for samples with NV concentrations spanning more than two orders of magnitude. Motivated by this understanding, we propose and implement a novel method for the nanoscale localization of individual charges within the diamond lattice; our approach relies upon the fact that the charge induces a NV dark state which depends on the electric field orientation.