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Point critique quantique de la phase pseudogap dans les cuprates supraconducteurs

Abstract : This experimental PhD thesis explores the properties of the pseudogap critical point in the phase diagram of superconducting cuprates. In a first part, I present a state of the art on the knowledge of the temperature-doping (T-p) phase diagram of these systems. Recent studies show a dramatic drop in the electronic carrier density near the critical point, suggesting a Fermi surface reconstruction. To understand the exact nature of the phase transition related to this reconstruction, I performed complementary high magnetic field measurements of thermal transport and specific heat on La1.8-xSrxEu0.2CuO4 and La1.6-xSrxNd0.4CuO4 cuprates.In a second part, after a theoretical introduction on specific heat and thermal transport, I detail how these two quantities were measured. In particular, an original technique for measuring specific heat has been developed to combine high resolution and absolute accuracy in high magnetic field and low temperature. Different thermal and electronic models have been developed to understand and analyze the measurements in order to optimize the different set-ups according to the temperature range.In a third part, I present the results obtained in thermal transport and specific heat. Thermal transport confirms the drop in carrier density in the normal state (without superconductivity) of cuprates, already observed in high magnetic field electrical transport. Moreover, this drop also exists within the superconducting phase (in zero magnetic field), showing that it is neither influenced by the presence of superconductivity nor by the magnetic field. In the normal state, the Wiedemann-Franz low is satisfied, proving the metallic character of the pseudogap phase.Electronic specific heat shows non-classical behavior in the vicinity of the critical point. This abnormal behavior is characterized by a logarithmic dependence as a function of temperature at the critical doping p *, corresponding to the drop in the carrier density. Moreover, these measurements suggest a divergence of the effective mass at p * as a function of doping. These two observations are the signature of a quantum critical point located at T = 0 and p = p *, whose origin is discussed in the last part. I discuss the possible universality classes, and I compare with others compounds (heavy fermions, pnictides) which present a quantum critical point.
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Submitted on : Tuesday, January 30, 2018 - 12:25:11 PM
Last modification on : Friday, October 9, 2020 - 3:00:19 AM


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  • HAL Id : tel-01696340, version 1




Bastien Michon. Point critique quantique de la phase pseudogap dans les cuprates supraconducteurs. Supraconductivité [cond-mat.supr-con]. Université Grenoble Alpes; Université de Sherbrooke (Québec, Canada), 2017. Français. ⟨NNT : 2017GREAY031⟩. ⟨tel-01696340⟩



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