Condensed concepts

When I was a graduate student at Princeton it was known that the President, William Bowen , regularly taught an undergraduate class. I recall reading that he thought that this was important so he did not lose touch with what the institution was all about. Much later in 2011 Bowen also said "Teaching and doing research are very good preparation for this kind of job because you have to analyze issues and understand them, and you have to be able to communicate," he said. "Teaching is a great way to hone whatever skills one has in that area. A lot of being president is about teaching." Also, while watching The Ivory Tower I noticed that Michael Roth, the president of Wesleyan College , seemed to be teaching undergraduates. Indeed, his web page says, He continues to teach undergraduate courses, and through Coursera has offered MOOCs, the most recent being “How to Change the World.” Does anyone know of other examples? I think Bowen and Roth should not be an

In a molecule one can observe excitation by infra-red photons of overtones of vibrational modes, i.e. if nu is the fundamental vibrational frequency, the absorption of photons with frequency of about 2 nu, 3 nu, ... can be observed. The quantum picture is below for a 4nu absorption. I recently learnt that overtone absorption is classically forbidden,  i.e. it is intrinsically quantum mechanical (just like tunnelling, reflection above a barrier, interference, entanglement, ...). It does not occur in the limit that Planck's constant goes to zero. Explicitly if you take an anharmonic oscillator and drive it with an external field of frequency 2 nu, you cannot get the oscillator to go at 2 nu. Furthermore, this involves dynamical tunnelling, i.e. there is no potential barrier in real space, but rather tunnelling occurs in phase space. There is a nice article by Eric Heller where he shows that overtone excitation is like reflection above a potential barrier. The figure belo

Basically, look at the figures. The amount of literature we might read is increasing exponentially. It is overwhelming. We all need some strong filters to focus on a few papers. This can save a lot of time. The question is really, "Should I read this particular paper?" This means answering two questions. 1. Does the paper contain some results that are of interest to me personally? 2. Are the results valid and important? These days I tend to only look at papers that someone else recommends to me or are cited or linked to in papers I have decided to "read" using the procedure below. The quickest and most efficient way to answer these questions is. a. Read the title and abstract. Is there potentially something of concrete interest to me? If not, ditch the paper. b. Look at the figures. Are they comprehensible? If not, ditch the paper. Do they contain new results, I did not know about? Are they interesting and important? Are they valid? Do they make

Peter Woit refers to this video. It has some good insights, even if the genre is of debatable taste. A few brought chuckles to me. But, I feel it is a bit like laughing at Yes, Minister.

My collaborators and I just finished a paper Spin-orbit coupling and odd-parity superconductivity in the quasi-one-dimensional compound Li0.9Mo6O17 Christian Platt, Weejee Cho, Ross H. McKenzie, Ronny Thomale, and Sri Raghu Here is the abstract. We welcome any comments. One thing I learnt and found interesting what the unusual spin-orbit coupling that arises due to lack of inversion symmetry in the four-atom unit cell. I will post separately about that next week as the story of the corresponding coupling in graphene is an interesting one.

The relationship between a Ph.D student and their advisor or supervisor is a complex one. I have written before about the importance of both parties having clear expectations and communicating and agreeing on them at the beginning of working together. Over the years I have seen or heard of some strange things. Below is a list of some things that students have found their advisor expected. work on my thesis topic prepare a slide or two about my thesis work that they will present at a conference write a small grant application for me to fund my travel to a conference give feedback on their draft grant application that is related to my project give one of their lectures while they are away at a conference organise a weekly seminar series act as de-facto supervisor for an undergraduate student research project that is not related to my project maintain the group website spend a morning on the registration desk for a conference they are organising referee a paper or

