Research Interests

Mesoscale and Nanoscale Physics
Ballistic conduction & transport of electrons, quantum Hall effect, spin-orbit interactions, 2DEG, graphene, nanofabrication.
Strongly correlated electrons
Heavy fermions, topological insulators, Berry phase, Moiré superlattices, metal-insulator transitions.
Low temperature physics
Superconductivity, superfluidity, phonons at low temperatures, cryogenics, operation of a dilution refrigerator.

Main skills

Solid State Physics & Chemistry and Applications
  • Cryogenics, dilution refrigerator, magnetoresistance measurements
  • Lock-in measurements, signal processing & filtering
  • Nanofabrication, graphene & 2D materials devices
  • Electron microscopy, synchrotron X-ray techniques, X-ray diffraction, X-ray photoemission spectroscopy, IR spectroscopy
  • Theory of scattering + diffraction, in-depth understanding of waves crystalline materials + quantum phenomena.
  • Showcase results, content marketing, public relations


Ph.D. in Physics Manchester, UK. grad. exp. 2022.
  • School of Physics and Astronomy, The University of Manchester
  • Van der Waals Heterostructures using combinations of graphene, and other 2D materials
  • Supervisor: Pr Andre K. Geim;
  • Scholarship: G1,
  • Awards: A1, A2
  • Publications: J1, J2, J3,C1,C2, C3
  • Talks: T1,T2, T3,T4,T5, T6.
Visiting student Researcher Menlo Park, CA, USA. 2018.
  • SLAC National Accelerator Laboratory
  • Understand the origin of octahedral tilt in hybrid perovskites
  • Advisor: Dr Michael F. Toney
  • Grant: G2,
  • Publications: U1, J4, C4, C5,
  • Talk: T7.
M.Sc. in Chemical Physics Paris, France. grad. 2018
  • ESPCI Paris: École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris
  • Diplôme d'ingénieur
B.Sc. in Physics Paris, France. grad. 2016
  • Sorbonne Université - Université Pierre-et-Marie-Curie
  • Minor: Chemistry


Tutor Manchester, UK. 2020-2021
  • Department of Physics & Astronomy, School of Natural Sciences, The University of Manchester
  • 2nd-year Tutorials in Quantum Mechanics, Electromagnetism and waves
  • Provide student pastoral support per group of 5
  • Marking of assignments
  • 2 hours per week
Graduate Teaching Assistant Manchester, UK. 2018-2019
& 2019-2020 & 2020-2021
  • Department of Physics & Astronomy, School of Natural Sciences, The University of Manchester.
  • Introduction to Programming for Physicists:
  • 2nd year undergraduate (Python & C++ in 2018-2019, Python & numerical methods in 2019-2020)
  • Assessed and advised students
  • Marking of assignments
  • 7 hours per week
  • Condensed Matter Physics labs:
  • 3rd year undergraduate (AFM, STM, NMR, Spin Echo, Hall effect, Schockley-Haynes experiment, graphene characterisation, particle detector, 2020-2021)
  • Assessed and advised students
  • 7 hours per week
Graduate Teaching Assistant Paris, France. 2016-2017
  • Mathematics (Algebra & Analysis)
  • Lycée Saint Louis, 1st year undergraduate
  • Prepared students attending “Classes Préparatoires aux Grandes Écoles” for the Mathematics oral exam to the French Grandes Écoles for scientific studies.
  • Provided pastoral support per group of 3
  • Assessed
  • 2 hours per week

Leadership and activities

Cohort Representative 2018-.
  • ESPCI Alumni Association
  • Organisation of the graduation ceremony and party.
  • Census of the graduates.
  • Organise cohort meetups (ski weekend, weekend in Normandy, etc.)
  • Relay ESPCI Alumni Association's mutual aid in the class of 2018.
  • Promote ESPCI Alumni's events.
Communications and Public Relations Officer 2016.
  • ESPCI Student's Sport Union
  • Set up communications and growth strategy.
  • Designed visual identity.
  • Mapped out, promoted and implemented the communications framework & platforms strategy.
  • Managed digital communications channels.
  • Designed and fundraised for the sport jerseys.
  • Negociated sponsorships.
  • Managed public & press relations.
  • Results: ×3 growth in membership, ×4 growth in sponsorship revenues.
Communications Officer 2009-2012.
  • Jappix, web-based communication platform
  • Co-founded the open-source program.
  • Managed UI design.
  • Developped a communications and marketing strategy.
  • Results: 100k+ downloads, 50k+ users on
Event organisation
  • ESPCI Gala Dinner, 2018, Communications Officer.
  • ESPCI Gala Dinner, 2016, Vice President.
  • Journée de l'Informatique Libre (Free Software Day) 2011, Conference Program committee officer.

