Ultrapure Graphite from Solid Refining

Graphite has sparked extensive quantum physical discoveries and demonstrated numerous cutting-edge applications. However, existing graphite typically contains considerable impurities, and effective purification is still lacking. Here, a solid refining purification method is reported for obtaining ultrapure graphite. Through this design, impurities are filtered by the atomic lattice of a solid-state nickel (Ni). Suitable absorption, diffusion, and precipitation energy barriers are utilized in this method, allowing only carbon (C) atoms to effectively migrate through the Ni lattice to form high-quality graphite. The obtained ultrapure graphite shows the lowest elemental impurity density (<10 parts per million (ppm), which is one order of magnitude lower than that of the best available graphite), the highest structural purity (<0.2 parts per billion (ppb) of in-plane structural defect density and >99% Bernal stacking), and the highest doping purity (carrier doping density <2.0 × 10¹⁰ cm^-2). Such superior purity of graphite facilitates the all-integer visible Landau levels and the ultralow quantum transition magnetic field in the fabricated graphene device. This solid refinement technique should inspire the purification of various layered crystals, leading to the discovery of new phenomena and the development of advanced applications.