--- OA_place: repository OA_type: free access _id: '21174' abstract: - lang: eng text: UTe2 exhibits the remarkable phenomenon of re-entrant superconductivity, whereby the zero-resistance state reappears above 40 tesla after being suppressed with a field of around 10 tesla. One potential pairing mechanism, invoked in the related re-entrant superconductors UCoGe and URhGe, involves transverse fluctuations of a ferromagnetic order parameter. However, the requisite ferromagnetic order - present in both UCoGe and URhGe - is absent in UTe2, and magnetization measurements show no sign of strong fluctuations. Here, we measure the magnetotropic susceptibility of UTe2 across two field-angle planes. This quantity is sensitive to the magnetic susceptibility in a direction transverse to the applied magnetic field - a quantity that is not accessed in conventional magnetization measurements. We observe a very large decrease in the magnetotropic susceptibility over a broad range of field orientations, indicating a large increase in the transverse magnetic susceptibility. The three superconducting phases of UTe2, including the high-field re-entrant phase, surround this region of enhanced susceptibility in the field-angle phase diagram. The strongest transverse susceptibility is found near the critical end point of the high-field metamagnetic transition, suggesting that quantum critical fluctuations of a field-induced magnetic order parameter may be responsible for the large transverse susceptibility, and may provide a pairing mechanism for field-induced superconductivity in UTe2. acknowledged_ssus: - _id: NanoFab acknowledgement: Thanks to Salvatore Bagiante, Evgeniia Volobueva, Lubuna Shafeek, Ali Bangura and Zoltan Kollo. article_processing_charge: Yes author: - first_name: Kimberly A full_name: Modic, Kimberly A id: 13C26AC0-EB69-11E9-87C6-5F3BE6697425 last_name: Modic orcid: 0000-0001-9760-3147 citation: ama: Modic KA. Research data for “Giant transverse magnetic fluctuations at the edge of re-entrant superconductivity in UTe2.” 2026. doi:10.15479/AT-ISTA-21174 apa: Modic, K. A. (2026). Research data for “Giant transverse magnetic fluctuations at the edge of re-entrant superconductivity in UTe2.” Institute of Science and Technology Austria. https://doi.org/10.15479/AT-ISTA-21174 chicago: Modic, Kimberly A. “Research Data for ‘Giant Transverse Magnetic Fluctuations at the Edge of Re-Entrant Superconductivity in UTe2.’” Institute of Science and Technology Austria, 2026. https://doi.org/10.15479/AT-ISTA-21174. ieee: K. A. Modic, “Research data for ‘Giant transverse magnetic fluctuations at the edge of re-entrant superconductivity in UTe2.’” Institute of Science and Technology Austria, 2026. ista: Modic KA. 2026. Research data for ‘Giant transverse magnetic fluctuations at the edge of re-entrant superconductivity in UTe2’, Institute of Science and Technology Austria, 10.15479/AT-ISTA-21174. mla: Modic, Kimberly A. Research Data for “Giant Transverse Magnetic Fluctuations at the Edge of Re-Entrant Superconductivity in UTe2.” Institute of Science and Technology Austria, 2026, doi:10.15479/AT-ISTA-21174. short: K.A. Modic, (2026). contributor: - contributor_type: project_member first_name: Valeska id: 467ed36b-dc96-11ea-b7c8-b043a380b282 last_name: Zambra orcid: 0000-0002-8806-5719 corr_author: '1' date_created: 2026-02-09T12:04:20Z date_published: 2026-02-19T00:00:00Z date_updated: 2026-05-11T06:35:59Z day: '19' ddc: - '530' department: - _id: KiMo doi: 10.15479/AT-ISTA-21174 file: - access_level: open_access checksum: 53157d908fba663275c2b8dc6ee84fdb content_type: text/plain creator: kmodic date_created: 2026-02-19T07:38:15Z date_updated: 2026-02-19T07:38:15Z file_id: '21332' file_name: README.txt file_size: 1347 relation: main_file success: 1 - access_level: open_access checksum: b2c8ca5620ee9c181a42082068d3d73c content_type: application/zip creator: kmodic date_created: 2026-02-19T07:39:03Z date_updated: 2026-02-19T07:39:03Z file_id: '21333' file_name: processed_data_bc_plane_Fig2d.zip file_size: 534853 relation: main_file success: 1 - access_level: open_access checksum: 