Monday, November 30, 2015

A student's questions about scientists responding to climate change

A first year undergraduate student who is deeply concerned about climate change asked me a number of questions by email and then came to my office to discuss them. Since I think they are excellent questions I thought I would post them here (with his permission) and give a brief version of my answers. I welcome readers to give their own answers.
I am interested in and passionate about climate change. At the moment, I'm considering my uni options - wondering what I can study to best equip me to help in the great, global effort to mitigate (I'm a bit less interested in adaptation) climate change. I have a couple of questions to ask of you.
1. How would you respond to each of the following, somewhat contradictory statements: 
- 'Climate change can be mitigated by developing and deploying renewable energy and energy efficiency technologies, without significantly impacting on our standard of living.' 
- 'Environmental crises, including climate change, require us to move away from a social and economic system based on consumerism and growth' .
First, I am no expert on this complex issue. An economist at UQ who is an expert is John Quiggin. But, my view is that with energy efficiency measures, renewable energy, and some modest lifestyle changes significant progress can be made towards mitigating climate change. On the other hand, I think there are compelling social  and political reasons why the world, particularly the Western world, would be better off if we moved away from this mindless and insatiable pursuit of consumerism and economic growth.

But, I really think the biggest obstacle to concerted and significant global action is a lack of political will and leadership. This is particularly driven by "fear mongering" from vested business and political interests who claim the first option is true. "If we don't burn more coal we will all end up back in the caves or at least riding bicycles..."
I don't think the biggest obstacle is missing technical and economic solutions. Of course, if someone can make a durable and reliable photovoltaic cell with 20 per cent efficiency, that costs 20 cents per square metre to manufacture, and with a lifetime of 20 years, it would "solve" the problem. But, I only foresee incremental advances in the next decade. The case of Gratzel cells is quite discouraging.
2. If the institutional ethos of the UQ science faculty were a person, how would he/she respond to the above statements? 
I think you would really encounter a range of views, probably reflecting a rang of political convictions. I would hope most staff would believe that climate change is real, a result of human activity, and a major issue to address. On the other hand, I am occasionally surprised and disappointed to meet scientists, who are skeptics, even though 97 per cent of climate scientists are not.

I think you would find that some would also claim we need lots more research money (especially for new technologies) to address these issues, but they are clouded by self interest.
3. What facets of science would you recommend that I study:  
- Earth science (better understanding of the climate system)
- Physics/Engineering (renewable energy technology) 
- Psychology (Why do people behave the way they do) 
- Ecology (how ecosystems respond to climate change and other pressures)
Given that I think the major obstacles are political I think that becoming a political activist you may have the biggest impact. Studying sociology and psychology may help design the most effective campaigns. But you do need to understand the technical issues.
On the other hand, you should consider what you are good at and enjoy. There is no point trying to put square pegs in round holes.
Hence, I think you should let your own interests and abilities be a consideration. But studying a mix of the above could be very helpful.
I am wondering if UQ has plans to develop a specific course, or even a program, devoted to climate change?
Not that I am aware of. There are significant postgraduate activities at The Global Change Institute and the Energy Initiative. There was recently a review of the Bachelor of Science. The possibility of some elective courses that are multi-disciplinary has been floated and climate change is one. However, my experience is that such courses become a can of worms once you get multiple departments involved. Everyone wants a piece of the pie, to do it their way, but are not willing to take responsibility, or to "force" their own students to take the course so it is viable. Hence, I doubt you will see the kind of course you are hoping for during your time here. Sorry.

We ended our discussion with me lending the student a copy of The Eye of the Storm: the autobiography of Sir John Houghton. He is nice example of someone who moved from basic research in climate science to public policy and advocacy.

I wish I had more discussions like this with students.

I welcome people to give their own answers.

Friday, November 27, 2015

I believe in irreproducible results

At UQ we just had an interesting colloquium from Signe Riemer-Sorensen about Dark matter emission - seeing the invisible. Central to the talk was the data below. Focus on the red data around 3.6 keV.


