发表机构
Rice University; University College London; Institut Laue Langevin; KTH Royal Institute of Technology; Université Paris-Saclay; University of California San Diego; European Spallation Source ERIC; University of California Santa Cruz（莱斯大学; 伦敦大学学院; 朗之万研究所; 瑞典皇家理工学院; 巴黎萨克雷大学; 加州大学圣地亚哥分校; 欧洲散裂光源; 加州大学圣克鲁兹分校）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过非弹性中子散射实验与微观理论框架，揭示UTe2中反铁磁自旋涨落在ac面内各向同性而沿b轴消失，排除伊辛各向异性，支持沿b方向的B1u三重态配对。
AI 中文摘要
超导材料UTe2在磁化率、上临界场和奈特位移方面沿晶格a、b、c方向表现出显著的方向各向异性，这暗示了自旋三重态库珀配对。如果自旋涨落束缚了库珀对，则需要确定其在自旋空间中的各向异性以表征超导态。在此，我们利用极化和非极化非弹性中子散射（INS）实验表明，在Y点的反铁磁（AFM）自旋涨落在ac平面内高度各向同性，但沿b轴方向没有可观测的幅度。我们的结果排除了假设的伊辛各向异性，并限制了可能的配对通道。AFM交换不再在三重态通道中形成配对，且沿b方向的d矢量受到强烈青睐。我们在一个包含5f电子双重性质的微观框架内捕捉了实验观测结果。我们将巡游和局域5f矩纳入一个拟合量子振荡数据的紧束缚模型中。与INS一致，局域矩之间的交换通常由强的铁磁（FM）二聚体内相互作用组成，最大值接近Y和T点，分别由5p_y和6d_{3z^2-r^2}轨道介导，并且ab平面在磁学上解耦。我们发现，矩的各向异性和二聚化可以导致有能隙的激发，这些激发与朗道阻尼相结合，可以产生在Y点观测到的过阻尼响应。我们提出，响应的增强及其观测到的近O(2)对称性可能都是由接近量子临界点驱动的，在该点二聚体激发隙闭合，并让位于不相称的螺旋序。对最近邻配对相互作用的线性化隙方程的分析支持B1u三重态，其主导d矢量分量沿b方向，尽管自旋单重态配对的可能性不能被排除。
英文摘要
The large directional anisotropy of superconducting UTe2 along the lattice a, b, c directions in magnetic susceptibility, upper critical fields, and Knight shift suggests spin-triplet Cooper pairing. If spin fluctuations bind the Cooper pair, one needs to determine their anisotropy in spin space to characterize the superconducting state. Here we use polarised and unpolarised inelastic neutron scattering (INS) experiments to show that antiferromagnetic (AFM) spin fluctuations at the Y point are highly isotropic within the ac-plane but have no observable magnitude along the b-axis. Our results rule out the assumed Ising anisotropy and constrain the possible pairing channels. AFM exchange is no longer pair forming in the triplet channel and the d vector along b is strongly favoured. We capture the experimental observations within a microscopic framework that encompasses the dual nature of 5f electrons. We include itinerant and localized 5f-moments in a tight-binding model fitted to quantum oscillations data. In congruence with INS, the exchange between localized moments generically consists of a strong FM intra-dimer interaction, maxima close to the Y and T points, mediated by 5p_y and 6d_{3z^2-r^2} orbitals respectively, and magnetically decoupled ab-planes. We find that anisotropy and dimerization of the moments can lead to gapped excitations that, in combination with Landau damping, can produce the observed overdamped response at the Y point. We suggest that enhancement of the response and its observed near-O(2)-symmetry could both be driven by proximity to a quantum critical point where the dimer excitation gap closes and gives place to incommensurate helical order. Analysis of the linearized gap equation for a nearest-neighbour pairing interaction favours the B1u triplet with a dominant d-vector component along b, although the possibility of spin singlet pairing cannot be ruled out.
Comments23 pages, 4 figures
