- 标题
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Singular spectrum analysis filtering and Fourier inversion: an efficient and fast way to improve resolution and quality of current density maps with low-cost Hall scanning systems
摘要： We provide a Biot–Savart inversion scheme that, for any two-dimensional, or bulk with planar crystallization, high-temperature superconducting (HTS) sample, determines current density maps with a higher resolution and accuracy than previous procedures and at a fraction of its computational cost. The starting point of our scheme is a Hall scanning microscopy map of the out-of-plane component of the magnetic field generated by the current. Such maps are noisy in scans of real samples with commercial-grade equipment, and their error is the limiting factor in any Biot–Savart inversion scheme. The main innovation of our proposed scheme is a singular spectrum analysis (SSA) filtering of the Hall probe maps, which cancels measurement errors such as noise or drifts without introducing any artifacts in the field map. The SSA filtering of the Hall probe data is so successful in this task that the resulting magnetic field map does not require an overdetermined QR inversion, allowing Fourier inversion of the Biot–Savart problem. Our implementation of SSA filtering of the Hall scan measurements, followed by Biot–Savart inversion using the fast Fourier transform (FFT), is applied to both simulations and real samples of HTS tape stacks. The algorithm works in cases where ill conditioning ruled out the application of Fourier inversion, and achieves a finer resolution for a fraction of the cost of the QR inversion used to date. The computation passes physical and statistical validity tests in all cases, and in three-dimensional samples it is shown to yield the average, with a depth-dependent weight, of the current density circulating in the different layers of the sample.
关键词： Hall magnetometry,SSA filtering,fast Fourier transform,high-temperature superconducting tapes,Biot–Savart inversion
更新于2025-09-23 15:23:52
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High-sensitivity three-axis vector magnetometry using the electron spin ensembles in single diamond
摘要： We demonstrate a three-axis vector magnetometer based on ensembles of negatively charged nitrogen vacancy centers in single-crystal diamond. Diamond with C3v symmetry was used to establish the coordinate system for vector magnetic field sensing. We control the external static magnetic field with three-axis Helmholtz coils. Four pairs of magnetic resonance peaks were obtained, which were used to calculate the three Cartesian components of the magnetic field with sensitivity of ~5 nT/√Hz for each Cartesian component, free of interaxis error. The magnetometer is suitable for single-chip manufacturing.
关键词： Nitrogen-Vacancy (NV) centers,ensemble,diamond,Magnetometry
更新于2025-09-23 15:22:29
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Effects of flux pinning on the DC characteristics of meander-shaped superconducting quantum interference filters with flux concentrator
摘要： Superconducting quantum interference filters, or SQIFs, are a promising class of highly sensitive magnetometers benefiting from a highly peaked and symmetric magnetic response at zero-input flux. They can be used in magnetometry, e.g., in wideband applications. A simple solution to increase further their sensitivity is to add a superconducting flux concentrator (SFC) to their design. Using the ion irradiation process, we designed a meander-shaped SQIF enhanced with an SFC. The SFC improved the SQIF transfer factor by a factor of 8.4. However, high temperature superconducting (HTSc) devices are vulnerable to flux pinning, which can severely hinder their response. On the one hand, HTSc technologies alleviate the burden of cryogenics. On the other hand, applications that use SFCs in noisy and unshielded environments will become possible only if a better understanding of how this flux impacts the device's properties is achieved. We studied the relationship between the field present during the cooling process of the SQIF antenna (thereafter called 'cooling field') and the evolution of its DC response. We developed a simple and phenomenological model and were able to reproduce the degradation of the SQIF response. This work demonstrates the usability of SFC-enhanced SQIFs based on ion irradiated junctions in rather harsh conditions, in particular, an unshielded environment, and also gives an insight into the implications that such conditions cause on the application of SFCs in general.
关键词： ion irradiation,flux pinning,magnetometry,flux concentrator,superconducting quantum interference filters
更新于2025-09-23 15:22:29
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Measuring the Lower Critical Field of Superconductors Using Nitrogen-Vacancy Centers in Diamond Optical Magnetometry
摘要： The lower critical magnetic field, Hc1, of superconductors is measured by optical magnetometry using ensembles of nitrogen-vacancy centers in diamond. The technique is minimally invasive and allows accurate detection of the vector magnetic field with subgauss sensitivity and submicrometer spatial resolution. These capabilities are used for detailed characterization of the first vortex penetration into superconducting samples from the corners. Aided by the revised calculations of the effective demagnetization factors of actual cuboid-shaped samples, these measurements provide precise determination of Hc1 and the related absolute value of the London penetration depth, λ. We apply this method to three well-studied superconductors: optimally doped Ba(Fe1?xCox)2As2, stoichiometric CaKFe4As4, and the high-Tc cuprate YBa2Cu3O7?δ. Our results compared well with the values of λ obtained with other techniques, thus adding another noninvasive and sensitive method to measure these important parameters of superconductors.