This has stimulated more than 100 theory papers!
This reminds me of the faster than speed of light neutrinos and the 17 keV neutrino, 500 GeV particles seen by the Fermi gamma ray telescope, BICEP2 "evidence" for cosmic inflation, ....

The above data is discussed in detail here.

I don't want to just pick on my astrophysics and high energy physics colleagues as this happens in condensed matter and chemistry too... remember cold fusion... think about periodic reports of room temperature superconductors!

The painful reality is that cutting edge science is hard. One can be incredibly careful about noise, subtracting background signals, statistical analysis, sample preparation, .... but in the end there is Murphy's law .... things do go wrong .... and crap happens...

Skepticism and caution should always be the default reaction; all the more so the greater the possible significance or surprise of the "observed" result.

I believe in irreproducible results.

Update (14 December).
Clifford Taubes brought to my attention two relevant papers on the possible 3.5 keV line. The first paper rules out a dark matter origin of the line and even mentions Occam's razor. The second has a mundane alternative explanation of the line in terms of charge exchange between hydrogen gas and sulfur ions.

Thursday, November 26, 2015

How the 80-20 rule may be undermining university quality

I recently learned about the Pareto principle, which according to Wikipedia

"(also known as the 80–20 rule, the law of the vital few, and the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes."

For example, if you are supervising a team of employees, 80% of your time will be spent in dealing with 20% of them, probably the mostly poorly performing or most vocal.

This past year I have had a minor administrative role, as a "Research Committee" chair. Probably 80% of the time, involves co-ordinating, supporting, and assessing grant funding applications, both internal and external to the university. Most of these grant programs have success rates at the 10-20% level. Virtually none of my time is actually spent on initiatives to help improve the quality or quantity of research done by the bulk of faculty members.

My experience has also made me more aware of what people in senior management appear to spend their time doing and what gets their interest and attention. Increasingly, it seems to be focussed on "high status" activities associated with "esteem measures" such as "prestigious" grants and fellowships, and of course, publication in luxury journals. The issue is well illustrated with a story about some researchers who were making a pitch for a new supercomputer centre.

University VP (Research): Will this help you get a Nature paper?

Researcher: Probably not, but it will help other researchers at the university publish a hundred other papers.

The problem is again that little attention or resources are directed to most of the research that is going on.

Tuesday, November 24, 2015

Postdoc available to work with me on strongly correlated electrons

UQ has just advertised for a new postdoc to work with me on a project, "The bad metallic state in quantum materials", funded by the Australian Research Council.
The position is for 2 years and 9 months.
Applications close on 31 January, 2016.

The official advertisement and job description is here and contains a link to a portal through which a formal application should be made.

Looking at the "bad metals" label on the blog will give a flavour of some of the problems I am interested in.

Looking at the "career advice" label will give some flavour of my philosophy and expectations of working together.

Monday, November 23, 2015

Quantum critical spin dynamics of a magnetic impurity in a semiconductor

There is an interesting paper
Quantum critical dynamics of a magnetic impurity in a semiconducting host
Nagamalleswararao Dasari, Swagata Acharya, A. Taraphder, Juana Moreno, Mark Jarrell, N. S. Vidhyadhiraja

The key physics of the Kondo model is the formation of a spin singlet state between the impurity spin and the spins of the electrons in the conduction band. We say, the impurity spin is “screened” by the spins in the conduction band.
The "screening" electrons involved span from the Fermi energy up to some higher energy.
The relevant energy scale is the Kondo temperature which depends in a non-analytic way on the density of states (DOS) at the Fermi energy, and is roughly the binding energy of the spin singlet.
As the DOS goes to zero the Kondo temperature goes to zero.

But, what if there is an energy gap at the Fermi energy, as in a semiconductor?
One might expect that the Kondo effect disappears and the local moment is no longer screened.
Specifically, is there a critical non-zero value of the energy gap below which the Kondo effect survives and one observes at Fermi liquid?
How about if the temperature is larger than the energy gap but less than the Kondo temperature?
Then perhaps the electrons that are thermally excited into the conduction band can screen the impurity spin.

