The most powerful idea in condensed matter physics?

To get some science discussion going, I thought I'd throw this out there. There are many candidates, but based purely on citations alone, one could make a credible argument that the most powerful idea in condensed matter physics is the (first) Hohenberg-Kohn theorem: the external potential V(r) of an electronic system can be determined exactly (to within a trivial additive constant) by the ground state electronic density rho(r). This means that, in principle anyway, if you know the ground state rho(r), you know everything - you've exactly specified the Hamiltonian, which means you've specified all the many-body wavefunctions for the ground and excited states of the system, all just by knowing the ground state density. Pretty impressive. It's the basis for all of density functional theory. The original paper's been cited 5059 times (as of this morning), and the followup paper that proposed a practical approximation method to make this useful for calculating electronic structure has been cited 11963 times (as of this morning).

On the other hand, I suspect that if you asked a modern CM theorist, they'd list other choices before getting to that one.

NRC survey of graduate programs

Like the Female Science Professor, I just participated in the NRC's once-a-decade survey of graduate programs. Since I'm nominally in charge of Rice's Applied Physics graduate program, I got to fill out both kinds of the survey - the faculty version, and the "program director" version. Double the pain. As the FSP observed, the survey is interested in both compiling objective statistics (graduation rates, admissions rates, funding levels for specific faculty involved with a program, publication information), and in getting the opinions of faculty (and others) on what constitutes a good basis for ranking a graduate program. For example, one of the "faculty" questions asks you to pick four things that you consider most important in evaluating a graduate program, with such choices as publication rate, citation rate, external funding, gender diversity in faculty and students, race diversity in faculty and students, etc. The problem with a question like this is that the way it is posed forces artificial choices. Obviously a strong graduate program needs good publication rates, good citations, good funding, etc. Just as obviously (to me, anyway), I'd like it if all such programs made sure that they address concerns of gender and ethnic underrepresentation. I don't see why this needs to be an either/or choice. It is possible to excel in both. (BTW, frequent commenter and ardent skeptic Sylow - it's clear from her post that the FSP filled out the faculty version of the NRC survey; that's as good a proof as you're likely to get that she is, in fact, an actual faculty member.)

This week in cond-mat

One paper this week, because real life continues to kick my butt.

cond-mat/0701119 - Minot et al., Single quantum dot nanowire LEDs
This is a really nice example of how impressively refined semiconductor nanowire growth has become. By carefully varying the growth conditions and precursors, the composition of growing InP nanowires can be tailored to form a single wire with a p-doped InP lead, an n-doped InP lead, and an interaction region in between formed from InP(1-x)As(x), which has a smaller bandgap than either of the InP segments. The result is a single nanowire LED, potentially well-suited for single-photon emission experiments and the like. Since the whole active region is vastly smaller than the relevant wavelength, the surrounding medium is essentially free space, and screening is comparatively poor in such tiny 1d structures, quantum confinement and charging effects both play a role. Very pretty.

Innumeracy or hypocrisy

According to the NY Times, some in the Senate (on both sides of the aisle) are unhappy about attempts by House Democrats to legislate the recommendations of the 9/11 commission. Now, that's not necessarily unreasonable - it's always easier to "recommend" something than actually implement it in real life. However, one of the objections is that inspecting all air freight coming into the US would cost "$3.6B over the next decade, while ship inspections could cost even more." Wait a second here. We're spending $3.6B every two weeks in Iraq. How on earth can a similar expense spread out over 10 years be too much, while the same amount every couple of weeks is an acceptable cost for the War on Terror? I'm not trying to make a value judgment about either one, but I don't see how one can hold both points of view at the same time.

The internet "memory hole" and Jan Hendrik Schon

First post of the new year. Whoo-hoo.

While revising the course webpage for the class that I'm teaching this coming semester, I noticed something interesting and disturbing. Anyone out there remember Jan Hendrik Schon? This fellow was the focus of arguably the most serious fraud in the physical sciences in the last 50 years while he was working at Bell Labs. As you can see from the wikipedia entry above, there was a thorough investigation and the fraud was discovered, though only after hundreds of person-years had been wasted by people around the world trying to replicate work that turned out to have been fabricated in the first place. The results of that investigation had been archived on the Bell Labs website. However, now that Alcatel has taken over Lucent, those links are dead, and a seach of the new Alcatel-Lucent site does not find any trace of Herr Dr. Schon. At the moment the links on the Internet Wayback Machine still work, but there is no guarantee that these will last forever. I know that old links to, e.g., previous years' problem sets from my courses go away after some time.

