Frequency Regime Research Articles

Primordial black holes in SB SUSY Gauss-Bonnet inflation

Here, we explore the formation of primordial black holes (PBHs) within a scalar field inflationary model coupled to the Gauss-Bonnet (GB) term, incorporating the low-scale spontaneously broken supersymmetric (SB SUSY) potential.The coupling function amplifies the curvature perturbations, consequently leading to the formation of PBHs and detectable secondary gravitational waves (GWs).Through the adjustment of the model parameters, the inflaton can be decelerated during an ultra-slow-roll (USR) phase, thereby augmenting curvature perturbations. Beside the observational constraints, the swampland criteria are investigated.Our computations forecast the formation of PBHs with masses around 𝒪(10)M ⊙, aligning with the observational data of LIGO-Virgo, and PBHs with masses 𝒪(10-6)M ⊙ as potential explanation for the ultrashort-timescale microlensing events recorded in the OGLE data.Additionally, our proposed mechanism can generate PBHs with masses around 𝒪(10-13)M ⊙, constituting roughly 99% of the dark matter.The density parameters of the produced GWs (ΩGW 0) intersect with the sensitivity curves of GW detectors. Two cases of our model fall within the nano-Hz frequency regime. One of them satisfies the power-law scaling as ΩGW(f) ∼ f 5-γ, with the γ = 3.51, which is consistent with the data of NANOGrav 15-year.

On-chip cryogenic low-pass filters based on finite ground-plane coplanar waveguides for quantum measurements.

Quantum technology exploits fragile quantum electronic phenomena whose energy scales demand ultra-low electron temperature operation. The lack of electron-phonon coupling at cryogenic temperatures makes cooling the electrons down to a few tens of millikelvin a non-trivial task, requiring extensive efforts on thermalization and filtering high-frequency noise. Existing techniques employ bulky and heavy cryogenic metal-powder filters, which prove ineffective at sub-GHz frequency regimes and unsuitable for high-density quantum circuits such as spin qubits. In this work, we realize ultra-compact and lightweight on-chip cryogenic filters based on the attenuation characteristics of finite ground-plane coplanar waveguides. These filters are made of aluminum on sapphire substrates using standard microfabrication techniques. The attenuation characteristics are measured down to a temperature of 500 mK in a dilution refrigerator in a wide frequency range of a few hundred kHz to 8.5GHz. We find their performance is superior by many orders compared to the existing filtering schemes, especially in the sub-GHz regime, negating the use of any lumped-element low-pass filters. The compact and scalable nature makes these filters a suitable choice for high-density quantum circuits such as quantum processors based on quantum dot spin qubits.

Susceptibility to Low-Frequency Breakdown in Full-Wave Models of Liquid Crystal-Coaxially-Filled Noise-Shielded Analog Phase Shifters

Building on the fully encapsulated architecture of liquid crystal (LC) coaxial phase shifters, which leverages noise-shielding advantages for millimeter-wave wideband reconfigurable applications, this study addresses the less-explored issue of low-frequency breakdown (LFB) susceptibility in modern full-wave solvers. Specifically, it identifies the vulnerability nexus between the tuning states (driven by low-frequency bias voltages) and the constitutive elements of LC-filled coaxial phase shifters—namely, the core line, housing grounding, and radially sandwiched tunable dielectrics—operating at millimeter-wave frequencies (60 GHz WiGig), microwave (1 GHz), and far lower frequency regimes (down to 1 MHz, 1 kHz, and 1 Hz) for long-wavelength or quasi-static conditions, with specialized applications in submarine communications and geophysical exploration. For completeness, the study also investigates the device state prior to LC injection, when the cavity is air-filled. Key computational metrics, such as effective permittivity and characteristic impedance, are analyzed. The results show that at 1 kHz, deviations in effective permittivity exceed four orders of magnitude compared to 1 GHz, while characteristic impedance exhibits deviations of three orders of magnitude. More critically, in the LFB regime, theoretical benchmarks from 1 MHz to 1 kHz and 1 Hz demonstrate an exponential increase in prediction error for both effective permittivity, rising from 16.8% to 1.5 × 104% and 1.5 × 107%, and for characteristic impedance, escalating from 8.1% to 1.15 × 103% and 3.9 × 104%, respectively. Consequently, the prediction error of the differential phase shift, minimal at 60 GHz (0.16%), becomes noticeable at 1 MHz (4.39%), increases sharply to 743.88% at 1 kHz, and escalates dramatically to 2.18 × 1010% at 1 Hz. The findings reveal a pronounced frequency asymmetry in LFB susceptibility for the LC coaxial phase shifter biased at extremely low frequencies.

