Tag Archives: Good Science

Science for Science’s Sake

A couple weeks ago, Sheila Patek was on the PBS News Hour and discussed eloquently how science and scientists work. She talked about how scientists are driven by curiosity to venture into the unknown, which may or may not lead to applications for humans. When you go somewhere no one has gone before, who knows if it’s going to be of any use? However, that doesn’t mean you shouldn’t go. Here’s the video:

Breadth Vs. Depth

One of the recurring struggles of being a physicist, especially for those early in their career, is how to balance depth and breadth of topics. In pursuing a PhD, it is necessary to study a particular topic in great detail, read the previous literature on the subject, and in some sense, become an expert in a very narrow area. One then needs to solve a problem in this area. In reality, this is all that is needed to obtain a PhD.

To become a good physicist, though, requires that one has a broad and general overview of, in our case, condensed matter physics and even topics beyond. Obviously, this is not the only trait one must have in order to become a good physicist, but it is indeed one of them.

Colloquially, there is therefore a balance that needs to be struck between “knowing a little bit about everything and a lot about nothing” vs. “knowing everything about something that is almost nothing and nothing about anything“.

Becoming a good physicist therefore requires both a broad physical knowledge and a depth of knowledge in a few specialized topics. It requires one to “zoom in” and focus on a narrow field, and solve a problem. It then requires one to “zoom out” to understand its implications on the grander scale for condensed matter physics or physics in general.

The thing about striking this balance between depth and breadth is that it is extremely difficult to do! There are questions that arise like:

  • How broad is broad enough?
  • For us in condensed matter physics, is learning particle physics “too broad”?
  • What about learning topics like computer science, electronics or economics?

I think that these questions are challenging to answer, partly because the answers will vary from person to person. There are numerous examples of physicists pursuing subjects like economics, biology, neuroscience, philosophy and computer science with great success.

During graduate school, the strategy I employed was to spend the day doing research, remaining narrow, while spending the evening reading widely in attempt to broaden my knowledge and understand why my research was of any importance at all. This was a decent strategy for me, but I can see others pursuing different schemes.

I still struggle with this dichotomy relatively often, and it is not one I see vanishing any time soon. I’m curious to know how others approach this problem, so please feel free to comment.

SciPost

Recently, I was invited to sign up for SciPost, an online platform similar to the arXiv. However, the major difference is that SciPost is creating a suite of free and open-access peer-reviewed online journals. Moreover, copyrights will be held by the authors of the papers, and not by publishers.

Publications will be free for both authors and readers. The journal articles will be completely open to everyone.

To be honest, such a platform has probably been a long time coming for our community. The FAQ page on the website states that SciPost is launching because:

The publishing landscape is evolving rapidly, and it is not clear that the best interests of science and scientists are being represented. SciPost offers a grassroots solution to the problem of scientific publishing, designed and implemented by scientists in the best interests of science itself.

SciPost is open for submissions starting June 2016. I sincerely hope that those in charge of SciPost have it running smoothly by then and that it reaches the critical mass to be successful. Good luck to the team and particularly J.-S. Caux, the condensed matter theorist who started this endeavor.

A First-Rate Experiment: The Damon-Eshbach Mode

One of the things I have tried to do on this blog is highlight excellent experiments in condensed matter physics. You can click the following links for posts I’ve written on illuminating experiments concerning the symmetry of the order parameter in cuprate superconductors, Floquet states on the surface of topological insulators, quantized vortices in superfluid 4He, sonoluminescence in collapsing bubbles and LO-TO splitting in doped semiconductors, just to highlight a few. Some of these experiments required some outstanding technical ingenuity, and I feel it important to document them.

In a similar vein, there was an elegant experiment published in PRL back in 1977 by P. Grunberg and F. Metawe that shows a rather peculiar spectral signature observed with Brillouin scattering in thin film EuO. The data is presented below. For those who don’t know, Brillouin scattering is basically identical to Raman scattering, but the energy scale observed is much lower, typically a fraction of a cm^{-1} ~ 5 cm^{-1} (1 cm^{-1} \approx 30GHz). Brillouin scattering is often used to observe acoustic phonons.

