Thursday, January 31, 2019

Postdocs are not junior faculty

Over the past decade, I have noticed a disturbing trend in Australian universities: postdocs are now often expected to be like junior faculty. Specifically, they are expected to apply for grants, recruit and supervise Ph.D. students, be involved in public outreach, help with teaching, engage with industry, ... This is quite different from the traditional role of a postdoc: purely to do research and not worry about money, teaching, and admin.

I don't think anyone is winning from this change. First, it is creating a lot more stress and anxiety for the postdocs. Second, their research productivity and quality are lower because they are distracted and spending significant time not doing research. Thus, the funding agency that is actually supporting them to do research is getting less for their money.

I think this change has been caused by several factors.
First, the job market for tenure-track positions has got even more competitive (from extreme to ridiculous) and so there is a hope that if you get a grant and have done some teaching experience (with stellar student evaluations) then you will have a better chance of getting a permanent position. Second, university management and funding agencies really want to promote the myth of scientific careers. Postdocs are "Early Career Researchers'' and so applying for grants etc. is just part of the ``natural'' progression in them developing into an independent faculty member. Management hopes that if postdocs believe this myth they will be highly motivated workers. They also see getting grants as a random process and the more applicants the better. More grants means more income from overhead and more status for the university ...
This career myth denies the painful reality that the vast majority of Ph.D. students and postdocs will not get permanent positions in research universities. If you are in doubt about this just do the following for your own department: divide the number of new tenure-track faculty hired each year (on average) by the number of Ph.D.'s graduated each year (on average).

The best thing for the vast majority would be to focus on doing some excellent research, enjoy what they are doing, gain diverse skills, and keep an eye out for exit strategies. The main hope for this to happen is for senior faculty to encourage them in these directions.

Tuesday, January 29, 2019

Why is condensed matter physics important and interesting?

I am trying to get some momentum in writing A Very Short Introduction to Condensed Matter Physics. The intended audience is the intellectually curious person with little background in science. My goal is to convince them that CMP is important and interesting. I can think of several reasons.

1. CMP is intimately connected with everyday technology ranging from liquid crystal displays to computer chips.
2. CMP comprises the majority of physics (employees, papers, conferences, ...) and has significant interaction with areas of science and engineering.
3. CMP is a rich source of creative ideas, concepts, and techniques that represent a significant intellectual achievement and are relevant to many other intellectual endeavors.
4. CMP is full of surprises. We keep discovering new unanticipated phases of matter.
5. CMP presents significant scientific challenges: theoretical, computational, and experimental (from characterisation to sample synthesis).

I am going to focus on 3.
However, it is interesting that the traditional route is 1. Furthermore, different people (including reviewers of the book proposal) are quite divided about 1. versus 3.
[More on that later following this article].

What are the big picture ideas of condensed matter, that are significant intellectual achievements in their own right and particularly relevant to other endeavors?
Here are a few suggestions. It provides very concrete systems to address, at both the mathematical and experimental level, the following issues, which turn out to be often inter-related.

A. Qualitative distinctions are defined by discontinuities. (Different phases of matter).

B. Simple models of complex systems. (Landau theory of phase transitions; Effective Hamiltonians).

C. Universality versus particularity. (Universality classes for critical phenomena).

D. Emergence and the hierarchal nature of reality. (Effective interactions. Renormalisation.)

What do you think are the great intellectual achievements of condensed matter that people need to know about?

Friday, January 25, 2019

Strategies for minimal effective Hamiltonians

An important step in understanding any class of complex materials is to find/discover the simplest possible effective Hamiltonian that can be used to describe the main properties of interest (e.g. a phase diagram).
Doing this well is a non-trivial and subjective process. I am thinking about this because I am currently trying to figure out the appropriate Hamiltonian for spin-crossover compounds.

Here are some key elements of the process. 
"Simplest possible" means having the fewest possible degrees of freedom and parameters.

1. What are the key degrees of freedom (molecular orbitals, vibrations, spins, ...)?
2. What are the key interactions and the associated Hamiltonian?
3. What approximation scheme can be used to calculate properties of the many-body Hamiltonian (ground state, thermodynamics, electronic, magnetic, ...)?
4. How do the calculated properties compare to experiment?
5. Can we estimate the values of the Hamiltonian parameters from the comparison of the calculated properties with experiments? 
6. Can we estimate the values of the Hamiltonian parameters from ab initio electronic structure methods, such as those based on density functional theory (DFT)?

Inevitably, things do not work out perfectly, sometimes qualitatively and always somewhat quantitatively. Then one has to face the difficult task of deciding what the problem is and what the next step is. There are several options.

A. There are some missing degrees of freedom in the original Hamiltonian.
B. There are some missing interactions.
C. The approximation scheme used to calculate properties was not reliable enough.
D. There is a problem with the experiments.
E. This is really the best one can hope to do and you should move on to other problems. i.e, know when to quit and face the law of diminishing returns.

This plethora of options is why falsifiability is so hard in the theory of strongly correlated electron materials. But, it does not mean we should give up on it.

The flow diagram below is one way of looking at the process. Some people like the picture. Others do not. As usual, real science is not quite so algorithmic.

Tuesday, January 22, 2019

Post-colonial science

Today there are many threats to science playing an appropriate role in education, public policy, and general public discourse. Some include anti-vaccination campaigns, climate change denial, young earth creationism, "health" products, ...
In the Western world issues such as these rightly get considerable attention. However, in the Majority World there is an issue that does considerable harm and is growing significantly. The basic claims are along the following lines. Modern science did not first arise in Europe but was already present in ancient cultures, often in religious texts. Post-colonial nations need to be proud of this heritage and this "science" should be an integral part of science education. Nations need to embrace their own methods and epistemologies consistent with their culture.