976bf113da4b1133313f0b292e71289f content_type: application/zip creator: kmodic date_created: 2026-02-19T07:39:07Z date_updated: 2026-02-19T07:39:07Z file_id: '21334' file_name: processed_data_ac_plane_Fig2c.zip file_size: 427144 relation: main_file success: 1 file_date_updated: 2026-02-19T07:39:07Z has_accepted_license: '1' keyword: - transverse magnetic susceptibility - magnetotropic - superconductivity - magnetic fluctuations license: https://creativecommons.org/licenses/by/4.0/ month: '02' oa: 1 oa_version: Published Version project: - _id: bd968c70-d553-11ed-ba76-cde40b0aba64 grant_number: '101078696' name: Gaining leverage with spin liquids and superconductors publisher: Institute of Science and Technology Austria related_material: link: - relation: preprint url: https://arxiv.org/pdf/2506.08984 record: - id: '21845' relation: used_in_publication status: public status: public title: Research data for "Giant transverse magnetic fluctuations at the edge of re-entrant superconductivity in UTe2" tmp: image: /images/cc_by.png legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0) short: CC BY (4.0) type: research_data user_id: 68b8ca59-c5b3-11ee-8790-cd641c68093d year: '2026' ... --- OA_place: publisher _id: '14547' abstract: - lang: eng text: "Superconductor-semiconductor heterostructures currently capture a significant amount of research interest and they serve as the physical platform in many proposals towards topological quantum computation.\r\nDespite being under extensive investigations, historically using transport techniques, the basic properties of the interface between the superconductor and the semiconductor remain to be understood.\r\n\r\nIn this thesis, two separate studies on the Al-InAs heterostructures are reported with the first focusing on the physics of the material motivated by the emergence of a new phase, the Bogoliubov-Fermi surface. \r\nThe second focuses on a technological application, a gate-tunable Josephson parametric amplifier.\r\n\r\nIn the first study, we investigate the hypothesized unconventional nature of the induced superconductivity at the interface between the Al thin film and the InAs quantum well.\r\nWe embed a two-dimensional Al-InAs hybrid system in a resonant microwave circuit allowing measurements of change in inductance.\r\nThe behaviour of the resonance in a range of temperature and in-plane magnetic field has been studied and compared with the theory of conventional s-wave superconductor and a two-component theory that includes both contribution of the $s$-wave pairing in Al and the intraband $p \\pm ip$ pairing in InAs.\r\nMeasuring the temperature dependence of resonant frequency, no discrepancy is found between data and the conventional theory.\r\nWe observe the breakdown of superconductivity due to an applied magnetic field which contradicts the conventional theory.\r\nIn contrast, the data can be captured quantitatively by fitting to a two-component model.\r\nWe find the evidence of the intraband $p \\pm ip$ pairing in the InAs and the emergence of the Bogoliubov-Fermi surfaces due to magnetic field with the characteristic value $B^* = 0.33~\\mathrm{T}$.\r\nFrom the fits, the sheet resistance of Al, the carrier density and mobility in InAs are determined.\r\nBy systematically studying the anisotropy of the circuit response, we find weak anisotropy for $B < B^*$ and increasingly strong anisotropy for $B > B^*$ resulting in a pronounced two-lobe structure in polar plot of frequency versus field angle.\r\nStrong resemblance between the field dependence of dissipation and superfluid density hints at a hidden signature of the Bogoliubov-Fermi surface that is burried in the dissipation data.\r\n\r\nIn the second study, we realize a parametric amplifier with a Josephson field effect transistor as the active element.\r\nThe device's modest construction consists of a gated SNS weak link embedded at the center of a coplanar waveguide resonator.\r\nBy applying a gate voltage, the resonant frequency is field-effect tunable over a range of 2 GHz.\r\nModelling the JoFET minimally as a parallel RL circuit, the dissipation introduced by the JoFET can be quantitatively related to the gate voltage.