Condensed concepts

It is all relative. I often read in physical chemistry papers statements along the line of "a major puzzle is the extremely high mobility of protons and hydroxide ions in liquid water ..... explaining this leads to consideration of non-diffusive transport mechanisms such as the Grotthuss mechanism ." Furthermore, a physics paper,   Ice: a strongly correlated system , cited by field theory enthusiasts [gauge theories, deconfinement, ....], states ice exhibits a high static permittivity comparable with the one of liquid water, and electrical mobility that is large when compared to most ionic conductors. In fact, the mobility is comparable to the electronic conduction in metals. It has taken a while for me to understand the real issues. Atkins' Physical Chemistry textbook actually has a helpful discussion, featuring the table below. Thus, we see that the mobility of H+ and OH- (hydroxide) is about 3-7 times larger than that of other charged ions. This is ha

Economist Thomas Piketty has recently become a celebrity because of his new 700 page best selling book, Capital in the 21st century . The latest issue of Science has a special section about "the science of inequality" . It features a review by Piketty and his longtime Berkeley collaborator Emmanuel Saez. In the introduction the editors make an important point about an exciting future for economic research: And in the past decade in developed capitalist nations, intensive effort and interdisciplinary collaborations have produced large data sets , including the compilation of a century of income data and two centuries of wealth data.... It is only a slight exaggeration to liken the potential usefulness of this and other big data sets to the enormous benefits of the Human Genome Project.   Researchers now have larger sample sizes and more parameters to work with, and they are also better able to detect patterns in the flood of data. Collecting data, organizing it, develo

Ferroelectric materials develop a non-zero electric polarisation below a transition temperature, sometimes referred to as the Curie temperature Tc in analogue with ferromagnetic materials. Some materials have technological applications, including in dynamic RAM, as reviewed here. The possibility of ferroelectricity and antiferroelectricity associated with different orderings of protons in some of the high pressure phases of ice is also a fascinating subject. In other materials hydrogen bonds also play a central role. Furthermore, the quantum dynamics of the protons is key, as revealed by isotope effects, where H is replaced with deuterium (D). For example, if you look in Ashcroft and Mermin, Table 27.4, you see that the transition temperatures of Potassium dihydrogen phosphate and Potassium dideuterium phosphate are 123 K and 213 K, respectively. This is a huge isotope effect! What does this tell us? What is its origin? First, if we treat the nuclei classically, as in the Born-Oppe

I fear that may be the case. Previous cases of premature announcements include cold fusion, "life on mars" [really dead germs on meteorites from mars], neutrinos travelling faster than the speed of light, a Caltech theoretical chemist claiming he had solved high-Tc superconductivity ,..... In march BICEP2 scientists called a press conference to announce they had discovered evidence for cosmic inflation. This coincided with them placing a paper on the arXiv and Stanford releasing a Youtube video, that subsequently went viral, showing Andrei Linde being presented with the exciting news. However, now questions are being asked. The chronology is described by Peter Woit on Not Even Wrong and there is a nice discussion of the science by Matt Strassler.  The key issue seems to be the method used for subtracting the background signal due to galactic dust. It seems that BICEP2 scientists estimated this background signal by "scraping data" off the powerpoint slide from

An interesting question is: to what extent does the local institutional environment and the status of an institution affect the quality of the science done by an individual? If I move to a more highly ranked institution will I do better science? Or, if I move to a more lowly ranked institution will the quality of my work decline? Some scientists are obsessed with "moving up", thinking that being at the "best" place is essential. They cannot fathom that one could do outstanding work at a mediocre institution. However, consider the following. People at a high status university may get Nobel Prizes but that is not necessarily where they actually did the prize-winning work. Here are a few examples. John Van Vleck: Wisconsin to Harvard Joe Taylor: U. Mass to Princeton Tony Leggett: Sussex to Urbana William Lipscomb : Minnesota to Harvard Can anyone think of other examples? So can one actually measure how career moves affect the quality of science? One recen

I have posted before that I think it is very important in teaching to present students with comparisons of theory with actual experimental data. It is disturbing that many teachers and textbook writers make little effort to do this. On a positive note, here is a particularly nice comparison. In PHYS4030 Condensed Matter Physics this week I am teaching Paramagnetism and diamagnetism, closely following chapter 31 of Ashcroft and Mermin. Consider non-interacting paramagnetic ions with total angular momentum J in a magnetic field B at thermal equilibrium at temperature T. Basic statistical mechanics can be used to derive an expression for the magnetisation, which is a universal function of B/T, known as the Brilloiun function . A&M do not compare this to experiment. However, I recalled that when I was an undergraduate we used a very nice book, Heat and Thermodynamics , [5th edition] by Mark Zemansky . It contains the comparison below, taken from a 1952 paper by Henry .

