Pinned Bilayer Wigner Crystals with Pseudospin Magnetism

We study a model of \textit{pinned} bilayer Wigner crystals (WC) and focus on the effects of interlayer coherence (IC) on pinning. We consider both a pseudospin ferromagnetic WC (FMWC) with IC and a pseudospin antiferromagnetic WC (AFMWC) without IC. Our central finding is that a FMWC can be pinned more strongly due to the presence of IC. One specific mechanism is through the disorder induced interlayer tunneling, which effectively manifests as an extra pinning in a FMWC. We also construct a general "effective disorder" model and effective pinning Hamiltonian for the case of FMWC and AFMWC respectively. Under this framework, pinning in the presence of IC involves \textit{interlayer} spatial correlation of disorder in addition to intralayer correlation, leading to \textit{enhanced} pinning in the FMWC. The pinning mode frequency (\wpk) of a FMWC is found to decease with the effective layer separation, whereas for an AFMWC the opposite behavior is expected. An abrupt drop of \wpk is predicted at a transition from a FMWC to AFMWC. Possible effects of in-plane magnetic fields and finite temperatures are addressed. Finally we discuss some other possible ramifications of the FMWC as an electronic supersolid-like phase.Comment: Slightly revised. The final version is published on PR

The Relation between EIT Waves and Coronal Mass Ejections

More and more evidence indicates that "EIT waves" are strongly related to coronal mass ejections (CMEs). However, it is still not clear how the two phenomena are related to each other. We investigate a CME event on 1997 September 9, which was well observed by both EUV imaging telescope (EIT) and the high-cadence MK3 coronagraph at Mauna Loa Solar Observatory, and compare the spatial relation between the "EIT wave" fronts and the CME leading loops. It is found that "EIT wave" fronts are co-spatial with the CME leading loops, and the expanding EUV dimmings are co-spatial with the CME cavity. It is also found that the CME stopped near the boundary of a coronal hole, a feature common to observations of "EIT waves". It is suggested that "EIT waves"/dimmings are the EUV counterparts of the CME leading loop/cavity, based on which we propose that, as in the case of "EIT waves", CME leading loops are apparently-moving density enhancements that are generated by successive stretching (or opening-up) of magnetic loops.Comment: 12 pages, 4 figures, accepted for publication in ApJ Letter