Yun Chen

In this paper, we propose independent conditional mutual information (ICMI) to measure the direct association between two variables (X and Y) having a confounding parent (Z). Compared with conditional mutual information, ICMI can distinguish the direct association strength of different situations for explicit or ambiguous relationships between variables, as shown in Fig.(a), (b) and, (c).

Nanobubbles wield a significant influence over the electronic properties of 2D materials, showing diverse applications ranging from flexible devices to strain sensors. Here, we reveal that a strongly correlated phenomenon, i.e., Kondo resonance, naturally takes place as an intrinsic property of graphene nanobubbles. The localized strain within the nanobubbles engenders pseudomagnetic fields, driving pseudo Landau levels with degenerate Landau orbits. Under the Coulomb repulsion, the Landau orbits form an effective SU(N) pseudospin coupled to the bath via exchange interaction. This results in a new flavor screening mechanism that drives an exotic flavor-frozen Kondo effect, which is absent in conventional Kondo systems. The resonance here also exhibits an unparalleled tunability via strain engineering, establishing a versatile new platform to simulate novel correlated phenomena based on pseudo Landau levels.

Vortex pinning is a crucial factor that determines the critical current of practical superconductors and enables their diverse applications. However, the underlying mechanism of vortex pinning has long been elusive, lacking a clear microscopic explanation. Here, using high-resolution scanning tunneling microscopy, we studied single vortex pinning induced by point defect in layered FeSe-based superconductors. We found the defect-vortex interaction drives low-energy vortex bound states away from E F , creating a “mini” gap that effectively lowers the system energy and enhances pinning. By measuring the local density of states, we directly obtained the elementary pinning energy and estimated the pinning force via the spatial gradient of pinning energy. The results are consistent with bulk critical current measurement. Furthermore, we showed that a general microscopic quantum model incorporating defect-vortex interaction can naturally capture our observation. It suggests that the local pairing near pinned vortex core is actually enhanced compared to unpinned vortex, which is beyond the traditional understanding that nonsuperconducting regions pin vortices. Our study thus unveils a general microscopic mechanism of vortex pinning in superconductors and provides insights for enhancing the critical current of practical superconductors. Published by the American Physical Society 2024