I was featured in a recent Sandia LabNews article along with other Sandia fellows (including fellow Stanford PhD Bette Webster). Check it out here.
Publication: Evidence of orbital ferromagnetism in twisted bilayer graphene aligned to hexagonal boron nitride
Our manuscript was accepted for publication in Nanoletters! Check it out here.
A new preprint I was involved in just came out (https://arxiv.org/abs/2105.01870). Here we study a twisted bilayer device with an angle (1.38 degrees) quite far away from the magic angle (1.05 degrees). In this device, we do not observe correlated insulating states. However, we do observe superconductivity and extremely strange behavior in magnetotransport. We observe large magnetoresistance over a large range in density near half filling. We also see that the gaps between Landau levels split and bend in field/density. Interestingly, it seems that this can be entirely modeled using a simple tight-binding model of Hofstadter’s butterfly on an entirely different lattice (square) if one includes anisotropic hopping term, indicating that they are likely a manifestation of some more generic class of phenomena.
A new preprint I was involved in came just came out (https://arxiv.org/abs/2012.10075). In this work, we have been looking at ballistic transport in an extremely clean material: PdCoO2. We can see all sorts of strange transport signatures from the system being both ballistic and having a hexagonal Fermi surface. The electrons will travel mostly along the facets of the Fermi surface in the limit of zero field, leading to anisotropy in the transport. We studied this by studying the transport through very long bars that are oriented at a specific angle relative to the crystal axis (and hence the Fermi surface).
Code for modeling ballistic transport in a mesoscopic device can be found at https://github.com/dgglab/ballistic_montecarlo
Preprint: Evidence of orbital ferromagnetism in twisted bilayer graphene aligned to hexagonal boron nitride
Check out our latest preprint (arXiv:2102.04039), where we perform hyestersis loops on the magnetic state found in twisted bilayer graphene at various tilt angles. We find that at above some threshold tilt angle, the magnetic state responds to a threshold out-of-plane magnetic field indicating that the magnetism is highly anistropic. This tells us that the orbital magnetic moment is likely dominant, as it is the most obvious route for a high degree of magnetic anisotropy. As the tilt angle becomes very small (field is mostly in the plane of the sample), the story becomes much more complicated and we no longer see this clear response.
Check out our latest preprint (https://arxiv.org/abs/2012.10075). Up to now, all of the moiré systems that have displayed correlated behavior have done so at an integer number of carriers per moiré unit cell. It is somewhat natural to expect this given that there may be a large exchange energy favoring the system to polarize the avaliable degrees of freedom near integer filling. In this preprint, we discuss some of our recent findings of evidence of magnetism away from integer filling of the lattice. It seems that there are also some similar rumblings of evidence of correlations at non-integer fillings in other moiré systems that may also be coming out soon!
Here are two press releases from Stanford regarding our recent publication: Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene.
Thanks to Stanford libraries and the Stanford Digital Repository. They host a number of great resources and helped us post all of the data for our publication.
Press release from LBL News regarding our recent publication: Tunable correlated Chern insulator and ferromagnetism in a moiré superlattice
Press release from LBL News regarding our recent publication: Signatures of tunable superconductivity in a trilayer graphene moiré superlattice
This recent article from the Journal Club for Condensed Matter Physics mentions our recent preprint arXiv:1901.03520, a [great paper by Matt Yankowitz et al] (http://science.sciencemag.org/content/early/2019/01/25/science.aav1910), and an incredibly interesting talk Dmitri Efetov gave as part of the moiré flat bands program hosted by KITP. I was lucky enough to attend this program and it is definitely worth checking out.
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