\r\nWe observed gate-tunable Kerr nonlinearity qualitatively in line with expectation.\r\nThe JoFET amplifier has 20 dB of gain, 4 MHz of instantaneous bandwidth, and a 1dB compression point of -125.5 dBm when operated at a fixed resonant frequency.\r\nIn general, the signal-to-noise ratio is improved by 5-7 dB when the JoFET amplifier is activated compared.\r\nThe noise of the measurement chain and insertion loss of relevant circuit elements are calibrated to determine the expected and the real noise performance of the JoFET amplifier.\r\nAs a quantification of the noise performance, the measured total input-referred noise of the JoFET amplifier is in good agreement with the estimated expectation which takes device loss into account.\r\nWe found that the noise performance of the device reported in this document approaches one photon of total input-referred added noise which is the quantum limit imposed in nondegenerate parametric amplifier." acknowledged_ssus: - _id: NanoFab - _id: Bio alternative_title: - ISTA Thesis article_processing_charge: No author: - first_name: Duc T full_name: Phan, Duc T id: 29C8C0B4-F248-11E8-B48F-1D18A9856A87 last_name: Phan citation: ama: Phan DT. Resonant microwave spectroscopy of Al-InAs. 2023. doi:10.15479/14547 apa: Phan, D. T. (2023). Resonant microwave spectroscopy of Al-InAs. Institute of Science and Technology Austria. https://doi.org/10.15479/14547 chicago: Phan, Duc T. “Resonant Microwave Spectroscopy of Al-InAs.” Institute of Science and Technology Austria, 2023. https://doi.org/10.15479/14547. ieee: D. T. Phan, “Resonant microwave spectroscopy of Al-InAs,” Institute of Science and Technology Austria, 2023. ista: Phan DT. 2023. Resonant microwave spectroscopy of Al-InAs. Institute of Science and Technology Austria. mla: Phan, Duc T. Resonant Microwave Spectroscopy of Al-InAs. Institute of Science and Technology Austria, 2023, doi:10.15479/14547. short: D.T. Phan, Resonant Microwave Spectroscopy of Al-InAs, Institute of Science and Technology Austria, 2023. corr_author: '1' date_created: 2023-11-17T13:45:26Z date_published: 2023-11-16T00:00:00Z date_updated: 2026-04-07T13:25:52Z day: '16' ddc: - '530' degree_awarded: PhD department: - _id: GradSch - _id: AnHi doi: 10.15479/14547 file: - access_level: open_access checksum: db0c37d213bc002125bd59690e9db246 content_type: application/pdf creator: pduc date_created: 2023-11-17T13:36:44Z date_updated: 2023-11-22T09:46:06Z file_id: '14548' file_name: Phan_Thesis_pdfa.pdf file_size: 34828019 relation: main_file - access_level: closed checksum: 8d3bd6afa279a0078ffd13e06bb6d56d content_type: application/zip creator: pduc date_created: 2023-11-17T13:44:53Z date_updated: 2023-11-17T13:47:54Z file_id: '14549' file_name: dissertation_src.zip file_size: 279319709 relation: source_file file_date_updated: 2023-11-22T09:46:06Z has_accepted_license: '1' keyword: - superconductor-semiconductor - superconductivity - Al - InAs - p-wave - superconductivity - JPA - microwave language: - iso: eng license: https://creativecommons.org/licenses/by-nc-sa/4.0/ month: '11' oa: 1 oa_version: Published Version page: '80' publication_identifier: issn: - 2663-337X publication_status: published publisher: Institute of Science and Technology Austria related_material: record: - id: '13264' relation: part_of_dissertation status: public - id: '10851' relation: part_of_dissertation status: public status: public supervisor: - first_name: Andrew P full_name: Higginbotham, Andrew P id: 4AD6785A-F248-11E8-B48F-1D18A9856A87 last_name: Higginbotham orcid: 0000-0003-2607-2363 title: Resonant microwave spectroscopy of Al-InAs tmp: image: /images/cc_by_nc_sa.png legal_code_url: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode name: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) short: CC BY-NC-SA (4.0) type: dissertation user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd year: '2023' ... --- _id: '10663' abstract: - lang: eng text: 'The superconducting state of matter enables one to observe quantum effects on the macroscopic scale and