Words of advice about giving talks

I know that there are many many resources out there on the web about how to give scientific talks (see here (pdf), here, here, and here, for example). Still, I have a few pointers to suggest, based on some recent talks that I've seen.

• Know your audience. If you're giving a seminar, remember that you need to give an introduction that is appropriate for first-year graduate students. If you're giving a colloquium, remember that you're facing a diverse crowd that could include (in a physics department) astrophysicists, biophysicists, high energy physicists, etc., as well as their graduate students. Pitch your talk appropriately. This is (at least) doubly important if you're giving a job talk, and as my postdoctoral mentor used to point out, every talk you give is potentially a job talk.
  
• Know your time constraints. Don't bring 140 slides for a 50 minute talk, and don't go way over the allotted time. In fact, for an hour talk slot I'd say aim for 50 minutes.
  
• Avoid jargon; if acronyms are necessary, define them. Just because an acronym or term may be common in your sub-field, don't assume that everyone knows it. Just like most condensed matter people don't know what pseudorapidity means to a high energy physicist, most high energy physicists don't know what ARPES or XAFS are.
  
• Minimize equations, even if (especially if) you're a theorist. You can always have a backup slide with enough math on it to make people's eyes bleed, if you want. For a main slide in a talk, no one (not even the experts) are going to get much out of a ton of equations. If you have to have equations, have a physical interpretation for them.
  
• Don't show big scanned text passages from papers. No one is going to read them.
  
• Explain the big picture. Why is this work interesting? You'd better have an answer that will be intelligible to a non-specialist. Even better, think about how you would explain your work and the point behind it to a sophomore.
  
• If you're giving a ten-minute talk, don't spend two minutes showing and explaining an outline.
  
• Avoid technology party fouls. Make sure that your technology works. Make sure that your fonts are readable and correct. Too many colors, too much animation, too many cutesy transitions - all of these things are distracting.
• Make sure to repeat a question back to the questioner. This helps everyone - the semisleeping audience gets to hear what was asked, and you get to make sure that you're actually understanding the question correctly. No one wins when the speaker and questioner are talking at cross-purposes.

Feel free to add your own recommendations or warnings in the comments.

Hard times.

Wow. I guess those rumors about Harvard getting burned playing hedge fund games are true. They're putting in place a staff hiring freeze and getting ready to cancel faculty searches. Steps like that aren't surprising at, e.g., public universities in states hit hard by the housing crunch or ensuing economic crisis, but for a university with an endowment bigger than the GDP of some countries, this seems rather drastic. Still, it's hard to have too much sympathy for them, since their endowment is coming off a high of nearly $37B.

A (serious) modest proposal

Hopefully someone in the vast (ahem.) readership of this blog will pass this along to someone with connections in the Obama transition team. I've already submitted this idea to change.gov, but who knows the rate at which that gets read.

As part of the forthcoming major economic stimulus package, I propose that the Obama administration fully fund the America Competes initiative immediately. If the goal of the package is to stimulate the economy while doing something for the long-term health of the country (e.g., creating jobs while fixing roads, bridges, etc.), then funding basic research via the various agencies is a great thing to do. Think about it: the US spends less as a percentage of GDP than most of the rest of the developed world on science research. Rectifying that to some degree would (a) help the long-term prospects for technological innovation in the US; (b) create jobs; (c) support the goal of developing energy-related technologies; (d) support our universities, many of which are getting hammered by falling state revenues and/or poor endowment returns. Best of all, you could do all of this and it would be a freakin' bargain! You could double the research funding in NSF, NIH, DOE, NASA, and NIST, and not even come close to the amount of money we've already given to AIG. I'm suggesting something far more modest and much less disruptive. Seriously, ask yourself what's better for the long-term health of the country. Cutting basic science to pay for propping up Goldman Sachs is perverse.

Update: If you think that this is a good idea, I encourage you to submit your suggestion here, here, and/or here.