High Frequency Gravitational Wave bounds from galactic neutron stars

High-Frequency Gravitational Waves (HFGWs) constitute a unique window on the early Universe as well as exotic astrophysical objects. While the current gravitational wave experiments are more dedicated to the low frequency regime, the graviton conversion into photons in a strong magnetic field constitutes a powerful tool to probe HFGWs. In this paper, we show that neutron stars, due to their extreme magnetic field, are a perfect laboratory to study the conversion of HFGWs into photons. Using realistic models for the galactic neutron star population, we calculate for the first time the expected photon flux induced by the conversion of an isotropic stochastic gravitational wave background in the magnetosphere of the ensemble of neutron stars present in the Milky Way. We compare this photon flux to the observed one from several telescopes and derive upper limits on the stochastic gravitational wave background in the frequency range 108 Hz–1025 Hz. We find our limits to be competitive in the frequency range 108 Hz–1012 Hz.

Enhancement of liner materials based on nanomaterials to promote sustainability in noise intercourse

Daily usage of devices has had a major influence on lives and existence, which would be unimaginable without them. Due to this, recent gadget dependability concerns need particular attention. PCs, hand mobile phones, and other computerized household gadgets need integrated circuits (ICs). Individual components must work together to accomplish their tasks and make the circuit operate. Hot carrier effect, oxide breakdown, and other system-level problems result from accommodating several devices in a planar IC. Vertical linking active components in one IC to another IC is a common method of three-dimensional IC integration (3D-IC). The main issue with 3D-IC adoption is electrical interference to neighboring through silicon via (TSV) and active transistors, which substantially reduces system performance. The electrical TSV (ETSV) model, which employs solely electrical signal carrying TSV, and the thermal TSV (TTSV) model, which incorporates thermal TSV during simulation, are used in this research to reduce electrical interference. The electrical signal transporting TSV to the substrate and other TSV was investigated for interference. With other models, this study also shows higher frequency regimes up to 1 THz. We found that the suggested methodology improves 3D-IC development by more than 30% by reducing electrical interference from signal-carrying TSV to other TSV.

Holographic zero sound for [formula omitted] SCFTs in 4d

We build up the notion of metallic holography for N=2 SCFTs in four dimensions, in the presence of a finite U(1) chemical potential. We compute two point correlation functions and study their properties in the regime of low frequency and low momentum. The color sector reveals gapless excitations, one of which propagates with a finite phase velocity while the other mode attenuates through scattering. The flavour sector, on the other hand, reveals spectrum that contains quasiparticle excitations which propagate with a definite phase velocity together with modes that propagate with a finite group velocity which quantum attenuates quite similar in spirit as that of Landau's zero sound modes. We also compute associated AC conductivities, which exhibit different characteristics for different (color and flavour) sectors of N=2 SCFTs.

High bulk modulus pentamodes: the three-dimensional metal water

Despite significant advances in the field of phononic crystals, the development of acoustic metafluids that replicate the behaviour of liquids in three dimensions remains elusive. For instance, water – the quintessential pentamode (PM) material – has a bulk modulus two orders of magnitude higher than current state-of-the-art PMs. The need for a low shear modulus inherently conflicts with the desire of high bulk modulus and density. In this letter, we shed light on the limitations of existing PM geometries and propose an innovative shape for the links that constitute the network. Inspired by the kinematics of ropes, these links are constructed from thin fibres and demonstrate the potential to create PMs with properties akin to those of liquids. As a prime example, we propose the design of the first metamaterial that fully deserves the name 3D metal water, since its acoustic properties in the low frequency regime are indistinguishable from water. Additionally, we highlight a shear band gap in the lattice dispersion diagram, and illustrate the influence of geometric parameters on the dynamic properties at higher frequencies. This novel design of metafluids holds promise for applications requiring anisotropic materials such as acoustic lenses, waveguides, and cloaks.

