When faculty politics becomes deadly

The Christian Science Monitor reports

A neuroscience professor at the University of Alabama-Huntsville has been charged with capital murder for killing three people after opening fire at a faculty hearing. Dr. Amy Bishop reportedly had learned that her request for tenure had been denied for a second time.

A Ph.D without knowledge?

Sometimes I struggle with defining the minimum that someone should be able to do and know before they are allowed to graduate. Here is a story (possibly an urban legend) which might put things in perspective.

At Princeton after a student submits their Physics Ph.D thesis they are given an oral exam by a faculty sub-committee. After a short presentation on the thesis by the student they are asked questions about it for half an hour or so. Then the faculty can ask the student ANY question about ANY area of physics (e.g., why is the sky blue? why is diamond called "ice" by criminals? explain the twin paradox in special relativity.) I believe the purpose of this is to show students how much they do NOT know, particularly about basic physics.

Many years ago there was a very bright young student who completed a thesis on general relativity and was about to go and do a postdoc with Stephen Hawking. He was asked, "How big is an atom?" He did not know!

But, he got his Ph.D.

So, who was the student? Someone once told me it was Nathan Myhrvold, who for many years was Chief Technology Officer at Microsoft.

Breakdown of the Born-Oppenheimer approximation

The Born-Oppenheimer approximation is the starting point for all quantum chemistry and crystal band structure calculations. It allows one to factorise the electron-nuclear quantum state. It can be justified because nuclei are much heavy than electrons. However, it breaks down near electronic degeneracies. A case that has attracted a lot of attention are conical intersections between two potential energy surfaces for different electronic states of molecules. Such intersections provide a rapid means for non-radiative decay of excited states.

Going beyond Born-Oppenheimer represents a major challenge. A nice recent review for molecules is by Worth and Cederbaum.

A few years ago in a Phys. Rev. A paper, Andrew Hines, Chris Dawson, Gerard Milburn and I considered two different Jahn-Teller model Hamiltonians and quantified the entanglement of the electronic and nuclear degrees of freedom. One of these models has a conical intersection.

A metal and an insulator at the same time?

Michael Smith brought to my attention a really nice preprint, Interplay charge dynamics in a valence-bond dynamical mean-field theory of cuprate superconductors, by Michel Ferrero, Olivier Parcollet, Gabriel Kotliar, and Antoine Georges.

This helps resolve the following major puzzle about the metallic state of the cuprate superconductors. In conventional metals (insulators) one observes that the resistivity monotonically increases (decreases) with increasing temperature. Indeed for currents parallel to layers the cuprates show the temperature dependence characteristic of a metal. But, for currents perpendicular to the layers underdoped systems show a temperature dependence characteristic of an insulator.

How can it be a metal in one direction and an insulator in another?

It turns out that the key physics involved is:

• the interlayer tunneling matrix element is momentum dependent (as required by the symmetry of the crystal) and vanishes in the parts of the Brillouin zone in which the nodes of the pseudogap occur in the underdoped system.
• this means that the interlayer charge dynamics is dominated by the antinodal region and so particularly sensitive to the pseudogap
• the temperature dependence of the scattering rate in the nodal region is sensitive to doping and at low temperatures the nodal quasi-particles become more coherent

Some of this physics was anticipated in a phenomenological "cold spots" model by Ioffe and Millis in 1998. What is new and important about Ferrero et al.'s work is that they start with a Hubbard model and calculate the temperature, frequency, and doping dependence that are consistent with experiment.

It is also interesting to me that rho* in the figure above has the value characteristic of a bad metal.

Artificial photosynthesis

Accounts of Chemical Research just published a special issue on Artificial Photosynthesis and Solar Fuels.

Articles I would particularly like to read include:

Structures and Energetics for O2 Formation in Photosystem II Per E. M. Siegbahn Theory of Proton-Coupled Electron Transfer in Energy Conversion Processes Sharon Hammes-Schiffer

Dye Sensitization of Single Crystal Semiconductor Electrodes Mark T. Spitler and B. A. Parkinson

Is this me?

Marriage counseling for chemists

Roald Hoffmann, Philippe Hiberty, and Sason Shaik are probably my three favourite theoretical chemists. They write beautiful papers which focus on the quantum mechanical basis for chemical concepts and understanding rather than computation. Being a fly on the wall when they are all in one room for a scientific discussion would be fascinating. Well I don't have to dream. There is a really nice paper in Accounts of Chemical Research, A Conversation on VB vs. MO theory: a never ending rivalry. The three discuss and argue the relative merits and relationship between valence bond theory and molecular orbital theory. Here are a few choice quotes:

RH: A standard technique in marriage counseling (and I do think that MO and VB are a partnership) is to have the two parties stop and repeat, with an effort at understanding, what was said by the other partner. Can we try that? ......

PH: .......Pauling was smart enough to disguise all these “physical” elements of VB and packaged it as simple resonance theory. This was good for the 1930s, but now chemists have more theoretical savvy, and can digest these bits of physics, couldn’t they?

RH: Maybe. Some of them think theory is computation, and dignify that with the name of physical insight. The best physicists I’ve known - people like Ed Purcell - were after a quality of understanding that is ... almost chemical.

SS: ........ what tipped the balance in favor of MO may have been simply the computer implementation of MO-based theories. Chemists are a practical lot; they simply went where they could calculate.

RH: As they are doing now with the software available - it’s amazing what gains prominence just because there is a button in Gaussian to do it!