This is bad. It should be the responsibility of Bell Labs to maintain this information in an accessible way for at least ten years, or some other reasonable period. In the meantime, I will host the documents on my own university account. Here is the executive summary, and here is the full report of the investigating committee.

This week in cond-mat

Two papers for this end-of-year post.

cond-mat/0612556 - Vartiainen et al., Nanoampere pumping of Cooper pairs
The single-electron transistor was developed almost twenty years ago, based on the observation that one could now fabricate a metal island (weakly coupled to leads via tunnel junctions) so small that it's capacitive charging energy could significantly exceed kT (this gets easier as T is lowered to within a fraction of a Kelvin of absolute zero, which is now readily achievable). In such a device, the charge on the island is generally well-defined and quantized to an integer number of electrons. By cleverly hooking islands together and cycling gate voltages appropriately, it's possible to make an electron "turnstile", such that one electron at a time may be pumped through the circuit. Doing this at high frequencies, f, would enable (ideally) a noiseless current source (with current ef). That's easier said than done, however, because the intrinsic RC charging timescales of such turnstiles tend to limit the frequency of operation. The Finnish group here has implemented an alternative scheme, using superconducting quantum interference devices (SQUIDs) rather than simple tunnel barriers, and can pump individual Cooper pairs of superconducting electrons through their circuit at a high enough rate to generate nanoamperes of current. This is very impressive, and could lead to real advances in metrology.

cond-mat/0612635 - Pereira et al., Kondo screening cloud and charge quantization in mesoscopic devices
In the Kondo effect, a localized spin coupled to mobile electrons undergoes a spin-flip scattering process that leads to spin correlations in the mobile electrons. At temperatures small compared to the characteristic energy of this process, the local spin is "screened" - that is, it is entangled with a cloud of the mobile electrons, forming a singlet state with no net spin. A question that has been around a long time in the solid state community is, how big is that screening cloud? The only successful attempts to measure the size have been in STM measurements of magnetic impurities on surfaces, as far as I know. In this paper, the authors propose a clever scheme to try this in a model system. One can have the local spin be living in a quantum dot, and use a electrons in a large 1d electronic box instead of truly free electrons to form the Kondo state. The idea is that the size of the Kondo cloud will be detected by looking at the single-particle levels of the 1d system (and varying system effective length). Neat, though tough to do!

Great rhetorical device

From an exchange between CNN's Whitehouse correspondent and a Frances Townsend, the Assistant to the President for Homeland Security and Counterterrorism:

HENRY: You know, going back to September 2001, the president said, dead or alive, we're going to get [Osama bin Laden]. Still don't have him. I know you are saying there's successes on the war on terror, and there have been. That's a failure.

TOWNSEND: Well, I'm not sure -- it's a success that hasn't occurred yet. I don't know that I view that as a failure.

Wow. Cool! I need to start using language that way. My Nobel Prize in Physics is a success that hasn't occurred yet.

Tagged.

This is my first introduction to silly blog games, which I suppose shows that I don't blog too much, since it's taken this long. Anyway, I've been tagged. In this game I'm supposed to grab the nearest book, go to page 123, go to the fifth sentence, and write down the next three sentences. Then I'm to tag three more people, presumably ones that I think will play the game. Hmm. Well, on holiday break the nearest book to me right now is The English Assassin by Daniel Silva. Here are the sentences:

He screamed at the room service boys when they didn't bring his coffee quickly enough. Soon the entire staff and most of the guests at the Hotel Laurens knew about the crazy Boche writer in the attic. On the way to Paris, he had stopped at the airport in Nice, dropped off the rented Mercedes, and collected a Renault.

As for tagging, I suppose I'll go with Rob, the Incoherent Ponderer, and the Female Science Professor. (Wolff, Bernie, I'll get you some other time....)

