arXiv subjects

Akira Miyazaki

Publications and source records attributed to Akira Miyazaki.

12 recordsLinked to original sources

arXiv2026

Effect of non-homogeneous non-magnetic Impurities in Superconductors: A comparison between Microscopic and Macroscopic theories

Non-homogeneous, non-magnetic impurities in superconductivity have recently gained traction as a promising approach to reduce surface resistance and increase the superheating field. We aim to deepen the understanding of impurities' role from a theoretical perspective by utilizing Eilenberger's equation, and to investigate the validity of a more phenomenological approach based on London's equation for determining the magnetic field profile within the superconductor. We show that the microscopic and macroscopic theories produce identical electromagnetic field distributions for any spatial distributions of impurities inside the superconductors. However, the two approaches provide different magnetic field-related quantities. The macroscopic model only gives the Bean-Livingston barrier, while the microscopic theory provides the experimentally-relevant superheating field. Based on the microscopic formalism, we determine a family of impurity profiles that make the superheating field $H_{\rm{sh}}$ equal to the critical field $H_c$, which is the maximum achievable.

cond-mat.supr-con↗

arXiv2026

Generalized Glauber theorem for dark-matter axion and graviton detection

We revisit the generalized Glauber theorem motivated by recent applications to dark-matter axion searches and graviton production. For Hamiltonian containing up to quadratic terms in annihilation and creation operators coupled to classical sources, the time-evolution operator can be factorized into displacement, squeezing, and rotation operators. We derive the differential equations governing time evolution of their parameters, reducing the quantum dynamics to c-number equations that can be solved analytically or numerically. To compare another form of the time-evolution operator, Dyson series, we demonstrate the essential role of time ordering. This formalism based on generalized Glauber theorem provides a unified description of particle production from classical backgrounds. Axion-photon conversion in microwave haloscopes is recovered as the linear-interaction limit, while squeezed graviton production from black-hole mergers follows naturally from quadratic interactions. Extending the theorem to thermal initial states yields a realistic quantum description of microwave cavities used in axion experiments. We show that higher-order photon statistics exhibit nontrivial behavior, providing a rigorous foundation for Monte Carlo simulations of quantum-enhanced axion searches beyond heuristic noise estimates.

hep-ph↗

arXiv2026

Analytical evaluation of surface barrier and resistance in iron-based superconducting multilayers for Superconducting Radio-Frequency applications

New superconducting materials, particularly iron-based superconductors (IBS), have recently attracted attention for their potential applications in particle detectors and accelerators. This paper discusses the application of these materials in multilayer structures for radio-frequency resonators used to accelerate charged particles, with the aim of improving performance compared to bulk niobium. These materials are compared with previously studied multilayers composed of conventional superconductors in terms of the maximum magnetic field they can withstand, their surface resistance, and their power loss per unit surface area. Finally, perspectives and future applications aimed at increasing operating temperatures are discussed.

cond-mat.supr-con↗

arXiv2024

SRF programs towards High-Q/High-G cavities in IJCLab

IJCLab has been leading the development and deployment of low-$β$ Superconducting Radio Frequency (SRF) cavities for proton and heavy ion accelerators. We are launching an electron accelerator project for sustainable Energy Recovery Linac (iSAS/PERLE) with state-of-the-art SRF cavities at 800~MHz. Our proposal includes advanced heat treatment of such cavities to reach an excellent quality factor of $3\times 10^{10}$ at $22$~MV/m. In this paper, we overview the status of this activity.

physics.acc-ph↗

arXiv2024

Potential of non-conventional superconductors for particle accelerator cavities

Superconducting RadioFrequency (SRF) cavities have been developed for modern particle accelerator projects in the world. These cavities are mainly made of bulk niobium operated in superfluid or normal fluid helium. Due to the price increase in niobium material as well as helium, superconductors beyond the niobium are investigated for more sustainable accelerators. In this paper, we consider the most fundamental loss mechanism of microwaves inside various superconductors caused by thermally excited quasi-particles in the Meissner state.

physics.acc-ph↗

arXiv2023

Millimeter-wave WISP search with coherent Light-Shining-Through-a-Wall towards the STAX project

A dark photon is one of the simplest extensions of the Standard Model of particle physics and can be a dark matter candidate. Dark photons kinetically mix with ordinary photons. The mass range from $10^{-4}$ to $10^{-3}$ eV of such dark photons is under-constrained by laboratory-based experiments and a new search is therefore motivated. In this mass range, dark photons behave like waves rather than particles and the corresponding electromagnetic waves are in the millimeter-wave range. The technical difficulties of the millimeter waves have prevented so far dark photon experiments in this mass range. We propose the use of coherent millimeter waves to search for dark photons in a Light-Shining-through-a-Wall (LSW) experiment. We clarify the merit and limitations of coherent wave detection and briefly investigate the potential of single photon sensors at microwaves. Development of millimeter-wave technology is not only limited to dark photons. Technically, an experiment for dark photons by using electromagnetic waves resembles that for axions, another light dark matter candidate, with static magnetic fields. This paper represents an essential step towards axion LSW in the millimeter-wave range (STAX experiment) as a potential successor of an on-going experiment in infrared.

