## Thursday, October 30, 2008

### Local news

You can learn all sorts of things reading your local paper. For example, I read yesterday that Rice and Baylor College of Medicine are talking about a possible merger. Unsurprisingly, everyone on campus already knew about that, but it's interesting to see the reporter's take on things, including various quotes from unnamed professors.

Today, I read about this. For those who didn't or can't click the link, it's an article about plagiarism. A professor at Texas Southern University's physics department had apparently asked a University of Houston physics professor for an example of a successful grant a couple of years ago. The UH prof gave him a copy of a grant that had been funded by DARPA in 2002-3. The TSU prof then allegedly sent in the same proposal, word for word (though editing out references to the UH prof's work) to the Army Research Lab, which then funded it to the tune of $800K. Lovely. TSU refused the grant, and the investigation is "ongoing". ## Tuesday, October 28, 2008 ### Boo hoo. So, Merrill Lynch advisors don't like their retention offers. Maybe I'll go into the lab and fab a nano-violin to play the world's saddest song for them. ## Sunday, October 26, 2008 ### This week in cond-mat While there are several interesting recent papers, one in particular touches on a nice piece of physics that I'd like to describe. arxiv:0810.4384 - Bluhm et al., Persistent currents in normal metal rings One of the remarkable properties that makes superconductors "super" is their capability to sustain currents that flow in closed loops indefinitely, without dissipation. We exploit this all the time in, for example, MRI magnets. What many people do not realize, however, is that normal metals (e.g., gold, silver) can also sustain persistent currents at very low temperatures, at least over length scales comparable to the coherence length. Think of electrons as waves for a minute. The coherence length is the distance that electrons can propagate in a metal and still have a well-defined phase (that is, the crests and troughs of the electron waves have a reproducible location relative to some initial point). At non-zero temperatures, inelastic interactions between the electrons and other degrees of freedom (including other electrons) fuzz out this phase relationship, suppressing quantum interference effects over a characteristic distance scale (the coherence length). Anyway, suppose you have a metal loop smaller than the coherence length. The phase of the electronic wave when you do one complete lap around the loop must increase (or decrease) by an integer multiple of 2pi (that is, there must be an integer multiple of wavelengths going around the loop) for the wave picture to make sense. The gradient of that phase is related to the current. It turns out that as T goes to zero, the allowed electronic states of such a loop have to have nonzero currents so that this phase winding picture holds. These currents also lead to a magnetic response - tiny current loops are magnetic dipoles that can be detected, and trying to thread external magnetic flux through these loops changes in the persistent currents (via the Aharonov-Bohm effect). These persistent currents have been measured before (see here, for a great example). However, there has been ongoing controversy concerning the magnitude and sign of these currents. In this experiment, Kam Moler's group at Stanford has used the incredibly sensitive scanning SQUID microscope to look at this phenomenon, one ring at a time, as a function of temperature and external magnetic field. This is a very pretty experiment probing some extremely finicky physics. ## Wednesday, October 22, 2008 ### Voted. I did early voting this morning here at a nearby supermarket. The line stretched halfway around the store - there must've been a hundred people in front of me, and I showed up right when they opened the polls. The line moved fairly quickly, but its length seemed unchanged by the time I voted half an hour later. I know that Houston is a big city, but if this is any indication of overall turnout, the number of voters this year is going to be enormous. ## Tuesday, October 21, 2008 ### Fortuitous physics Every now and then you stumble across a piece of physics, some detail about how the universe works, that is extremely lucky in some sense. For example, it's very convenient that Si is a great semiconductor, and at the same time SiO2 is an incredibly good insulator - in terms of the electric field that it can sustain before breakdown, SiO2 is about as good as it gets. Another example is GaAs. While it doesn't have a nice oxide, it does have some incredibly nice crystal growth properties. I've been told that through some fortunate happenstance of growth kinetics, you can do growth (e.g., in a molecular beam epitaxy system - a glorified evaporator) under nearly arbitrarily As-rich conditions and still end up with stoichiometric GaAs. Somehow the excess As just doesn't stick around. A third example is the phase diagram of 3He/4He mixtures. Mixtures of the two helium isotopes phase separate at low temperatures (T below 600 mK) >3He-rich phase that's almost pure, and a dilute phase with about 6% 3He in 4He. If you pump the 3He atoms out of the dilute phase, more 3He atoms are pulled from the concentrated phase to maintain the 6% concentration in the dilute phase. There is a latent heat associated with removing a 3He atom from the concentrated phase. The result is a form of evaporative cooling: the temperature of the concentrated phase decreases as the pumping continues, and unlike real evaporative cooling, the effective vapor pressure of the 3He in the dilute phase remains fixed even as T approaches zero. This happy piece of physics is the basis for the dilution refrigerator, which lets us cool materials down to within a few mK of absolute zero. Any suggestions for other fortunate, useful pieces of physics? ## Sunday, October 19, 2008 ### Faculty searches, 2008 version As I did last year, I'm revising a past post of mine about the faculty search process. I know that the old posts are still find-able via google, but it never hurts to present this topic again at this time of the year. Here are the steps in the faculty search process: • The search gets authorized. This is a big step - it determines what the position is, exactly: junior vs. junior or senior; a new faculty line vs. a replacement vs. a bridging position (i.e. we'll hire now, and when X retires in three years, we won't look for a replacement then). The main challenges are two-fold: (1) Ideally the department has some strategic plan in place to determine the area that they'd like to fill. Note that not all departments do this - occasionally you'll see a very general ad out there that basically says, "ABC University Dept. of Physics is authorized to search for a tenure-track position in, umm, physics. We want to hire the smartest person that we can, regardless of subject area." The danger with this is that there may actually be divisions within the department about where the position should go, and these divisions can play out in a process where different factions within the department veto each other. This is pretty rare, but not unheard of. (2) The university needs to have the resources in place to make a hire. As the economy slides and state budgets are hammered, this can become more challenging. I know anecdotally of public universities having to cancel searches even after the authorization if the budget cuts get too severe. A well-run university will be able to make these judgments with some leadtime and not have to back-track. • The search committee gets put together. In my dept., the chair asks people to serve. If the search is in condensed matter, for example, there will be several condensed matter people on the committee, as well as representation from the other major groups in the department, and one knowledgeable person from outside the department (in chemistry or ECE, for example). The chairperson or chairpeople of the committee meet with the committee or at least those in the focus area, and come up with draft text for the ad. • The ad gets placed, and canvassing begins of lots of people who might know promising candidates. A special effort is made to make sure that all qualified women and underrepresented minority candidates know about the position and are asked to apply (the APS has mailing lists to help with this, and direct recommendations are always appreciated - this is in the search plan). Generally, the ad really does list what the department is interested in. It's a huge waste of everyone's time to have an ad that draws a large number of inappropriate (i.e. don't fit the dept.'s needs) applicants. The exception to this is the generic ad like the type I mentioned above. Historically MIT and Berkeley run the same ad every year, trolling for talent. They seem to do just fine. The other exception is when a university already knows who they want to get for a senior position, and writes an ad so narrow that only one person is really qualified. I've never seen this personally, but I've heard anecdotes. • In the meantime, a search plan is formulated and approved by the dean. The plan details how the search will work, what the timeline is, etc. This plan is largely a checklist to make sure that we follow all the right procedures and don't screw anything up. It also brings to the fore the importance of "beating the bushes" - see above. A couple of people on the search committee will be particularly in charge of oversight on affirmative action/equal opportunity issues. • The dean meets with the committee and we go over the plan, including a refresher for everyone on what is or is not appropriate for discussion in an interview (for an obvious example, you can't ask about someone's religion, or their marital status). • Applications come in and are sorted; rec letters are collated. Each candidate has a folder. Every year when I post this, someone argues that it's ridiculous to make references write letters, and that the committee should do a sort first and ask for letters later. I understand this perspective, but I largely disagree. Letters can contain an enormous amount of information, and sometimes it is possible to identify outstanding candidates due to input from the letters that might otherwise be missed. (For example, suppose someone's got an incredible piece of postdoctoral work about to come out that hasn't been published yet. It carries more weight for letters to highlight this, since the candidate isn't exactly unbiased about their own forthcoming publications.) • The committee begins to review the applications. Generally the members of the committee who are from the target discipline do a first pass, to at least wean out the inevitable applications from people who are not qualified according to the ad (i.e. no PhD; senior people wanting a senior position even though the ad is explicitly for a junior slot; people with research interests or expertise in the wrong area). Applications are roughly rated by everyone into a top, middle, and bottom category. Each committee member comes up with their own ratings, so there is naturally some variability from person to person. Some people are "harsh graders". Some value high impact publications more than numbers of papers. Others place more of an emphasis on the research plan, the teaching statement, or the rec letters. Yes, people do value the teaching statement - we wouldn't waste everyone's time with it if we didn't care. Interestingly, often (not always) the people who are the strongest researchers also have very good ideas and actually care about teaching. This shouldn't be that surprising. Creative people can want to express their creativity in the classroom as well as the lab. • Once all the folders have been reviewed and rated, a relatively short list (say 20-25 or so out of 120 applications) is arrived at, and the committee meets to hash that down to, in the end, five or so to invite for interviews. In my experience, this happens by consensus, with the target discipline members having a bit more sway in practice since they know the area and can appreciate subtleties - the feasibility and originality of the proposed research, the calibration of the letter writers (are they first-rate folks? Do they always claim every candidate is the best postdoc they've ever seen?). I'm not kidding about consensus; I can't recall a case where there really was a big, hard argument within the committee. I know I've been lucky in this respect, and that other institutions can be much more fiesty. The best, meaning most useful, letters, by the way, are the ones who say things like "This candidate is very much like CCC and DDD were at this stage in their careers." Real comparisons like that are much more helpful than "The candidate is bright, creative, and a good communicator." Regarding research plans, the best ones (for me, anyway) give a good sense of near-term plans, medium-term ideas, and the long-term big picture, all while being relatively brief and written so that a general committee member can understand much of it (why the work is