Estefani Marchiori

We demonstrate the fabrication of scanning superconducting quantum interference devices (SQUIDs) on the apex of sharp quartz scanning probes -- known as SQUID-on-tip probes -- using conventional magnetron sputtering. We produce and characterize SQUID-on-tips made of both Nb and MoGe with effective diameters ranging from 50 to 80 nm, magnetic flux noise down to \SI{300}{\nano\Phi_{0}/\sqrt{\hertz}}, and operating fields as high as \SI{2.5}{\tesla}. Compared to the SQUID-on-tip fabrication techniques used until now, including thermal evaporation and collimated sputtering, this simplified method facilitates experimentation with different materials, potentially expanding the functionality and operating conditions of these sensitive nanometer-scale scanning probes.

Cavity magnetron

10.1063/5.0150222

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Mapping the flux penetration profile in a 2G-HTS tape at the microscopic scale: deviations from a classical critical state model

Superconductor Science and Technology (2018)

Estefani Marchiori S. J. Bending

Understanding vortex behaviour at microscopic scales is of extreme importance for the development of higher performance coated conductors with larger critical currents. Here, we study and map the critical state in a YBCO-based coated conductor at different temperatures using two distinct operation modes of scanning Hall microscopy. An analytical Bean critical state model for long superconducting strips is compared with our measurements and used to estimate the critical current density. We find several striking deviations from the model; pronounced flux front roughening is observed as the temperature is reduced below 83 K due to vortex-bundle formation when strong broadening of the flux front profile is also seen. In higher magnetic fields at the lower temperature of 65 K, fishtail-like magnetization peaks observed in local magnetization measurements are attributed to flux-locking due to an increase in the critical current density near the edges of the tape, which we tentatively link to vortex pinning matching effects. Our measurements provide valuable insights into the rich vortex phenomena present in coated conductor tapes at the microscopic scale.

Vortex state

10.1088/1361-6668/aaf2f5

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Magnetic, Thermal, and Topographic Imaging with a Nanometer-Scale SQUID-On-Lever Scanning Probe

Physical Review Applied (2022)

M. Wyss K. Bagani Daniel Jetter Estefani Marchiori Andriani Vervelaki

Scanning superconducting quantum interference device (SQUID) microscopy is a magnetic imaging technique combining high-field sensitivity with nanometer-scale spatial resolution. State-of-the-art SQUID-on-tip probes are now playing an important role in mapping correlation phenomena, such as superconductivity and magnetism, which have recently been observed in two-dimensional van der Waals materials. Here, we demonstrate a scanning probe that combines the magnetic and thermal imaging provided by an on-tip SQUID with the tip-sample distance control and topographic contrast of a non-contact atomic force microscope (AFM). We pattern the nanometer-scale SQUID, including its weak-link Josephson junctions, via focused ion beam milling at the apex of a cantilever coated with Nb, yielding a sensor with an effective diameter of 365 nm, field sensitivity of 9.5 $\text{nT}/\sqrt{\text{Hz}}$ and thermal sensitivity of 620 $\text{nK}/\sqrt{\text{Hz}}$, operating in magnetic fields up to 1.0 T. The resulting SQUID-on-lever is a robust AFM-like scanning probe that expands the reach of sensitive nanometer-scale magnetic and thermal imaging beyond what is currently possible.

Lever

Nanometre

Scanning SQUID microscopy

10.1103/physrevapplied.17.034002

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Citations (29)

Technical Review: Imaging weak magnetic field patterns on the nanometer-scale and its application to 2D materials

arXiv (Cornell University) (2021)

Estefani Marchiori Lorenzo Ceccarelli N. Rossi Luca Lorenzelli Christian L. Degen

Nanometer-scale imaging of magnetization and current density is the key to deciphering the mechanisms behind a variety of new and poorly understood condensed matter phenomena. The recently discovered correlated states hosted in atomically layered materials such as twisted bilayer graphene or van der Waals heterostructures are noteworthy examples. Manifestations of these states range from superconductivity, to highly insulating states, to magnetism. Their fragility and susceptibility to spatial inhomogeneities limits their macroscopic manifestation and complicates conventional transport or magnetization measurements, which integrate over an entire sample. In contrast, techniques for imaging weak magnetic field patterns with high spatial resolution overcome inhomogeneity by measuring the local fields produced by magnetization and current density. Already, such imaging techniques have shown the vulnerability of correlated states in twisted bilayer graphene to twist-angle disorder and revealed the complex current flows in quantum Hall edge states. Here, we review the state-of-the-art techniques most amenable to the investigation of such systems, because they combine the highest magnetic field sensitivity with the highest spatial resolution and are minimally invasive: magnetic force microscopy, scanning superconducting quantum interference device microscopy, and scanning nitrogen-vacancy center microscopy. We compare the capabilities of these techniques, their required operating conditions, and assess their suitability to different types of source contrast, in particular magnetization and current density. Finally, we focus on the prospects for improving each technique and speculate on its potential impact, especially in the rapidly growing field of two-dimensional (2D) materials.