Much of chemistry can be described in terms of potential energy surfaces. They describe the energy of an electronic state of a set of molecules as a function of the positions of the atoms in the molecules. Local minima on the surface describe stable molecules (reactants and products of chemical reactions). Chemical reactions proceed by thermal activation over saddle points ( transition states ). Hence, an interesting and important question concerns how many possible transition states there might be on a surface? How are the number of transition states related to the number of local minima? In the process of writing a paper on double proton transfer I have stumbled across a very general result that I have never seen stated before. For me there is some curious personal history because the result uses a theorem in the first paper I ever published, thirty years ago, resulting from my undergraduate honours [final year] thesis on general relativity! More on that below. Here is the r

8 " Now, O king, establish   the injunction and sign the document , so that it cannot be changed, according to the law of the Medes and the Persians, which cannot be revoked.”   9  Therefore King Darius signed the document and injunction. Daniel 6 [Later King Darius regretted he signed the document because it landed Daniel in the Lion's den.] Over the years I been fortunate to work with some excellent undergraduates and Ph.D students on projects. However, there have been a few that I regret agreeing to work with. Problems can include a poor work ethic, disorganisation, a weak technical background, procrastination, ..... On reflection, I think there was a common dynamic whereby I originally took them on. Often they came to me in a rush that they had a form that had to be signed. There was some impending deadline for enrolment and if I could just sign it we can work out the details later. This is a mistake. This should be a warning sign. It can often signify disorganisation

Gradually with more teaching experience most lecturers slowly learn that "easy" exam questions can be a good test of students knowledge, understanding, and skills. In several earlier posts I have discussed my concern that some undergraduate students seem to be able to get to second, third, or even fourth year without being able to perform basic tasks such as sketch a simple function keep track of physical units in a calculation have a feel for orders of magnitude so they can notice if a calculation gives a ridiculous answer examine a plot of experimental data and note whether its qualitative and quantitative features to the predictions of a theory Hence, I like, and think it is important, to set exam questions that test some of these skills. Here are some samples for a fourth year solid state physics course. Slowly I learnt it is also important and worthwhile to slightly change recycled questions.

An important and fundamental question concerning a strongly interacting many-body system is whether there are fundamental limits (lower bounds) to transport coefficients such as the conductivity and viscosity . A related issue is whether there are upper bounds on energy, phase, and momentum relaxation rates, such as the buzz-concept of  planckian dissipation. There are two basic reasons why some believe this is true. First, a simple argument is that it "does not make sense" to have mean free paths less than a lattice constant and the wavelength of the relevant quasi-particles. This leads to the Mott-Ioffe-Regel limit for the conductivity. Second, in calculations based on the AdS-CFT correspondence one does find such bounds do hold. However, I remain to be convinced that such bounds must hold. One reason is the existence of bad metals. In some strongly correlated electron materials the resistivity can increase smoothly above the Mott-Ioffe-Regel limit as the temperature

Am I the only person irritated by this? When you download an article from Science, IOP,  or AIP journals the first page is content free. Samples are below. The "Articles you may be interested in" are usually a random collection of peripheral connection to the article. When you want to print the article you can always just not print this page; but that does require a little more effort beyond hitting the "Print" key. I realise there are more important things in the world to get upset about [schoolgirls getting kidnapped in Africa, scientific fraud, the latest Australian government budget , climate change....], but I just don't see why this is necessary.....