important, what is new) without being an expert in the target field. It's also good to know that, at least at my university, if we come across an applicant that doesn't really fit our needs, but meshes well with an open search in another department, we send over the file. This, like the consensus stuff above, is a benefit of good, nonpathological communication within the department and between departments. That's pretty much it up to the interview stage. No big secrets. No automated ranking schemes based exclusively on h numbers or citation counts. Tips for candidates: • Don't wrap your self-worth up in this any more than is unavoidable. It's a game of small numbers, and who gets interviewed where can easily be dominated by factors extrinsic to the candidates - what a department's pressing needs are, what the demographics of a subdiscipline are like, etc. Every candidate takes job searches personally to some degree because of our culture, but don't feel like this is some evaluation of you as a human being. • Don't automatically limit your job search because of geography unless you have some overwhelming personal reasons. The Incoherent Ponderer posted about this recently. I almost didn't apply to Rice because neither my wife nor I were particularly thrilled about Texas, despite the fact that neither of us had ever actually visited the place. Limiting my search that way would've been a really poor decision. • Really read the ads carefully and make sure that you don't leave anything out. If a place asks for a teaching statement, put some real thought into what you say - they want to see that you have actually given this some thought, or they wouldn't have asked for it. • Research statements are challenging because you need to appeal to both the specialists on the committee and the people who are way outside your area. My own research statement back in the day was around three pages. If you want to write a lot more, I recommend having a brief (2-3 page) summary at the beginning followed by more details for the specialists. It's good to identify near-term, mid-range, and long-term goals - you need to think about those timescales anyway. Don't get bogged down in specific technique details unless they're essential. You need committee members to come away from the proposal knowing "These are the Scientific Questions I'm trying to answer", not just "These are the kinds of techniques I know". I know that some people may think that research statements are more of an issue for experimentalists, since the statements indicate a lot about lab and equipment needs. Believe me - research statements are important for all candidates. Committee members need to know where you're coming from and what you want to do - what kinds of problems interest you and why. The committee also wants to see that you actually plan ahead. These days it's extremely hard to be successful in academia by "winging it" in terms of your research program. • Be realistic about what undergrads, grad students, and postdocs are each capable of doing. If you're applying for a job at a four-year college, don't propose to do work that would require an experienced grad student putting in 60 hours a week. • Even if they don't ask for it, you need to think about what resources you'll need to accomplish your research goals. This includes equipment for your lab as well as space and shared facilities. Talk to colleagues and get a sense of what the going rate is for start-up in your area. Remember that four-year colleges do not have the resources of major research universities. Start-up packages at a four-year college are likely to be 1/4 of what they would be at a big research school (though there are occasional exceptions). Don't shave pennies - this is the one prime chance you get to ask for stuff! On the other hand, don't make unreasonable requests. No one is going to give a junior person a start-up package comparable to a mid-career scientist. • Pick letter-writers intelligently. Actually check with them that they're willing to write you a nice letter - it's polite and it's common sense. (I should point out that truly negative letters are very rare.) Beyond the obvious two (thesis advisor, postdoctoral mentor), it can sometimes be tough finding an additional person who can really say something about your research or teaching abilities. Sometimes you can ask those two for advice about this. Make sure your letter-writers know the deadlines and the addresses. The more you can do to make life easier for your letter writers, the better. As always, more feedback in the comments is appreciated. ## Monday, October 13, 2008 ### This week in cond-mat Three interesting papers from this past week.... arxiv:0810.1308 - Chen et al., Non-equilibrium tunneling spectroscopy in carbon nanotubes One persistent challenge in condensed matter physics is the fact that we are often interested in physical quantities (e.g., the entropy of some system) that are extremely challenging or impossible to measure directly (e.g., you can't call up Agilent and buy an entropy measuring box). For example, in nanoscale systems, particularly those with strong electron-electron interactions, we would love to be able to study the energy transfer in nonequilibrium situations. As a thought experiment, this might involve injecting particular electrons at known energies and following them through the nanostructure, watching them scatter. Well, we can't do that, but we can do something close. Using a superconducting electrode as a probe (because it has a particularly sharp feature in its density of states near the edge of the superconducting gap), we can perform tunneling spectroscopy on a system of interest. This assumes that the measured tunneling current is proportional to the product of the tunneling probe's density of states and that of the system of interest. It also assumes that the tunneling process is weak enough that it doesn't strongly influence the system. From the resulting data it is possible to back out what the distribution of electrons as a function of energy is in the system. Here a collaboration between UIUC and Michigan State apply this technique to study electrons moving in carbon nanotubes. I need to think a bit about the technical details, but the experimental data look very nice and quite intriguing. arxiv:0810.1873 - Tal et al., The molecular signature of highly conductive metal-molecule-metal junctions This is another in a series of extremely clean experiments by the van Ruitenbeek group, looking at conduction through single molecules via the mechanical break junction technique. Using