Étude en transport de la phase pseudogap des cuprates supraconducteurs : point critique, limite Planckienne et transformation de la surface de Fermi

Abstract : Despite thirty years of intense research on cuprates, the origin of the electronic pairing in the superconducting state of these materials remains a mystery. Probably linked to this pairing, we find in their (T, doping) diagram the enigmatic pseudogap phase, responsible for a great number of exotic properties in the normal state. The debate about the nature of this phase in the hole-doped cuprates motivated the experimental work presented here. More specifically, we are interested in the T = 0 critical point p*. In order to study this region of the phase diagram, we work, on one hand, on obtaining single crystals of overdoped cuprates and, on the other hand, on transport measurements in several cuprates, either in little-studied compounds near p*, or by using new probes to study the pseudogap. We grow single crystals of HgBa ₂CuO₄₊δ with a self-flux technique, then modify the doping of these crystals along with Bi₂Sr₂CaCu₂O₈₊δ crystals thanks to thermal treatments under controlled atmosphere. The first transport study focus on the T-linear resistivity at T → 0, characteristic of a strange metal, at p ≥ p*. We measure the resistivity in high magnetic field of a Bi2212 sample at p ≥ p*, revealing again this phenomenon. We study the slope of this resistivity and compare it in different hole-doped and electron-doped cuprates, highlighting that the diffusion rate corresponds to the Planckian limit (ħ/τ = kBT) in cuprates. The second study focus on the Fermi surface transformation across p*. We establish for the first time the angle-dependent magnetoresistance across p*, in La₁.₆-ₓNd₀.₄SrₓCuO₄ in high magnetic field, which should lead eventually to new information about the transformation of the Fermi surface. The third study focus on the nature of the pseudogap phase at p ≤ p*, down to low dopings. A study of the Hall effect in a large doping range (down to p = 0) and in four different cuprates allows us to unveil a new signature of the pseudogap, involving magnetism.
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Anaëlle Legros. Étude en transport de la phase pseudogap des cuprates supraconducteurs : point critique, limite Planckienne et transformation de la surface de Fermi. Supraconductivité [cond-mat.supr-con]. Université Paris-Saclay; Université de Sherbrooke (Québec, Canada), 2018. Français. ⟨NNT : 2018SACLS482⟩. ⟨tel-02020139⟩

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