The above fundamental questions are relevant to understanding magnetic semiconductors. They can be addressed by studying the gapped single impurity Anderson model. A number of numerical and analytical studies over the years have produced different answers to the above questions. The current paper gives definitive answers based on state-of-the art Quantum Monte Carlo calculations.

The phase diagram is shown below, with temperature versus the energy gap, delta.
Both are scaled by the Kondo temperature in the absence of the gap. LM denotes an unscreened local moment and GFL a Generalised Fermi Liquid.
The phase diagram is universal in the sense that it is independent of U in the Kondo regime (for large U) and the only relevant energy scale is the Kondo temperature (not the band width or the hybridisation energy).
It is not at all obvious (at least to me) that the universality of the delta=0 case has to extend to the non-zero delta case. But it does.

One sees that the critical value of the energy gap is zero.
Furthermore, above some non-zero temperature, of the order of a fraction of Kondo temperature and about one half of delta, a Generalised Fermi liquid forms where the local moment is completely screened.
The authors also show that the dynamic spin susceptibility associated the spin of impurity exhibits “quantum critical scaling” in the sense that it depends only on omega/T where T is the temperature and omega is the frequency.

Hopefully the paper will stimulate some experiments, either in quantum dots or in semiconductors, to observe this fascinating physics.

Friday, November 20, 2015

Fulfilling the bureaucratic minimum

There is no doubt that universities and research institutions are becoming more bureaucratic. This is arguably from the increased demand for accountability and from the rise of the managerial class. This means more paperwork, more boring meetings, and more rules and regulations. How do we cope?
Let me first give two extreme responses and suggest an alternative.
John and Joan could be faculty, postdocs, or graduate students.

1. John is focussed on research and teaching. Afterall that is the mission of the university not all this bureacractic nonsense. Any emails from administrators are deleted. In fact he has placed a “block sender” on some. He never responds to requests to complete on line surveys, fire safety training, or annual reports. He does not attend departmental meetings. If forced to attend meetings he brings his laptop and catches up on email.
Deadlines for reports, drafts of grant applications, and exam papers are missed. The only way he will complete an administrative task, even after several email requests, is if someone comes and knocks on his door. Sometimes he tells secretaries, administrators, or colleagues if they want the task done they should do it for him. The only tasks he does actually complete are done at the last minute.
John is not “well liked” either by colleagues or local administrators.

2. Joan is the opposite of John. She is a very conscientiousness member of the community. She reads all the admin emails (including the attachments) carefully, actively participates in all the meetings, updates all the databases, and writes carefully crafted reports. She completes all the tasks in a timely manner. Sometimes she agonises about the content and wording of her reports and gets colleagues to give her feedback on drafts. She gives managers detailed and constructive feedback about a range of their iniatives and issues.

Both extremes present problems.
Basically, John is selfish because he leaves others to cover for him, on some tasks that one just cannot avoid doing.
On the other hand, Joan is wasting a lot of her time, that could arguably be better spent on teaching or research (or on non-work pursuits!). She is also “enabling” the propogators of bureacratic nonsense.

Somehow we need to find a balance between John and Joan. Let me suggest a simple question to decide what to do and what not to do.
If I don’t complete this task (or at least complete it in a timely manner) is it going to inconvenience someone else (because they will have to do it or keep bugging me to do it)?
Fulfilling this bureacratic minimum leaves significant room for tuning out a lot of the noise, deleting a lot of email, skipping some meetings, and quickly completing reports by "box ticking" and cutting and pasting.

Wednesday, November 18, 2015

Emergent quantum matter at JNU

Today I am giving a seminar on Emergent Quantum Matter in the School of Physical Sciences at JNU. My host is Brijesh Kumar. Here are the slides.

