We report thermopower measurements under hydrostatic pressure on the cuprate superconductor ${\mathrm{La}}_{1.6-x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ (Nd-LSCO), at low temperature in the normal state accessed by suppressing superconductivity with a magnetic field up to $H=31\mathrm{T}$. Using an ac thermopower measurement technique suitable for high pressure and high field, we track the pressure evolution of the Seebeck coefficient $S$. At ambient pressure and low temperature, $S/T$ in Nd-LSCO was recently found to suddenly increase below the pseudogap critical doping $p^{★}=0.23$, consistent with a drop in carrier density $n$ from $n=1+p$ above $p^{★}$ to $n=p$ below. Under a pressure of 2.0 GPa, we observe that the large $S/T$ value just below $p^{★}$ is suppressed. This confirms a previous pressure study based on electrical resistivity and Hall effect, which found that pressure lowers $p^{★}$, thereby reinforcing the interpretation that this effect is driven by the pressure-induced shift of the van Hove point. It implies that the pseudogap only exists when the Fermi surface is hole-like, which puts strong constraints on theories of the pseudogap phase. We also report thermopower measurements on Nd-LSCO and ${\mathrm{La}}_{1.8-x}{\mathrm{Eu}}_{0.2}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ in the charge density wave phase near $p\sim 1/8$, which reveals a weakening of this phase under pressure.

中文翻译：

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压力对热功率测量探测的铜酸盐Nd-LSCO伪间隙和电荷密度波相位的影响

我们报告了铜酸盐超导体在静水压力下的热功率测量结果 ${\mathrm{啦啦}}_{1.6-X}{钕}_{0.4}{r}_X{\mathrm{氧化铜}}_4$ （Nd-LSCO），在常温下处于低温状态，通过抑制超导电性而获得，磁场强度最高可达 $H=31\mathrm{Ť}$。使用适用于高压和高场的交流热电测量技术，我们跟踪塞贝克系数的压力演变$\mathrm{小号}$。在环境压力和低温下，$\mathrm{小号}/Ť$ 最近发现Nd-LSCO中的Nb突然增加到伪间隙临界掺杂以下 $p^{\mathrm{★★}}=0.23$，与载流子密度的下降相一致 $ñ$ 从 $ñ=\mathrm{1个}+p$ 以上 $p^{\mathrm{★★}}$ 至 $ñ=p$以下。在2.0 GPa的压力下，我们观察到$\mathrm{小号}/Ť$ 值刚好低于 $p^{\mathrm{★★}}$被抑制。这证实了先前基于电阻率和霍尔效应进行的压力研究，发现压力降低了$p^{\mathrm{★★}}$，从而加强了这种影响是由压力引起的范霍夫点偏移引起的解释。这意味着伪间隙仅在费米表面为孔状时才存在，这对伪间隙相的理论施加了严格的约束。我们还报告了Nd-LSCO和${\mathrm{啦啦}}_{1.8-X}{\mathrm{欧洲联盟}}_{0.2}{r}_X{\mathrm{氧化铜}}_4$ 在电荷密度波相附近 $p〜\mathrm{1个}/8$，这表明该阶段在压力下会减弱。