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Theses

Charge instabilities, Mott transition and transport in Hund metals

Abstract : Strongly correlated electron systems represent one of the most active research fields in condensed matter physics, exhibiting intriguing phenomena like unconventional superconductivity and anomalous transport. In this thesis we theoretically analyze the multi-orbital Hund metals, using Slave Spins Mean-Field (SSMF) and Dynamical Mean-Field Theory (DMFT).We study the emergence of a charge instability towards phase separation/charge-density wave, signalled by a diverging electronic compressibility, in doped multi-orbital Mott insulators for a finite "Hund's" intra-atomic exchange coupling. The effect is enhanced once the local spin or orbital symmetry is broken by e.g. a crystal field splitting and is understood in terms of energetics. The results are in agreement with realistic studies of iron-based superconductors.We also connect the first order of the Mott metal-insulator transition found in the Hund metals at half-filling to the coexistence of two metallic solutions away from half-filling, giving rise to the charge instability zone which at zero temperature ends in a quantum critical point (QCP). Using perturbation theory we analytically describe this physics within Landau's theory of phase transitions. We single out a small energy scale (here the Hund’s coupling) splitting a degenerate atomic ground state as the ultimate cause of this phenomenology.We finally adapt the Exact Diagonalization algorithm for solving the DMFT equations to the calculation of transport properties, to an accuracy comparable in some cases to the more accurate but numerically heavier Numerical Renormalization Group solver. We then apply our method on different multi-orbital systems and study their resistivity.
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Submitted on : Thursday, October 21, 2021 - 3:24:12 PM
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  • HAL Id : tel-03391043, version 1

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Maria Chatzieleftheriou. Charge instabilities, Mott transition and transport in Hund metals. Physics [physics]. Université Paris sciences et lettres, 2021. English. ⟨NNT : 2021UPSLS056⟩. ⟨tel-03391043⟩

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