Condensed concepts

He gives away his whole salary to a not-for-profit. He is reluctant to go into administration because he has to give up teaching. He serves as president at the same institution for 35 years. He increases the endowment from $9 million to $350 million. When he takes over the university is mostly known for football. When he leaves it is a major research university. He does not embrace the football program. He introduces enrolment of female students. He stands up to the president of the country over civil rights. He is a major leader of campus opposition to a controversial war. He changes the governance of the university so that it is no longer controlled by the sectarian founders, although he is one of them. He speaks out often about issues of justice, human rights, racism, and poverty. A survey of his peers identify him as the most effective college president in the country. Is this fantasy? Could such a person actually exist? Previously I posted about a dream graduation s

Maybe it is just my personality but I increasingly find that in science and life I am out of step with the surrounding culture. I just have modest goals .  I just want to understand a few things and make some sort of reliable contribution. This means publishing in PRB, J. Chem. Phys., and occasionally in PRL. I don't aspire to publish in luxury journals, double my funding, to see my university the most highly "ranked" in Australia, or claim that my research will revolutionise materials science and molecular biology, ... This is why I increasingly find it hard and tedious to write grant applications. I will also be happy if Liverpool just finish in the top 4 of the Premier League.... I think good science is really hard and most advances come from long term projects with painstaking hard work and from the occasional serendipity. Yet it seems society is sold on hype, the winner takes all mentality, and everyone should aspire to be a winner... I am certainly interest

Yesterday, at UQ  Robert Mann gave a nice Quantum Science seminar, " Hot and Cold Accelerating Detectors". It concerned the  Unruh effect : suppose one observer is constantly accelerating relative to another. Then, what is a quantum vacuum (for a free boson or fermion field) to one observer is a thermally populated state to the other. Specifically, if one considers a field with wave vector k and energy  Ω   k. Then the expectation of the number operator is, (5) ⟨ 0 | b k † b k | 0 ⟩ = ( e 2 π Ω k / g − 1 )

Given the complexity of human subjects in economics, sociology, and medicine it is hard to find data that clearly indicates a correlation between two variables. I read The Economist each week and many of the graphs that they present just look like random noise to me. However, a year ago they showed the curves below, that I found rather convincing. The graphs are in an article  Tobacco and health: Where there's smoke  that marked the fiftieth anniversary of the USA Surgeon Generals report which contained the graph on the left showing a correlation between life expectancy and smoking. The graph on the right shows how cigarette consumption in the USA has changed over time, reaching a maximum around the time of the report and decreasing after the banning of broadcast advertising. Unfortunately, the response of tobacco companies to their reduces markets in affluent countries has been to shamelessly promote smoking in the Majority World and to intimidate those who oppose them. Thi

How is a Hubbard model related to Density Functional Theory? Jure Kokalj and I recently wrote a paper where considered the effect of strong correlations on thermal expansion, all within the framework of a Hubbard model. This is mostly concerned with explaining anomalies in organic charge transfer salts at temperatures less than 100 K, i.e. much less than the Fermi energy. One referee stated “However conceptually this Hamiltonian can not capture the free energy of the relevant electrons loyally. Recall the total energy decomposition in density functional theory, the Hamiltonian corresponds only to the band energy part (which is a summation of occupied Khon-Sham states and different from the kinetic energy) plus interaction term. And the remaining Hartree part, exchange-correlated part and also ionic part, which depend on the lattice constants, are totally ignored. It is not known whether the contributions from such terms are trivial or monotonic especially when strong correlation

There is an interesting preprint Breakdown of Fermi liquid description for strongly interacting fermions  Yoav Sagi, Tara E. Drake, Rabin Paudel, Roman Chapurin, Deborah S. Jin It describes some nice ultra cold atom experiments that tune through the BEC-BCS crossover with a Feshbach resonance, focusing on the properties of the normal (i.e. non-superfluid) phase. All the measurements are at a temperature of T=0.2T_F, just above the superfluid transition. It is like an ARPES [Angle Resolved PhotoEmission Spectroscopy] experiment in the solid state. Specifically, the one-fermion spectral function A(k,E) is measured, shown in the colour intensity plots below. The left and right side correspond to the BCS and BEC limits respectively. The unitary limit [i.e. infinite interaction occurs close to the middle]. On the left one can clearly see dispersing quasi-particle excitations, as one would expect in a Fermi liquid. As the interaction strength increases this feature is broader and

