Tunable Oscillations Research Articles

Locally repulsive coupling-induced tunable oscillations.

The precise amplitude and period of neuronal oscillations are crucial for the functioning of neuronal networks. We propose a chain model featuring a repulsive coupling at the first node, followed by attractive couplings at subsequent nodes. This model allows for the simultaneous regulation of both quantities. The repulsive coupling at the first neuron enables it to act as a pacemaker, generating oscillations whose amplitude and period are correlated with the coupling strength. At the same time, attractive couplings help transmit these oscillations along the chain, leading to collective oscillations of varying scales. Our study demonstrates that a three-node chain with locally repulsive coupling forms the fundamental structure for generating tunable oscillations. By using a simplified neuron model, we investigate how locally repulsive coupling affects the amplitude and period of oscillations and find results that align with numerical observations. These findings indicate that repulsive couplings play a crucial role in regulating oscillatory patterns within neuronal networks.

Antiferromagnetic–ferromagnetic heterostructure-based spin Hall nano-oscillator

Spin oscillators relying on ferromagnetic (FM) materials have been limited to frequency generation in the range of only a few gigahertz. In contrast, antiferromagnetic (AFM) material-based oscillators have a potential for beyond gigahertz range oscillations. However, the use of AFM oscillators is limited due to challenges in detecting and controlling magnetic orientation. This arises from the inherent lack of significant net magnetization in AFMs. This work focuses on exploring the dynamic characteristics of a spin Hall nano-oscillator (SHNO) that addresses these challenges by leveraging the inter-layer exchange interaction between AFM and FM layers. The proposed design demonstrates stable and power-efficient oscillation in the FM layer, relying on the dynamics of the AFM layer. The proposed AFM–FM-based SHNO design achieves a maximum frequency of 16.4 GHz at ISOT = 180 μA. Furthermore, considering the thermal effects at 300 K, the stable oscillation frequency is achieved at 15.94 GHz. The proposed device exhibits robust and tunable oscillations over a wide frequency range with a power consumption of 4 μW. Moreover, this oscillator achieves 3.35× and 2.44× higher oscillation frequency compared to spin torque nano-oscillators and conventional SHNO-based oscillators, respectively.

Optically Tunable Electrical Oscillations in Oxide-Based Memristors for Neuromorphic Computing.

The application of hardware-based neural networks can be enhanced by integrating sensory neurons and synapses that enable direct input from external stimuli. This work reports direct optical control of an oscillatory neuron based on volatile threshold switching in V3O5. The devices exhibit electroforming-free operation with switching parameters that can be tuned by optical illumination. Using temperature-dependent electrical measurements, conductive atomic force microscopy (C-AFM), in situ thermal imaging, and lumped element modelling, it is shown that the changes in switching parameters, including threshold and hold voltages, arise from overall conductivity increase of the oxide film due to the contribution of both photoconductive and bolometric characteristics of V3O5, which eventually affects the oscillation dynamics. Furthermore, V3O5 is identified as a new bolometric material with a temperature coefficient of resistance (TCR) as high as -4.6% K-1 at 423 K. The utility of these devicesis illustrated by demonstrating in-sensor reservoir computing with reduced computational effort and an optical encoding layer for spiking neural network (SNN), respectively, using a simulated array of devices.

Tunable High-Frequency Acoustoelectric Current Oscillations in Fluorine-Doped Single-Walled Carbon Nanotubes