Any worthwhile scientific project will be large, challenging, and ambitious. Even a small project, particularly for a beginner, can be intimidating and overwhelming. A key skill is to learn how to break a project down into small and manageable parts. This applies whether one is trying to solve a particular scientific problem [how does a particular enzyme work? what is the origin of superconductivity in the iron pnictides?], write a large computer code, perform a multi-step chemical synthesis, solve a quantum many-body Hamiltonian with a specific approximation, fabricating a solar cell.... How does one do this? Are there some general principles? I am not sure and I welcome comments and suggestions. I also fear that current pressures to publish quickly lead to hastily put together projects without due attention to the robustness of the sub-projects. My main suggestions are: *be realistic. make sure each part/step is arguably manageable/doable. * start with easy steps and pro

Here are the slides for the talk I am giving today at the UQ Physics colloquium. I will show the video Quantum levitation , and discuss what is and isn't quantum about it. A good discussion of some of the issues raised is Laughlin and Pines article The Theory of Everything.  A more extensive and introductory discussion by Pines is at Physics for the 21st Century. Postscript. Based on comments and questions afterwards, particularly from some undergraduates, there are few things I would do slightly differently. I should have said what a Hamiltonian is: a function that defines the energy as a function of the system variables, e.g., the position and velocity of all of the particles. The stratification of reality shown by my boxes is a simplification for schematic purposes. There is no clearly defined boundary between strata. For example, at the boundary between chemistry and physics one has chemical physics and physical chemistry. The boundary between biology and biochemi

It is a fallible human tendency to want to include in a paper the most favourable comparison between your pet theory and experiment. My collaborators and I were recently confronted with this issue when writing our recent paper on Quantum nuclear effects in hydrogen bonding. We calculated a particular vibrational frequency for both hydrogen and deuterium isotopes. Experimentalists had previously reported that this ratio has large and non-monotonic variations as a function of the donor-acceptor distance R. The plot below shows a comparison of our calculations [curves] to experimental data on a wide range of chemical complexes [each point is a separate compound]. I was quite happy with this result, particularly because getting the frequency ratio down to values as small as one was significant [Aside: this is an amazing thing because in most compounds the isotope frequency ratio is close to 1.4 = sqrt(2), as expected from a simple harmonic oscillator analysis]. It was tempting just

Which institutions the best job training scientists at the undergraduate level in the USA? If you want a job teaching highly gifted and motivated undergraduates where should you try and work? The answer is not what you might think? [Ivy League, Berkeley, Stanford, ....] If you look at the undergraduate origin of the recipient of doctoral degrees from US universities you find something surprising. For all academic fields, of  the top ten , six are small private liberal arts colleges [i.e. they have no Ph.D program]: Harvey Mudd, Swarthmore, Reed, Carleton, Grinnell, and Oberlin. For science, the results are similar. Thomas Cech  shared the 1989 Nobel Prize in Chemistry and was President of the Howard Hughes Medical Institute for a decade. He graduated from Grinnell and has an interesting article Science at Liberal Arts Colleges: A Better Education? Asides: Reed College is interesting [for many reasons!] because it has resisted involvement in institutional ranking exercises  (ev

Today I am giving a talk "Mental Health for Scientists" to the Early Career Researcher group at the Institute for Molecular Biosciences at UQ. Here are the slides.

To me this seems at first to be a strange idea. The phenomenology of the cuprates and doped Hubbard models is roughly that as the doping decreases one goes from a Fermi liquid (large overdoping with no superconductivity) to an anisotropic marginal Fermi liquid  (overdoped but superconducting) to strange metal (marginal Fermi liquid) (optimal doping) to pseudogap state (underdoping). Hence, I would have thought that everything was rather non-Fermi liquid like in the pseudogap state. However, the observation in the pseudogap range of copings of quantum magnetic oscillations (that could be associated with a small Fermi surface) and Fermi arcs, raised the question of a Fermi liquid state. Over the past few years Martin Greven and collaborators have performed a range of transport measurements on a relatively clean single layer cuprate material Hg1201. They find Fermi liquid type behaviour [e.g. resistivity quadratic in temperature, scattering rates quadratic in frequency] for a range of

Next week I am giving another talk on mental health issues for scientists. Since I am doing this more I have been doing a bit more reading. Also, people are starting to send me various relevant articles. Here are a few things I have learnt, in no particular order. Andrew Lange  was one of the world's leading observational cosmologists and Chair of the Division of Physics,  Maths, and Astronomy at Caltech. He was the lead investigator on BICEP, the forerunner of the experiment that recently found evidence for cosmic inflation. He suffered from depression. Tragically, he committed suicide in 2010. Lewis Wolpert FRS is a distinguished developmental biologist who has suffered through several severe periods of depression. Years ago he wrote an article about his experience in The Guardian newspaper. He says that he received more feedback than for anything he had written in his whole career. This was followed with a book Malignant Sadness: The Anatomy of Depression and an associated