Actively Tunable and Polarization-independent Toroidal Resonance in Hybrid Metal-Vanadium Dioxide Metamaterial

Actively tunable and polarization-independent toroidal resonance in hybrid metal-vanadium dioxide metamaterial is proposed and demonstrated numerically in terahertz regime. Simulation results illustrate that a toroidal dipolar resonance is excited by hybrid metal and vanadium dioxide resonator and insensitive with polarization angle of incident plane wave, calculated scattered powers verify the toroidal resonance is strengthened. A novel modulation of resonance strength in proposed toroidal metamaterial is obtained as the phase transition process of vanadium dioxide and contrary to former hybrid metal-vanadium dioxide toroidal metamaterials. The theoretical fitting results reveal that physical mechanism of active modulation in resonance strength can be attributed to the variation of overall damping rate caused by tuning conductivity of vanadium dioxide.

Advanced Electromagnetic Metamaterials for Temperature Sensing Applications

Metamaterials with novel properties have excited much research attention in the past several decades. Many applications have been proposed and developed for the reported metamaterials in various engineering areas. Specifically, for the resonant-type metamaterials with narrow resonance line width and strong resonance strength, the resonant frequency and strength are highly depended on the changings of meta-atom structure and/or substrate media properties induced by the environment physical or chemistry parameters varying. Therefore, physical or chemistry sensing applications for the resonant-type metamaterial units or arrays are developed in recent years. In this mini review, to help the researchers in those fields to catch up with the newly research advances, we would like to summarize the recently reported high-performance metamaterial-inspired sensing applications, especially the temperature sensing applications, based on different kinds of metamaterials. Importantly, by analyzing the advantages and disadvantages of several conventional metamaterial units, the newly proposed high quality-factor metamaterial units are discussed for high-precision sensing applications, in terms of the sensitivity and resolution. This mini review can guide researchers in the area of metamaterial-inspired sensors to find some new design routes for high-precision sensing.

Optimal operation points for ultrafast, highly coherent Ge hole spin-orbit qubits

Strong spin-orbit interactions make hole quantum dots central to the quest for electrical spin qubit manipulation enabling fast, low-power, scalable quantum computation. Yet it is important to establish to what extent spin-orbit coupling exposes qubits to electrical noise, facilitating decoherence. Here, taking Ge as an example, we show that group IV gate-defined hole spin qubits generically exhibit optimal operation points, defined by the top gate electric field, at which they are both fast and long-lived: the dephasing rate vanishes to first order in the electric field noise along with all directions in space, the electron dipole spin resonance strength is maximized, while relaxation is drastically reduced at small magnetic fields. The existence of optimal operation points is traced to group IV crystal symmetry and properties of the Rashba spin-orbit interaction unique to spin-3/2 systems. Our results overturn the conventional wisdom that fast operation implies reduced lifetimes and suggest group IV hole spin qubits as ideal platforms for ultra-fast, highly coherent scalable quantum computing.

Multipolar Plasmonic Resonances of Aluminum Nanoantenna Tuned by Graphene

We numerically investigate the multipolar plasmonic resonances of Aluminum nanoantenna tuned by a monolayer graphene from ultraviolet (UV) to visible regime. It is shown that the absorbance of the plasmonic odd modes (l = 1 and l = 3) of graphene–Al nanoribbon structure is enhanced while the absorption at the plasmonic even modes (l = 2) is suppressed, compared to the pure Al nanoribbon structure. With the presence of the monolayer graphene, a change in the resonance strength of the multipolar plasmonic modes results from the near field interactions of the monolayer graphene with the electric fields of the multipolar plasmonic resonances of the Al resonator. In particular, a clear absorption peak with a high quality (Q)-factor of 27 of the plasmonic third-order mode (l = 3) is realized in the graphene–Al nanoribbon structure. The sensitivity and figure of merit of the plasmonic third-order mode of the proposed Graphene–Al nanoribbon structure can reach 25 nm/RIU and 3, respectively, providing potential applications in optical refractive-index sensing.

Effects of Ih and TASK-like shunting current on dendritic impedance in layer 5 pyramidal-tract neurons

