tag:blogger.com,1999:blog-13869903.post6511495902675413404..comments2024-03-29T02:45:10.096-05:00Comments on nanoscale views: Superconductivity in graphene bilayers - why is this exciting and importantDouglas Natelsonhttp://www.blogger.com/profile/13340091255404229559noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-13869903.post-21306318827009082382018-03-16T15:17:46.393-05:002018-03-16T15:17:46.393-05:00Pablo's talk was actually recorded, and can be...Pablo's talk was actually recorded, and can be found at https://www.youtube.com/watch?v=O2HVCjhuJlEAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-13869903.post-7586662838408082782018-03-12T09:44:39.096-05:002018-03-12T09:44:39.096-05:00Someone has to say it: this is by far the most imp...Someone has to say it: this is by far the most important discovery made in graphene since its discovery 14 years ago. All the other findings made in this "promising" material were either repeats (with some variations) of effects observed in other high-mobility systems, or simpler single-electron effects predicted by the band structure. So I think there was some disappointment in what had been done so far, especially given the number of groups working on graphene. So I say: finally! Something interesting for the physics community! And kudos to the MIT group!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-13869903.post-15656171041920714052018-03-10T03:18:16.819-06:002018-03-10T03:18:16.819-06:00Doug, thanks for a great review of Pablo's tal...Doug, thanks for a great review of Pablo's talk. I missed it and regret it, but this is a great substitute. I wanted to focus on one of the points you mentioned.<br />"This system is effectively a triangular lattice - that's a very different beast than the square lattice of the cuprates or the pnictides."<br />I believe this is what actually saves the high-Tc state. Single-band Hubbard model on a square lattice would show strong antiferromagnetic correlations (albeit not order thanks to Mermin-awagner), but those are killed anyway. Pnictides are multiorbital. Does the right angle stacking break valley degeneracy? (In other way how many orbitals in the effective model should I see)Andrey Antipovhttps://www.blogger.com/profile/06839878296377260533noreply@blogger.comtag:blogger.com,1999:blog-13869903.post-46058654549294237142018-03-08T09:34:43.717-06:002018-03-08T09:34:43.717-06:00Anon@9:22, not explicitly, though the physics is r...Anon@9:22, not explicitly, though the physics is related, in the sense that both have to do with hybridization between states in the upper and lower layers. I do think that slight changes in angle can change the physics a lot - the insulating states ascribed to Mott physics only exist in very narrow (fractions of a degree) ranges of twist angle around the "magic" angle. This questions are one reason why theorists are going to have a field day. (Thanks for the kind words.)Douglas Natelsonhttps://www.blogger.com/profile/13340091255404229559noreply@blogger.comtag:blogger.com,1999:blog-13869903.post-24037003952882057492018-03-08T09:22:04.281-06:002018-03-08T09:22:04.281-06:00In the talk, did Pablo address at all the influenc...In the talk, did Pablo address at all the influence of the network of topological modes, as imaged here: https://arxiv.org/abs/1802.02999 ? It seems that twisting can lead to different kinds of effects; do they co-exist, or do slight changes in angle change the physics drastically, or something else?<br /><br />Thanks again for your great APS summaries!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-13869903.post-89911392124249697812018-03-07T12:56:07.274-06:002018-03-07T12:56:07.274-06:00Anon, your intuition is correct. The bilayers are...Anon, your intuition is correct. The bilayers are made by manual stacking (!), and at room temperature and large areas under typical conditions they will sit still, but if you elevate the temperature a bit (say 150C) they will try to snap back into Bernal stacking unless they're otherwise fixed. Douglas Natelsonhttps://www.blogger.com/profile/13340091255404229559noreply@blogger.comtag:blogger.com,1999:blog-13869903.post-11620637242286346322018-03-07T12:07:27.337-06:002018-03-07T12:07:27.337-06:00As someone not in the field, I am curious as to ho...As someone not in the field, I am curious as to how these twisted bilayers are made. Naively, I would think if I take two sheets of graphene and stack them it would be energetically favorable for the two layers to be aligned rather than twisted with respect to one another. Is there some reason that is not the case and you can arbitrarily change their orientation?Anonymousnoreply@blogger.com