This week in cond-mat

Just one paper this week. End-of-semester crunch + trying to write up some new stuff in my group is cutting into my blogging....

cond-mat/0612278 - Jeltes et al., Hanbury Brown Twiss effect for bosons versus fermions.
Hanbury Brown and Twiss did a beautiful experiment using light that has since been extended to examine the quantum statistics of other kinds of particles. Consider a source of particles and a couple of detectors. For Bose particles, the symmetry of the wave function under exchange of the particles implies that particles will tend to bunch. In handwavy language, the Bose distribution favors particles to be in the same state rather than different states, all other things being equal. HB and T showed this bunching in space for photons. Conversely, because of Fermi Dirac statistics (the Pauli principle), fermions tend to anti-bunch. All other things being equal, fermions tend to avoid each other. This antibunching has been seen in electrons in solids as well as in free electrons. The authors of this paper have done a beautiful version of this experiment with cold atoms, using the same trapping setup to look at either 3He or 4He, which are chemically identical but possess Fermi and Bose statistics, respectively. They use a multichannel plate detector to look at the positional correlations between pairs of atoms when they hit the detector, and see the expected HB-T correlations. Extremely clean, like all good atomic physics experiments.

Rumor mills: don't trust 'em.

Since I'm heavily involved in our faculty search, I can't really talk too much about it online. However, I do want to point out something about rumor mill sites. These have existed for about a decade in the high energy and astrophysics communities, and for the last three years or so there has been a condensed matter/AMO rumor mill site as well. The idea is that this is a way for the candidates (primarily) to keep track of who is interviewing for the various jobs, and who is getting offers. The problem is, these sites are only as good as their sources of information. Now that just about every department puts their seminar calendars online, it's not hard to go through the schedules and try to figure out who is giving job talks. Of course, you have to use a bit of common sense, too. As a cautionary example: yesterday the CM/AMO rumor mill listed two candidates allegedly on the short list for our position. However, (a) both are theorists, (b) one is an AMO person, and (c) our search committee hasn't even had its first meeting yet. Doh! The lesson: don't take the rumor mills very seriously. They can be very wrong, have no fact-checking, and in principle can be manipulated via disinformation.

This week in cond-mat

Two papers on the arxiv this week that give me an excuse to talk about the standard picture of metals and how bits of it can fail.

cond-mat/0611714 - Pisana et al., Born-Oppenheimer breakdown in graphene
The Born-Oppenheimer approximation is one of the most commonly made in quantum mechanical treatments of atoms, molecules, and solids. It's a specific example of the adiabatic approximation: if the potential energy term V(t) of the single-particle Schroedinger equation changes slowly enough (basically compared to \hbar divided by the energy difference between the single-particle energy levels of the system at some instant in time), then it's ok to say that the true single-particle solutions are well approximated at time t by the solutions to the static Schroedinger equation with V = V(t). The Born-Oppenheimer approximation applies this to electrons around atoms. It assumes that the atoms move slowly compared to the electronic energy timescales, so that one can do calculations of molecular (for example) states by assuming that the ions are fixed in space. This paper reports Raman scattering measurements of the vibrational modes of graphene as a function of gate voltage (and hence electronic density). What they find is that the electronic population affects the lattices vibrational modes in a way that violates the Born-Oppenheimer approximation. I haven't read this very carefully, but this is interesting and surprising, at least to me. Given how well the basic graphene electronic structure can be approximated by a simple tight-binding calculation, a big violation here seems weird.

cond-mat/0611724 - Qazilbash et al., Correlated metallic state of vanadium dioxide
The mean free path is a simple concept: it's the average distance a particle travels before scattering off of something. For a classical gas of hard spheres, the mean free path would be the inverse of (number density times cross-section). For quantum mechanical electrons in a metal, the electrons scatter off anything that breaks the periodicity of the crystal lattice - grain boundaries, defects, impurities, distortions of the lattice due to phonons. The mean free path in a metal is typically found from the conductivity, via something called the Einstein relation. Tacit here is the assumption that the electrons behave like well-defined particles that can propagate along for a while between scattering events. Indeed, a general requirement for the validity of this quasiparticle picture for electronic states in a metal is that the ratio of the mean free path to the wavelength of the electron is much greater than one. If the electron scatters many times before even traveling one wavelength, obviously the traveling wave picture of the electron is not valid. The point of this is that there is a physical lower limit to the mean free path: in a "good metal", the mean free path should never be shorter than the lattice spacing between atoms. This is called the Ioffe-Regel-Mott limit.
Now look at vanadium dioxide, which has a transition at 340 K between a high temperature metallic phase and a low temperature insulating phase. The phase transition is complicated, and includes a change in the unit cell shape. The authors of this paper have used optical techniques to infer the frequency-dependent conductivity in both phases. They confirm that the Ioffe-Regel-Mott limit is violated in the metallic phase at high temperatures, and they infer that the dominant scattering mechanism is due to electron-electron interactions. Basically this is one more nice piece of evidence that VO2 is a "bad metal", in which the quasiparticle way of thinking about distinct electrons isn't really valid.

