Remarkable Suppression of TC by Pressure in NdFeAsO1-y ( y = 0.4)
Remarkable Suppression of TC by Pressure in NdFeAsO1-y ( y = 0.4)
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DOI：
10.1143/jpsj.77.075003
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发表时间：
2008-06
影响因子：
1.7
通讯作者：
N. Takeshita;A. Iyo;H. Eisaki;H. Kitô;T. Ito
中科院分区：
文献类型：
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作者：
N. Takeshita;A. Iyo;H. Eisaki;H. Kitô;T. Ito
自从发现含TC¼26 K的lafea （O， F）的超导性以来，世界范围内对这类新型超导体进行了广泛的研究。未掺杂的LaFeAsO在150K左右的电阻率出现异常，可能与自旋密度波（SDW）跃迁有关，未发生超导跃迁。氟对氧的化学取代将电子载流子掺杂到FeAs平面上，从而产生超导性。请注意，在x¼0:11 （LaFeAsO1ÀxFx）附近似乎有最佳掺杂水平，在该系统中获得了最高的26K TC。最近研究表明，稀土元素（RE）取代La可以显著增强掺f体系（例如，RE= Gd, Sm, Ce, Nd）中的TC。2,3)在FeAs平面上不仅可以掺杂电子，还可以掺杂空穴，在（La0: 87Sr0: 13） OFeAs中报道了25K时的超导性。4) FeAs平面是超导体的一个新阶段，我们可以通过各种方式调整掺杂水平，如高tc Cu氧化物超导体中的CuO2平面。最近关于无f氧缺陷REFeAsO1Ày体系中超导性的研究结果开辟了一种新的掺杂调谐方法。令人惊讶的是，SmFeAsO0: 85中的转变温度达到55k5)，这是除高tc铜酸盐外最高的超导转变温度。由于人们普遍认为外压力可以调节高tc铜酸盐中的掺杂水平，因此，一个有趣的问题出现了，即外压力是否也会改变FeAs平面中的载流子掺杂水平。Takahashi等人在高达31GPa的高压下展示了掺f LaO1ÀxFxFeAs的非常有趣的物理性质。7)实验结果表明，当温度为4 GPa时，温度从28 K升高到43 K时，由转变开始决定的TC迅速增加。重要的是，转变温度TC在4 GPa以上单调降低，在最高实验压力31GPa下，转变温度TC在10 K以下降低。高温铜酸盐的这种有趣的压力依赖性特征，即超导的钟形压力相图，在高温铜酸盐中经常发现。也就是说，这一结果表明在FeAs平面上存在一个最佳掺杂值。此外，外部压力可以控制掺杂水平。为了…
Since the discovery of the superconductivity in LaFeAs (O, F) with TC ¼ 26 K, 1) extensive research studies on this new class of superconductor are conducted worldwide. Non-doped LaFeAsO shows an anomaly in electrical resistivity at around 150K which may be concerned with spin-density wave (SDW) transition and no superconducting transition occurs. Chemical substitution of fluorine for oxygen dopes electron carriers to FeAs plane, then superconductivity emerges as a result. Note that there seems to be the optimum doping level at around x ¼ 0: 11 (LaFeAsO1ÀxFx) where the highest TC of 26K is obtained in this system. Recently it is shown that the substitution of rare-earth elements (RE) for La induced a striking enhancement of TC in F-doped system (eg, RE= Gd, Sm, Ce, Nd). 2, 3) It is possible to dope not only electrons but also holes to FeAs plane, the superconductivity at 25K is reported in (La0: 87Sr0: 13) OFeAs. 4) The FeAs plane is a new stage of superconductor where we can tune the doping level by various way such like the CuO2 plane in high-TC Cu oxide superconductors.Very recent result of superconductivity in F-free oxygen deficient REFeAsO1Ày systems 3, 5) opens a new tuning method of doping. Surprisingly, transition temperature reaches 55 K 5) in SmFeAsO0: 85 which is the highest superconducting transition temperature except for high-TC cuprates. Since it is commonly accepted that the external pressure can tune the doping level in the high-TC cuprates, 6) therefore an intriguing problem arises whether the external pressure will modify the carrier doping level also in FeAs plane. Takahashi et al. show very interesting physical properties of F-doped LaO1ÀxFxFeAs under high pressures up to 31GPa. 7) According to this result, TC which is determined by onset of the transition increases rapidly with applying pressure from 28 to 43 K at 4 GPa which is the apex of the transition temperature in their experiment. What is important is that the transition temperature TC decreases monotonously above 4 GPa and is lowered below 10 K at the highest experimental pressure of 31GPa. Such interesting feature of pressure dependence of TC, that is, the bell-shape pressure phase diagram of superconductivity is often found in high-TC cuprates. In other words, this result suggests that there is a optimum doping value in FeAs plane. Moreover, the external pressure can control the doping level. In order to