Two-Dimensional Pb Square Nets from Bulk (RO)_nPb (R = Rare Earth Metals, n = 1,2)

Abstract

All two-dimensional (2D) materials of group IV elements from Si to Pb are stabilized by carrier doping and interface bonding from substrates except graphene which can be free-standing. The involvement of strong hybrid of bonds, adsorption of exotic atomic species, and the high concentration of crystalline defects are often unavoidable, complicating the measurement of the intrinsic properties. In this work, we report the discovery of seven kinds of hitherto unreported bulk compounds (RO) n Pb (R = rare earth metals, n = 1,2), which consist of quasi-2D Pb square nets that are spatially and electronically detached from the [RO]δ+ blocking layers. The band structures of these compounds near Fermi levels are relatively clean and dominantly contributed by Pb, resembling the electron-doped free-standing Pb monolayer. The R 2O2Pb compounds are metallic at ambient pressure and become superconductors under high pressures with much enhanced critical fields. In particular, Gd2O2Pb (9.1 μB/Gd) exhibits an interesting bulk response of lattice distortion in conjunction with the emergence of superconductivity and magnetic anomalies at a critical pressure of 10 GPa. Our findings reveal the unexpected facets of 2D Pb sheets that are considerably different from their bulk counterparts and provide an alternative route for exploring 2D properties in bulk materials.

Decoupling of Rattling Mode and Superconductivity in Filled-Skutterudite BaxIr4Sb12

“…Interestingly, the initial smooth downturn of the onset 𝑇c becomes notably sharp at magnetic fields of 𝐻 = 0.25 T and 0.5 T, different from the general observation of field suppression of superconductivity. [31][32][33][34][35] A plausible explanation is the presence of an inhomogeneous composition, where 𝑇c of the acquired polycrystal ranges from 1.2 K to 0.8 K (judging from the onset 𝑇c), while higher-trace superconductivity is quickly suppressed under a magnetic field, and the sharp transition at 0.8 K represents the bulk superconductivity of the acquired sample. Nevertheless, the realized 𝑇c is only one fourth or one fifth of that of Ba0.85Ir4As12 and Ba0.89Ir4P12, unambiguously indicating a monotonic degradation of superconductivity with the enhancement of rattling modes.…”

Stereochemical Rearrangement of Functional Units in Pressurized Sn4As3 Superconductor

“…An intuitive understanding of structural variations under high pressure is of paramount importance as it not only expeditiously validates the accuracy of the calculated results but also offers valuable insights into optimizing their properties. This objective can, in principle, be achieved by conceptualizing intact or less-varied functional units as “LEGO pieces” and deducing their arrangement under pressure. − Furthermore, starting from these functional units enables us to grasp the essence of the corresponding physical properties. − For instance, the square lattices in cuprates , and iron-based superconductors − hold the key to elucidating pairing mechanisms, while the Kagome lattice guarantees the emergence of flat bands, Dirac points, and Van Hove singularities.…”