Professional Experience

R&D Intern Lyons + Chambéry, France. 2017
  • Synthesised + characterised nanocharged acrylic adhesives for the encapsulation of optoelectronic devices.
  • Enhanced the barrier properties towads gases and water with proper dispersion of nanocharges.
  • Carried out compatibility tests of the produced adhesives to Organic and Perovskite Solar Cells.
  • Synthesised solgel zirconium phosphate nanoplatelets, and functionnalised their surfaces.
  • Advisors: Dr Stéphane Cros (CEA), Dr Frédéric Chaput (ENS) and Dr Manuel Hidalgo (Arkema)
  • Talks: T8, T9.


Preprints, currently under review
  1. J. Barrier, R. E. Beal, A. Gold-Parker, J. A. Vigil, E. Wolf, L. Waquier, N. J. Weadock, Z. Zhang, L. T. Schelhas, A. F. Nogueira, M. D. McGehee, and M. F. Toney, Heterogeneity in Cs1-yFayPb(I1-xBrx)3 Perovskite Films, Preprint Available upon Request (2021).
      author = {Barrier, Julien and Beal, Rachel E and Gold-Parker, Aryeh and Vigil, Julian A and Wolf, Eli and Waquier, Louis and Weadock, Nicholas J and Zhang, Zihan and Schelhas, Laura T and Nogueira, Ana Flávia and McGehee, Michael D and Toney, Michael F},
      title = {Heterogeneity in Cs1-yFayPb(I1-xBrx)3 Perovskite Films},
      year = {2021},
      journal = {preprint available upon request}
Peer-reviewed papers
  1. S. Xu, M. M. Al Ezzi, N. Balakrishnan, A. Garcia-Ruiz, B. Tsim, C. Mullan, J. Barrier, N. Xin, B. A. Piot, T. Taniguchi, K. Watanabe, A. Carvalho, A. Mishchenko, A. K. Geim, V. I. Fal’ko, S. Adam, A. H. Castro Neto, K. S. Novoselov, and Y. Shi, Tuneable Van Hove Singularities and Correlated States in Twisted Monolayer-Bilayer Graphene, Nature Physics (2021). [arXiv:2004.15040] [DOI]
      author = {Xu, Shuigang and Al Ezzi, Mohammed M. and Balakrishnan, Nilanthy and Garcia-Ruiz, Aitor and Tsim, Bonnie and Mullan, Ciaran and Barrier, Julien and Xin, Na and Piot, Benjamin A. and Taniguchi, Takashi and Watanabe, Kenji and Carvalho, Alexandra and Mishchenko, Artem and Geim, Andre K. and Fal'ko, Vladimir I. and Adam, Shaffique and Castro Neto, Antonio Helio and Novoselov, Kostya S. and Shi, Yanmeng},
      title = {Tuneable van Hove Singularities and Correlated States in Twisted Monolayer-Bilayer Graphene},
      journal = {Nature Physics},
      year = {2021},
      arxiv = {2004.15040},
      doi = {10.1038/s41567-021-01172-9}
  2. J. Barrier, P. Kumaravadivel, R. Krishna-Kumar, L. A. Ponomarenko, N. Xin, M. Holwill, C. Mullan, M. Kim, R. V. Gorbachev, M. D. Thompson, J. R. Prance, T. Taniguchi, K. Watanabe, I. V. Grigorieva, K. S. Novoselov, A. Mishchenko, V. I. Fal’ko, A. I. Berdyugin, and A. K. Geim, Long-Range Ballistic Transport of Brown-Zak Fermions in Graphene Superlattices, Nature Communications 11, 5756 (2020). [arXiv:2006.15040] [DOI] [PDF] [SI]
      title = {Long-range ballistic transport of Brown-Zak fermions in graphene superlattices},
      author = {Barrier, Julien and Kumaravadivel, Piranavan and Krishna-Kumar, Roshan and Ponomarenko, Leonid A. and Xin, Na and Holwill, Matthew and Mullan, Ciaran and Kim, Minsoo and Gorbachev, Roman V. and Thompson, Michael D. and Prance, Jonathan R. and Taniguchi, Takashi and Watanabe, Kenji and Grigorieva, Irina V. and Novoselov, Kostya S. and Mishchenko, Artem and Fal'ko, Vladimir I. and Berdyugin, Alexey I. and Geim, Andre K.},
      journal = {Nature communications},
      volume = {11},
      pages = {5756},
      year = {2020},
      publisher = {Nature Publishing Group},
      doi = {10.1038/s41467-020-19604-0},
      arxiv = {2006.15040}