This year I am on a committee that looks at funding applications from all areas of science. Inevitably, this will lead to problematic comparisons of the track records of mathematicians versus physicists versus biologists. The quick, lazy, and unjustified recourse is to start invoking impact factors and publications in luxury journals. There is a very thorough and helpful report Citation Statistics from the International Mathematical Union that clearly shows how problematic citation metrics are. Of particular interest is the graph below. Note that mathematicians are cited three times less than physicists and six times less than life scientists. Aside: I am not clear what the distinction is between life sciences and biological sciences. Is the latter more oriented to humans [e.g. medicine] and the latter plants and animals? This report is cited in the San Francisco Declaration on Research Assessment , initiated by biologists, that is attracting significant interest and mention

One of the most crazy and disturbing ideas of the current Australian government for "reform" of universities is to "become more like the USA" which means to "deregulate", "make users pay" and "increase competition" and allow more "private [i.e. for profit] providers". This video by the inimitable John Oliver shows why for-profit colleges [coupled with generous government loan schemes] are a really bad idea. A less entertaining but thorough analysis of the Australian proposals, and with similar concerns, has been given by my UQ economics colleague Paul Frijters on the Core Economics blog. 

One of the most fascinating, challenging, and frustrating aspects of the iron-based superconductors is the presence of many competing energy scales , particularly associated with Hund's rule coupling. There are debates about just how strong the correlations are, how large the spin moments are, and how relevant Mott physics is. Furthermore, Hund's rule seems to lead to an unusual metallic state that is both difficult to characterise and describe theoretically. It has some signatures of a bad metal, as emphasised by (amongst others) Haule, Kotliar, Si, and Abrahams, but this characterisation is disputed by Johnston in his review [see Section 3.8.2]. Given the chemical and structural diversity of this large class of materials, we should be cautious about claiming the same physics is dominant in all the materials. There is a nice paper that illustrates the richness of this system. Local Quantum Criticality of an Iron-Pnictide Tetrahedron  T. Tzen Ong and Piers Coleman I

Recently I was asked about how universities around the world are changing. I found my answer a bit depressing, as I see most of the changes as negative. However, the other day I reflected on some positive changes that have occurred at Australian universities since I was an undergraduate at the Australian National University (ANU), 35 years ago. [There are also some significant negative changes, but I just want to acknowledge some positives]. I think some of these positives are particularly well done by my department, and by UQ, but I think they are also present at other universities. Outreach to high school students. A host of different programs bring students on campus for a range of activities. Faculty or "outreach officers" visit high schools. Although, ANU did run a friday afternoon math club for high school nerds in Canberra [where I grew up], I never had the opportunity to participate in a program such as the Queensland Junior Physics Olympiad. International exch

In 2010 MIT put out a press release about connections between string theory and cuprate superconductors that led to some breath taking articles in the media discussed on Peter Woit's blog. The key issue is whether holographic techniques produce results that are relevant to real materials. It is interesting to look at a recent paper Holographic duality and the resistivity of strange metals Richard A. Davison, Koenraad Schalm, and Jan Zaanen They state Analyses of this kind [based on the AdS-CFT correspondence] have found examples of systems, controlled by quantum critical infrared fixed points, with linear resistivities, among other interesting phenomena. While interesting, many of these results appear to be highly dependent upon the microscopic details of the infrared fixed point being considered, and, a priori, it is not clear whether these details are generic and could be realized in real electron systems, or whether they are artefacts of the kinds of highly symmetric

It is currently grant writing season in Australia. Arghh...! Writing grant applications is a painful and demanding process. It is bad enough for old timers like me, but even worse for beginners. In the School of Mathematics and Physics at UQ, we are experimenting with different ways to support applicants and provide constructive feedback. Previously, I spoke at one such workshop. We already have a "Reader" program where applicants give their whole application (50-100 pages) to a senior faculty member for feedback. However, I don't think this program gets used as much as it might or should be. That includes by me! By the time I have finished the application I am sometimes so "burnt out" I don't want to spend time and energy changing it. This highlights the importance of early feedback : even before the writing starts, when people are picking projects, co-investigators, and planning budgets. Today we tried something different. About twenty people came

Previously, I posted about possible quantum limits to the shear viscosity in quantum many-body systems. This has attracted a lot of interest because of claims, based on string theory techniques [AdS-CFT correspondence] that there is a universal lower bound for the ratio of the shear viscosity to the entropy. There are two interesting papers Hydrodynamic fluctuations and the minimum shear viscosity of the dilute Fermi gas at unitarity Clifford Chafin and Thomas Schäfer Temperature evolution of the shear viscosity in a unitary Fermi gas   Gabriel Wlazłowski, Piotr Magierski, Aurel Bulgac, and Kenneth J. Roche The main result of the latter is shown in the Figure below. The error bars arise because the results are based on a Quantum Monte Carlo simulation with imaginary time data that must be analytically continued to real frequencies [a thorny problem]. Tc is the superfluid transition temperature and T* the pseudogap temperature. A few reasons why this is interesting. 1.