Damon-Eshbach

From the image above there is immediately something striking in the data: the peak labeled M2 only shows up on either the anti-Stokes side (the incident light absorbs a thermally excited mode) or the Stokes side (the incident light excites a mode) depending on the orientation of the magnetic field. In his Nobel lecture, Grunberg revealed that they discovered this effect by accident after they had hooked up some wires in the opposite orientation!

Anyway, in usual light scattering experiments, depending on the temperature, modes are observed on both sides (Stokes and anti-Stokes) with an intensity difference determined by Bose-Einstein statistics. In this case, two ingredients, the slab geometry of the thin film and the broken time-reversal symmetry give rise to the propagation of a surface spin wave that travels in only one direction, known as the Damon-Eshbach mode. The DE mode propagates on the surface of the sample in a direction perpendicular to the magnetization, B, of the thin film, obeying a right-hand rule.

When one thinks about this, it is truly bizarre, as the dispersion relation would for the DE mode on the surface would look something like the image below for the different magnetic field directions:

Damon-Eshbach

One-way propagation of Damon Eshbach Mode

The dispersion branch only exists for one propagation direction! Because of this fact (and the conservation of momentum and energy laws), the mode is either observed solely on the Stokes or anti-Stokes side. This can be understood in the following way. Suppose the experimental geometry is such that the momentum transferred to the sample, q, is positive. One would then be able to excite the DE mode with the incident photon, giving rise to a peak on the Stokes side. However, the incident photon in the experiment cannot absorb the DE mode of momentum -q, because it doesn’t exist! Similar reasoning applies for the magnetization in the other direction, where one would observe a peak in only the anti-Stokes channel.

There is one more regard in which this experiment relied on a serendipitous occurrence. The thin film was thick enough that the light, which penetrates about 100 Angstroms, did not reach the back side of the film. If the film had been thin enough, a peak would have shown up in both the Stokes and anti-Stokes channels, as the photon would have been able to interact with both surfaces.

So with a little fortune and a lot of ingenuity, this experiment set Peter Grunberg on the path to his Nobel prize winning work on magnetic multilayers. As far as simple spectroscopy experiments go, one is unlikely to find results that are as remarkable and dramatic.

Envisioning the Future Technological Landscape

I recently read the well-written and prescient piece entitled As We May Think by Vannevar Bush, which was published in The Atlantic magazine in July of 1945. With World War II coming to a close, and with many physicists and engineers involved in the war effort, Bush outlines what he sees as the future work of physical scientists when they return to their “day jobs”. Many of his predictions concentrate on technological advancements. Reading it today, one is struck by how visionary this article has turned out to be (though it may be argued that some of the prophesies were self-fulfilling). It should be pointed out that this article was written before the discovery of the transistor, which Bardeen and Brattain discovered in 1947.

The most stunning of his predictions to my mind were the following:

  1. Personal computers
  2. Miniature storage capable of holding vast amounts of data (including encyclopedias)
  3. Something akin to digital photography, which he calls dry photography
  4. The internet and world wide web
  5. Speech recognition (though he foresaw people using this more widely than is currently used)
  6. Portable or easily accessible encyclopedias with hyperlinked text
  7. Keyboard- and mouse-controlled computers

Reading about how he saw the future makes it less surprising that Bush was Claude Shannon‘s thesis advisor. For those of you who don’t know, Shannon’s work gave rise to the field now known as information theory and also to the idea that one could use transistors (or binary logic/Boolean algebra) to implement numerical relationships. His ideas underpin the language of the modern computer.

It is amazing the clarity with which Bush saw the technological future. I heartily recommend the article as some eye-opening bedtime reading, if that makes sense.

Reflecting on General Ideas

In condensed matter physics, it is easy to get lost in the details of one’s day-to-day work. It is important to sometimes take the time to reflect upon what you’ve done and learned and think about what it all means. In this spirit, below is a list of some of the most important ideas related to condensed matter physics that I picked up during my time as an undergraduate and graduate student. This is of course personal, and I hope that in time I will add to the list.