Spin

Many particles possess an internal degree of freedom called "spin" that is an intrinsic amount of angular momentum associated with that particle. The name is meant to evoke a spinning top, which has some rotational angular momentum about its axis when, well, spinning. Electrons have "spin 1/2", meaning that if you pick a convenient axis of reference ("quantization axis") that we'll call z, the z-component of the electron's spin angular momentum is either +1/2 hbar or -1/2 hbar. All too often we treat spin in a rather cavalier way. When people talk about "spintronics", they are interested in using the spin degree of freedom of electrons to store and move information, rather than using the charge as in conventional electronics. One complication is that while charge is strictly conserved, spin is not. If you start off with a population of spin-aligned electrons and inject them into a typical solid, over time the spin orientation of those electrons will become randomized. Now, angular momentum is strictly conserved, so this relaxation of the electron spins must coincide with a transfer of angular momentum to the rest of the solid. Feynman pointed this out (somewhere in vol. III of his lectures on physics) - if you fire a stream of spin-polarized electrons into a brick hanging on the end of a thread, you are really applying a torque to the brick since you are supplying a flow of angular momentum into it, and the thread will twist to apply a balancing torque. Well, Zolfagharkhani et al. have actually gone and done this experiment. They use a ferromagnetic wire to supply a polarized spin current and an extremely sensitive nanomechanical torsional oscillator to measure the resulting torque. Very nice stuff.

Nature Journal Club

My media onslaught continues. This past week I had a Journal Club contribution in Nature, which was fun and a nice opportunity for a wider audience. Here's a version of it before it was (by necessity) trimmed and tweaked, with added hyperlinks....

Tunable charge densities become very large, with super consequences

The electronic properties of materials depend dramatically on the density of mobile charge carriers. One way to tune that density is through doping, the controlled addition of impurity atoms or molecules that either donate or take up an electron from the rest of the material. Unfortunately, doping also leads to charged dopants that can act as scattering sites.

Fortunately, there is a way to change the carrier concentration without doping. In 1925 J. E. Lilienfeld first proposed what is now called the “field effect”, in which the sample material of interest is used as one electrode of a capacitor. When a voltage is applied to the other (“gate”) electrode, equal and opposite charge densities accumulate on the gate and sample surfaces, provided charge can move in the sample without getting trapped. While the density of charge that can be accumulated this way is rather limited by the properties of the insulating spacer between the gate and the sample, the field effect has been incredibly useful in transistors, serving as the basis for modern consumer electronics.

Recently it has become clear that another of Lilienfeld’s inventions, the electrolytic capacitor, holds the key to achieving much higher field effect charge densities. The dramatic consequences of this were made clear by researchers at Tohoku University in Sendai, Japan (K. Ueno et al., Nature Mater. 7, 856-858 (2008)), who used a polymer electrolyte to achieve gated charge densities at a SrTiO₃ surface sufficiently large to produce superconductivity. While superconductivity had been observed previously in highly doped SrTiO₃, this new approach allows the exploration of the 2d superconducting transition without the disorder inherent in doping.

The most exciting aspect of this work is that this approach, using mobile ions in an electrolyte for gating, can reach charge densities approaching those in chemically doped, strongly correlated materials such as the high temperature superconductors. As an added bonus, this approach should also be very flexible, not needing special substrates. Tuning the electronic density in strongly correlated materials without the associated pain of chemical doping would, indeed, be super.

This week in cond-mat

One paper today in the arxiv:
arxiv:0811.2914 - Zwanenburg et al., Spin states of the first four holes in a silicon nanowire quantum dot
This is another typically exquisite paper by the Kouwenhoven group at Delft, in collaboration with Charlie Lieber at Harvard. The Harvard folks have grown a Si wire segment in the middle of a long NiSi wire. The NiSi ends act as source and drain electrodes for conduction measurements, and the Si segment acts as a quantum dot, with the underlying substrate acting as a gate electrode. As usual, the small size of the Si segment leads to a discrete level spectrum, and the weak electronic coupling of the Si segment to the NiSi combined with the small size of the Si segment results in strong charging effects (Coulomb blockade, which I'll explain at length for nonexperts sometime soon). By measuring at low temperatures very carefully, the Delft team can see, in the conductance data as a function of source-drain voltage and gate voltage, the energy level spectrum of the dot. By looking at the spectrum as a function of magnetic field, they can deduce the spin states of the ground and excited levels of the dot for each value of dot charge. That's cute, but the part that I found most interesting was the careful measurement of excited states of the empty dot. The inelastic excitations that they see are not electronic in nature - they're phonons. They have been able to see evidence for the launching (via inelastic tunneling) of quantized acoustic vibrations. Figure 5 is particularly nice.

