Iodine Vacancy Redistribution in Organic–Inorganic Halide Perovskite Films and Resistive Switching Effects

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138254/1/adma201700527_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138254/2/adma201700527-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138254/3/adma201700527.pd

Voltage-Controlled Magnetic Reversal in Orbital Chern Insulators

Chern insulator ferromagnets are characterized by a quantized anomalous Hall effect, and have so far been identified experimentally in magnetically-doped topological insulator (MTI) thin films and in bilayer graphene moir{\'e} superlattices. We classify Chern insulator ferromagnets as either spin or orbital, depending on whether the orbital magnetization results from spontaneous spin-polarization combined with spin-orbit interactions, as in the MTI case, or directly from spontaneous orbital currents, as in the moir{\'e} superlattice case. We argue that in a given magnetic state, characterized for example by the sign of the anomalous Hall effect, the magnetization of an orbital Chern insulator will often have opposite signs for weak $n$ and weak $p$ electrostatic or chemical doping. This property enables pure electrical switching of a magnetic state in the presence of a fixed magnetic field.Comment: 11 pages, 6 figure

Twisted bilayer graphene reveals its flat bands under spin pumping

The salient property of the electronic band structure of twisted bilayer graphene (TBG), at the so-called magic angle (MA), is the emergence of flat bands around the charge neutrality point. These bands are associated with the observed superconducting phases and the correlated insulating states. Scanning tunneling microscopy combined with angle resolved photoemission spectroscopy are usually used to visualize the flatness of the band structure of TBG at the MA. Here, we theoretically argue that spin pumping (SP) provides a direct probe of the flat bands of TBG and an accurate determination of the MA. We consider a junction separating a ferromagnetic insulator and a heterostructure of TBG adjacent to a monolayer of a transition metal dichalcogenide. We show that the Gilbert damping of the ferromagnetic resonance experiment, through this junction, depends on the twist angle of TBG, and exhibits a sharp drop at the MA. We discuss the experimental realization of our results which open the way to a twist switchable spintronics in twisted van der Waals heterostructures.Comment: 8 pages + supplemental material (revised version

Theory of ARPES in Graphene-Based Moiré Superlattices

Graphene-based moir´e superlattices are now established as an interesting platform for strongly- correlated many-electron physics, and have so far been characterized mainly by transport and scan- ning tunneling microscopy (STM) measurements. Motivated by recent experimental progress, we present a theoretical model study whose aim is to assess the potential of angle-resolved photoemis- sion spectroscopy (ARPES) to resolve some of the many open issues in these systems. The theory is developed specifically for graphene on hexagonal boron nitride (G/hBN) and twisted bilayer graphene (TBG) moir´e superlattices, but is readily generalized to any system with active degrees of freedom in graphene sheets.This research was primarily supported by the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooper- ative Agreement No. DMR-1720595. We acknowledge helpful interactions with Dan Dessau, Eli Rotenberg and Simon Moser.Center for Dynamics and Control of Material

Correlated Insulating States in Twisted Double Bilayer Graphene

We present a combined experimental and theoretical study of twisted double bilayer graphene with twist angles between 1{\deg} and 1.35{\deg}. Consistent with moir\'e band structure calculations, we observe insulators at integer moir\'e band fillings one and three, but not two. An applied transverse electric field separates the first moir\'e conduction band from neighbouring bands, and favors the appearance of correlated insulators at 1/4, 1/2, and 3/4 band filling. Insulating states at 1/4 and 3/4 band filling emerge only in a parallel magnetic field (B_{||}), whereas the resistance at half band filling is weakly dependent on B_{||}. These findings suggest that correlated insulators are favored when a moir\'e flat band is spectrally isolated, with spin polarization at 1/4 and 3/4 band filling and valley polarization at 1/2 band filling.Comment: 5 pages, 4 figures, includes supplementary materia