I recently become aware of just how prevalent these views are and the powerful political forces promoting them. You can get some of the flavour from this recent newspaper article and watching some of this video.

A relevant book is
Lost Discoveries: The Ancient Roots of Modern Science—from the Babylonians to the Maya
(Aside: The author, Dick Teresi wrote The God Particle with Leon Lederman.)
This book is authoritatively quoted in a recent book by a prominent South Asian political leader.
A helpful and critical review of Teresi's book is in Science. Basically, it is bad history. There is no doubt that various ancient civilisations did develop some pre-cursors of various aspects of modern mathematics, science, and technology. However, they were never comparable in scope, coherence, conceptual framework, and longevity to what happened in the "scientific revolution" in Europe. A very detailed debunk of some specific claims was given by Meera Nanda, and unfortunately received a vicious response.

So what is the source of the problem here?
I think several very distinct entities get conflated: colonialism, Western civilisation, science, technology, the greed and duplicity of some multinational corporations, and modernism.
A particularly tragic example of this conflation was arguably instrumental in the AIDS-HIV denialism of the South African government from 1999-2008. It was probably responsible for the death of hundreds of thousands of people.

Colonialism was a brutal system which ruthlessly exploited, humiliated, raped, and murdered millions of people across the globe. (See for example). Countless nations today labour under that horrific legacy. No doubt the colonising powers had a patronising view of the "natives", claiming they were bringing them the great achievements of Western civilisation such as science and modernism, and they ruthlessly used technology to maximise their exploitative agenda.
The subtle interplay between scientific, colonial, and theological ideas is described by Sarah Irving in
Natural Science and the Origins of the British Empire.

However, one can decry European colonialism but affirm good things about Western civilisation such as science.
One can decry how technology [based on science] is used to harm people but still affirm science.
Modernism is a particular world view or philosophical framework that claims scientific foundations. One can embrace science without embracing modernism.

I consider postcolonialism an understandable struggle for post-colonial nations to find an identity and direction in the era of globalisation. Somehow these nations need to honor the good parts of their own culture and history [including an accurate assessment of their scientific achievements], accept some good achievements of the West [science, democracy, rule of law, individual freedoms] without uncritically accepting dubious aspects of the West [consumerism, neoliberalism, narcissism, arrogance, ....].

Friday, January 18, 2019

First-order transitions and critical points in spin-crossover compounds

An interesting feature of spin-crossover compounds is that the transition from low-spin to high-spin with increasing temperature is usually a first-order phase transition. This is associated with hysteresis and the temperature range of the hysteresis varies significantly between compounds.
If there was no interaction between the transition metal ions the transition would be a smooth crossover. This is nicely illustrated in a figure taken from the paper below.

Abrupt versus Gradual Spin-Crossover in FeII(phen)2(NCS)2 and FeIII(dedtc)3 Compared by X-ray Absorption and Emission Spectroscopy and Quantum-Chemical Calculations 
Stefan Mebs, Beatrice Braun, Ramona Kositzki, Christian Limberg, and Michael Haumann

For the first compound, the transition is abrupt [much earlier work found a narrow hysteresis region of about 0.15 K]. For the second compound, the transition is a crossover.

The authors fit their data to an empirical equation that has a parameter n, describing the "interactions". You have to read the Supplementary Material to find the details. This equation cannot describe hysteresis.

 However, there is an elegant analytical theory going back to a paper by Wajnflasz and Pick from 1971. This is nicely summarised in the first section of a paper by Kamel Boukheddaden, Isidor Shteto, Benoit Hôo, and François Varret.
The system can be described by the Ising model

where the Ising spin denotes the high- and low-spin states. Delta is the energy difference between them and ln g the entropy difference.
The mean-field Hamiltonian for q nearest neighbours is

There are two independent dimensionless variables, d and r. Solving for the fraction of high-spin states (HS) versus temperature gives the graphs below for different values of d.
The vertical arrows show the hysteresis region for a specific value of d=2. 
As d increases the hysteresis region gets smaller. Above the critical value of d=r/2, the crossover temperature T0=Delta/ln g is larger than the mean-field critical temperature Tc= qJ, and the transition is no longer first-order but a crossover.
Using DFT-based quantum chemistry the authors calculate the change in vibrational frequencies and the associated entropy change for the SCO transition in a single molecule. The values for compound 1 and 2 are 0.68  and 0.21 meV/K respectively. The spin entropy changes are 0.21and 0.22 meV/K respectively. The total entropy changes are thus 0.89 and 0.43 meV/K respectively. The values of Delta are 175 and 125 meV, respectively. The corresponding crossover temperatures are 210 and 360 K, compared to the experimental values of 176 and 285 K.

If we assume that J is roughly the same for both compounds then the fact that the entropy change is half as big for compound 2, means r is twice as big. This naturally explains why the second compound has a smooth crossover, compared to the first, which is very close to the critical point.

Tuesday, January 15, 2019

Thinking skills for scientists (and engineers)

I keep coming back to the basic claim that the key ingredient of education is learning to think in particular ways. [n.b. In science, I am not at all playing up theory over experiment. You have to learn to think about what experiment to do and how to think about your results.].

In the past year, several people brought to my attention that MIT recently reviewed their engineering curricula. It is interesting that a key element is to teach students 11 ways of thinking. The list is worth reading and contemplating.

I have two minor comments. Although I affirm this as an admirable goal. I think the list is incredibly ambitious (even for MIT students) both in scope and content. But, maybe that is a good thing.
What do you think?

One of the 11 ways is Systems Thinking
Predicting emergence of the whole by examining inter-related entities in context, in the face of complexity and ambiguity, for homogeneous systems and systems that integrate multiple technologies.
Again, I love it. But, some would even argue you cannot predict emergence...