Last time I gave this talk, someone asked the tricky and controversial question "Is ferromagnetism an example of spontaneously broken symmetry?" Peierls said yes. Anderson says no. I previously discussed their exchange here.

Aside. One thing I  enjoy about JNU is the very large posters that student political activists have placed on buildings. Many contain challenging quotations that are worth considering, such as this one.




Tuesday, November 17, 2015

Spin liquid state in the spin-1 Kagome antiferromagnet

There is a nice paper
Plaquette-triplon analysis of a trimerized spin-1 Kagomé Heisenberg antiferromagnet 
Pratyay Ghosh, Akhilesh Kumar Verma, Brijesh Kumar

They consider an antiferromagnetic Heisenberg model on the Kagome lattice with three different interactions, J, J', and J'', shown below.
The case J'=J and J''=0 is the regular Kagome lattice model.

For J'=J''=0 one has isolated triangles for which the ground state is a singlet with an energy gap to three low-lying triplet states.
[Aside: for a nice general treatment of such triangles (and tetrahedrons) see this paper].
This state is the starting point for an analysis using bosonic excitations corresponding the triplet excitations on the triangular plaquette.
The calculated phase diagram is below.
 
One sees that turning on the inter triangle interaction J' has no effect on the quantum numbers or symmetry of the ground state. It remains a singlet, with no spontaneously broken symmetry, with an energy gap to the lowest lying triplet, i.e. a spin liquid. 

I found this surprising and interesting. But, it is also consistent with some numerical work, such as a recent DMRG study by Changlani and Lauchli. 

Only when one turns on the further frustrating next nearest neighbour interaction (J'') does one obtain a different ground state. Furthermore, a relatively small value of J''/J less than 0.2 is sufficient.

For a discussion about a possible spin liquid grounds state in the spin-1/2 Kagome model, see the suggested reading in an earlier post.

I thank the authors for helping me understand the paper.

Monday, November 16, 2015

Hydrogen bonding talks in Delhi

Today I am giving a seminar "Effect of Quantum Nuclear Motion on Hydrogen Bonding" in the Chemistry Department at IIT Delhi. My host is Charusita Chakravarty.

On thursday I am giving a similar talk in a seminar in the School of Physical Sciences at JNU (Jawaharlal Nehru University). There my host is Brijesh Kumar.

Here is the current version of the slides.

What is a "world class" undergraduate science education?

Most undergraduate science curricula are essentially what they were fifty years ago. Furthermore, in Australia they are very specialised. Due to internal university politics and funding pressures departments actually design programs to discourage students from taking courses in other departments. For example, in one university that loves to promote itself as "world class" chemistry majors are not required to take any courses in physics and mathematics. How can you even do basic physical chemistry with only high school maths and physics?

This specialisation is antiquated. Consider what science is like today. It is very multi-disciplinary. Furthermore, the vast majority of research, both pure and applied, involves biology or materials. Biology and medicine are becoming increasingly quantitative. Everything involves substantial use of computers and advanced instrumentation. Previously, I posted about one course every science undergraduate should take. But that is not enough, if you really want to be "world class".

Science students should get a solid basic foundation in physics, chemistry, biology, computing, statistics, and mathematics.

Consider also what type of jobs the majority of science graduates end up doing. These non-research jobs include high school teaching, engineering, industry, and computing. Again multi-disciplinarity is usually central.

There was a time when all Caltech students had to do a quantum mechanics course.
I recently visited the Indian Institute for Science Education and Research (IISER) at Pune. I was very impressed to see that all of their undergraduates do the same courses for the first two years (physics, chemistry, maths, biology) at the beginning of a 5 year BS/MS.  
To me this is "world class".

Friday, November 13, 2015

Comparing theory and experiment for metals: look at the frequency dependence of the reflectivity not the conductivity

The frequency dependence of the real part of the conductivity of a metal gives a lot of information, both qualitative and quantitatively. For example, one can extract a scattering rate and see if a Drude model is relevant. Hence, it is natural that experimentalists present “measurements” of this quantity.

