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Field induced states in the quantum limit of graphite - Benoit Fauqué

ESPCI et Collège de France

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When a magnetic field confines the carriers of a Fermi sea to their lowest Landau level, electron-electron interactions are expected to play a significant role in determining the electronic ground state. Graphite is known to host a sequence of field-induced states driven by such interactions [1]. Three decades after their discovery, thermodynamic signatures of these instabilities are still elusive. Here, we report the first detection of these transitions with sound velocity. We find that the phase transition occurs in the vicinity of a magnetic field at which at least one of the Landau level crosses the Fermi energy. The evolution of elastic constant anomalies with temperature and magnetic field allows to draw a complete phase diagram that shows that the ground state evolve in a sequence of 2nd order and first order thermodynamic phase transitions . Our thermodynamic analysis concludes that electron-electron interaction is not the sole driving force of these transitions and the lattice degree of freedom plays an unanticipated important role [2].

[1] B. Fauqué and al., Phys. Rev. Lett. 110, 266601 (2013)
[2] D. Le Boeuf and al., Nat Com, 8, 1337 (2017)


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