Ahh, Texas II

One of the things I miss about California is the quaint state politics, like the Peace and Freedom Party, which doesn't sound too bad ("Hey - I like peace and freedom!") until you realize that they're radical Marxists. Texas provides its own amusement, though. From this morning's Houston Chronicle:

AUSTIN — A Texas official who receives any sum of cash as a gift can satisfy state disclosure laws by reporting the money simply as "currency," without specifying the amount, the Texas Ethics Commission reiterated Monday.

The 5-3 decision outraged watchdog groups and some officials who unabashedly accused the commission of failing to enforce state campaign finance laws.

"What the Ethics Commission has done is legalize bribery in the state of Texas. We call on the commission to resign en masse," said Tom "Smitty" Smith, who heads Texas Citizen, an Austin-based group that advocates for campaign finance reform.

Thank goodness I live in a state where officials are allowed to take suitcases full of cash, and it's ok as long as they write down "currency" on their ethics disclosure forms. Wow.

A good scientific interaction

The science: one of my colleagues, Prof. Vicki Colvin, can make magnetite nanoparticles via chemical techniques. Magnetite is an interesting material for a number of reasons, some of which I'll probably write about later. It's a ferrimagnet with a Curie temperature of over 800 K. Nanoparticles smaller than about 40 nm in diameter are single-domain, and those smaller than about 16 nm in diameter are superparamagnetic at room temperature. That means that while the spins are ferrimagnetically ordered, the energy required to reorient the magnetization direction of a given particle is less than the thermal energy scale, kT. Anyway, magnetic particles have been used in the chemical engineering world for a long time to do separations. Make magnetic particles that adsorb your favorite nasty contaminant of water; mix the particles in with the water, and then use large magnetic field gradients to pull the now-dirty particles out, leaving behind cleaned water. Just looking at the magnetic forces on individual magnetic particles tells you that nanoparticles shouldn't work well: the magnetic forces scale like diameter cubed, while viscous forces scale linearly with diameter, and Brownian forces scale like one over the diameter. However, she tried the separation process anyway using a little bench-top separator, and it worked exceedingly well! She asked me why, and after scratching my head for a little while, I realized that the key is actually interactions between the particles. The field gradients near single-domain nanoparticles can readily be 10000 times higher than externally applied gradients, leading to much larger forces than those due to the external field directly. To avoid permanent agglomeration of the particles, yet maximize separability at modest fields, one wants to use the biggest particles that are still single-domain superparamagnets. The real upside is that the nanoparticles have enormous specific surface area. So, a cleanup task that used to take a kilogram of big particles only needs a few grams of nanoparticles.

The sociology: Prof. Colvin could easily have written this up and just thanked me, rather than really inviting my participation and making me a co-author. Instead, she very much wanted my input and gave me ample opportunities to help in the writing of the manuscript. The result was a Science paper, and there is real promise (at least according to our environmental engineering coauthor, who is the expert on cost estimates and water purification) that variations of this work could greatly help in cleaning up arsenic-contaminated drinking water in the developing world. Very cool.

A bad scientific interaction.

The science: One of my collaborators supplies interesting molecules to lots of people. Six months ago, my student and I wrote up a paper on our measurements of some of these. We were pretty pleased with ourselves, because our data lets us make a pretty strong statement about the underlying conduction process in this system.

The sociology: While we wrote this up, a competing big group had been doing measurements on the same molecules with a very different technique. They reached the opposite conclusion as us in their case. At the suggestion of my chemistry colleague, we had a discussion about this with them once we both submitted our papers. There is some chance that we're both right, since the measurement systems are so different, so when we revised our paper, we allowed for that possibility. Our paper came out very quickly - five months ago. In the meantime, our competitors had a much longer review process (this doesn't necessarily say anything about their paper; review can be extremely variable.). Their paper just came out in a different journal. Not only is their wording much stronger than ours (basically stating that their suggested explanation is the only possible conclusion, period). They don't even reference our work, despite having known about it for several months. Not cool.