Magnetism

Macroscopic quantum phenomena

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Magnetic, thermal, and topographic imaging with a nanometer-scale SQUID-on-cantilever scanning probe

arXiv (Cornell University) (2021)

M. Wyss K. Bagani Daniel Jetter Estefani Marchiori Andriani Vervelaki

Scanning superconducting quantum interference device (SQUID) microscopy is a magnetic imaging technique combining high-field sensitivity with nanometer-scale spatial resolution. State-of-the-art SQUID-on-tip probes are now playing an important role in mapping correlation phenomena, such as superconductivity and magnetism, which have recently been observed in two-dimensional van der Waals materials. Here, we demonstrate a scanning probe that combines the magnetic and thermal imaging provided by an on-tip SQUID with the tip-sample distance control and topographic contrast of a non-contact atomic force microscope (AFM). We pattern the nanometer-scale SQUID, including its weak-link Josephson junctions, via focused ion beam milling at the apex of a cantilever coated with Nb, yielding a sensor with an effective diameter of 365 nm, field sensitivity of 9.5 $\text{nT}/\sqrt{\text{Hz}}$ and thermal sensitivity of 620 $\text{nK}/\sqrt{\text{Hz}}$, operating in magnetic fields up to 1.0 T. The resulting SQUID-on-lever is a robust AFM-like scanning probe that expands the reach of sensitive nanometer-scale magnetic and thermal imaging beyond what is currently possible.

Nanometre

Scanning Probe Microscopy

Scanning SQUID microscopy

Thermal fluctuations

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Magnetic imaging of superconducting qubit devices with scanning SQUID-on-tip

Applied Physics Letters (2022)

Estefani Marchiori Lorenzo Ceccarelli N. Rossi Giulio Romagnoli J. Herrmann

We use a scanning superconducting quantum interference device (SQUID) to image the magnetic flux produced by a superconducting device designed for quantum computing. The nanometer-scale SQUID-on-tip probe reveals the flow of superconducting current through the circuit as well as the locations of trapped magnetic flux. In particular, maps of current flowing out of a flux-control line in the vicinity of a qubit show how these elements are coupled, providing insight on how to optimize qubit control.

Flux qubit

Scanning SQUID microscopy

Charge qubit

Magnetic flux quantum

10.1063/5.0103597

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Reconfigurable superconducting vortex pinning potential for magnetic disks in hybrid structures

Scientific Reports (2017)

Estefani Marchiori P. J. Curran Jang‐Yong Kim Nathan Satchell Gavin Burnell

Abstract High resolution scanning Hall probe microscopy has been used to directly visualise the superconducting vortex behavior in hybrid structures consisting of a square array of micrometer-sized Py ferromagnetic disks covered by a superconducting Nb thin film. At remanence the disks exist in almost fully flux-closed magnetic vortex states, but the observed cloverleaf-like stray fields indicate the presence of weak in-plane anisotropy. Micromagnetic simulations suggest that the most likely origin is an unintentional shape anisotropy. We have studied the pinning of added free superconducting vortices as a function of the magnetisation state of the disks, and identified a range of different phenomena arising from competing energy contributions. We have also observed clear differences in the pinning landscape when the superconductor and the ferromagnet are electron ically coupled or insulated by a thin dielectric layer, with an indication of non-trivial vortex-vortex interactions. We demonstrate a complete reconfiguration of the vortex pinning potential when the magnetisation of the disks evolves from the vortex-like state to an onion-like one under an in-plane magnetic field. Our results are in good qualitative agreement with theoretical predictions and could form the basis of novel superconducting devices based on reconfigurable vortex pinning sites.

10.1038/srep45182

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Data for the publication: Reconfigurable superconducting vortex pinning potential for magnetic disks in hybrid structures

Estefani Marchiori

This dataset contains raw data and images from Marchiori, E. et al. Reconfigurable superconducting vortex pinning potential for magnetic disks in hybrid structures. Sci. Rep. 7, 45182; doi: 10.1038/srep45182 (2017).

10.15125/bath-00340

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Imaging magnetic spiral phases, skyrmion clusters, and skyrmion displacements at the surface of bulk Cu2OSeO3

Communications Materials (2024)

Estefani Marchiori Giulio Romagnoli Lukas Schneider B. Gross Pardis Sahafi

Skyrmion

10.1038/s43246-024-00647-5

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Response of lead deposited on glass to acetic acid exposure, with potential for its application as an acetic acid dosimeter/sensor

Terje Grøntoft Estefani Marchiori Marianne Odlyha

Abstract Small glass substrates were coated with a thin granular lead film by thermal vapour deposition in order to test the feasibility of using lead-coated glass as sensors for detecting the presence of gaseous acetic acid in air. The lead glass samples were exposed to acetic acid in increasing concentrations, at a controlled temperature of 23oC and 54% relative humidity for a period of 60 days. The change in the lead films on exposure was systematically investigated by measuring the variation in light transmission at a wavelength of 379 nm. Initial corrosion of the deposited reactive thin lead films leading to lead oxide and lead hydroxycarbonates and/or lead carbonates probably occurred. The analysis showed that the main response was due to corrosion of the lead film and granules with conversion to lead hydroxyl-carbonates and/or carbonates and formation of lead acetate. In addition, about 30% of the response was found to be due to acetic acid adsorption on the lead glass samples. After about 15 days exposure significant saturation and decrease in sensitivity was observed.

Lead oxide

Lead acetate

Lead (geology)

Lead glass

Deposition

Saturation (graph theory)

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Estefani Marchiori

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