Fashionable physics

One of my favorite physicist bloggers, Doug Natelson of Rice University, once observed with mock exasperation:

Doug was writing in 2009. A year later—as I’ve only just found out—a team led by Takashi Takahashi of the WPI Advanced Institute for Materials Research at Tohoku University created an iron pnictide material, barium iron arsenide (BaFe₂As₂), whose electronic properties resemble those of graphene and topological insulators. If Doug or anyone else wants to start research programs in the three hottest areas of condensed-matter physics, it can be done with just one material.

To burst on the physics scene and spawn scores of preprints, a new discovery must be interesting and potentially important. But it must also be somewhat accessible to researchers. Adding super-heavy elements to the periodic table on the way to discovering the island of stability may be interesting and important, but only three groups—at the GSI Helmholtz Center for Heavy Ion Research in Garching, Germany; the Joint Institute for Nuclear Research in Dubna, Russia; and Lawrence Berkeley National Laboratory in California—have the expensive specialized equipment needed to participate in the quest.

Graphene is far more accessible. Indeed, the material became hot in part because Andre Geim and Kostya Novoselov discovered a simple, cheap way to make it. If you opt to work on the arsenide members of the iron pnictide family, you’ll need to follow your institution’s rules about working with poisonous materials. Still, as attested by the explosion of papers that followed Hideo Hosono’s 2008 discovery paper, making the materials doesn’t appear to be especially challenging.

As for topological insulators, the first material to exhibit the phenomenon, mercury telluride, is difficult to work with because of mercury’s low melting point. I don’t know about the other materials, but the theorists who rushed to work on topological insulators—graphene and iron pnictides, too—faced no experimental impediments to their creativity.

QPOs and cuprates

I was an astronomy graduate student in 1986 when Georg Bednorz and Alex Müller discovered high-T_c cuprates. Although the explosion of research ignited by their discovery soon reached me at Cambridge University, I barely felt its shock wave.

I did, however, experience the (albeit more modest) frenzy that accompanied Michiel van der Klis and Fred Jansen’s 1985 discovery of quasi-periodic oscillations in the light curves of x-ray-emitting binary stars. In retrospect, QPOs manifested their hotness in the same way that graphene, iron pnictides, and topological insulators do—in a burst of theoretical explanations and further observations or experiments.

Being part of a global race to elucidate and understand a new phenomenon is thrilling. I don’t think the powers that be in science—that is, funding agencies—should put too many restrictions on what curiosity-driven scientists want to work on, even if giving scientists a free hand entails diverting resources.

That said, in so far as following physics fashion prevents you from doing other things, hot fields have their drawbacks. In October 2008, the Institute of Physics of the Chinese Academy of Sciences held a workshop on the recently discovered iron pnictides. Speaking the workshop, Koichi Kitazawa, a veteran of the high-T_c cuprate boom, admitted that, in retrospect, he wished he’d followed the advice of his junior colleagues and not focused so narrowly on cuprate materials. “If I’d listened to them,” he said, “maybe we’d have discovered the iron pnictides.”