Pt electrodes, they routinely see extremely strong coupling (and consequently high conductance, approaching the conductance quantum) for small molecules bridging the junctions. They further are able to confirm that the molecule of interest is in the junction via inelastic electron tunneling spectroscopy; molecular vibrational modes show up as features in the conductance as a function of bias voltage. They can see isotope effects in those modes (comparing normal vs. deuterated molecules, for example), and they can see nontrivial changes in the vibrational energies as the junctions are stretched. Neat stuff. arxiv:0810.1890 - Gozar et al., High temperature interface superconductivity between metallic and insulating cuprates There is no doubt that the ability to grow complex materials one unit cell at a time is a tremendously powerful technique. Here, a collaboration anchored by growth capabilities at Brookhaven have succeeded in creating a novel superconducting state that lives at the interface between two different cuprate oxides, neither of which are superconducting by themselves. Remember, all kinds of wild things can happen at interfaces (e.g., spontaneous charge transfer, band bending) even without the strong electronic correlations present in this class of materials. There is a real possibility here that with appropriate understanding of the physics, it may be possible to engineer superconductivity above previously accessible temperatures. That would be huge. ## Saturday, October 11, 2008 ### What's interesting about condensed matter physics Inspired by this post and this one over at Uncertain Principles, I thought that I should explain what think is interesting about condensed matter physics. Clearly Chad's main observation is that condensed matter has historically had a major industrial impact, but he wants to understand why the science is interesting, and what draws people to it. Condensed matter physics largely exists at the junction between statistical physics and quantum mechanics. Statistical physics tries to understand the emergence of collective phenomena (whether that's crystalline order, magnetic order, the concept of temperature, or the whole idea of phase transitions and broken symmetry) from a large number of particles obeying relatively simple rules. Throw in the fact that the rules of quantum mechanics are rich and can have profound consequences (e.g., the Pauli principle, which says that no two identical fermions can have identical quantum numbers, leads both to the stability of white dwarf stars and the major properties of most metals), and you get condensed matter physics. It's amazing how many complicated phenomena result from just simple quantum mechanics + large numbers of particles, especially when interactions between the particles become important. It's this richness, which we still do not fully understand, that is a big part of the intellectual appeal of the subject, at least for me. I will also shamelessly crib Chad's list of points that he likes about AMO physics, and point out that CM physics is also well-described by them: • "AMO physics is cool because it's the best field for exploring quantum effects." Well, while AMO is a nice, clean area for studying quantum effects, CM is just as good for some topics, and better for others. There's probably just as many people studying quantum computation using solid state systems, for example, as AMO systems. • "AMO physics is cool because it's concrete." Again, it doesn't get much more concrete that CM physics; it's all atoms and electrons. One fascinating area of study is how bulk properties arise from atomic properties - one gold atom is not a metal, but 1000 gold atoms together are distinctly "metallic". One carbon atom is not an insulator, but 1000 of them together can be a nanodiamond on one hand, or a piece of graphene on the other, How does this work? That's part of what CM is about. • "Experimental AMO physics is cool because it's done on a human scale." Experimental CM physics is the same way. Sure, occasionally people need big user facilities (synchrotrons, e.g.). Still, you can often do experiments in one room with only one or two people. Very different than Big Science. • "AMO physics has practical applications." So does CM, and personally that's something that I like quite a bit. The computer and monitor that I'm using right now are applied CM physics. • "AMO physics provides technologies that enable amazing discoveries in lots of other fields." Again, so does CM. Silicon strip detectors for particle physics, anyone? CCD detectors for all the imaging that the AMO folks do? Superconducting magnets for MRI? Solid-state lasers? Photon-counting detectors for astro? So, in my opinion most of what Chad says about AMO applies just as well to CM, and I hope I've conveyed a little about what the intellectual interest is behind CM physics. Coming soon: posts on recent papers/preprints. ## Wednesday, October 08, 2008 ### Rant - updated. I was going to post about some neat new papers on the arxiv, and mention the very good talk on science policy that I heard today from Norm Augustine, former CEO of Lockheed-Martin and leader of the National Academy committee that wrote the now-famous Gathering Storm report. Instead, I read some news about which I must rant. Remember the$85B (or, as I like to think of it, the 17 years worth of NSF budgets) that the US government used to "save" reinsurer AIG? Turns out, that wasn't enough. They've already blown through it without actually liquidating their assets as everyone was expecting. Now they've managed to get another $37.8B (7.5 years worth of NSF budgets) from the Federal Reserve. I'm sure they're all done now - after all, they've already spent$440K on a luxury retreat for executives (including $150K for meals and$23K for spa charges) after the \$85B bailout. (You know you've gone over the line when the Bush administration calls you "despicable".) In the mean time, the US government is considering taking an ownership stake in a number of banks basically to convince the banks that yes, it's ok to lend money to each other since everyone would be backed by the feds. Of course, that plan may meet with resistance from the banks because it may limit executive compensation for the people who run the banks. Right, because unless we pay top dollar for these geniuses, there's a risk that the banks may not be well-run. Heaven forbid. If this keeps up, it'll be time to invest in tar and feather suppliers. At least I can refer you to a handy guide on how the economic meltdown may affect you.

