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arXiv 1102.2804cond-mat.supr-concond-mat.str-el
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高温铜氧化物超导涨落的高场研究:小能隙与大赝能隙不同的证据

High Field Studies of Superconducting Fluctuations in High-T_c Cuprates: Evidence for a Small Gap distinct from the Large Pseudogap

F. Rullier-Albenque, H. Alloul, G. Rikken

摘要:

我们用高达60 T的脉冲磁场抑制了超导涨落(SCF)对YBa_2Cu_3 O_(6 +x)系列从深赝能隙态到轻微过掺杂的Tc以上电导率的贡献。准确测定了超导体电导率随温度和磁场的变化关系。他们的联合定量分析能斯特数据使我们能够建立,热波动的金斯堡-朗道(GL)计划是占主导地位的近最佳掺杂样品。在1.01Tc<T<1.2Tc的情况下,推导出的相干长度xi(T)与高斯(Aslamazov-Larkin)贡献完全一致。一个相位波动的贡献可能会调用最欠掺杂的样品在T范围内增加时,引入电子辐照控制的障碍。对于所有的掺杂,我们的证据表明,波动是高度阻尼时,增加T或H。这些数据使我们能够定义一个磁场Hc^prime和一个温度Tc^prime,在这个温度以上,SCF被完全抑制。在GL方法中对涨落磁导的分析使我们能够确定临界场Hc 2(0)。发现Hc 1(0)和Hc 2(0)的实际值非常相似,并且两者都随着空穴掺杂而增加。这些depairing领域,这是直接连接到SC间隙的大小,因此遵循Tc的变化,这是在急剧下降的赝间隙T* 与增加空穴掺杂不一致。这与我们先前的证据一致,即T* 不是配对的开始。最后,我们提出了一个三维相图,包括一个无序轴,它可以解释最奇特的观察到目前为止,不同的铜酸盐家庭。

英文摘要:

We have used pulsed magnetic fields up to 60Tesla to suppress the contribution of superconducting fluctuations(SCF)to the conductivity above Tc in a series of YBa2Cu3O6+x from the deep pseudogapped state to slight overdoping. Accurate determinations of the SCF conductivity versus temperature and magnetic field have been achieved. Their joint quantitative analyses with respect to Nernst data allow us to establish that thermal fluctuations following the Ginzburg-Landau(GL) scheme are dominant for nearly optimally doped samples. The deduced coherence length xi(T) is in perfect agreement with a gaussian (Aslamazov-Larkin) contribution for 1.01Tc<T<1.2Tc. A phase fluctuation contribution might be invoked for the most underdoped samples in a T range which increases when controlled disorder is introduced by electron irradiation. For all dopings we evidence that the fluctuations are highly damped when increasing T or H. The data permits us to define a field Hc^prime and a temperature Tc^prime above which the SCF are fully suppressed. The analysis of the fluctuation magnetoconductance in the GL approach allows us to determine the critical field Hc2(0). The actual values of Hc^prime(0) and Hc2(0) are found quite similar and both increase with hole doping. These depairing fields, which are directly connected to the magnitude of the SC gap, do therefore follow the Tc variation which is at odds with the sharp decrease of the pseudogap T* with increasing hole doping. This is on line with our previous evidence that T* is not the onset of pairing. We finally propose a three dimensional phase diagram including a disorder axis, which allows to explain most peculiar observations done so far on the diverse cuprate families.

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