Condensed concepts

There is a nice paper Strong-versus weak-coupling paradigms for cuprate superconductivity S Asban, M Shay, M Naamneh, T Kirzhner, A Keren They report very careful measurements of the resistivity versus temperature for four different classes of cuprate superconductors at optimal doping. The goal is to test  Homes relation  which relates the normal state resistivity to the superfluid density. Aside: surely it is not appropriate to call this Homes law . Somehow, it does not have the status of Newton's laws or thermodynamics... In particular, they compare their results to two distinctly different theoretical models that claim to explain Homes relation. The first model is a conventional "weak-coupling" BCS model for the superconductivity with the resistivity dominated by disorder. One problem with applying this model is that it does not capture the large temperature dependence of the resistivity and that the YBCO materials appear to be particularly clean. The seco

Earlier I posted about a basic skill: take initiative! Don't wait for someone else to tell you what to do. Try stuff. It is exciting when you think that you have finally obtained some research results. It is even more exciting if they seem interesting and potentially important. But, don't fool yourself. They may be wrong! Mistakes happen in research. More often than many want to admit. Furthermore, the more complicated the technique and the system under investigation, the more likely something will go wrong. Murphy's law! So how do you check your results? I am not sure. There is no simple universal procedure to check results. Just repeating the experiment or calculation is not good enough. You [or the instrument or software...] may be making the same mistake. Learning to check results is an art and requires patience, discipline, and creativity. Furthermore, different individuals and different research fields often have quite different standards as to how many differe

A basic but important and interesting question in physical chemistry concerns a chemical reaction or process that involves two steps: A to B to C. Do they occur sequentially or can they occur simultaneously, i.e., in a concerted or co-operative manner? Two examples of particular interest are coupled electron-proton transfer and double proton transfer. The figure below shows a carboxylic acid dimer involving two hydrogen bonds The configuration above has the same energy as the tautomer with the top H moved to the right and the bottom H moved to the left. But, does this reaction occur by simultaneously moving the protons or first moving one and then the second. For the case of double proton transfer in dimers of a model of a DNA base pair [shown in the picture below] there has been some controversy about whether the process is concerted or sequential. This brief letter by  Kwon and Zewail in PNAS gives the relevant references. They stress that some of the controversy seems to

Last year  the article,  The neoliberal assault on academia by Tarak Barkawi, was brought to my attention. It was originally published as an Opinion piece in Aljazeera   and has generated some interest and discussion. First, what is "neoliberalism"? According to Wikipedia The  term "neoliberal"  is now used mainly by those who are critical of legislative initiatives that push for  free trade ,  deregulation , enhanced  privatization , and an overall reduction in government control of the economy. The article is written with a quasi-Marxist tone, emphasising class struggle. This may put off some. Yet I am reluctant to admit that there are a couple of ideas in the article that are painfully true. A. The changes that are happening in universities reflect changes in broader society. B. New administrative procedures such the Research Assessment Exercise in the UK, uniform course profiles, widespread use of metrics for staff assessment, are not just annoying bu

Generally I am skeptical about quantum criticality as an important organising principle for strongly correlated electron materials (see for example, this earlier post, Are elemental metals quantum critical? ). The most significant evidence is probably in heavy fermion compounds. However, particularly in the cuprates, I see quantum criticality as one of several competing "hand waiving" explainations of unusual properties. It is important to keep coming back to the idea that a true quantum critical point (QCP) will be associated with some diverging correlation length for some type of "order". Furthermore, this should lead to power laws in physical quantities over several orders in magnitude. There is an interesting paper Transport near a quantum critical point in BaFe2(As1−xPx)2 James G. Analytis,  H-H. Kuo, Ross D. McDonald,  Mark Wartenbe,  P. M. C. Rourke, N. E. Hussey,  and I. R. Fisher The relevant background and context is this review article  which conta

