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Atomic and Laser Physics
Credit: Jack Hobhouse

Andrea Cavalleri

Professor of Physics

Sub department

  • Atomic and Laser Physics
andrea.cavalleri@physics.ox.ac.uk
Telephone: 01865 (2)72365
Clarendon Laboratory, room 316.3
  • About
  • Publications

Generation of ultrafast magnetic steps for coherent control

Nature Photonics Springer Nature (2025) 1-6

Authors:

G De Vecchi, G Jotzu, M Buzzi, S Fava, T Gebert, M Fechner, AV Kimel, A Cavalleri
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Metastable photo-induced superconductivity far above T c

npj Quantum Materials Nature Research 10:1 (2025) 34

Authors:

Sambuddha Chattopadhyay, Christian J Eckhardt, Dante M Kennes, Michael A Sentef, Dongbin Shin, Angel Rubio, Andrea Cavalleri, Eugene A Demler, Marios H Michael

Abstract:

Inspired by the striking discovery of metastable superconductivity in K3C60 at 100K, far above Tc = 20 K, we discuss possible mechanisms for long-lived, photo-induced superconductivity. Starting from a model of optically-driven Raman phonons coupled to inter-band electronic transitions, we develop a microscopic mechanism for photo-controlling the pairing interaction. Leveraging this mechanism, we first investigate long-lived superconductivity arising from the thermodynamic metastable trapping of the driven phonon. We then propose an alternative route, where the superconducting gap created by an optical drive leads to a dynamical bottleneck in the equilibration of quasi-particles. We conclude by discussing the implications of both scenarios for experiments that can be used to discriminate between them. Our work provides falsifiable explanations for the nanosecond-scale photo-induced superconductivity found in K3C60, while simultaneously offering a theoretical basis for exploring metastable superconductivity in other quantum materials.
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Probing optically driven K<sub>3</sub>C<sub>60</sub> thin films with an ultrafast voltmeter.

Structural dynamics (Melville, N.Y.) 12:2 (2025) 024503

Authors:

JD Adelinia, E Wang, M Chavez-Cervantes, T Matsuyama, M Fechner, M Buzzi, G Meier, A Cavalleri

Abstract:

Optically enhanced superconductivity in K3C60 is supported by transient optical spectra, by pressure responses, and by ultrafast nonlinear transport measurements. However, the underlying physics and in fact the similarity or dissimilarity to most properties of equilibrium superconductivity are not clear. In this paper, we study the ultrafast voltage response of optically driven K3C60 thin films. Photo-conductive switches are used to measure changes in voltage as a function of time after irradiation, both below and above Tc. These measurements can be understood if one considers the role of granularity in the photo-induced transport response. They reveal fast voltage changes associated with the kinetic inductance of the in-grain carriers and a slower response that may be attributed to Josephson dynamics at the weak links. Fits to the data yield estimates of the in-grain photo-induced superfluid density after the drive and the dynamics of phase slips at the weak links. This work underscores the increasing ability to make electrical measurements at ultrafast speeds in optically driven quantum materials and demonstrates a striking new platform for optoelectronic device applications.
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Photo-induced chirality in a nonchiral crystal

Science American Association for the Advancement of Science 387:6732 (2025) 431-436

Authors:

Z Zeng, M Först, M Fechner, M Buzzi, Eb Amuah, C Putzke, Pjw Moll, D Prabhakaran, Pg Radaelli, A Cavalleri

Abstract:

Chirality, a pervasive form of symmetry, is intimately connected to the physical properties of solids, as well as the chemical and biological activity of molecular systems. However, inducing chirality in a nonchiral material is challenging because this requires that all mirrors and all roto-inversions be simultaneously broken. Here, we show that chirality of either handedness can be induced in the nonchiral piezoelectric material boron phosphate (BPO4) by irradiation with terahertz pulses. Resonant excitation of either one of two orthogonal, degenerate vibrational modes determines the sign of the induced chiral order parameter. The optical activity of the photo-induced phases is comparable to the static value of prototypical chiral α-quartz. Our findings offer new prospects for the control of out-of-equilibrium quantum phenomena in complex materials.

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Observation of polarization density waves in SrTiO3

Nature Physics (2025)

Authors:

G Orenstein, V Krapivin, Y Huang, Z Zhang, G de la Peña Muñoz, RA Duncan, Q Nguyen, J Stanton, S Teitelbaum, H Yavas, T Sato, MC Hoffmann, P Kramer, J Zhang, A Cavalleri, R Comin, MPM Dean, AS Disa, M Först, SL Johnson, M Mitrano, AM Rappe, D Reis, D Zhu, KA Nelson, M Trigo

Abstract:

The nature of the incipient ferroelectric transition in SrTiO3 has been a long-standing puzzle in condensed matter physics. One explanation involves the competition between ferroelectricity and an instability characterized by the mesoscopic modulation of the polarization. These polarization density waves, which should intensify near the quantum critical point, break local inversion symmetry and are difficult to characterize with conventional X-ray scattering methods. Here we probe inversion symmetry breaking at finite momenta and visualize the instability of the polarization at the nanometre scale in SrTiO3 by combining a femtosecond X-ray free-electron laser with terahertz coherent control methods. We found polar-acoustic collective modes that are soft, particularly at the tens of nanometre scale. These precursor collective excitations provide evidence for the conjectured mesoscopic-modulated phase in SrTiO3.
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