(General Student Poster Award Winner, 3rd Place) Designing and Evaluating Microelectrodes for Molten Salt Corrosion Electrochemistry

Due to the coupling of high temperature operation (>500°C) and propensity to contain oxidizing impurities (e.g., moisture, metallic cations), corrosion of structural alloys in molten chloride and fluoride salts is a major concern among developers of Generation IV nuclear reactors. To mitigate corrosion, it is essential to understand the corrosion mechanism and accurately determine its rate. Prior studies employ a forensic approach for corrosion testing, which does not provide insights on instantaneous rate of corrosion [1]. The use of electrochemical impedance spectroscopy (EIS) can provide in-operando method to interrogate dissolution processes. However, due to the high electrical conductivity and double-layer capacitance of metal salt interface [2], low frequency regimes normally dominated by polarization resistance (Rp) in aqueous systems require data acquisition at low frequencies. (<10-3 Hz). This renders access to charge-transfer resistance (Rct) and diffusional impedance effects difficult. This difficulty is compounded by issues such as signal noise associated with the use of long cables in conventional molten salt corrosion cells [2].To overcome this challenge, a working electrode may be designed as a 2D microdisk electrode to was used to interrogate the low-frequency impedance regimes. This disk has a non-uniform current distribution at such low Wagner number but it is easier to access the charge transfer and/or diffusional impedance regime, otherwise unattainable with the conventionally used partially immersed 3D macro-electrodes utilized in most studies [3]. In this work, a flush mounted microdisk electrode, compatible for use in molten LiF-NaF-KF (i.e., FLiNaK) salts at 600°C was designed and evaluated for its effectiveness towards accurately determining Rp through the EIS method. Pure Cr was selected as the model working electrode since its corrosion behavior in FLiNaK at 600°C has been thoroughly investigated [4,5,6],. Cr microdisks, with areas ranging from 100 to 10-2 cm2, were fabricated and subsequently exposed in FLiNaK containing 1 wt.% of EuF3 at 600°C for 24 hrs. EIS measurements were carried out over the commonly utilized frequency range from 105 to 10-2 Hz. Moreover, the error introduced by implementing various low “cut off” frequencies was examined. Acknowledgment Research is primarily supported as part of the fundamental understanding of transport under reactor extremes (FUTURE), an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES). This work was performed in the Department of Materials Science and Engineering (DMSE) in the Center for Electrochemical Science and Engineering (CESE) at the University of Virginia. Utilization of the Malvern-Panalytical Empyrean diffractometer was supported by Nanoscale Materials Characterization Facility (NMCF) with National Science Foundation (NSF) under award CHE-2102156. H.C. acknowledges the National Science Foundation Graduate Research Fellowship (GRFP), GRANT#: 1842490.

Anomalous Floquet Phases. A resonance phenomena

Floquet topological phases emerge when systems are periodically driven out-of-equilibrium. They gained attention due to their external control, which allows to simulate a wide variety of static systems by just tuning the external field in the high frequency regime. However, it was soon clear that their relevance goes beyond that, as for lower frequencies, anomalous phases without a static counterpart are present and the bulk-to-boundary correspondence can fail. In this work we discuss the important role of resonances in Floquet phases. For that, we present a method to find analytical solutions when the frequency of the drive matches the band gap, extending the well-known high frequency analysis of Floquet systems. With this formalism, we show that the topology of Floquet phases with resonances can be accurately captured in analytical terms. We also find a bulk-to-boundary correspondence between the number of edge states in finite systems and a set of topological invariants in different frames of reference, which crucially do not explicitly involve the micromotion. To illustrate our results, we periodically drive a SSH chain and a &amp;#x03C0;-flux lattice, showing that our findings remain valid in various two-band systems and in different dimensions. In addition, we notice that the competition between rotating and counter-rotating terms must be carefully treated when the undriven system is a semi-metal. To conclude, we discuss the implications to experimental setups, including the direct detection of anomalous topological phases and the measurement of their invariants.

