Charge carrier densities in electronic heterostructures are typically responsive to external electric fields or chemical doping but rarely to their magnetization history. Here, we demonstrate that magnetization acts as a non-volatile control parameter for the density of states in bilayer graphene (BLG) interfaced with the antiferromagnetic insulator chromium oxychloride (COC). Using capacitance measurements, we observe a hysteretic behavior in the density of states of BLG on a COC substrate in response to an external magnetic field, which is unrelated to the history of electrostatic gating. First-principles calculations revealed that such hysteresis arises from the magnetic-field-controlled charge transfer between BLG and COC during the antiferromagnetic (AFM) to ferrimagnetic-like (FiM) state phase transition of COC. Our work demonstrates that interfacial charging states can be effectively controlled magnetically, and it also shows that capacitance measurement is a suitable technique for detecting subtle changes not detectable via conventional resistivity measurements. These findings broaden the scope of proximity effects and open new possibilities for nanoelectronics applications.
The generation of pseudo-magnetic fields in strained graphene leads to quantized Landau levels in the absence of an external magnetic field, providing the potential to achieve a zero-magnetic-field analogue of quantum Hall effect. Here, we report the realization of pseudo-magnetic field in epitaxial graphene by building monolayer CrCl2/graphene heterointerface. The CrCl2 crystal structure exhibits spontaneous breaking of three-fold rotational symmetry, yielding anisotropic displacement field at the interface. Using scanning tunneling spectroscopy, we have discovered a sequence of pseudo-Landau levels associated with massless Dirac fermions. A control experiment performed on CrCl2/NbSe2 interface confirms the origin as the pseudo-magnetic field in the graphene layer that strongly interacts with the CrCl2. More interestingly, the strength of the pseudo-magnetic fields can be tuned by the twist angle between the monolayer CrCl2 and graphene, with a variation of up to threefold, depending on the twist angle of 0° to 30°. This work presents a rare 2D heterojunction for exploring PMF-related physics, such as valley Hall effect, with the advantage of easy and flexible implementation.
Scanning tunneling microscopy (STM) vibronic spectroscopy, which has provided submolecular insights into electron-vibration (vibronic) coupling, faces challenges when probing the pivotal low-frequency vibronic excitations. Because of eigenstate broadening on solid substrates, resolving low-frequency vibronic states demands strong decoupling. This work designs a type II band alignment in STM junction to achieve effective charge-transfer state decoupling. This strategy enables the successful identification of the lowest-frequency Hg(ω1) (Raman-active Hg mode) vibronic excitation within single C60 molecules, which, despite being notably pronounced in electron transport of C60 single-molecule transistors, has remained hidden at submolecular level. Our results show that the observed Hg(ω1) excitation is “anchored” to all molecules, irrespective of local geometry, challenging common understanding of structural definition of vibronic excitation governed by Franck-Condon principle. Density functional theory calculations reveal existence of molecule-substrate interfacial charge-transfer dipole, which, although overlooked previously, drives the dominant Hg(ω1) excitation. This charge-transfer dipole is not specific but must be general at interfaces, influencing vibronic coupling in charge transport.
Pai Wang, Kunyu Li, Tongwei Wu, Wei Ji, and Yanning Zhang
Abstract:
The performance of two-dimensional transition-metal (oxy)hydroxides (TMOOHs) for the electrocatalytic oxygen evolution reaction (OER), as well as their large-scale practical applications, are severely limited by the sluggish kinetics of the four-electron OER process. Herein, using a symmetry-breaking strategy, we simulated a complex catalyst composed of a single Co atom and a 1,10-phenanthroline (phen) ligand on CoOOH through density functional theory studies, which exhibits excellent OER performance. The active site Co undergoes a valence oscillation between +2, +3 and even high valence +4 oxidation states during the catalytic process, resulting from the distorted coordination effect after the ligand modification. The induced asymmetry in the electronic states of surrounding nitrogen and oxygen atoms modulates the eg occupation of Co-3d orbitals, which should be of benefit to reduce the overpotential in the OER process. By studying similar catalytic systems, the prominent role of ligands in creating asymmetric electronic structures and in modulating the valence of the active site and the OER performance was reconfirmed. This study provides a new dimension for optimizing the electrocatalytic performance of various TM–ligand complexes.
