Electronic structure and spatial inhomogeneity of iron-based superconductor FeS

Iron-based superconductor family FeX(X=S,Se,Te)has been one of the research foci in physics and material science due to their record-breaking superconducting temperature(FeSe film)and rich physical phenomena.Recently,FeS,the least studied Fe X compound(due to the difficulty in synthesizing high quality macroscopic crystals)attracted much attention because of its puzzling superconducting pairing symmetry.In this work,combining scanning tunneling microscopy and angle resolved photoemission spectroscopy(ARPES)with sub-micron spatial resolution,we investigate the intrinsic electronic structures of superconducting FeS from individual single crystalline domains.Unlike FeTe or FeSe,FeS remains identical tetragonal structure from room temperature down to 5 K,and the band structures observed can be well reproduced by our ab-initio calculations.Remarkably,mixed with the 1×1 tetragonal metallic phase,we also observe the coexistence of √5×√5 reconstructed insulating phase in the crystal,which not only helps explain the unusual properties of FeS,but also demonstrates the importance of using spatially resolved experimental tools in the study of this compound.

Moir patterns and step edges on few-layer graphene grown on nickel films

Few-layer graphene grown on Ni thin films has been studied by scanning tunneling microscopy. In most areas on the surfaces, moir6 patterns resulted from rotational stacking faults were observed. At a bias lower than 200 mV, only one sublattice shows up in regions without moir6 patterns while both sublattices are seen in regions with moir6 pattens. This phenomenon can be used to identify AB stacked regions. The scattering characteristics at various types of step edges are different from those of monolayer graphene edges, either armchair or zigzag.

Ferromagnetic half levitation of LK-99-like synthetic samples

We successfully synthesized polycrystalline LK-99-like ceramic samples with a solid-state-sintering method.Powder X-ray diffraction shows that the main contents are Pb_(10-x)Cu_(x)(PO_(4))_(6)O and Cu_(2)S,consistent with recent reports (arXiv:2307.12037;arXiv:2308.01192).In some small flaky fragments,we successfully observed“half levitation”atop a Nd_(2)Fe_(14)B magnet.Using magnetization measurements on such small pieces,as well as on a large piece which does not exhibit the half levitation,we show that the samples ubiquitously contain weak yet definitive soft ferromagnetic components.We argue that,together with the pronounced shape anisotropy of the small fragments,the soft ferromagnetism is sufficient to explain the observed half levitation in strong vertical magnetic fields.Our measurements do not indicate the presence of the Meissner effect,nor zero resistance,in our samples,leading us to believe that our samples do not exhibit superconductivity.The precise chemical composition and the physics behind the ferromagnetic component remain outstanding questions to be addressed in future research.

Evolution of the Raman spectrum of graphene grown on copper upon oxidation of the substrate

在在一部铜电影上种的单个层的 graphene 的拉曼光谱的重要变化在发生在周围的条件下面的内在的底层的自发的氧化以后被观察。graphene G 和 2D 拉曼模式的频率被发现经历红移动，当二个乐队的紧张由超过一个数量级变化时。为了理解这些的起源，完成，我们进一步由扫描通道描绘了样品显微镜学(STM ) ，扫描通道光谱学(圣) ，和原子力量显微镜学(AFM ) 。没有破坏 graphene overlayer 的水晶的顺序或改变做水平的搬运人，底层的氧化在底层生产了可估计的折皱。我们以 graphene 层的折皱导致的张力的紧张解释拉曼频率的红移动。在有氧化的拉曼紧张的变化从对在散布过程的拉曼结合 graphene 层的光的效率的薄亚铜的氧化物电影的影响产生。

Nanoscale superconductivity of ?-Ga islands grown by molecular beam epitaxy

We report on the preparation and superconductivity of metastable γ-Ga islands on Si(111) substrate. The Ga grows in a typical Volmer-Weber mode at a low temperature of 110 K, resulting in formation of Ga nanoislands at various sizes with the identical γ-phase. In-situ low temperature scanning tunneling spectra reveal quantized electronic states in ultrathin Ga islands. It is found that both the lateral size and thickness of the Ga islands strongly suppress the superconductivity. Due to substantial surface energy contribution, the transition temperature Tc scales inversely with the island thickness and the minimum thickness for the occurrence of superconductivity is calculated to be two monolayers.