Spin fluctuations and the pseudogap in organic superconductors
Spin fluctuations and the pseudogap in organic superconductors
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DOI：
10.1103/physrevb.80.054505
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发表时间：
2009-08-01
影响因子：
3.7
通讯作者：
McKenzie, Ross H.
中科院分区：
文献类型：
--
作者：
Powell, B. J.;Yusuf, Eddy;McKenzie, Ross H.
我们发现，有很强的相似性，在自旋晶格弛豫的有机电荷转移盐，这些相似性可以理解的自旋波动。此外，我们表明，在所有的卡帕相有机超导体，有核磁共振数据，自旋波动的能量尺度与赝能隙的能量尺度相一致。这表明赝能隙是由短程自旋关联引起的。在弱阻挫金属kappa-（BEDT-TTF）（2）Cu[N（CN）（2）]Br、kappa-（BEDT-TTF）（2）Cu（NCS）（2）和kappa-（BEDT-TTF）（2）Cu[N（CN）（2）]Cl（在压力下）中，赝能隙在与（层内）输运中出现相干性相同的温度下打开。我们认为，这是因为自旋相关性被切断的层内相干性在高温下的损失。我们讨论了这两个能量标度在高压下可能发生的情况，其中电子相关性较弱。在这些弱阻挫材料中，化学压力假设（阴离子取代等效于流体静压）很好地描述了数据。然而，我们发现kappa-（BEDT-TTF）（2）Cu-2（CN）（3）的金属态存在重要差异，其高度受抑并显示自旋液体绝缘相。我们还表明（TMTSF）（2）ClO 4中自旋涨落的特征温标与超导临界温度相同，这可能是自旋涨落介导贝奇加德盐超导电性的证据。
We show that there are strong similarities in the spin-lattice relaxation of nonmagnetic organic charge-transfer salts and that these similarities can be understood in terms of spin fluctuations. Further, we show that, in all of the kappa-phase organic superconductors for which there is nuclear-magnetic-resonance data, the energy scale for the spin fluctuations coincides with the energy scale for the pseudogap. This suggests that the pseudogap is caused by short-range spin correlations. In the weakly frustrated metals kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, kappa-(BEDT-TTF)(2)Cu(NCS)(2), and kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl (under pressure) the pseudogap opens at the same temperature as coherence emerges in the (intralayer) transport. We argue that this is because the spin correlations are cutoff by the loss of intralayer coherence at high temperatures. We discuss what might happen to these two energy scales at high pressures, where the electronic correlations are weaker. In these weakly frustrated materials the data is well described by the chemical pressure hypothesis (that anion substitution is equivalent to hydrostatic pressure). However, we find important differences in the metallic state of kappa-(BEDT-TTF)(2)Cu-2(CN)(3), which is highly frustrated and displays a spin liquid-insulating phase. We also show that the characteristic temperature scale of the spin fluctuations in (TMTSF)(2)ClO4 is the same as superconducting critical temperature, which may be evidence that spin fluctuations mediate the superconductivity in the Bechgaard salts.