A basic question that comes up in introductory solid state physics is: Why does the Sommerfeld model for metals work so well? It assumes that electrons are non-interacting fermions. Yet if you calculate the first order correction (in e^2 where e is the electronic charge) in the Coulomb energy you find it is comparable to the kinetic energy associated with the ground state. Aside: the success of Sommerfeld is such a puzzle that Wigner mentioned it (for the wrong reasons in my view) at the end of his famous 1962 essay, The Unreasonable Effectiveness of Mathematics in the Physical Sciences. The standard answer we give students is screening  plus Landau's Fermi liquid theory. However, an interesting question is what happens if you try to actually do some sort of systematic many-body expansion with respect to the Coulomb interaction. Can you get the calculation to converge to experiment and see why Sommerfeld is good? In Telluride last (northern) summer I heard a nice talk by

I think this is an issue that is rarely discussed. People just assume their point of view is the valid one. Then they are surprised or upset when the "representative" does not act as they "should". Suppose Professor Smith from the Chemistry department is on a committee from the College of Arts and Sciences that determines some internal funding or policies for the departments within the College. Here is a list of different interests and perspectives that she could represent: -her own -her research subfield of synthetic organic chemistry -the chemistry department -just the science departments -all the departments in the College -the Dean of the College -senior management of the university -tax payers, alumni, students., .. Idealists might say that of course she should consider and understand all views. But that rarely happens. Some seem to think that in this cruel world representatives should fight tool and nail for their own interests, or at least those

How do you calculate the absorption intensity associated with a molecular vibration? First, why might you care? This is not just a basic scientific issue that is only of interest to people working in molecular spectroscopy. It actually lies at the heart of global warming. For example, why is methane a much worse greenhouse gas than carbon dioxide? It is because it has a much larger infrared (IR) absorption intensity in the relevant frequency range. In the electronic ground state consider a transition from a vibrational level with quantum number j to one with i. The absorption intensity is given by where the dipole matrix element between the two vibrational states is I  use r to denote all the nuclear co-ordinates. mu_g (r)  is the dipole moment of the molecule in the electronic ground state. For notational simplicity I neglect the vector character of the dipole moment. One can now make an approximation to greatly simplify evaluation of this matrix element and

The New York Times has a nice obituary  Michael W. Davidson, a Success in Microscopes and Neckwear, Dies at 65 I did not know Davidson personally but I did benefit from his art. I visited the National High Magnetic Field Lab at Florida state several times in the 1990s. In appreciation my host Jim Brooks gave me a few of the neckties [which I still wear, on the rare event I actually wear a tie!] and a series of prints of images of  Australian products such as that of Vegemite below. I still have these prints on display in my office. The website  Molecular expressions  contains not just a gallery of many beautiful microscope images but also more technical discussions about microscopy. One thing I did not know about Davidson that I learnt from the obituary was the important role he played in the work for which the Chemistry Nobel Prize of 2014 was awarded.

John Quiggin lists a litany of cases where the answer to the question is yes. It particularly makes for depressing reading given the blind push for privatisation by the Australian government. I think for-profit private education is particularly likely to be problematic when two criteria are met: 1. Consumers are not paying up front. For example, if they are paying tuition from government loans that they will only have to pay back a decade later. 2. Consumers (students and parents) don't have the ability and/or information necessary to assess the quality of what they are getting for their money. For example, a poor parent who never finished high school may struggle to know what a good ollege education should look like. These criteria means the "free" market is not very responsive. Until a month ago I thought that the answer to this question was universally, Yes! However, one should never say never. For my birthday my son gave me a copy of The Beautiful Tree:

Best wishes for the New Year! Here is a selection of posts from last year I thought were the best and/or the most satisfying to write. Are American universities Crystal Cathedrals? Is DMFT the "only game in town"? Battling High Impact Factor Syndrome. II What the ten key concepts in quantum many-body physics? The two biggest obstacles to science Ph.Ds getting a job in industry A nice write up in Physics World Common challenges with constructing diabatic states and Wannier orbitals Conical intersections vs. Dirac cones. Chemistry vs. Physics. Emergence and singular asymptotic expansions. II Engaging Indian school students in real science experiments There is no metal-insulator transition in extremely large magnetoresistance materials. 2. Thanks again to all the readers who provided positive feedback last year, and particular thanks to those who wrote comments on the blog. Hope to see more in 2016! I welcome suggestions on possible topics for future