Host Galaxy Demographics Of Individually Detectable Supermassive Black-hole Binaries with Pulsar Timing Arrays

Abstract Massive black hole binaries (MBHBs) produce gravitational waves (GWs) that are detectable with pulsar timing arrays. We determine the properties of the host galaxies of simulated MBHBs at the time they are producing detectable GW signals. The population of MBHB systems we evaluate is from the \textit{Illustris} cosmological simulations taken in tandem with post processing semi-analytic models of environmental factors in the evolution of binaries. Upon evolving to the GW frequency regime accessible by pulsar timing arrays, we calculate the detection probability of each system using a variety of different values for pulsar noise characteristics in a plausible near-future International Pulsar Timing Array dataset. We find that detectable systems have host galaxies that are clearly distinct from the overall binary population and from most galaxies in general. With conservative noise factors, we find that host stellar metallicity, for example, peaks at $\sim2Z_\odot$ as opposed to the total population of galaxies which peaks at $\sim0.6Z_\odot$. Additionally, the most detectable systems are much brighter in magnitude and more red in color than the overall population, indicating their likely identity as large ellipticals with diminished star formation. These results can be used to develop effective search strategies for identifying host galaxies and electromagnetic counterparts following GW detection by pulsar timing arrays.

Method for extracting the surface impedance of a generic reflective metasurface

We develop a method for the extraction of the surface impedance tensor of a generic reflective metasurface using an analytic relation between the tensorial surface impedance and the four polarisation-dependent reflection coefficients. We apply this technique to experimental data obtained from a metasurface with a rhomboidal unit cell in the 16–26 GHz range, but note that it could be applied to reflective metasurfaces in any frequency regime. The extraction method can also be applied to model data to facilitate the design process of spatially graded tensorial metasurfaces that allow for full control of the form of the scattered field.

Viscoelastic-Support-Layer-Based Macroscopic Conformal Transfer of van der Waals Materials Compatible with Plasmonic Application.

This study showcases the conformal geometries of van der Waals materials with metallic structures utilizing viscoelastic support layers. Mechanically exfoliated nanometer-thick graphite flakes were transferred onto metal structures with various side slopes using two different polymers: polycarbonate (PC) and polyethylene (PE). We proposed a morphology-based evaluation of the macroscale conformity that can contribute to the selection of a proper support layer. Although both support layers ensured high conformity on the sloped side, the PE layer offered superior conformity on the vertical metal structure. To further investigate the impact of conformal structures, we compared the terahertz transmission changes of a metal bowtie antenna before and after transferring graphite onto the bowtie gap for two distinct conformal structures. The conformity of graphite to the metal gap structure significantly influenced the optical response in the terahertz frequency regime. This suggests that the conformal structuring technique can be leveraged in various terahertz devices composed of metals and van der Waals materials, opening avenues for quantitative analysis in light-matter interactions.

Numerical investigation on the effect of an orifice plate on the flow-induced and acoustically induced vibration of a gas transmission pipe

In this paper, a numerical method is proposed for investigating the flow-induced vibration (FIV) and acoustically induced vibration (AIV) of a straight pipe with an orifice plate. First, the turbulent pressure (TP) and acoustic pressure (AP) signals on the pipe wall were obtained through the simulation of an unsteady flow field and the application of Mohring's analogy, respectively. Subsequently, the FIV and AIV of the pipe were calculated by means of one-way fluid-structure interaction and acoustic-structure interaction, respectively. The calculated pressures, flow velocities, and sound powers at the monitoring point were in good agreement with the experimental results reported in the literature. The numerical results revealed that the power spectral densities of the AP were significantly higher than those of the TP on the surface of the tested end pipe, particularly at the natural frequencies of the acoustic modes. In the low-frequency regime, FIV was the dominant factor, whereas in the medium-high frequency regime, particularly above the cutoff frequency of the plane wave, AIV was the dominant factor. The findings of the parametric studies demonstrated that the AP and AIV of the pipe exhibited a considerable increase with the Mach number. Conversely, the TP and FIV demonstrated a more pronounced rise when the Mach number increased from 0.1 to 0.2, followed by a less pronounced increase when the Mach number increased from 0.2 to 0.3. A reduction in the orifice diameter resulted in an increase in the AP and AIV. In contrast, the TP and FIV exhibited a comparatively minor increase.

