Abstract
The Seebeck coefficient $S$ of the cuprate superconductor La$ _{2-x} $Sr$_{x} $CuO$ _{4}$ (LSCO) was measured in magnetic fields large enough to access the normal state at low temperatures, for a range of Sr concentrations from $x = 0.07$ to $x = 0.15$. For $x = 0.11$, 0.12, 0.125 and 0.13, $S/T$ decreases upon cooling to become negative at low temperatures. The same behavior is observed in the Hall coefficient $R_{H}(T)$. In analogy with other hole-doped cuprates at similar hole concentrations $p$, the negative $S$ and $R_{H}$ show that the Fermi surface of LSCO undergoes a reconstruction caused by the onset of charge-density-wave modulations. Such modulations have indeed been detected in LSCO by X-ray diffraction in precisely the same doping range. Our data show that in LSCO this Fermi-surface reconstruction is confined to $0.085 < p < 0.15$. We argue that in the field-induced normal state of LSCO, charge-density-wave order ends at a critical doping $p_{\rm CDW} = 0.15 \pm 0.005$, well below the pseudogap critical doping $p^\star \simeq 0.19$.
Highlights
Since the discovery of quantum oscillations [1] and a negative Hall coefficient RH [2] in the cuprate superconductor YBa2Cu3Oy (YBCO), it has become clear that the Fermi surface of underdoped YBCO undergoes a reconstruction at low temperatures that produces a small electron pocket [3], in a doping range from p 1⁄4 0.08 to p ≃ 0.15 [4]
The drop is attributed to the CDW modulations detected by x-ray diffraction (XRD) [11,12] and NMR [21] below a temperature TCDW in the same doping range as the Fermi-surface reconstruction (FSR) [4], with TCDW peaking at p 1⁄4 0.12 [Fig. 1(a)]
We report high-field measurements of the Seebeck coefficient in LSCO single crystals at several dopings, which show that S becomes negative in the normal state at low temperatures in precisely the doping range where CDW modulations are detected by XRD
Summary
Since the discovery of quantum oscillations [1] and a negative Hall coefficient RH [2] in the cuprate superconductor YBa2Cu3Oy (YBCO), it has become clear that the Fermi surface of underdoped YBCO undergoes a reconstruction at low temperatures that produces a small electron pocket [3], in a doping range from p 1⁄4 0.08 to p ≃ 0.15 [4] This Fermi-surface reconstruction (FSR) was detected as a sign change in the Seebeck coefficient SðTÞ, going from positive at high temperatures to negative at low temperatures [5]. The drop is attributed to the CDW modulations detected by XRD [11,12] and NMR [21] below a temperature TCDW in the same doping range as the FSR [4], with TCDW peaking at p 1⁄4 0.12 [Fig. 1(a)]
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