关键词： optical magnetometry,nitrogen-vacancy centers,London penetration depth,superconductors,lower critical field
更新于2025-09-23 15:22:29
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Development of All-Diamond Scanning Probes Based on Faraday Cage Angled Etching Techniques
摘要： We are proposing a novel fabrication method for single crystal diamond scanning probes for atomic force microscopy (AFM), exploiting Faraday cage angled etching (FCAE). Common, oxygen-based, inductively coupled plasma (ICP) dry etching processes for diamond are limited with respect to the achievable geometries. The fabrication of freestanding micro- and nanostructures is therefore challenging. This is a major disadvantage for several application fields e.g., for realizing scanning magnetometry probes based on nitrogen vacancy (NV) centres and capable of measuring magnetic fields at the nanoscale. Combining a planar design with FCAE and state-of-the-art electron beam lithography (EBL) yields a reduction of process complexity and cost compared to the established fabrication technology of micro-opto-mechanical diamond devices. Here, we report on the direct comparison of both approaches and present first proof-of-concept planar-FCAE-prototypes for scanning probe applications.
关键词： Faraday cage angled etching,scanning magnetometry,atomic force microscopy,diamond scanning probes,nitrogen vacancy centres
更新于2025-09-23 15:19:57
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Photoinduced effects on the magnetic properties of the (Fe <sub/>0.2</sub> Cr <sub/>0.8</sub> ) <sub/>1.5</sub> [Cr(CN) <sub/>6</sub> ] Prussian blue analogue.
摘要： One of the most attractive characteristics of some Prussian blue derivatives is the sensitivity of their magnetic properties to the irradiation with light. In this work photoinduced effects in the (Fe0.2Cr0.8)1.5 [Cr(CN)6]·15 H2O PBA have been studied by means of X ray-based spectroscopies and magnetometry. It is found that the photosensitivity of this compound is mostly centred on the Fe cations: the exposure to green light induces a transfer of electrons from them to the Cr that provokes a reversal of the previously existing linkage isomerization and increases the elastic strain caused by the mis?t of the unit cells of the Fe–NC–Cr and Cr–NC–Cr sublattices. The green light also quenches the magnetism of the FeII high-spin (HS) ions present in the sample and reduces the magnetic moments of most of the Cr cations except for CrII HS. Our study highlights the important role played by the mismatch between the unit cells of the coexisting sub-lattices in ternary Prussian blue analogues.
关键词： magnetometry,photoinduced effects,magnetic properties,elastic strain,X-ray spectroscopies,Prussian blue analogues,linkage isomerization
更新于2025-09-19 17:15:36
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Apparent delocalization of the current density in metallic wires observed with diamond nitrogen-vacancy magnetometry
摘要： We report on a quantitative analysis of the magnetic field generated by a continuous current running in metallic microwires fabricated on an electrically insulating diamond substrate. A layer of nitrogen-vacancy (NV) centers engineered near the diamond surface is employed to obtain spatial maps of the vector magnetic field, by measuring Zeeman shifts through optically detected magnetic resonance spectroscopy. The in-plane magnetic field (i.e., parallel to the diamond surface) is found to be significantly weaker than predicted, while the out-of-plane field also exhibits an unexpected modulation. We show that the measured magnetic field is incompatible with Ampère’s circuital law or Gauss’s law for magnetism when we assume that the current is confined to the metal, independent of the details of the current density. This result was reproduced in several diamond samples, with a measured deviation from Ampère’s law by as much as 94(6)% (i.e., a 15σ violation). To resolve this apparent magnetic anomaly, we introduce a generalized description whereby the current is allowed to flow both above the NV sensing layer (including in the metallic wire) and below the NV layer (i.e., in the diamond). Inversion of the Biot-Savart law within this two-channel description leads to a unique solution for the two current densities that completely explains the data, is consistent with the laws of classical electrodynamics, and indicates a total NV-measured current that closely matches the electrically measured current. However, this description also leads to the surprising conclusion that in certain circumstances the majority of the current appears to flow in the diamond substrate rather than in the metallic wire, and to spread laterally in the diamond by several micrometers away from the wire. No electrical conduction was observed between nearby test wires, ruling out a conventional conductivity effect. Moreover, the apparent delocalization of the current into the diamond persists when an insulating layer is inserted between the metallic wire and the diamond or when the metallic wire is replaced by a graphene ribbon. The possibilities of a measurement error, a problem in the data analysis, or a current-induced magnetization effect are discussed, but do not seem to offer a more plausible explanation for the effect. Understanding and mitigating this apparent anomaly will be crucial for future applications of NV magnetometry to charge transport studies.