Herein, we report on a fluorine-doped single-walled carbon nanotube (FSWCNT) phenomenon, that yields tunable high-frequency self-sustained acoustoelectric direct current (ADC) oscillations. A tractable analytical method was used in the hypersound domain, to base the calculations on carriers in the lowest miniband. Hypothetically, the energy of interaction between the carriers and the acoustic phonons is less than the energy of the typical carriers. High-order harmonics of the acoustic phonons’ effective field could be disregarded under this supposition. The ADC was observed to exhibit a nonlinearity, that resulted from the carrier distribution function’s distortion as a result of interaction with the acoustic phonons, which had strong nonlinear effects. Theoretically, we demonstrated that the dynamics of space charge instabilities, due to Bragg reflection of Bloch oscillating carriers in the FSWCNT’s miniband, were the only factors which contributed to the creation of radiation in the terahertz (THz) frequency range. The study also investigated the influence of various FSWCNT parameters such as the overlapping integrals (Δs and Δz), ac-field E1, and carrier concentration noon the behaviour of the ADC. The results showed that the intensity of the ADC oscillation Jzzae/Joae could be tuned by adjusting Δs, Δz, E1, and no.This tunability suggests that FSWCNTs could be used as an active device operating at very high frequencies, potentially reaching the submillimeter wavelength range. The study also suggests the possibility of domain suppression and acoustic Bloch gain through dynamic ADC stabilisation.

Broad tunable photonic microwave signal generation using optically-injected 1310 nm spin-VCSELs

We theoretically propose and demonstrate photonic microwave signal generation with a very broad tunability range from below 2.5 GHz to around 100 GHz. The proposed scheme is based on sustained oscillation dynamics produced in spin-VCSELs under right circularly polarized optical injection. The generated microwave frequencies can be tuned by detuning the frequency of the optical injection signal. The system also takes the advantage of polarization switching phenomena to generate broader microwave frequencies where the generated frequencies are equal to the sum of the absolute detuning frequency and the birefringence split between the spin-VCSEL modes which is 47.7 GHz. Sustained oscillation dynamics provokes tunable periodical oscillations through the adjustment of the frequency detuning and injection strength which can be used as a microwave signal generator. Enhancement of the RF power of the oscillations can be achieved by increasing the injection strength towards the locking regions. The microwave linewidth is reduced from 58 MHz to a medium linewidth of about 14 MHz under optical injection technique. This simple configuration paves the way for potential uses of spin-VCSELs in Radio-over-Fiber (RoF) applications and future technologies.

Impurity screening and Friedel oscillations in Floquet-driven two-dimensional metals

We develop a theory for the non-equilibrium screening of a charged impurity in a two-dimensional electron system under a strong time-periodic drive. Our analysis of the time-averaged polarization function and dielectric function reveals that Floquet driving modifies the screened impurity potential in two main regimes. In the weak drive regime, the time-averaged screened potential exhibits unconventional Friedel oscillations with multiple spatial periods contributed by a principal period modulated by higher-order periods, which are due to the emergence of additional Kohn anomalies in the polarization function. In the strong drive regime, the time-averaged impurity potential becomes almost unscreened and does not exhibit Friedel oscillations. This tunable Friedel oscillations is a result of the dynamic gating effect of the time-dependent driving field on the two-dimensional electron system.

Magnetically tunable Shubnikov–de Haas oscillations in MnBi2Te4

Shubnikov-de Hass oscillations are directly observed in undoped antiferromagnetic topological insulator MnBi2Te4. With increasing magnetic fields, the oscillation period decreases gradually in the magnetic transition from canted antiferromagnetism to ferromagnetism and then saturates in high magnetic fields, indicating the field-induced evolution of the band structure. From the analysis of the high-field oscillations, a nontrivial Berry phase and a small effective mass are extracted, in agreement with the predicted Weyl semimetal phase in ferromagnetic MnBi2Te4. Furthermore, rotating the magnetization of MnBi2Te4 can lead to a splitting of the high-field oscillations, which suggests the enhanced asymmetry of the Weyl cones in tilted fields. Therefore, the observation of these magnetically tunable quantum oscillations clearly demonstrates the indispensable role of field in tuning the band structure or physical properties of MnBi2Te4.

A tale of two rhythms: Locked clocks and chaos in biology.