A primer on faculty searches, part II

Continuing my description of the faculty search process.... Candidates come in for interviews. Each interview is a two-day affair. The candidate is scheduled to meet pretty much everyone on the search committee, and maybe a couple of other people in addition if there's time. Usually at 4:00pm on the first day, we have the candidate give a departmental colloquium. We point out to them when we invite them that the audience for our colloquia is very general - it can include undergrads, and the areas of research of the faculty members in the crowd can range from astrophysics to biophysics to high energy to AMO and CM. The point is we want to see how well the candidate communicates to a general audience about their work (usually their postdoc results, with a slide or a few at the end on future directions). After the talk is dinner with a couple of members of the committee. There are more visits on the second day. In the late morning (usually), the candidate sits down with the committee and gives a shorter (say 20 minutes) research plan talk. This is where the candidate tells us what they want to do in the near and longer term, and what kind of resources they think they'll need to do it (e.g. a big laser system, or a dilution refrigerator, or access to fab and microscopy tools, etc.). This is generally less formal than the colloquium, but it needs to be taken seriously, since this is really where the committee gets a sense of how the candidate approaches planning research. This is also where discussions about teaching happen. Depending on travel plans, there either is a second dinner, or the candidate heads out at the end of day 2.

Once the candidates have all visited, the committee sits down, compares notes, and comes up with a recommendation for the department to vote on. Once the department has made a decision, the department chair is the one who talks with the candidate about offer details. An unofficial offer letter is then prepared and sent out by the dean. Those in the game know what I mean by "unofficial": full-on offer letters come from the office of the president or the board of trustees, depending on the institution, and are essentially only prepared at the very last minute. The candidate is invited to come for a second visit - to look at lab and office space, meet the dean, bring the spouse or significant other if that's relevant, get a look at real estate, etc.

I'll write a third post about faculty searches with a few generic tips for candidates sometime soon.

Weird Al is the man.

Watch this. It's Weird Al's new video. Bonus points for having the Schroedinger equation show up. This may be my favorite Weird Al song since The Saga Begins.

CIAR Nanoelectronics workshop

Blogging from the scenic Calgary airport, as I wait for my flight back to Houston. I've been attending a very fun nanoelectronics workshop in Banff run by the Canadian Institute for Advanced Research. The CIAR is kind of an institute-without-walls that spans Canada. They have seven (I think) sections, each of which funds some research. One of these sections is Nanoelectronics, and the workshop this weekend was very good. Some highlights of the talks:

• Ted Sargent at Toronto is making optoelectronic devices using semiconductor nanocrystals. His group has succeeded in getting nice surface passivation of PbS nanocrystals, such that they get good photoconductive response in a solution-deposited film of these things. Because the bandgap of the nanocrystals is so small (about 400 meV), they can use these in the mid-IR. In an impressive demo, they took a readout chip for a conventional silicon CCD camera, coated it with their PbS nanocrystals, and voila: instant visible-to-midIR video camera. Neat!
• Supriyo Datta gave a nice talk about the general problem of modeling transport through a system that couples not just to its contacts, but also to the environment. As a story-telling device, he framed the discussion in terms of Maxwell's Demon: can one use the spin-selective transmission of a certain type of barrier (containing paramagnetic impurities) as a way of extracting work from the contacts? This is a solid-state gedanken version of Feyman's ratchet-and-pawl. Unsurprisingly, one can't beat the second law of thermodynamics. You can extract some work from the contacts, but at the cost of increasing the entropy of the barrier. If the barrier is cooled to allow work to be continuously extracted, what you've really done is set up a heat engine running on the temperature difference between the contacts and the barrier. I know this isn't a very coherent summary; the talk was infinitely more lucid.
• Several nice talks about charge transport through molecules. Besides me, there were: Heiko Weber talking about his break junction systems; Latha Venkataraman talking about her break junction systems; Mark Ratner talking about charge transport in DNA; Nicolas Agrait talking about transport through 1d chains of Au atoms; and Philip Kim talking about graphene and nanotubes.
• Mark Reed showed some interesting results on top-down fabrication and surface functionalization of Si nanowires for integrated sensors.
  
