Song Yu, Wang Weiyi, Van Dyke John S, Pouse Naveen, Ran Sheng, Yazici Duygu, Schneidewind A, Čermák Petr, Qiu Y, Maple M B, Morr Dirk K, Dai Pengcheng
Department of Physics and Astronomy, Rice University, Houston, TX 77005, USA.
Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA.
Commun Phys. 2020;3. doi: 10.1038/s42005-020-0365-8.
Spin-fluctuation-mediated unconventional superconductivity can emerge at the border of magnetism, featuring a superconducting order parameter that changes sign in momentum space. Detection of such a sign-change is experimentally challenging, since most probes are not phase-sensitive. The observation of a spin resonance mode (SRM) from inelastic neutron scattering is often seen as strong phase-sensitive evidence for a sign-changing superconducting order parameter, by assuming the SRM is a spin-excitonic bound state. Here we show that for the heavy fermion superconductor CeCoIn, its SRM defies expectations for a spin-excitonic bound state, and is not a manifestation of sign-changing superconductivity. Instead, the SRM in CeCoIn likely arises from a reduction of damping to a magnon-like mode in the superconducting state, due to its proximity to magnetic quantum criticality. Our findings emphasize the need for more stringent tests of whether SRMs are spin-excitonic, when using their presence to evidence sign-changing superconductivity.
自旋涨落介导的非常规超导性可出现在磁性边界，其超导序参量在动量空间中会改变符号。由于大多数探测手段不具备相位敏感性，探测这种符号变化在实验上具有挑战性。通过假设自旋共振模式（SRM）是一种自旋激子束缚态，非弹性中子散射中自旋共振模式的观测通常被视为超导序参量发生符号变化的有力相位敏感证据。在此我们表明，对于重费米子超导体CeCoIn，其自旋共振模式不符合自旋激子束缚态的预期，并非超导序参量符号变化的表现。相反，CeCoIn中的自旋共振模式可能源于超导态下对类磁振子模式阻尼的降低，这是由于它接近磁量子临界点。我们的研究结果强调，在利用自旋共振模式的存在来证明超导序参量符号变化时，需要对其是否为自旋激子进行更严格的测试。