The fundamental mechanisms that control and regulate biological organisms exhibit a surprising level of complexity. Oscillators are perhaps the simplest motifs that produce time-varying dynamics and are ubiquitous in biological systems. It is also known that such biological oscillators interact with each other-for instance, circadian oscillators affect the cell cycle, and somitogenesis clock proteins in adjacent cells affect each other in developing embryos. Therefore, it is vital to understand the effects that can emerge from non-linear interaction between oscillations. Here, we show how oscillations typically arise in biology and take the reader on a tour through the great variety in dynamics that can emerge even from a single pair of coupled oscillators. We explain how chaotic dynamics can emerge and outline the methods of detecting this in experimental time traces. Finally, we discuss the potential role of such complex dynamical features in biological systems.

Optoelectronic dynamic memristor systems based on two-dimensional crystals

Abstract Optical modulation of resistive switching in an optoelectronic memristor allows it to be optically controlled at ultra-high speed and ultra-low power consumption. Optical memristive systems with memory elements switched by electromagnetic radiation can be used in optically reconfigurable and tunable neural networks for neuromorphic computing and brain-inspired artificial intelligence systems. Two-dimensional (2D) crystals with unique electrical and optical properties demonstrate tremendous potential in the creation of highly efficient information and sensor systems for real-time data monitoring and processing. In this paper, we consider optoelectronic structures based on graphene, graphene oxide, and molybdenum disulfide for dynamic memristive signal processing. 2D optoelectronic memristor structures exhibit multiple states, which can be monitored in a wide range of optical excitations and used as sensors for pattern recognition and image processing. An optoelectronic dynamic memristive structure with quantum dots (QDs), controlled by ultrafast photoinduced structural phase transitions, is promising for creating information systems with stochastic data processing. The phase transition, controlled by charge and temperature, results in tunable periodic oscillations due to two state variables that exhibit chaotic behavior similar to that which occurs in a biological neuron network.

Tunable discrete scale invariance in transition-metal pentatelluride flakes

Log-periodic quantum oscillations discovered in transition-metal pentatelluride give a clear demonstration of discrete scale invariance (DSI) in solid-state materials. The peculiar phenomenon is convincingly interpreted as the presence of two-body quasi-bound states in a Coulomb potential. However, the modifications of the Coulomb interactions in many-body systems having a Dirac-like spectrum are not fully understood. Here, we report the observation of tunable log-periodic oscillations and DSI in ZrTe5 and HfTe5 flakes. By reducing the flakes thickness, the characteristic scale factor is tuned to a much smaller value due to the reduction of the vacuum polarization effect. The decreasing of the scale factor demonstrates the many-body effect on the DSI, which has rarely been discussed hitherto. Furthermore, the cut-offs of oscillations are quantitatively explained by considering the Thomas-Fermi screening effect. Our work clarifies the many-body effect on DSI and paves a way to tune the DSI in quantum materials.

Triangular pulse generation by using chalcogenide fibers and creation of tunable High frequency oscillations from the Interaction of reshaped pulse pair

Designing few normal dispersion chalcogenide fibers leads to obtain a Normal Dispersion Decreasing Chalcogenide Fiber with a value of group velocity dispersion (β2) varying from ∼ 240.45 ps2/km to 221.52 ps2/km and nonlinear coefficient (γ) within a range from ∼ 62.82 W−1 km−1 to 108.17 W−1 km−1 throughout a fiber length of 75 m. The so designed fiber is preferable for generation of Triangular Pulse at relatively shorter optimum length (Lopt) when compared to previously reported works. Such reshaped pairs of triangular pulses interact as their tails start to overlap while propagating through the fiber and generates high frequency (∼THz) oscillating pulse train. This frequency can be easily altered in a controlled manner by carefully changing the propagation length or the separation between the input pulse pair. The so designed fiber alongwith the optimum input pulse parameters can be potentially applied in the domain of tunable high frequency pulse generators along with many standard applications of TP.