However, it is important to acknowledge that the conductivity is not directly measured; rather, the reflectivity or absorption of a thin film or single crystal.
The real and imaginary parts of the conductivity are then extracted from a Kramers-Kronig analysis. This procedure is only stable and reliable if there is experimental data out to sufficiently high frequencies.
Several experimentalists have privately told me this can be a can of worms. It is not clear how high a frequency cutoff you need and interband transitions can complicate things…
Hence, one should be particularly nervous about people claiming exotica such as quantum criticality and non-Fermi liquid behaviour such as anomalous power laws.

There is a simple way to avoid these complications and ambiguities when comparing theory and experiment. The reflectivity can be written in terms of the conductivity as follows

From theory one can calculate the full complex conductivity and thus the reflectivity and
compare this to experiment.

This is the procedure followed by Jure Kokalj, Nigel Hussey, and I in this paper about overdoped cuprates.

I thank Swagata Acharya for motivating this post.

Thursday, November 12, 2015

When the conflicting values of faculty and students collide

Previously I posted about how faculty members should respond to student evaluations of teaching. 
There is an interesting article at Faculty Focus, that highlights the increasingly conflicting values and expectations between some faculty, students and parents. It’s Not Me, It’s You: Coping with Student Resistance by Nicola Winstanley.
Nearly 20 years ago, Neil Postman warned in The End of Education that education was being replaced by “schooling,” a means whereby learning becomes deeply embedded in a capitalist structure that values knowledge only for its industrial utility. In other words, education is a means to an end—getting a job—rather than an ongoing process at the heart of culture. It’s within this context that some students have come to see education as no more than a deliverable—one that they have paid for dearly. 
The fact that many students accept this paradigm is made evident every day in both their comments and behavior. For instance, some students may think that pedagogical deviation from hard facts and skills is simply a waste of time. Some may even go so far as to abdicate all responsibility for learning anything, because, after all, they’ve paid for it, and as practiced consumers they are used to getting what they want as long as they lay down the cash.
This reminded me of a colleague who taught with a flipped classroom. A student complained that this is not what he paid for. The student said he paid the lecturer to be teach him, not to leave the student to figure things out for himself!

It also reminded me of a colleague at an Ivy League university who encountered students and parents who thought that because they were paying $40K per year the student was entitled to an A! In Australia it is not unheard of for full fee paying international students to claim that they are entitled to a degree because they are paying for it. The fact that they do minimal work and are unable to complete the most rudimentary academic tasks (e.g. write a coherent paragraph in English) is considered irrelevant.

 Reading the beginning of the article I found it disturbing and sad to seeing the negative impact of the student evaluations on the mental health of the author. I now realise that I need to add an additional point to my Survival and sanity guide to new faculty. Don’t take too personally negative feedback from students. It may say more about them than you.

These conflicts of values can be particularly acute in the Majority World where there is a fixation on rote learning and "teaching to the test". This is nicely and sadly described in a recent New York Times article, "Teaching the Common Core in China.".

I thank Chacko Jacob for bringing the article to my attention.

Wednesday, November 11, 2015

The robustness of any materials computation needs to be tested

A blessing and curse is the easy and wide availability of powerful software for computational materials modelling: classical molecular dynamics, quantum chemistry, density functional theory based methods, …
Although easy to use, interpreting the results, and establishing their robustness and reliability can be subtle and challenging.

Any computation requires the user to make many choices from an alphabet zoo.
For example, for classical molecular dynamics simulations of water there is a multitude of force fields (TIP3P, SPC/E, TIP4P-D, …).
For density functional theory (DFT) one has to choose between LDA, GGA, and  different density functionals (B3LYP, PBE, ….).
For plane wave approaches one must choose the energy cutoff.
For quantum chemistry of molecules one has to choose the basis set (STO-3G, cc-pVDZ -Double-zeta,... ) and the level of theory for treating electron correlations (HF, MP2, CCSD, CAS-SCF, …)
If one does combined quantum-classical simulations (e.g. for a chromophore in a solvent or protein) one has to choose the quantum-classical boundary (i.e. how much of the sub-system to treat fully quantum mechanically)…

I encounter two extremes that are disconcerting and unhelpful.