  3. Y. Shi, S. Xu, Y. Yang, S. Slizovskiy, S. V. Morozov, S.-K. Son, S. Ozdemir, C. Mullan, J. Barrier, J. Yin, A. I. Berdyugin, B. A. Piot, T. Taniguchi, K. Watanabe, V. I. Fal’ko, K. S. Novoselov, A. K. G. Geim, and A. Mishchenko, Electronic Phase Separation in Multilayer Rhombohedral Graphite, Nature 584, 210 (2020). [arXiv:1911.04565] [DOI]
      title = {Electronic phase separation in multilayer rhombohedral graphite},
      author = {Shi, Yanmeng and Xu, Shuigang and Yang, Yaping and Slizovskiy, Sergey and Morozov, Sergei V. and Son, Seok-Kyun and Ozdemir, Servet and Mullan, Ciaran and Barrier, Julien and Yin, Jun and Berdyugin, Alexei I. and Piot, Benjamin A. and Taniguchi, Takashi and Watanabe, Kenji and Fal'ko, Vladimir I. and Novoselov, Kostya S. and Geim, Andre K. Geim and Mishchenko, Artem},
      journal = {Nature},
      volume = {584},
      pages = {210--214},
      year = {2020},
      publisher = {Nature Publishing Group},
      doi = {10.1038/s41586-020-2568-2},
      arxiv = {1911.04565}
  4. R. E. Beal, N. Z. Hagström, J. Barrier, A. Gold-Parker, R. Prasanna, K. A. Bush, D. Passarello, L. T. Schelhas, K. Brüning, C. J. Tassone, H.-G. Steinrück, M. D. McGehee, M. F. Toney, and A. F. Nogueira, Structural Origins of Light-Induced Phase Segregation In Organic-Inorganic Halide Perovskite Photovoltaic Materials, Matter 2, 207 (2020). [DOI]
      title = {Structural origins of light-induced phase segregation in
          organic-inorganic halide perovskite photovoltaic materials},
      author = {Beal, Rachel E. and Hagström, Nanna Zhou and Barrier, Julien and Gold-Parker, Aryeh and Prasanna, Rohit and Bush, Kevin A. and Passarello, Donata and Schelhas, Laura T. and Brüning, Karsten and Tassone, Christopher J. and Steinrück, Hans-Georg and McGehee, Michael D. and Toney, Michael F. and Nogueira, Ana Flávia},
      journal = {Matter},
      volume = {2},
      issue = {1},
      pages = {207-219},
      year = {2020},
      doi = {10.1016/j.matt.2019.11.001}
Peer-reviewed conference abstracts
  1. J. Barrier, A. I. Berdyugin, P. Kumaravadivel, V. I. Fal’ko, and A. K. Geim, Long-Range Ballistic Transport of Brown-Zak Fermions in Graphene Superlattices, in Bulletin of the American Physical Society (APS March, Online, 2021). [url]
  2. J. Barrier, A. I. Berdyugin, P. Kumaravadivel, V. I. Fal’ko, and A. K. Geim, Ballistic Transport in the Magnetic Bloch States of Graphene Superlattices, in Graphene Conference (Grenoble, France, 2020). Best Talk Prize. [url]
  3. J. Barrier, A. I. Berdyugin, P. Kumaravadivel, T. Taniguchi, K. Watanabe, V. I. Fal’ko, and A. K. Geim, Direct Observation of Brown-Zak Mini-Bands in Graphene Superlattices, in Graphene Week, Graphene Flagship (Helsinki, Finland, 2019).
  4. M. F. Toney, R. E. Beal, J. Barrier, H.-G. Steinrück, M. D. McGehee, and A. F. Nogueira, Structural and Mechanistic Origins of Light-Induced Phase Segregation in Organic- Inorganic Halide Perovskite Photovoltaic Materials, in RSC MC 14 (Birmingham, UK, 2019).
  5. J. Barrier, A. Gold-Parker, E. Wolf, R. E. Beal, M. D. McGehee, and M. F. Toney, Tetragonal to Cubic Phase Transition In FA1-xCsxPb(I1-yBry)3: Temperature Dependance and Impact on Band Gap, in MRS Fall (Boston, MA, USA, 2018). [url]

Workshops & Schools

  1. Participation in Graphene for research, Innovation, Collaboration, Graphene Flaship, 22-24 September 2020;
  2. Moiré in Paris, Laboratoire de Physique, ENS Paris, PSL Research University, 3-4 June 2019;
  3. UC Mesoscale Summer School, University of California at Irvine, CA, USA. August 2018.

