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Upper limit on magnetic field expulsion in optically driven $K_{3} C_{60}$

G. De Vecchi ^1,*, M. Buzzi ^1,*,†, G. Jotzu ^1,*, S. Fava ¹, T. Gebert ¹, G. Magnani ², D. Pontiroli ², M. Riccò ², and A. Cavalleri ^1,3,‡

¹Max Planck Institute for the Structure and Dynamics of Matter, 22761 Hamburg, Germany
²Dipartimento di Scienze Matematiche, Fisiche e Informatiche, Università degli Studi di Parma, 43121 Parma, Italy
³Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, United Kingdom

^*These authors contributed equally to this work.
^†Contact author: michele.buzzi@mpsd.mpg.de
^‡Contact author: andrea.cavalleri@mpsd.mpg.de

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Phys. Rev. Research 7, 043270 – Published 9 December, 2025

DOI: https://doi.org/10.1103/21g5-x5bj

Abstract

Photoexcited $K_{3} C_{60}$ displays several properties reminiscent of equilibrium superconductivity, including transient optical spectra, pressure dependence, and $I$ – $V$ characteristics. However, these observations do not decisively establish nonequilibrium superconductivity, which may be further evidenced by transient magnetic field expulsion measurements, as shown recently in driven $YB a_{2} C u_{3} O_{6.48}$ . Here, we search for transient magnetic field expulsion in $K_{3} C_{60}$ by measuring Faraday rotation in a magneto-optic material placed in its vicinity. Unlike in the case of $YB a_{2} C u_{3} O_{6.48}$ , inhomogeneous, metallic $K_{3} C_{60}$ powders reduce the size of the effect. With the ∼50 nT magnetic field resolution achieved in our experiments, we provide an upper limit for the photoinduced diamagnetic volume susceptibility ( $χ_{v} > - 0 . 1$ ). On this basis, we conclude that the photoinduced phase has weaker magnetic susceptibility than superconducting $K_{3} C_{60}$ at zero temperature. Yet, from recent nonlinear transport measurements in this granular material, we expect a light-induced state similar to the equilibrium superconductor near $0.8 T_{c}$ , for which $χ_{v} > - 0 . 1$ . A definitive conclusion on the presence or absence of Meissner diamagnetism cannot be made for $K_{3} C_{60}$ with the current resolution.

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Phys. Rev. Research 7, 043270– Published 9 December, 2025

Vol. 7, Iss. 4 — December - December 2025

Received 27 February 2025
Accepted 8 October 2025

DOI: https://doi.org/10.1103/21g5-x5bj

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by Max Planck Society.

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Upper limit on magnetic field expulsion in optically driven $K_{3} C_{60}$

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Upper limit on magnetic field expulsion in optically driven K3C60

Abstract

Physics Subject Headings (PhySH)

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Supplemental Material

References (37)

Upper limit on magnetic field expulsion in optically driven $K_{3} C_{60}$