Condensed concepts

For the past few months I have been travelling in North America and the UK, for a mixture of work and holiday. In a range of professional and social settings I have had conversations with different people associated with universities: faculty, students, parents, and NGOs. It is amazing (and disturbing) how many times one subject keeps coming come up: student mental health problems. It was never me who brought up the subject and I don't think any of the people who did bring it up knew that I am interested in the issue, partly because of my own struggles. Two important questions people have asked are: Has the incidence of student mental health problems increased or is it just that reporting of problems has increased? Is the situation likely to improve in the near future? Unfortunately, I think the problems have substantially increased and that they unlikely to decrease in the near future. I hope I am wrong. But, I think that there are a multitude of inter-related social, econom

Suppose a motivated and intelligent high school student or first year undergraduate comes to you and says, ``Condensed matter physics sounds really cool! What should I read or look at to learn more about it?" Obviously, suggesting the student look at classic graduate texts such as Ashcroft and Mermin or Chaikin and Lubensky is not helpful. They need something that will inspire them to want to learn more as well as introduce them to some of the basic ideas and topics. I would suggest the following. David Pines, Unit 8 in Physics for the 21st Century , an on-line course Emergent Behavior in Quantum Matter Robert Laughlin, A Different Universe: Reinventing Physics from the Bottom Down Stephen Blundell, Superconductivity: A Very Short Introduction Rodney Cotterell, The Material World But when then have read some of these it would be nice if the student could look at something more technical. To second year undergrads I give a series of lectures on Thermodynamics and Con

I was recently asked to give a talk to an NGO about how universities are changing. There is no doubt that there are rapid changes, many for the worse, happening. For me the biggest change has been the rising influence of neoliberalism (free market ideology) in the values, goals, and decision making within universities. But that is another story... In the past few weeks some relevant articles "came across my desk" [through my web browser...]. I would be particularly interested to hear readers comments on the first one. My wife sent me this New York Times piece to read and I really despaired The iGen Shift: Colleges Are Changing to Reach the Next Generation  The newest students are transforming the way schools serve and educate them, including sending presidents and deans to Instagram and Twitter. Why do I despair? I believe a university education should largely be about two things. The first goal is explicit and the second is implicit. The first and primary goal of

The two terms are often used interchangeably, but that is not appropriate. Condensed matter physics does not just involve solids but also phenomena in liquids, liquid crystals, superfluids, and polymer melts.  Solid state physics is a subset of condensed matter physics. The latter term was arguably coined by Phil Anderson, when he and Mott renamed their research group at Cambridge in the 1970s. One can view research fields or course titles as a list of topics or as a way of thinking about certain parts of reality. Solids exhibit rich phenomena including magnetism and superconductivity. However, it is best to actually view the solids as (an almost irrelevant) substrate for the phenomena . Like many things, this perspective arguably started with Landau. His theory of phase transitions in the 1930s did not consider atomic structure or chemical composition. Even structural phase transitions were viewed in terms of symmetry change, not in terms of explicit microscopic details. In 1950

Unfortunately, hype in science reflects hype in broader society, including in business. The complete DNA sequencing of the human genome was an amazing scientific achievement. Unfortunately, it was also associated with a lot of hype about what this would mean for medicine and for the pharmaceutical industry. This issue is made painfully and succinctly in a recent column in the business section of  The Guardian by Nils Pratley. It has been almost two decades since the first bosses of the newly merged GlaxoSmithKline talked up the medical wonders that would flow from the unravelling of the human genome. GSK would become the “Microsoft of the pharmaceutical industry”, they said.    To put it mildly, the corporate vision hasn’t been realised. GSK’s share price stood at £20 at the time of the turn-of-the-century merger and is £15.42 today. Lack of productivity in the labs has been a constant complaint. The genetics revolution is happening, but not at the pace originally promised, at lea

An important and fascinating issue in many-body physics is the emergence of new energy scales, particularly scales that are orders of magnitude smaller than the energy scales in the underlying Hamiltonian. One example is the coherence temperature associated with the crossover from a Fermi liquid (with coherent quasi-particles) to a bad metal. Recently, I posted about the crossover from a Hund's metal to a bad metal, seen in the c ollapse of the Drude peak in the optical conductivity , and the issue of capturing this slave-particle theories . One commenter mentioned the relevance of the paper below and another asked about the claim that the Kondo effect is associated with the collapse. I agree that Kondo physics is associated with the crossover. Although, far from obvious this is also the case in the single-band Hubbard model. The Kondo effect was first studied with isolated magnetic impurities in metals and can be described by a single-impurity Anderson model (SIAM). Alt

Condensed matter physics is a source of a multitude of beautiful examples of emergence.  On the other hand, f or more than a century philosophers have thought seriously about emergence , partly motivated by profound and difficult questions concerning human consciousness and free will. Prior to the past decade, there appear to have been no substantial interactions between physicists and philosophers about the subject. A few years ago I posted about some recent work by philosophers of science on quasi-particles. One of the big issues that philosophers wrestle with is the relative merits of weak emergence and strong emergence , which are sometimes distinguished as epistemological and ontological emergence. I am very happy that in the past year or so that philosophy journals have published more than half a dozen papers about emergence in condensed matter. One of the papers, by Stephen Blundell, I blogged about earlier. Here I will mention two others and discuss one. All the papers a

I like "collecting" interesting phase diagrams, partly because they are fun to show students when teaching introductory thermodynamics. I recently discovered the one below that I feel I really should have known about. It shows the morphology of different snow crystals as a function of temperature and water supersaturation (relative to ice). It should be pointed out that this is a non-equilibrium phase diagram as it involves supercooled liquid water. The figure below is taken from the beautiful review The physics of snow crystals  Kenneth G Libbrecht This diagram was originally constructed by Ukichiro Nakaya in the 1930's. The physics behind it is still poorly understood. I came across the diagram while browsing through the Forces of Nature book by Brian Cox and Andrew Cohen. While on the subject here is a nice video.