Enhancement of Negative Differential Mobility Effect in Recessed Barrier Layer AlGaN/GaN HEMT for Terahertz Applications

A recessed barrier layer (RBL) structure is proposed in themicrometer-sized AlGaN/GaN high-electron mobility transistor (HEMT) for terahertz applications. It is found by using numerical simulation that the properly designed RBL structure can trigger the formation and propagation of electron domains in the 2-D electron gas (2-DEG) channel. As a result, the fundamental frequency can be extended even up to terahertz regime, and also it can be tuned in a certain range by the bias voltage of Schottky contact gate that acts as a hot-electron injector just like the notch-dopedGunn diode. Our simulations showthat the 0.3- $\mu \text{m}$ -gate HEMT with the RBL structure having the depth of 10–15 nm and the length of 200–400 nm can generate the stable and tunable oscillations in the range of around 0.8–1.6 THz under the normally gate bias of −0.2–0.4 V, as well as the ratio of RF-to-dc current component ranging from 3.04% to 7.2%. These available characteristics come from the redistribution of electric field in the 2-DEG channel. Compared with the ungated and the top-gated planar Gunn diodes ever reported, the proposed RBL structural AlGaN/GaN HEMT can be easily fabricated and operated under normal conditions, demonstrating a great potential application in terahertz radiation sources.

Tunable and switchable C-band and L-band multi-wavelength erbium-doped fiber laser employing a large-core fiber filter

In this paper, we propose and experimentally demonstrate a C- and L-band erbium-doped fiber laser (EDFL) with tunable single-, dual- and triple-wavelength lasing emissions. A tapered structure large-core fiber filter (LCFF) is inserted to serve as tuning component and wavelength selector for tunable and stable multi-wavelength oscillations. Based on the axial strain response of LCFF, two tunable triple-wavelength regimes within the range from 1558.71 to 1579.81 nm are obtained with side mode suppression ratio (SMSR) as high as 55 dB. Moreover, tunable single- and dual-wavelength regimes are also achieved with total tuning range of 11 nm and 6.23 nm, respectively. The tuning step for overall laser regimes is 0.02 nm, and the maximum wavelength sensitivity reaches to 1.87 pm/με. In addition, this proposed versatile EDFL is proved to be very stable since the lasing wavelength shifts and power fluctuations are less than 0.02 nm and 0.78 dB during an hour.

Molecular tuning of electroreception in sharks and skates.

Ancient cartilaginous vertebrates, such as sharks, skates, and rays, possess specialized electrosensory organs that detect weak electric fields and relay this information to the central nervous system1–4. Sharks exploit this sensory modality for predation, whereas skates may also use it to detect signals from conspecifics5. Here we analyze shark and skate electrosensory cells to ask if discrete physiological properties could contribute to behaviorally-relevant sensory tuning. We show that sharks and skates use a similar low threshold voltage-gated calcium channel to initiate cellular activity but employ distinct potassium channels to modulate this activity. Electrosensory cells from sharks express specially adapted voltage-gated potassium channels that support large, repetitive membrane voltage spikes capable of driving near-maximal vesicular release from elaborate ribbon synapses. In contrast, skates use a calcium-activated potassium channel to produce small, tunable membrane voltage oscillations that elicit stimulus-dependent vesicular release. We propose that these sensory adaptations support amplified indiscriminate signal detection in sharks versus selective frequency detection in skates, potentially reflecting the electroreceptive requirements of these elasmobranch species. Our findings demonstrate how sensory systems adapt to suit an animal’s lifestyle or environmental niche through discrete molecular and biophysical modifications.

Tunable Gunn oscillations in a top-gated planar nanodevice

The frequency of a Gunn diode is usually determined by the length of its oscillation channel, hard to be change after the device has been fabricated. We show that in a top-gated planar nanodevice the frequency of Gunn oscillations can be conveniently increased, i.e. tuned by the top-gate bias. Ensemble Monte Carlo (EMC) simulations indicate that the achieved maximum frequency reaches 1 THz, about three times of that of an un-gated device. Moreover, the tunable frequency-range also increases with the length of the top-gate, resulting in a widest range of ∼0.7 THz. Detailed analysis of the Gunn-domain dynamics shows that this tunable effect is related to the simultaneous formation of multi-domains, which are excited by the top-gate induced non-uniformed electricfield along the oscillation channel.