• Eli Yablonovitch had some thought-provoking points about nanoelectronics and what we should all really be working on. I told him I wouldn't blog about this until he got it written up, so you'll hear more about this from me once it shows up on the arxiv.

Overall a very good meeting, though I regret not bringing hiking boots or having enough time to go skiing in the gorgeous Canadian Rockies.

A primer on faculty searches

It's been suggested that it would be valuable for me to post a brief description of the faculty search process. An obvious disclaimer: this is based on my experience, and may not generalize well to other departments with vastly differing cultures or circumstances. Anyway, here are the main steps in a search:

1. 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).
2. 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.
3. 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). 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 typically placed by MIT and Berkeley: "We are looking for smart folks. Doing good stuff. In some area." They run the same ad every year, trolling for talent. They seem to do ok. 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.
   
4. 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. A couple of people on the search committee will be particularly in charge of oversight on affirmative action/equal opportunity issues.
   
5. 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.).
   
6. Applications come in and are sorted; rec letters are collated. Each candidate has a folder.
   
7. 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. As a friend of mine at a large state school once half-joked to me: 15% of the faculty in any department do the best research; 15% do the best teaching; 15% do the most service and committee work; and it's often the same 15%.
   
8. 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.

Ahhh, Texas.

While I generally enjoy living here, there are times when I really, really don't like living in Texas. For example, earlier today our governor (who is almost certainly going to be re-elected tomorrow, since the opposition to him will be split three ways, or four if you count the libertarian candidate) made me feel extra welcome. From the Dallas Morning News:

Gov. Rick Perry, after a God and country sermon attended by dozens of political candidates Sunday, said that he agreed with the minister that non-Christians will be condemned to hell.

Great. Why did the governor feel the need to talk about this at all? Apparently he feels that he needs to say things like that to get re-elected by my fellow Texas residents. Unsurprisingly, one of his opponents had a bon mot about this that I think says it all:

"He doesn't think very differently from the Taliban, does he?" independent Kinky Friedman said.

The h parameter....

Well, since several folks are commenting on the h parameter, I might as well put in my two cents. The h number is defined here. In brief, if you've published h papers (and no more) that each have h or more citations, then your h number is, well, h. In principle, your h number is not supposed to count self-citations (though once h is above 10 or so, that becomes pretty irrelevant anyway). In some fields (e.g. CS) where people tend to publish on public electronic archives rather than in journals, citations of those preprints are counted. The idea is that the H number is a metric of scientific performance and impact, and is more robust than mere citation counting. Steady output that people actually cite is rewarded more than being one co-author on a Science paper that happened to get 750 citations. There are variations, too. You can calculate the h number divided by a person's years of "professional experience", or actually figure out dh/dt. For a fair comparison between people, one should normalize h numbers by subfield. In condensed matter physics, a typical person near tenure time has an h of around 10. In mid-career, an h of around 20-30 is about the average, and exceptional people like National Academy members tend to have h values higher than 50. The h number can be skewed in certain cases. Some people publish little, but their work can have enormous impact. Others, such as materials growers, can have enormous h numbers because they supply materials used by dozens of experimental groups.

Obviously trying to quantify a person's scientific impact and productivity in one number is a crude and rough thing to do, just as the subject GREs and qualifying exams are often crude indicators of actual aptitude. Just as I think the physics GRE is only really good at identifying outliers (the best 2.5% do very well on it; the worst 2.5% do very poorly; the middle 95% get scores that don't seem to correlate with their actual talent or ability), the h number is similar. I would never dream of assigning too much importance to it in tenure cases. As in grad school or postdoc or faculty applications, detailed letters of recommendation are far more useful, and in my experience correlate much better with actual performance. However, if someone has an h number far outside the expected norm in either direction, I'd like to know that. For example, I heard recently of an externally appointed dean at a research university where the faculty were rather shocked to find that the dean's h number was about 4. Unsurprisingly, people who have had vastly larger scientific impacts don't really like being told what to do or have their decisions scrutinized by someone who has essentially been a professional administrator.

Anyway, I wouldn't lose too much sleep over h numbers. They just get a lot of attention because they're a relatively new idea, and they do seem superior to the previous crude metric, citation counting.