1. Someone has a favourite and specific choice and does all of their calculations with this single choice for a specific system.
They may justify this by giving one or more references that they claim have systematically established this is the best choice.
The problem is that they may be sweeping under the rug that different choices may give significantly different results, possibly not just quantitively but also qualitatively.

A dramatic example is in any system with moderate strength hydrogen bonds. As discussed here, the energy barrier in the proton transfer potential can vary dramatically with the level of theory or density functional that is used. In general the more interesting the system (usually the more complex and the existence of new and interesting physics and/or chemistry) (e.g. because of the presence of strong correlations) the more likely that “standard” choices will be problematic.

Users really should be making some alternative choices from the alphabet zoo to test and justify the reliability of their results.

2. Someone does an exhaustive study using a plethora of methods and choices.
This is probably motivated by the dream of Jacob's ladder.
Their paper has lots of tables and results and comparisons but there is little insight about the relative merits of the different possible choices. Furthermore, sometimes it is claimed that one choice may be better than the rest just because it gets one or maybe a few experimental numbers "correct." To me these may just be a Pauling point.
It is also disturbing that I encounter papers that compare methods but do not contain comparisons with experiment, even when there is data available. (I gave a specific example here).

Another basic point that I (and others) have made before is that the paper needs to give enough specifics of the technical details so that the calculations and results can be reproduced by readers.
Too often I am told by people that they have not been able to reproduce the results in someone else’s paper. This does not inspire confidence. It is also worrisome how some people actually deliberately omit special "tricks of the trade" so they can keep ahead of their "competitors".

Monday, November 9, 2015

Emergent quantum matter talk at IIT Kharagpur

The next two days I am visiting the Physics Department at IIT Kharagpur. My host is Arghya Taraphder. I am giving my regular talk on "Emergent quantum matter". Here is the latest versions of the slides.

I have given this talk about half a dozen times now. Yet last time I gave it I realised there was a significant typo in the formula for the Hall resistance of the Fractional quantum Hall effect. It is amazing that neither I nor anyone in my audiences caught this typo before. I am not sure what that says...


Wednesday, November 4, 2015

There is no metal-insulator transition in extremely large magnetoresistance materials. II

Two months ago I made this claim. I made some specific suggestions as to how one could quantitatively analyse the experimental data to support the claim. The same day of my post I received an email from Zhili Xiao with a copy of a submitted manuscript that had already done exactly what I suggested. The paper has now been published:

Origin of the turn-on temperature behavior in WTe2 
Y. L. Wang, L. R. Thoutam, Z. L. Xiao,  J. Hu, S. Das, Z. Q. Mao, J. Wei, R. Divan, A. Luican-Mayer, G. W. Crabtree, and W. K. Kwok

Below I show the relevant Kohler plot.

This is consistent with the simple idea that the origin of the magnetoresistence is simply the Lorentz force, the same as in elemental metals such as copper and zinc!
No exotic physics is required.

Tuesday, November 3, 2015

The challenge of the infra-red spectra of hydrogen bonded systems

The schematic picture below shows the evolution of the spectral line of an OH stretch mode in a hydrogen bonded system as the donor acceptor distance R changes.
Not only does the mode frequency significantly red shift but the spectral intensity, line width and line shape changes significantly.
The figure is taken from a helpful (short) review from 1991 by S. Bratos, H. Ratajczak, P. Viot

The redshift with increasing bond strength (and decreasing R) is quantitatively described and explained here. I am currently using the same model with collaborators to describe the increase in spectral intensity (by up to two orders of magnitude).

The problem of the line width and the line shape is more difficult and controversial. I discussed some related issues previously here and here.