Dynamics of paramagnetic permanent chains and self-assembled clusters under a rapidly rotating magnetic field.

We study experimentally and theoretically the dynamics of permanent paramagnetic chains and mixed clusters formed by permanent paramagnetic chains and paramagnetic particles under the influence of a time-varying magnetic field. First, we examine the dynamics of permanent chains at high frequencies (∼50 to 1000Hz). These permanent chains exhibit continuous rotational motion with a frequency several orders of magnitude lower than that of the magnetic field. We develop a theoretical model that accurately describes the dependence of the rotational dynamics of chains on their length, as well as the amplitude and frequency of the external magnetic field in this high frequency regime. Next, we examine how cluster dynamics are affected by the presence of permanent chains. We show that the rotation of clusters composed of a high proportion of permanent chains is slowed down but remains qualitatively well described by the theoretical model we developed for homogeneous clusters of isotropic particles. We propose that the decrease in angular velocity for mixed clusters is due to the hardening of the cluster's 2D elastic modulus caused by the increase of the steric interaction parameter stemming from the presence of chemical links between particles in the chains.

Catalytic enhancement in the performance of the microscopic two-stroke heat engine.

We consider a model of heat engine operating in the microscopic regime: the two-stroke engine. It produces work and exchanges heat in two discrete strokes that are separated in time. The working body of the engine consists of two d-level systems initialized in thermal states at two distinct temperatures. Additionally, an auxiliary nonequilibrium system called catalyst may be incorporated with the working body of the engine, provided the state of the catalyst remains unchanged after the completion of a thermodynamic cycle. This ensures that the work produced by the engine arises solely from the temperature difference. Upon establishing the rigorous thermodynamic framework, we characterize twofold improvement stemming from the inclusion of a catalyst. Firstly, we prove that in the noncatalytic scenario, the optimal efficiency of the two-stroke heat engine with a working body composed of two-level systems is given by the Otto efficiency, which can be surpassed by incorporating a catalyst with the working body. Secondly, we show that incorporating a catalyst allows the engine to operate in frequency and temperature regimes that are not accessible for noncatalytic two-stroke engines. We conclude with a general conjecture about the advantage brought by a catalyst: including the catalyst with the working body always allows to improve efficiency over the noncatalytic scenario for any microscopic two-stroke heat engines. We prove this conjecture for two-stroke engines where the working body is composed of two d-level systems initialized in thermal states at two distinct temperatures, as long as the final joint state leading to optimal efficiency in the noncatalytic scenario is not a product state, or at least one of the d-level system is not thermal.

Utilizing polydispersity in three-dimensional random fibrous based sound absorbing materials

The distribution of fiber diameters plays a crucial role in the transport and sound absorbing properties of a three-dimensional random fibrous (3D-RF) medium. Conventionally, volume-weighted averaging of fiber diameters has been utilized as an appropriate microstructural descriptor to predict the static viscous permeability of 3D-RF media. However, the long wavelength acoustical properties of a 3D-RF medium are also sensitive to the smallest fibers, this is particularly true in the high-frequency regime. In our recent research, we demonstrated that an inverse volume-weighted averaging of fiber diameters can effectively serve as a complementary microstructural descriptor to capture the high-frequency behavior of polydisperse fibrous media. In the present work, we reexamine the identification of two representative volume elements (RVEs) which relies on the reconstruction of 3D-RF microstructures having volume-weighted and inverse-volume weighted averaged fiber diameters, respectively in the low-frequency and high frequency regimes. We investigate the implication of such a weighting procedure on the transport and sound absorbing properties of polydisperse fibrous media, highlighting their potential advantages. Furthermore, we discuss the challenges associated with this research field. Finally, we provide a brief perspective of the future directions and opportunities for advancing this area of study.

