Nanoscale probing of broken-symmetry states in graphene induced by individual atomic impurities

Abstract

Inherent symmetries of a system lead to multiple degeneracies of its energy spectra. Introducing individual atomic impurities can locally break these symmetries,which is expected to lift the degenerate degrees of freedom around the impurities. Although central to our understanding of the fundamental properties of solids, the broken-symmetry states induced by individual atomic impurities have so far eluded observation. Here, we report nanoscale probing of the broken-symmetry states in graphene induced by two types of individual atomic impurities, i.e., isolated nitrogen dopants and isolated hydrogen atoms chemisorbed on graphene. Our experiments demonstrate that both types of atomic impurities can locally break sublattice symmetry of graphene and generate valley-polarized states, which extends several nanometers around the impurities. For the isolated hydrogen atom chemisorbed on graphene, the enhanced spin-orbit coupling, which arises from the sp 3 distortion of graphene due to the hydrogen chemisorption, further lifts the spin degeneracy, resulting in a fully spin and valley polarized states within about 1 nm around the hydrogen atom. Our result paves the way to control various broken-symmetry states at the nanoscale by various atomic impurities.

Quantum Interferences of Pseudospin-Mediated Atomic-Scale Vortices in Monolayer Graphene

“…To explore the atomic-scale vortex nature of the single carbon defects, we carried out scanning tunneling microscopy (STM) measurements. At a given STM tip position, the charge densities are governed by the interference of the electronic waves between electrons in the tip pointing toward the single carbon defect and their reflection from the defect by coupling a phase shift (Figure c). , Meanwhile, the STM tip can probe the local density of states (LDOS) of electrons with high spatial resolution. − Therefore, we can obtain the defect-induced Friedel oscillations of the intervalley scattering from the STM images. In our experiments, we carried out measurements of the decoupled top-most graphene monolayer with a high density of single carbon defects on multilayer graphene, which was directly synthesized on Ni foils using a facile chemical vapor deposition (CVD) method − (see Methods and Figure S1).…”

Visualization of Macroscopic Ising Superconducting State in Superconductor‐Graphene Junctions

“…Moreover, the proximity effect of spin‐orbit coupling in NbSe 2 can hardly leak into graphene for several tens of nanometers. [ 48 ] Taken together, we believe that the Ising superconductivity of SL NbSe 2 with spin‐momentum locking Cooper pair is key to such an abnormal proximity effect, which needs more experimental and theoretical explorations.…”

Recent advances of defect-induced spin and valley polarized states in graphene

“…[6] An individual hydrogen-atom chemisorbed on graphene leads to an out-of-plane atomic configuration, which significantly enhances the atomic spin-orbit coupling (SOC) of graphene, thus resulting in a fully spin and valley polarized state at the nanoscale. [7,8] Moreover, both an individual hydrogen-atom chemisorbed on graphene and an isolated single-carbon vacancy in graphene can generate local magnetic moments, and such magnetic moments can be controllably manipulated by tuning the gate voltage and the local curvature. [9][10][11][12] Therefore, atomic-scale defects in graphene provide ideal model systems to systemically study the novel quantum states, highlighting promising directions for spintronics and valleytronics.…”

“…If both the valley and spin degrees of freedom are removed, the N = 0 Landau level will split into four peaks with fully spin-valley polarization. Reproduced with permission from Ref [8]…”