In The Field

APS: Iron pnictides. WTF?

graphene.jpgPretty much anything with iron pnictides in the title is guaranteed to draw a crowd at this year’s meeting. I snapped this picture at a random session this morning, but others have been so rammed that it’s been hard to get in the door. Iron pnictides are the hottest new superconductor, so it’s not surprising that they’re getting a lot of attention. But I’ve been to a few of these talks, and I’m going to be frank—if you’re not an expert it’s very hard to follow. And I know what you’re thinking (particularly if you’re one of my editors): This guy’s a senior reporter with Nature and you’re telling me he can’t understand this stuff?

Well before you get on my case, it turns out I’m in good company. At a reception last night I sat down with David Singh, a theorist at Oak Ridge National Laboratory, and he told me that nobody really understands the pnictides. We’ve published a few papers recently suggesting that, unlike the cuprates (the other main class of high-temperature superconductors) pnictides seem to facilitate electron flow in three dimensions. But there’s still a lot of questions about what induces this superconductivity. “It’s new, it’s different and people don’t understand it,” Singh says.

So WTF? What’s all the excitement at this meeting about? Well Singh tells me that there’s a couple of things worth noting. First, people are synthesizing better quality pnictide samples. In particular, they’ve got single crystal samples that are of very high purity and thus yield better data. The second thing that’s happening is that groups are synthesizing a bunch of different compounds and checking them out. I sat in on a talk by Hai-Hu Wen of the National Laboratory for Superconductivity in Beijing, where he discussed the latest results for pnictide compounds that use iridium, rhodium and cobalt to name a few.

These compounds all superconduct in a similar range of temperatures, so there’s no big breakthrough as yet. But Singh says that they’ll help us to better understand what’s going on, and you never know, there could be a surprise. The main point, he says, is that after decades of working on just the cuprates, the community now has another high-temperature model to work with. “Nature has given us two different routes to high-Tc,” he says.


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