Centrifugal pump impeller wheel inspired acoustic metamaterial for low frequency sound absorption

Addressing low-frequency noise is a significant concern within the realm of acoustics and noise management. Labyrinthine channel based acoustic metamaterials have been proved to control low frequency noise using local resonance effect and thermoviscous dissipations. Drawing inspiration from centrifugal pump impeller wheel, an acoustic metamaterial absorber has been devised. The design incorporates impeller vanes to create a channel with variable widths and a micro-perforate panel through which sound wave propagates to the channels. Numerical simulations using COMSOL Multiphysics and experimental analysis are conducted employing Two microphone impedance tube method. Acoustic pressure and acoustic particle velocity distribution plots from numerical simulation study are used to comprehend the sound absorption mechanism. Sound absorption coefficient results reveal that this design offers a tunable sound absorption peak in low frequency regime. Furthermore, this paper discusses the influence of various geometric parameters such as, number of vanes, panel thickness and micro-hole diameter. The subwavelength dimensions of the design contribute to noise control in machineries with space constraints.

Full-wave simulations on helicon and parasitic excitation of slow waves near the edge plasma

Helicon waves are thought to be promising in various tokamaks, such as DIII-D, because they can penetrate reactor-grade high-density cores and drive the off-axis current with higher efficiency. In the frequency regime ∼ 476 MHz, both slow electrostatic and fast electromagnetic helicon waves can coexist in DIII-D. If the antenna parasitically excites the slow mode, these waves can propagate along the magnetic field line into the scrape-off layer (SOL). Although the importance of the misalignment of the Faraday screen and the electron density in the SOL on the excitation and propagation of slow modes is well known, the conditions for minimizing slow mode excitation have yet to be optimized. Using the Petra-M simulation code in the 2D domain, we analyze the effects of the misalignment of the antenna in the poloidal direction, the misalignment of the Faraday screen in the toroidal direction, and the density in front of the antenna on slow mode generation. Our results suggest that the misalignment of the Faraday screen is a critical factor in reducing the slow mode and that the misalignment angle should be below ∼ 5° to minimize the slow wave excitation. When the electron density is higher than 3.5×1018 m−3 in the SOL, the generation of the slow mode from the antenna is minimized and unaffected by the misalignment of the Faraday screen.

Brillouin light scattering spectral fingerprinting of magnetic microstates in artificial spin ice

The family of nanomagnetic arrays termed artificial spin ice (ASI) possess a vast range of metastable microstates. These states exhibit both exotic fundamental physics and more recently applied functionality, garnering attention as reconfigurable magnonic circuits and neuromorphic computing platforms. However, open questions remain on the role of microstate imperfections or angular disorder – particularly in the GHz response of the system. We report a study on the GHz dynamics of a series of five carefully prepared microstates in the same ASI sample, with both coexistence of vortex and uniformly magnetized macrospins, and disorder in the orientation of the macrospins at different vertices. We observe microstate-specific mode frequency shifting, mode creation and mode crossing. This versatility of characteristic spin-wave (SW) peaks for specific magnetic microstates in ASI enables identification of microstate configurations via SW spectral characterization. The wide reconfigurability of microstate-specific SW dynamics also opens avenues for developing rich magnonic devices operating in the GHz frequency regime and advances the understanding of ASI physics.

Non-Foster approach to broadband optical metamaterials based on Lorentzian gain materials

All passive metamaterials are inherently narrowband due to fundamental dispersion-energy constraints, and their dispersive properties are usually approximated by a Lorentz model. However, there are broadband active metamaterials in the radio frequency (RF) regime based on negative capacitors with non-Foster dispersion properties. Non-Foster dispersion is usually considered as an “electronic-engineering trick” that cannot be applied at optical frequencies. Here, we demonstrate that the dispersion relation of a RF non-Foster capacitor is similar to that of an optical gain material described by a Lorentz model. This insight paves the way to realize non-Foster optical metamaterial structures. As the simplest example, we develop a broadband non-Foster optical epsilon-near-zero slab with a 1:10 bandwidth.