  1. Relationship between measurements and correlation functions
  2. Relationship between equilibrium fluctuations and non-equilibrium dissipative channels (i.e. the fluctuation-dissipation theorem)
  3. Principle of entropy maximization/free-energy minimization for matter in equilibrium
  4. Concept of the quasi-particle and screening
  5. Concept of Berry phase and the corresponding topological and geometrical consequences
  6. Broken symmetry, the Landau paradigm of phase classification and the idea of an order parameter
  7. Sum rules and the corresponding constraints placed on both microscopic theories and experimental spectra
  8. Bose-Einstein and Cooper Pair condensation and their spectacular properties
  9. Logical independence of physical theories on the theory of everything
  10. Effects of long-range vs. short-range interactions on macroscopic properties of solids
  11. Role of dimensionality in observing qualitatively different physical properties and phases of matter

The first two items on the list are well-explained in Forster’s Hydrodynamics, Fluctuations, Broken Symmetry and Correlation Functions without the use of Green’s functions and other advanced theoretical techniques. Although not yet a condensed matter phenomenon, Bell’s theorem and non-locality rank among the most startling consequences of quantum mechanics that I learned in graduate school. I suspect that its influence will be observed in a condensed matter setting in due time.

Please feel free to share your own ideas or concepts you would add to the list.

Misconduct and The Wire

Season five of the critically acclaimed TV show The Wire tackles the issue of journalistic fraud and misconduct. In particular, Scott Templeton, a young ambitious journalist at the Baltimore Sun, writes a series of articles where he embellishes details, conjures up quotes out of thin air and ultimately fabricates events. His articles win him wide praise among those in the journalism community. He also garners the Pulitzer Prize, one of the highest accolades one can earn in the field. Even though flags are raised by some of his peers at the Baltimore Sun, at the upper management level, Scott Templeton’s stories are celebrated with enthusiasm.

Of course The Wire is fictional, but at the time The Wire was written, there was precedent for such journalistic falsification. Stephen Glass at the New Republic, Janet Cooke at the Washington Post and Jayson Blair at the New York Times had all been found guilty of journalistic misconduct associated with either plagiarism or fabrication in effort to advance their careers. Cooke was even awarded a Pulitzer Prize for her stories, which she eventually returned.

The reason I bring this all up is because I saw a very strong parallel between the fictional events that occurred in The Wire surrounding Scott Templeton and the actual events that occurred with respect to Jan-Hendrik Schon. In both cases, their notebooks were empty, there were claims by both that their information (e.g. data and notes) had somehow been corrupted and their sources were a closely guarded secret. While working at Bell Labs, Schon famously claimed to use the evaporator in Konstanz, Germany, so that he could “work” in isolation, making it more difficult to for others to reproduce his methods.

The question as to why this kind of misconduct takes place is an interesting one. In the case of Jayson Blair, Wikipedia says:

On the NPR radio show Talk of the Nation, Blair explained that his fabrications started with what he thought was a relatively innocent infraction: using a quote from a press conference which he had missed. He described a gradual process whereby his ethical violations became worse and contended that his main motivation was a fear of not living up to the expectations that he and others had for his career.

As can be gleaned from the quote above, there is little doubt that there is a certain amount of careerism and elevated expectation that is tied in with these instances of misconduct. That these and similar cases occur with relative frequency and happen in different fields suggests that the root cause is societal — an emphasis on perceived career success rather than valuing honesty and hard work. Because this is a sociological problem, all of us have a role to play in correcting it. The solution to the problem may require us to emphasize different values: integrity, meaningfulness of labor and honest motivations. Often these are not the qualities that advance one’s career, but this is because of a lack of emphasis on these values. Perhaps they should.

While the Wire is a fictional show and some readers are no doubt a little fed up with my frequent references to it, I do think that one can learn a lot from its main themes. As Tim O’Brien, author of The Things They Carried, said:

That’s what fiction is for. It’s for getting at the truth when the truth isn’t sufficient for the truth.