标题： 光谱学证据表明向轨道 Fulde-Ferrell-Larkin-Ovchinnikov 状态的一阶转变 显示英文标题

标题： Spectroscopic evidence for a first-order transition to the orbital Fulde-Ferrell-Larkin-Ovchinnikov state

摘要： 常规的超导态可能被另一种无耗散态取代，该态承载具有有限动量的库珀对，并为此相变留下热力学痕迹。 最近，提出了一种新型的有限动量配对，即所谓的轨道 Fulde-Ferrell-Larkin-Ovchinnikov（FFLO）态，可能在自旋-轨道耦合超导体如双层$2\mathrm{H-NbSe_{2}}$中出现。 到目前为止，缺乏一种热力学演示，这对于确立这种奇特相是关键的。 在这里，我们在多层$2\mathrm{H-NbSe_{2}}$的隧穿谱测量中揭示了向轨道 FFLO 态的一阶量子相变。 该相变表现为平面内磁场$B_{//}$下方超导能隙的突然增强，远低于上临界场。 此外，通过来回扫描$B_{//}$，此转变表现出显著的滞后效应，并且一旦磁场偏离样品平面不到一度，就会迅速消失。 我们获得了轨道 FFLO 态的全面相图，并将其与考虑约瑟夫森涡旋重排的理论计算进行了比较。 我们的工作阐明了轨道 FFLO 态出现的微观机制。 显示英文摘要

摘要： A conventional superconducting state may be replaced by another dissipationless state hosting Cooper pairs with a finite momentum, leaving thermodynamic footprints for such a phase transition. Recently, a novel type of finite momentum pairing, so-called orbital Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, has been proposed to occur in spin-orbit coupled superconductors such as bilayer $2\mathrm{H-NbSe_{2}}$. So far, a thermodynamic demonstration, which is key for establishing this exotic phase, has been lacking. Here, we reveal a first-order quantum phase transition to the orbital FFLO state in tunneling spectroscopic measurements on multilayer $2\mathrm{H-NbSe_{2}}$. The phase transition manifests itself as a sudden enhancement of the superconducting gap at an in-plane magnetic field $B_{//}$ well below the upper critical field. Furthermore, this transition shows prominent hysteresis by sweeping $B_{//}$ back and forth and quickly disappears once the magnetic field is tilted away from the sample plane by less than one degree. We obtain a comprehensive phase diagram for the orbital FFLO state and compare it with the theoretical calculation that takes into account the rearrangement of Josephson vortices. Our work elucidates the microscopic mechanism for the emergence of the orbital FFLO state.