Grants, Awards & Scholarships

  1. Best student talk October 2020
    Graphene Conference 2020
  2. Ingénieur du futur dans la catégorie Recherche (Engineer of the future in research) December 2019
    L'Usine Nouvelle, UTC & Sorbonne Université
Grants & Scholarships
  1. Doctoral Training Partnership Bursary September 2018
    (wrote the proposal)
  2. Mobility Scholarship for Visiting Student Researcher at SLAC March 2018
    Fonds ESPCI Paris
    (wrote the proposal)

Invited Talks

  1. Ballistic transport of Brown-Zak fermions, Low Temperature Physics group, Lancaster University, 11 September 2020;
  2. Ultra-low temperatures properties of Brown-Zak fermions and degeneracy lifting, Oxford Instruments Nanoscience Virtual Roadshow, 13 July 2020;
  3. Unravelling properties of Brown-Zak fermions at ultra-low temperatures, Oxford Instruments Nanoscience Virtual Roadshow, 2 July 2020;
  4. Ballistic transport in the magnetic Bloch states of graphene superlattices, National Graphene Institute, Manchester, 17 April 2020;
  5. Novel quantum phenomena in graphene, Trophée des Ingénieurs du Futur, Paris, 3 December 2019;
  6. Quantum electrons to the naked eye, Pint of Science, Manchester, 21 May 2019;
  7. Phase transition in mixed halide perovskites, impact on band-gap, Stanford Synchrotron Radiation Lightsource, Menlo Park, 24 August 2018;
  8. Encapsulation of flexible electronic devices, Laboratoire de Chimie - ENS de Lyon, Lyons, 22 December 2018;
  9. Gas barrier adhesives for encapsulation of organic and perovskite solar cells, LMPO CEA Liten, Chambéry, 19 December 2017;
  10. Jappix, free social network, Université de Genève, Geneva, 10 July 2012;
  11. Le web social, ISEN, Toulon, 28 April 2012;
  12. Réseaux sociaux libres, Unistra, Strasbourg, 12 July 2011;
  13. Jappix, réseau social libre, FOL83, Toulon, 15 January 2011;
  14. Jappix, un micro-réseau social libre, Polytech Nice, Sophia-Antipolis, 27 November 2010;
  15. Jappix, ENSEIRB, Bordeaux, 9 July 2010.


  • New family of quasiparticles appears in graphene, 30 November 2020. Reported by Isabelle Dumé, Physics World. U.K.
  • Graphene researchers throw physics out the window, 16 November 2020. Reported by Sarah Lawton, Laboratory News. U.K.
  • Poursuivre sa thèse confiné(e), issue 59, September 2020. Reported by Lilia Bouraoui, 10 rue V@uquelin - Le bulletin d'ESPCI Alumni. France.
  • Thophée des ingénieurs du futur : lauréats et nommés dans la catégorie Recherche, 23 December 2019. Reported by Manuel Moragues, Industrie & Technologies. France.
  • Julien Barrier, l'électron libre, 5 December 2019. Reported by Olivier James, L'Usine Nouvelle. France.
  • Découvrez le monde le l’informatique libre. 27 April 2012. Reported by Myriam Tricocci Robert, Metro Toulon. France.
  • Informatique : la liberté à portée de clic. 14 January 2011. Reported by Thierry Turpin, La Marseillaise. France.
  • Actualités locales, 31 August 2010. Reported by Jacky Laurent, Var Matin La Seyne-sur-Mer. France.
  • Cyber Culture. 27 Septembre 2014, 2:00 PM, Radio Ici & Maintenant FM 95.2 MHz, Paris, France. Produced by Olivier Piquepé. 3h30’.
  • Jappix. La Voix du Libre, 13 July 2011, 9:30 AM, Radio RMLL (web), Québec, Canada. Produced by Yannick Pavard. 19’.
  • Morning News, 10 January 2010, 7:30 AM, France Bleu Provence FM 109.2 MHz, Toulon, France. 4’
  • A research story: advancing mesoscopic physics 27 November 2020. Reported by Sarah Lawton. Laboratory News. U.K.
  • “Nous voulons garantir les libertés des utilisateurs.” 29 April 2012. Reported by David Latour. Var Matin Toulon. France.
  • Jappix, interview de Julien Barrier Dossier spécial Tchat, web & messagerie, October 2010. Reported by Aline Hof. Linux Pratique Essentiel. Issue 16. pages 5–7. France.


  • Born in January 1994 in Paris, France.
  • Hobbies comprise sailing, skiing, hiking, bike riding & cooking.
  • Current address:
    National Graphene Institute, office 1.006
    The University of Manchester
    Manchester M13 9PL, UK.