Are you working on the hottest topic in your field? Many scientists may think so, but it has been a tough assertion to prove — until now, that is. A German physicist has devised a way of answering the ‘Hot or not?’ question for his discipline. If it stands up to scrutiny, it could be used to rate topics across the sciences. In physics, the results show that hotness — measured by a parameter known as m — correlates well with the promise of future wealth... and that promise is greatest in nanotechnology.

12.85 Carbon nanotubes

Credit: S. HEINZE

Super-strong materials and blisteringly fast electronic circuits: the potential applications of these tiny carbon tubes, discovered in 1991, are so enticing that everyone is pouring money into the field.

8.75 Nanowires

Credit: NIST

Less well studied than nanotubes, but the possible uses are similar. Nanowires could eventually prove more useful than nanotubes, because their chemistry is easier to tailor and they can be used to create nano-sized lasers.

7.84 Quantum dots


Another nanotechnology with a huge range of potential applications. These tiny specks of semiconductor material, measuring as little as a few nanometres across, have already been used to create dyes for cell biologists and new kinds of laser. Physicists hope they might one day form the basis of a quantum computer.

7.78 Fullerenes

Credit: H. JAEGER & W. LOPES

These spheres of carbon atoms are attracting significant research interest. But the latest ranking rewards newness, so the topic may have slipped down the list because it predates nanotubes by around six years. The discovery of fullerenes earned a Nobel prize and spawned studies of numerous potential uses, such as drug delivery agents.

6.82 Giant magnetoresistance


Not a new topic, but still hot because of its economic importance. Modern hard disk drives were made possible by the discovery of giant magnetoresistant materials, which show marked falls in electrical resistance — more than around 5% — when a magnetic field is applied. Researchers are now aiming to make hard disks even more powerful.

How the topics were ranked

The ranking is an extension of a recently proposed system for rating the research output of individual scientists. The h index uses the highest number of papers a scientist has published that have each received at least that number of citations: for example, a researcher with an h of 50 has written 50 papers that have each had at least 50 citations (see Nature 436, 900; 2005). The index has attracted interest from bibliometricians, but was first described only last year and has yet to be studied in depth.

Michael Banks, a PhD student at the Max Planck Institute for Solid State Research in Stuttgart, Germany, totted up the h index for physics topics, rather than people, and then calculated the parameter m by dividing by the number of years over which the papers involved had been published (

Jim Giles

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