LPS, University of Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex, France.
Phys Rev Lett. 2013 May 24;110(21):217001. doi: 10.1103/PhysRevLett.110.217001. Epub 2013 May 21.
A mesoscopic hybrid normal-metal-superconductor ring is characterized by a dense Andreev spectrum with a flux dependent minigap. To probe the dynamics of such a ring, we measure its linear response to a high frequency flux, in a wide frequency range, with a multimode superconducting resonator. We find that the current response contains, besides the well-known dissipationless Josephson contribution, a large dissipative component. At high frequency compared to the minigap and low temperature, we find that the dissipation is due to transitions across the minigap. In contrast, at lower frequency there is a range of temperature for which dissipation is caused predominantly by the relaxation of the Andreev states' population. This dissipative response, related via the fluctuation dissipation theorem to a nonintuitive zero frequency thermal noise of supercurrent, is characterized by a phase dependence dominated by its second harmonic, as predicted long ago but never observed thus far.
一个介观混合超导-正常金属环的特征是存在一个与磁通相关的小能隙，以及一个密集的安德烈夫能谱。为了探测这样一个环的动力学，我们用一个多模超导谐振器测量了它对高频磁通的线性响应，频率范围很宽。我们发现，除了众所周知的无耗散约瑟夫森贡献之外，电流响应还包含一个很大的耗散分量。在与小能隙相比高频且低温的情况下，我们发现耗散是由于跨越小能隙的跃迁引起的。相比之下，在较低的频率和温度范围内，有一个温度范围，其中耗散主要是由安德烈夫态的群体弛豫引起的。这种耗散响应，通过涨落耗散定理与超电流的非直觉的零频热噪声相关联，其特征是相位依赖性主要由其二阶谐波主导，这是很久以前就预测到的，但迄今为止从未观察到。