I recently finished a preprint that I am particularly proud of Effect of quantum nuclear motion on hydrogen bonding Ross H. McKenzie, Christiaan Bekker, Bijyalaxmi Athokpam, Sai G. Ramesh I welcome any comments. I hope to submit to J. Chem. Phys. at the end of the week. Many of the issues involved I have blogged about before. Here I will just mention two issues that I found particularly interesting. Both relate to the significance of very small changes in bond lengths due to quantum nuclear effects [tunneling and zero-point motion]. In hydrogen bonded complexes [A-H...B] one observes a subtle secondary isotope effect: when the hydrogen atom is replaced by a deuterium atom the distance R between the A and B atoms changes slightly, on the scale of one-hundredth of an Angstrom [and denoted Delta R]. Furthermore, as shown below, the variation of Delta R with R is a non-trivial non-monotonic function. In the paper we show that for R less than 2.7 A these trends are captured sem

It is very rare that physics is the centre of a play, particularly anything that receives popular or critical acclaim. An exception is the play, Copenhagen by Michael Frayn . It centres around the famous meeting between Heisenberg and Bohr, in Nazi-occupied Copenhagen in 1941. I enjoyed watching the film version produced by the BBC. Daniel Craig [of James Bond fame] plays Werner Heisenberg. It nicely captures the complexities of not just Heisenberg's visit, but also that of the relationship between Heisenberg and his mentor, the role of Bohr's wife, the passion for physics, and the moral issues associated with nuclear weapons.

It is always fascinating to me when one can experience some scientific concept in everyday life. I particularly like it when one can see things with the naked eye. Recently I realised that a macroscopic manifestation of spin-orbit coupling is ferromagnetic domains and hysteresis. This is because they arise from spin anisotropy which is due to spin-orbit coupling. But I digress. The other day I was maintaining my pool [a bain of my existence] and I mixed some solid "Hardness increaser" in water. It got really warm! I had noticed this before but not thought about it much. Why does this happen? The chemical is mostly Calcium chloride . It turns out that this has a particularly large "heat of solution" [the enthalpy change associated with dissolving it in water] of -83 kJ/mol. For this reason it is used in "hot packs" and some undergraduate chemistry labs to illustrate heat of solution. [See articles  one and two in the Journal of Chemical Education ]. In

My apologies to readers who saw the draft beginnings of this post. I mistakenly posted it rather than saving it as a draft. Quite embarrassing. Teenagers who don't receive enough affirmation at home will be prone to seek affirmation in the wrong places. (A classic and controversial issue is the possible correlation between absent fathers and teenage pregnancy ). Scientists are human and we all need and enjoy affirmation for our work. But, many of us don't get as much as we would like. Just l ike teenagers we are prone to seek affirmation from the wrong sources.  We write papers that get rejected by luxury journals. We publish papers and they may be largely ignored. Our grant applications get rejected. We don't get the invited conference invitations that we think we deserve. This can be particularly hard for the young and inexperienced. I think it is important to be secure in yourself about the quality of your work and not start seeking affirmation from the "wron

Some basic research skills that I feel are important may be increasingly neglected in the training of students. I fear this neglect is partly due to the pressure to "produce" leading to people cutting corners and supervisors treating students like technicians. The first skill is Take initiative. Students, regardless of their limited knowledge and experience, should not sit around waiting for directions and feedback. They should not just do what they are told. They should just "try stuff". What does this mean? Look at the literature on your own, beyond what has been recommended to you. Try to reproduce other peoples results. Try doing the experiment under slightly different conditions. Try a different sample or device. Try doing the computer simulation with slightly different parameters. Try doing the analytical calculation using a different method. Ask questions. Don't be scared of looking and feeling "dumb". To begin with most of what y

I would appreciate some clarity and comments on the issue of "Researcher ID's". A couple of years ago I made the mistake of signing up for "ResearchGate". This led to an incredible amount of spam in my email inbox. Then my School was being reviewed and so all the staff had to sign up for " ResearcherID ". This was quite some work because one had to "tag" all of your publications. Then I thought I was done... Now I find that journals I publish in are asking for my ORCID . I am reluctant to waste more time jumping through more hoops to create another "unique" identity. But maybe this is the "special one", the author version of the DOI. I am also getting tired/concerned/frustrated with all the metric focus. I am also concerned how these initiatives seem to have a strong commercial element to them. But, perhaps I just have to bite the bullet and do it. I welcome comments and clarification.

This video discusses the results contained in the Science article The Challenge of Education and Learning in the Developing World Michael Kremer, Conner Brannen, Rachel Glennerster It uses the same approach of randomised trials that feature in the book Poor Economics.