hosts many fascinating phenomena. Topological defects of the superconducting order parameter, such as vortices and fluxoid states in multiply connected structures, are often the key ingredients of these phenomena. This dissertation describes a new mode of magnetic force microscopy (Φ0-MFM) for investigating vortex and fluxoid sates in mesoscopic superconducting (SC) structures. The technique relies on the magneto-mechanical coupling of a MFM cantilever to the motion of fluxons. The novelty of the technique is that a magnetic particle attached to the cantilever is used not only to sense the state of a SC structure, but also as a primary source of the inhomogeneous magnetic field which induces that state. Φ0-MFM enables us to map the transitions between tip-induced states during a scan: at the positions of the tip, where the two lowest energy states become degenerate, small oscillations of the tip drive the transitions between these states, which causes a significant shift in the resonant frequency and dissipation of the cantilever. For narrow-wall aluminum rings, the mapped fluxoid transitions form concentric contours on a scan. We show that the changes in the cantilever resonant frequency and dissipation are well-described by a stochastic resonance (SR) of cantilever-driven thermally activated phase slips (TAPS). The SR model allows us to experimentally determine the rate of TAPS and compare it to the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory for TAPS in 1D superconducting structures. Further, we use the SR model to qualitatively study the effects of a locally applied magnetic field on the phase slip rate in rings containing constrictions. The states with multiple vortices or winding numbers could be useful for the development of novel superconducting devices, or the study of vortex interactions and interference effects. Using Φ0-MFM allows us to induce, probe and control fluxoid states in thin wall structures comprised of multiple loops. We show that Φ0-MFM images of the fluxoid transitions allow us to identify the underlying states and to investigate their energetics and dynamics even in complicated structures.' alternative_title: - Graduate Dissertations and Theses at Illinois article_processing_charge: No author: - first_name: Hryhoriy full_name: Polshyn, Hryhoriy id: edfc7cb1-526e-11ec-b05a-e6ecc27e4e48 last_name: Polshyn orcid: 0000-0001-8223-8896 citation: ama: Polshyn H. Magnetic force microscopy studies of mesoscopic superconducting structures. 2017. apa: Polshyn, H. (2017). Magnetic force microscopy studies of mesoscopic superconducting structures. University of Illinois at Urbana-Champaign. chicago: Polshyn, Hryhoriy. “Magnetic Force Microscopy Studies of Mesoscopic Superconducting Structures.” University of Illinois at Urbana-Champaign, 2017. ieee: H. Polshyn, “Magnetic force microscopy studies of mesoscopic superconducting structures,” University of Illinois at Urbana-Champaign, 2017. ista: Polshyn H. 2017. Magnetic force microscopy studies of mesoscopic superconducting structures. University of Illinois at Urbana-Champaign. mla: Polshyn, Hryhoriy. Magnetic Force Microscopy Studies of Mesoscopic Superconducting Structures. University of Illinois at Urbana-Champaign, 2017. short: H. Polshyn, Magnetic Force Microscopy Studies of Mesoscopic Superconducting Structures, University of Illinois at Urbana-Champaign, 2017. date_created: 2022-01-25T14:54:14Z date_published: 2017-09-18T00:00:00Z date_updated: 2024-10-14T11:13:43Z day: '18' degree_awarded: PhD extern: '1' keyword: - physics - superconductivity - magnetic force microscopy - phase slips language: - iso: eng main_file_link: - open_access: '1' url: http://hdl.handle.net/2142/99178 month: '09' oa: 1 oa_version: Published Version page: '103' publication_status: published publisher: University of Illinois at Urbana-Champaign status: public supervisor: - first_name: Raffi full_name: Budakian, Raffi last_name: Budakian title: Magnetic force microscopy studies of mesoscopic superconducting structures type: dissertation user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87 year: '2017' ...