UPDATE: You've got to be kidding me. AIG is planning another gathering, this time at the Ritz-Carlton in Half Moon Bay, CA, for 150 of their agents. Here's a clue, AIG: When you're so desperate for money that the taxpayers have to keep you afloat, maybe you should, I don't know, consider cutting back on ridiculous luxury expenditures? Don't tell me that you need to pamper your agents or they'll quit. I'm done. I don't care what it does to the global financial system: AIG needs to fail, and their executives need to lose their compensation, and the shareholders of AIG should sue those same executives for the last 10 years worth of compensation.

UPDATE 2: If you want to hear the most lucid explanation I've come across for this whole mess, particularly the problem of credit default swaps, listen to this. It's informative. And scary.

## Sunday, October 05, 2008

### 2008 Nobel Prize in Physics

Surprisingly, I haven't seen the usual blogfest of speculation about the Nobel Prize in Physics. The announcement will be this Tuesday. I will throw out my same suggestion as last year, Michael Berry and Yakir Aharonov for nonclassical phase factors in quantum mechanics, though the fact that the prize went to condensed matter folks last year means that this is probably less likely. Another pair I've heard floated every couple of years is Guth and Linde for inflationary cosmology. Any ideas out there?

### Open faculty positions

It's that time of year again. My department is conducting faculty searches in three areas: solar physics (which I won't discuss here because it's not my area and I doubt many solar physics types read this), condensed matter theory, and cold atoms/optical lattices theory. There is a joint search committee for the latter two (yes, I'm on it), and here's the ad, which is running in Physics Today and Physics World:

The Department of Physics and Astronomy at Rice University invites applications for two anticipated tenure-track Assistant Professor positions in theoretical physics. One of the positions is in condensed matter physics, with emphasis on fundamental theory, while the other is in ultra-cold atom physics, with a focus on connections to condensed matter. These positions will complement and extend our existing experimental and theoretical strengths in condensed matter and ultra-cold atom physics (for information on the existing efforts, see http://physics.rice.edu/). Applicants should send a dossier that includes a curriculum vitae, statements of research and teaching interests, a list of publications, and two or three selected reprints, and arrange for at least three letters of recommendation to be sent to R. G. Hulet or Q. Si, Co-Chairs, Faculty Search Committee, Dept. of Physics and Astronomy - MS 61, Rice University, 6100 Main Street, Houston, TX 77005 or by email to Valerie Call (vcall@rice.edu). Applications will be accepted until the positions are filled, but only those received by November 15, 2008 will be assured full consideration. The appointments are expected to start in July 2009.

To be completely clear: There are two distinct positions available, and the total number of interviews will reflect this. If you have questions I'll try to answer them or refer you to my colleagues who cochair the committee.