Monthly Archives: March 2019

Escape into the wonders of physics

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Post by Giulia Pacchioni

LabEscape is an escape room based on physics – I got the opportunity to explore it during the APS March meeting in Boston, where it was set up for one week away from its usual site in Urbana, Illinois.

Prof. Schrödenberg went missing, and an important grant needs to be submitted. As her new interns we need to log into the computer and hit the submit button. Easy… well, we need to figure out the password, but luckily the professor left hints around the lab in case she forgot it!

Together with a team of five other physicists (the other interns in the lab), before entering the room I was handled information sheets covering some essential physics concepts laid out in a very digestible way. Indeed, the room, which is the brainchild of Paul Kwiat, a physics professor at the University of Illinois, is by all means not designed for physicists (even though it’s an absolute delight for them). It was created to provide an experience that demonstrates to the general public that physics is useful, permeates everyday objects and is, yes, fun.

Peter recommended we read the material carefully no matter how well we thought we knew it already, as knowing which concepts are illustrated in the room can help understanding how to crack the puzzles inside. Apparently, a group of physicists who refused to go through the material couldn’t escape in the set time, whereas a family with no scientific background who did their reading (as any good intern should do!) aced the challenge.

The main suggestion from Paul was to work as a team, with two or three people looking at each hint or object to combine different points of view, and to share all information with the others. He had to help us a bit, reminding us to work together each time we went our separate ways exploring the fascinating bits and pieces scattered around the lab.

The room contains a clever mix of challenges ranging from the usual looking around for hints and tools to actual small experiments using lab equipment that needs to be manipulated and sometimes completed with missing pieces. As in any good lab, instructions on how to use the instruments are provided, accompanied by extra explanations about how each experience works for the curious explorer. I don’t want to give too much away, but we got to play with an oscilloscope and a laser, polarizing glasses and, of course, a dead/alive cat in a box!

The riddles are generally simple, but require some lateral thinking and careful observation, which makes the experience fun and varied without it ever getting boring or frustrating. The experiments use scientific instruments in very creative ways, the type that stimulates a wow reaction both in science novices who think ‘how is this even possible!’ and physicists who think ‘I never thought of using it like THIS!’ Marveling at the various tricks was so fun that escaping the room became a bit of a secondary focus. Even after we did work out the password and could have escaped, my fellow interns had plenty of questions for Paul about how everything worked and how they could use some of the ideas in their own outreach activities.

For me, the take home message is that that working on a problem together and listening to each team member’s ideas is essential for overcoming challenges in the lab. Also in real life.

Interactions: Chen Fang and the Materiae database

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Post by Anastasiia Novikova.

In theory, many ordinary materials can have exotic topological phases. But how can we find them? In 2018 a research group from the National Laboratory for Condensed Matter Physics in Beijing scanned 39519 materials to predict which phases of the already-known compounds might exhibit topological properties. These materials were summarised into an interactive database Materiae, where you can browse compounds containing particular elements, check if they have any topological phases and visualise their band structure.

We asked Prof. Chen Fang — one of the team members who worked on Materiae along with Prof. Hongming Weng —  to give us more details of the project, which has now been published in Nature.

When did the database start? What were the main challenges of this project? What goals do you have for the future?

The database has been online since 23 July 2018; it appeared simultaneously with the posting of the corresponding paper on arXiv. By now there have been over 10000 unique visitors (1=ip*day). The most difficult part is, naturally, the calculation that was done to obtain the topological properties of about 30000 materials. The theory, the underlying work was accomplished back in late 2017 (arXiv:1711.11049 and 1711.11050), but even so, it was an effort to implement the fully automated algorithm shown in the flowchart. Currently we have the band structures plotted for topological materials only, and in the future we will add the band structure plots for all materials, topological and non-topological.

Using your algorithm, you scanned 39519 materials. How much time did the whole calculation process take?

We didn’t track the CPU hours used on this, but if we count the time spent on debugging small bugs now and then, it took us about three to four months in total for the bulk results to come out.

You mention that 8056 materials from your database are actually topological. How many of these materials were experimentally studied?

All materials have been reportedly synthesized in literature, but most of them were not studied from a “topological perspective”, but were studied for superconductivity or ferroelectricity, for example. I think at most few hundreds of these materials have been studied for potential topological properties.

What is the most “underestimated” material?

One example is Tl2Nb2O7. Oxides are seldom considered as topological materials in literature, yet our database registers it as a topological semi-metal. Surprised by this result, we further looked into this material, and realized that the mixed-valence nature of Tl ion is the origin of the nontrivial topology.

Another is Ba3Cd2As4. The layered structure made us expect it to be a weak topological insulator, but our database shows it to be a new type of topological crystalline insulator (having so-called C2-anomalous surface states). Shortly after the prediction, experimental groups have started synthesizing this material.

We expect the study of certain materials, like the ones above, may be “revived” by what we show in the database.

The database contains only non-magnetic materials. Is it possible to envision a similar type of database for magnetic materials?

The entire prediction is based on first-principle calculation, but magnetism is notoriously difficult to predict/include in any first-principle calculations. Therefore, while some theoretical work on the mapping between symmetry data and topological data has been out there for a while (arXiv:1707.01903), I do not think a similar material database can be obtained in near future because of the inherent difficulty of DFT mentioned above.