Thermopower across the phase diagram of the cuprate La1.6−xNd0.4SrxCuO4 : signatures of the pseudogap and charge-density-wave phases

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Collignon, Clément
Ataei, Amirreza
Gourgout, Adrien
Badoux, Sven
Lizaire, Maude
Legros, Anaelle
Licciardello, Salvatore
Wiedmann, Steffan
Yan, Jiaqiang
Zhou, Jie

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The Seebeck coefficient (thermopower) S of the cuprate superconductor La1.6−xNd0.4SrxCuO4 was measured across its doping phase diagram (from p = 0.12 to p = 0.25), at various temperatures down to T ≃ 2 K, in the normal state accessed by suppressing superconductivity with a magnetic field up to H = 37.5 T. The magnitude of S/T in the T = 0 limit is found to suddenly increase, by a factor ≃ 5, when the doping is reduced below p

⋆ = 0.23, the critical doping for the onset of the pseudogap phase. This confirms that the pseudogap phase causes a large reduction of the carrier density n, consistent with a drop from n = 1 + p above p

⋆ to n = p below p⋆, as previously inferred from measurements of the Hall coefficient, resistivity and thermal conductivity. When the doping is reduced below p = 0.19, a qualitative change is observed whereby S/T decreases as T → 0, eventually to reach negative values at T = 0. In prior work on other cuprates, negative values of S/T at T → 0 were shown to result from a reconstruction of the Fermi surface caused by charge- density-wave (CDW) order. We therefore identify pCDW ≃ 0.19 as the critical doping beyond which there is no CDW-induced Fermi surface reconstruction. The fact that pCDW is well separated from p

⋆ reveals that there is a doping range below p⋆ where the transport signatures of the pseudogap phase are unaffected by CDW correlations, as previously found in YBa2Cu3Oy and La2−xSrxCuO4.



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