关键词： diamond magnetometry,nitrogen-vacancy centers,Biot-Savart law,Ampère's law,magnetic field imaging,current density
更新于2025-09-19 17:15:36
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[IEEE 2019 Thirteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Rome, Italy (2019.9.16-2019.9.21)] 2019 Thirteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Highly sensitive magnetometry method based on the magnetoplasmonic crystal
摘要： A novel concept of the room-temperature magnetoplasmonic magnetic field sensor with high sensitivity and spatial resolution is presented. The advanced flux-gate technique is used. Magnetization of the fully saturated magnetic film is rotated in the film plane and the monitored magnetic field is measured by detecting variation of optical transmittance through the sensing element. The sensing element is a magnetoplasmonic crystal consisting of a gold grating with subwavelength period deposited on a thin transparent dielectric film of bismuth substituted iron-garnet. Geometrical parameters of the magnetoplasmonic crystals are adjusted to have pronounced resonances of the longitudinal magneto-photonic intensity effect (LMPIE). The experimental study revealed that such approach allows one to reach the 2nT sensitivity level which was limited by the noise of the laser. The demonstrated magnetoplasmonic magnetometry method is promising for mapping and visualization of ultra-small magnetic fields.
关键词： magnetic field sensor,magnetometry,LMPIE,magnetoplasmonic crystal
更新于2025-09-16 10:30:52
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Concept of an Optical Magnetometer Based on the Spectroscopy of Alkali Vapors Confined in Nanometric-Thick Cells
摘要： In this article, we present the concept of an optical scalar magnetometer based on the spectroscopy of hot alkali vapors confined in nanometric-thick cells. We present an appropriate theoretical model to describe the interaction of linearly and circularly polarized light with atomic alkali vapors confined in extremely thin cells where a longitudinal magnetic field is applied. This model can be used to perform consecutive fittings of experimental spectra recorded by derivative selective reflection method, in order to measure the value of magnetic field. We illustrate the model with various calculated spectra for natural Rb vapor, while equivalent results hold for other alkalis (Na, K, Cs). We analyze the feasibility of the concept for different cases depending on light polarization and cell thickness, and discuss possible limitations of the technique.
关键词： nanocell,selective reflection,Zeeman effect,optical magnetometry,alkali vapors
更新于2025-09-10 09:29:36
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Influence of Dynamical Decoupling Sequences with Finite-Width Pulses on Quantum Sensing for AC Magnetometry
摘要： Dynamical decoupling sequences with multiple pulses can be considered to exhibit filter functions for the time evolution of a qubit superposition state. They contribute to the increase of coherence time and qubit-phase accumulation due to a time-varying field and can thus be used to achieve high-frequency-resolution spectroscopy. Such behaviors find useful application in highly sensitive detection based on qubits for various external fields, such as a magnetic field. Hence, decoupling sequences are indispensable tools for quantum sensing. In this study, we experimentally and theoretically investigate the effects of finite-width pulses in the sequences on ac magnetometry using nitrogen-vacancy centers in an isotopically controlled diamond. We reveal that the finite pulse widths cause a deviation of the optimum time to acquire the largest phase accumulation due to the sensing field from that expected by filter functions ignoring the pulse widths, even if the widths are considerably shorter than the time period of the sensing field. Moreover, we experimentally demonstrate that the deviation can be corrected by an appropriate time-frequency conversion. Our results provide a guideline for the detection of an ac field with an accurate frequency and linewidth in quantum sensing with multiple-pulse sequences.
关键词： nitrogen-vacancy centers,quantum sensing,dynamical decoupling,ac magnetometry,finite-width pulses
更新于2025-09-09 09:28:46