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arXiv 1408.0665cond-mat.supr-con
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超导体-铁磁体-超导体三层结构中0- PI量子跃迁的热力学性质

Thermodynamic nature of the 0-PI quantum transition in superconductor-ferromagnet-superconductor trilayers

N. Pompeo, K. Torokhtii, C. Cirillo, A. V. Samokhvalov, E. A. Ilyina, C. Attanasio, A. I. Buzdin, E. Silva

摘要:

在由交替的超导层和铁磁层(S/F/S异质结构)组成的结构中,已知在一定的温度和几何条件下,基态的宏观量子波函数将其穿过F-层的相位差从0改变到PI,因此将这种交叉称为“0-PI”。我们在这里提出了一个联合实验和理论证明,“0-PI”是一个真正的热力学相变:用微波测量了Nb/Pd_(0.84)Ni_(0.16)/Nb三层超导体的伦敦穿透深度与温度的关系,发现超导凝聚体的密度突然地、不寻常地降低(宏观量子波函数的平方模量)随着温度的降低而降低,这是由这里开发的理论预测的,作为从0-到PI-状态的转变。我们对序参量振幅跳跃的结果是这种温度驱动的量子跃迁的第一个热力学表现。

英文摘要:

In structures made up of alternating superconducting and ferromagnet layers (S/F/S heterostructures), it is known that the macroscopic quantum wavefunction of the ground state changes its phase difference across the F--layer from 0 to PI under certain temperature and geometrical conditions, whence the name "0-PI" for this crossover. We present here a joint experimental and theoretical demonstration that the "0-PI" is a true thermodynamic phase transition: microwave measurements of the temperature dependence of the London penetration depth in Nb/Pd_0.84Ni_0.16/Nb trilayers reveal a sudden, unusual decrease of the density of the superconducting condensate (square modulus of the macroscopic quantum wavefunction) with decreasing temperature, which is predicted by the theory here developed as a transition from the 0- to the PI-state. Our result for the jump of the amplitude of the order parameter is the first thermodynamic manifestation of such temperature-driven quantum transition.

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