Tuesday, February 28, 2006

This week in cond-mat

I'm going to try to get more serious about regularly blogging condensed matter physics issues. First, I intend to have a weekly discussion of cool results on the arxiv preprint server, and here is my inaugural attempt. Think of it as a poor man's Condensed Matter Journal Club. The Bell Labs version is fine, but their tastes run rather to the theory side for me....

cond-mat/0602623 - Troisi and Ratner, Molecular Transport Junctions: Propensity Rules for Inelastic Electron Tunneling Spectroscopy
This paper is a snapshot of a whole subfield that lies at the interface between physics and physical chemistry. The molecular electronics community has long been interested in ways of characterizing molecular layers or even single molecules by their "fingerprint" one electronic conduction. Correctly formulating a theoretical approach to electron transport through a realistic system is very challenging: this is basically a nonequilibrium problem, with both electronic and vibrational degrees of freedom driven far from thermal equilibrium. This paper shows that IETS intensities can often be strongly affected by symmetry considerations.

cond-mat/0602608 - Wunderlich et al., Coulomb blockade anisotropic magnetoresistance: single electronics meets spintronics
The anisotropic magnetoresistance (AMR) is a band structure effect relevant in ferromagnets, in which the resistance of the material depends on the relative orientation of the current and the magnetization. Large versions of AMR have recently been observed in ferromagnetic constrictions here, here, and here, as well as in dilute magnetic semiconductors here. This paper reports a very interesting experiment, in which single-electron transistors are formed from a dilute magnetic semiconductor (GaMnAs). The resulting devices show single-electron charging effects in their conduction, but strongly modified by large tunneling AMR. Neat stuff.

cond-mat/0602565 - Novoselov et al., Unconventional quantum Hall effect and Berry's phase of 2pi in bilayer graphene
This is another great example of the work going on in a comparatively newly examined material system: electronic transport in essentially single (or in this case double) graphene layers. Because of the unusual band structure of graphene, charge carriers have an effective mass of (ideally) zero (!), which has all kinds of strange consequences. This material was first examined essentially simultaneously by about four groups (1, 2, 3, 4), three of whom spoke in a session I organized last year at the March Meeting of the APS. It absolutely blows me away that one can put single sheets of graphene down on surfaces, wire them up, and not have disorder completely bugger all the transport.