$Y_{1-x}Ca_xBa_2Cu_3O_{7-delta}$量子临界点以上氧同位素的大位移
Large oxygen-isotope shift above the quantum critical point of $Y_{1-x}Ca_xBa_2Cu_3O_{7-delta}$
摘要：
本文研究了氧同位素效应对过掺杂$_{1-x}$-Ca-$_{x}$-$_{2}$ $_{3}$-$_{7-δ}$（$x$ = 0.10，0.20和0.25）超导转变温度的影响。我们发现氧同位素指数$α_{O}$在$x$ = 0.10时很小（$\sim$ 0.02），但在$x$ = 0.20和0.25时很大（$\sim$ 0.1）。$α_{O}$急剧增加的掺杂水平与正常态赝能隙开始减小的量子临界点一致。本文的同位素效应实验为铜酸盐高温超导的配对机制提供了直接和定量的约束。
英文摘要：
We have studied the oxygen-isotope effect on the superconducting transition temperature $T_{c}$ in overdoped Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-δ}$ with $x$ = 0.10, 0.20, and 0.25. We find the oxygen-isotope exponent $α_{O}$ to be small ($\sim$0.02) for $x$ = 0.10 but substantial ($\sim$0.1) for $x$ = 0.20 and 0.25. The doping level above which $α_{O}$ increases sharply coincides with a quantum critical point where the normal-state pseudogap starts to diminish. The present isotope-effect experiments provide direct and quantitative constraints on the pairing mechanism of high-temperature superconductivity in cuprates.
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