Pyramidal neurons in neocortex have complex input-output relationships that depend on their morphologies, ion channel distributions, and the nature of their inputs, but which cannot be replicated by simple integrate-and-fire models. The impedance properties of their dendritic arbors, such as resonance and phase shift, shape neuronal responses to synaptic inputs and provide intraneuronal functional maps reflecting their intrinsic dynamics and excitability. Experimental studies of dendritic impedance have shown that neocortical pyramidal tract neurons exhibit distance-dependent changes in resonance and impedance phase with respect to the soma. We therefore investigated how well several biophysically-detailed multi-compartment models of neocortical layer 5 pyramidal tract neurons reproduce the location-dependent impedance profiles observed experimentally. Each model tested here exhibited location-dependent impedance profiles, but most captured either the observed impedance amplitude or phase, not both. The only model that captured features from both incorporates HCN channels and a shunting current, like that produced by Twik-related acid-sensitive K+ (TASK) channels. TASK-like channel activity in this model was dependent on local peak HCN channel conductance (Ih). We found that while this shunting current alone is insufficient to produce resonance or realistic phase response, it modulates all features of dendritic impedance, including resonance frequencies, resonance strength, synchronous frequencies, and total inductive phase. We also explored how the interaction of Ih and a TASK-like shunting current shape synaptic potentials and produce degeneracy in dendritic impedance profiles, wherein different combinations of Ih and shunting current can produce the same impedance profile.

The Study of the 22Ne(α,γ)26Mg Reaction at LUNA

The 22Ne(α,γ)26Mg reaction is the competitor of the 22Ne(α,γ)25Mg reaction, an effective neutron source for element synthesis through s-process in massive and AGB stars. Currently the ratio between the rates of these two reactions is poorly constrained because of the high uncertainty affecting the 22Ne(α,γ)26Mg reaction rate. Indeed a wide range of values for the 395 keV resonance strength (10−15 - 10−9 eV) is reported in literature, all of them from indirect measurements. The present study represents the first direct measurement which was performed at the ultra-low background LUNA laboratory. An high efficiency detector was installed at the gas target beamline of LUNA 400kV accelerator and the 99% enriched in 22Ne neon gas was irradiated with a 399.9 keV α-beam. No significant signal was detected in the 22Ne(α,γ)26Mg region of interest, thus an upper limit for the 395 keV resonance strength was estimated. A new campaign was completed in August 2019 with an improved setup and some details are reported here.

Dust distribution around low-mass planets on converging orbits

Context. Super-Earths can form at large orbital radii and migrate inward due to tidal interactions with the circumstellar disk. In this scenario, convergent migration may occur and lead to the formation of resonant pairs of planets. Aims. We explore the conditions under which convergent migration and resonance capture take place, and what dynamical consequences can be expected on the dust distribution surrounding the resonant pair. Methods. We combine hydrodynamic planet–disk interaction models with dust evolution calculations to investigate the signatures produced in the dust distribution by a pair of planets in mean-motion resonances. Results. We find that convergent migration takes place when the outer planet is the more massive. However, convergent migration also depends on the local properties of the disk, and divergent migration may result as well. For similar disk parameters, the capture in low degree resonances (e.g., 2:1 or 3:2) is preferred close to the star where the resonance strength can more easily overcome the tidal torques exerted by the gaseous disk. Farther away from the star, convergent migration may result in capture in high degree resonances. The dust distribution shows potentially observable features typically when the planets are trapped in a 2:1 resonance. In other cases, with higher degree resonances (e.g., 5:4 or 6:5) dust features may not be sufficiently pronounced to be easily observable. Conclusions. The degree of resonance established by a pair of super-Earths may be indicative of the location in the disk where capture occurred. There can be significant differences in the dust distribution around a single super-Earth and a pair of super-Earths in resonance.

Fano-Resonance in Hybrid Metal-Graphene Metamaterial and Its Application as Mid-Infrared Plasmonic Sensor

Fano resonances in nanostructures have attracted widespread research interests in the past few years for their potential applications in sensing, switching and nonlinear optics. In this paper, a mid-infrared Fano resonance in a hybrid metal-graphene metamaterial is studied. The hybrid metamaterial consists of a metallic grid enclosing with graphene nanodisks. The Fano resonance arises from the coupling of graphene and metallic plasmonic resonances and it is sharper than plasmonic resonances in pure graphene nanostructures. The resonance strength can be enhanced by increasing the number of graphene layers. The proposed metamaterial can be employed as a high-performance mid-infrared plasmonic sensor with an unprecedented sensitivity of about 7.93 μm/RIU and figure of merit (FOM) of about 158.7.

Study of the 22Ne(α , γ)26Mg reaction at LUNA

The 22Ne( α , γ)26Mg reaction competes with the 22Ne(α, n)25Mg reac-tion which is the main source of neutrons for the s-process in low-mass Asymptotic Giant Branch (AGB) and massive stars. The 22Ne( α , γ)26Mg reaction rateis affected by a high uncertainty mainly due to the poorly constrained 395 keVresonance which has been studied only indirectly leading to a wide range of pos-sible values for its resonance strength (10-14 - 10-9 eV). The present study represents the direct measurement of the 395 keV resonance of the 22Ne( α , γ)26Mgreaction at LUNA (Laboratory for Underground Nuclear Astrophysics), located at Gran Sasso National Laboratory. Here, the experimental campaigns, setupand some very preliminary results are presented.