Long negative feedback loop enhances period tunability of biological oscillators

Oscillatory phenomena play a major role in organisms. In some biological oscillations such as cell cycles and heartbeats, the period can be tuned without significant changes in the amplitude. This property is called (period) tunability, one of the prominent features of biological oscillations. However, how biological oscillators produce tunable oscillations remains largely unexplored. We tackle this question using computational experiments. It has been reported that positive-plus-negative feedback oscillators produce tunable oscillations through the hysteresis-based mechanism. First, in this study, we confirmed that positive-plus-negative feedback oscillators generate tunable oscillations. Second, we found that tunability is positively correlated with the dynamic range of oscillations. Third, we showed that long negative feedback oscillators without any additional positive feedback loops can produce tunable oscillations. Finally, we computationally demonstrated that by lengthening the negative feedback loop, the Repressilator, known as a non-tunable synthetic gene oscillator, can be converted into a tunable oscillator. This work provides synthetic biologists with clues to design tunable gene oscillators.

Tunable NF-κB Oscillations in Yeast.

Studies of genetic networks in situ are confounded by unknown interactions with native networks. In Zhang etal. (2017), the authors capitalize on the fact that yeast lacks the NF-κB pathway to study the human NF-κB pathway in isolation and develop a predictive model.

Collective modes of trapped spinor Bose–Einstein condensates

We study the structure of quasi-one-dimensional Bogoliubov–de Genes collective excitations of inhomogeneous F = 1 spinor Bose–Einstein condensates confined by a harmonic trap potential and loaded into an optical lattice. Employing a perturbative method, we report general analytical expressions for the polar and ferromagnetic confined collective oscillations. In both cases, the excited eigenfrequencies are given as functions of the effective 1D coupling constants, the trap frequency and the optical lattice parameters. While the presence of the trap yields quantized longitudinal collective modes, whose spectra depends on the collision scattering lengths, the optical lattice shifts their frequencies and, more importantly, yields tunable oscillations of the spin populations, for the even modes, as experimentally observed.

Spatiotemporal network coding of physiological mossy fiber inputs by the cerebellar granular layer.

The granular layer, which mainly consists of granule and Golgi cells, is the first stage of the cerebellar cortex and processes spatiotemporal information transmitted by mossy fiber inputs with a wide variety of firing patterns. To study its dynamics at multiple time scales in response to inputs approximating real spatiotemporal patterns, we constructed a large-scale 3D network model of the granular layer. Patterned mossy fiber activity induces rhythmic Golgi cell activity that is synchronized by shared parallel fiber input and by gap junctions. This leads to long distance synchrony of Golgi cells along the transverse axis, powerfully regulating granule cell firing by imposing inhibition during a specific time window. The essential network mechanisms, including tunable Golgi cell oscillations, on-beam inhibition and NMDA receptors causing first winner keeps winning of granule cells, illustrate how fundamental properties of the granule layer operate in tandem to produce (1) well timed and spatially bound output, (2) a wide dynamic range of granule cell firing and (3) transient and coherent gating oscillations. These results substantially enrich our understanding of granule cell layer processing, which seems to promote spatial group selection of granule cell activity as a function of timing of mossy fiber input.

The Optical Bloch oscillation in chirped one-dimensional superconducting photonic crystal

We exploit theoretically the propagation properties of electromagnetic waves in nanoscale one-dimensional superconducting photonic crystal. The Wannier Stark ladders can be formed in the photonic crystal by varying the thickness of the dielectric layers linearly across the structure. The dynamics behavior of a Gaussian pulse transmitting through the structure is simulated theoretically. We find that photons undergo Bloch oscillations inside tilted photonic bands and the Bloch oscillations are sensitive to the change of temperature in the range of 3–8K. It is demonstrated that our structure is possible to realize tunable optical Bloch oscillations by controlling the temperature of superconducting material.