hep-ph↗

arXiv2023

Searching For Dark Matter with Plasma Haloscopes

We summarise the recent progress of the Axion Longitudinal Plasma HAloscope (ALPHA) Consortium, a new experimental collaboration to build a plasma haloscope to search for axions and dark photons. The plasma haloscope is a novel method for the detection of the resonant conversion of light dark matter to photons. ALPHA will be sensitive to QCD axions over almost a decade of parameter space, potentially discovering dark matter and resolving the Strong CP problem. Unlike traditional cavity haloscopes, which are generally limited in volume by the Compton wavelength of the dark matter, plasma haloscopes use a wire metamaterial to create a tuneable artificial plasma frequency, decoupling the wavelength of light from the Compton wavelength and allowing for much stronger signals. We develop the theoretical foundations of plasma haloscopes and discuss recent experimental progress. Finally, we outline a baseline design for ALPHA and show that a full-scale experiment could discover QCD axions over almost a decade of parameter space.

hep-ph↗

arXiv2021

Impact of geometry on the magnetic flux trapping of superconducting accelerating cavities

Controlling trapped magnetic flux in superconducting radiofrequency (RF) cavities is of crucial importance in modern accelerator projects. In order to study flux trapping efficiency and sensitiv- ity of surface resistance, dedicated experiments have been carried out on different types of low-\b{eta} superconducting accelerating cavities. Even under almost full trapping conditions, we found that the measured magnetic sensitivities of these cavity geometries were significantly lower than the theoretical values predicted by commonly-used models based on local material properties. This must be resolved by taking account of geometrical effects of flux trapping and flux oscillation under RF surface current in such cavity shape. In this paper, we propose a new approach to convolute the influence of geometries. We point out a puzzling contradiction between sample measurements and recent cavity experiments, which leads to two different hypotheses to simulate oscillating flux trapped in the cavity surface. A critical reconsideration of flux oscillation by the RF Lorentz force, compared with temperature mapping studies in elliptical cavities, favoured the results of previous sample measurements, which suggested preferential flux trapping of normal component to the cavity inner surface. Based on this observation, we builded a new model to our experimental results and the discrepancy between old theory and data were resolved.

physics.acc-ph↗

arXiv2018

Vortex dynamics and losses due to pinning: Dissipation from trapped magnetic flux in resonant superconducting radio-frequency cavities

We use a model of vortex dynamics and collective weak pinning theory to study the residual dissipation due to trapped magnetic flux in a dirty superconductor. Using simple estimates, approximate analytical calculations, and numerical simulations, we make predictions and comparisons with experiments performed in CERN and Cornell on resonant superconducting radio-frequency NbCu, doped-Nb and Nb$_3$Sn cavities. We invoke hysteretic losses originating in a rugged pinning potential landscape to explain the linear behavior of the sensitivity of the residual resistance to trapped magnetic flux as a function of the amplitude of the radio-frequency field. Our calculations also predict and describe the crossover from hysteretic-dominated to viscous-dominated regimes of dissipation. We propose simple formulas describing power losses and crossover behavior, which can be used to guide the tuning of material parameters to optimize cavity performance.

cond-mat.supr-con↗

arXiv2016

Interplay between conducting and magnetic systems in the antiferromagnetic organic superconductor $κ$-(BETS)$_2$FeBr$_4$

The mutual influence of the conduction electron system provided by organic donor layers and magnetic system localized in insulating layers of the molecular charge transfer salt $κ$-(BETS)$_2$FeBr$_4$ has been studied. It is demonstrated that besides the high-field re-entrant superconducting state, the interaction between the two systems plays important role for the low-field superconductivity. The coupling of normal-state charge carriers to the magnetic system is reflected in magnetic quantum oscillations and can be evaluated based on the angle-dependent beating behaviour of the oscillations. On the other hand, the conduction electrons have their impact on the magnetic system, which is revealed through the pressure-induced changes of the magnetic phase diagram of the material.

cond-mat.str-el↗

arXiv2016

Resistive properties and phase diagram of the organic antiferromagnetic metal $κ$-(BETS)$_2$FeCl$_4$

The low-temperature electronic state of the layered organic charge-transfer salt $κ$-(BETS)$_2$FeCl$_4$ was probed by interlayer electrical resistance measurements under magnetic field. Both above and below $T_{\mathrm{N}}=0.47\,$K, the temperature of antiferromagnetic ordering of $3d$-electron spins of Fe$^{3+}$ localized in the insulating anion layers, a non-saturating linear $R(T)$ dependence has been observed. A weak superconducting signal has been detected in the antiferromagnetic state, at temperatures $\leq 0.2\,$K. Despite the very high crystal quality, only a tiny fraction of the sample appears to be superconducting. Besides a small kink feature in the resistivity, the impact of the antiferromagnetic ordering of localized Fe$^{3+}$ spins on the conduction $π$-electron system is clearly manifested in the Fermi surface reconstruction, as evidenced by Shubnikov-de Haas oscillations. The "magnetic field -- temperature" phase diagrams for the field directions parallel to each of the three principal crystal axes have been determined. For magnetic field along the easy axis a spin-flop transition has been found. Similarities and differences between the present material and the sister compound $κ$-(BETS)$_2$FeBr$_4$ are discussed.

cond-mat.str-el↗

arXiv2010

Positronium Hyperfine Splitting

Positronium is an ideal system for the research of QED in the bound state. The hyperfine splitting of positronium (Ps-HFS: about 203 GHz) is a good tool to test QED and also sensitive to new physics beyond the Standard Model. Previous experimental results show 3.9\,$σ$ (15 ppm) discrepancy from the QED $\mathrm{O}\left(α^3 \ln{1/α}\right)$ prediction. We point out probable common systematic errors in all previous experiments. I measure the Ps-HFS in two different ways. (1) A prototype run without RF system is described first. (2) I explain a new direct Ps-HFS measurement without static magnetic field. The present status of the optimization studies and current design of the experiment are described. We are now taking data of a test experiment for the observation of the direct transition.

physics.ins-det↗