Workshop on new iron arsenide superconductors

This weekend is a big workshop at the University of Maryland on the new iron arsenide high temperature superconductors. Since it's not really my area, I didn't go. Anyone want to give a little update? Any cool news?

Poor Doug's Almanack

Welcome, readers of Discover Magazine! Thanks for coming by, and I hope that you find the discussion here interesting. The historical target audience of this blog has been undergrads, grad students, and faculty interested in condensed matter (solid state) physics and nanoscience. The readership also includes some science journalists and other scientific/engineering professionals. I would like very much to reach a more general lay-audience as well, since I think we condensed matter types historically have been pretty lousy at explaining the usefulness and intellectually richness of our discipline. Anyway, thanks again.

(By the way, I don't compare in any serious way with Ben Franklin - that was a bit of hyperbole from Discover that I didn't know was coming. Fun science fact: Franklin's to blame that the electron charge is defined to be negative, leading to the unfortunate annoyance that current flow and electron flow point in opposite directions. He had a 50/50 chance, and in hindsight his choice of definition could've been better.)

This week in cond-mat

This week the subject is boundary conditions. When we teach about statistical physics (as I am this semester), we often need to count allowed states of quantum particles or waves. The standard approach is to show how boundary conditions (for example, the idea that the tangential electric field has to go to zero at the walls of a conducting cavity) lead to restrictions on the wavelengths allowed. Boundary conditions = discrete list of allowed wavelengths. We then count up those allowed modes, converting the sum to an integral if we have to count many. The integrand is the density of states. One remarkable feature crops up when doing this for confined quantum particles: the resulting density of states is insensitive to the exact choice of boundary conditions. Hard wall boundary conditions (all particles bounce off the walls - no probability for finding the particle at or beyond the walls) and periodic boundary conditions (particles that leave one side of the system reappear on the other side, as in Asteroids) give the same density of states. The statistical physics in a big system is then usually relatively insensitive to the boundaries.

There are a couple of physical systems where we can really test the differences between the two types of boundary conditions.
arxiv:0811.1124 - Pfeffer and Zawadzki, "Electrons in superlattices: birth of the crystal momentum"
This paper considers semiconductor superlattices of various sizes. These structures are multilayers of nanoscale thickness semiconductor films that can be engineered with exquisite precision. The authors consider how the finite superlattice result (nonperiodic potential; effective hardwall boundaries) evolves toward the infinite superlattice result (immunity to details of boundary conditions). Very pedagogical.

arxiv:0811.0565, 0811.0676, 0811.0694 all concern themselves with graphene that has been etched laterally into finite strips. Now, we already have a laboratory example of graphene with periodic boundary conditions: the carbon nanotube, which is basically a graphene sheet rolled up into a cylinder. Depending on how the rolling is done, the nanotube can be metallic or semiconducting. In general, the larger the diameter of a semiconducting nanotube, the smaller the bandgap. This makes sense, since the infinite diameter limit would just be infinite 2d graphene again, which has no band gap. So, the question naturally arises, if we could cut graphene into narrow strips (hardwall boundary conditions transverse to the strip direction), would these strips have an electronic structure resembling that of nanotubes (periodic boundary conditions transverse to the tube direction), including a bandgap? The experimental answer is, yes, etched graphene strips to act like they have a bandgap, though it's clear that disorder from the etching process (and from having the strips supported by an underlying substrate) can dominate the electronic properties.

Two new papers in Nano Letters

Two recent papers in Nano Letters caught my eye.

Kuemmeth et al., "Measurement of Discrete Energy-Level Spectra in Individual Chemically Synthesized Gold Nanoparticles"
One of the first things that I try to teach student in my nano courses is the influence of nanoscale confinement on the electronic properties of metals. We learn in high school chemistry about the discrete orbitals in atoms and small molecules, and how we can think about filling up those orbitals. The same basic idea works reasonably well in larger systems, but the energy difference between subsequent levels becomes much smaller as system size increases. In bulk metals the single-particle levels are so close together as to be almost continuous. In nanoparticles at low temperatures, however, the spacing is reasonably large compared to the available thermal energy that one can do experiments which probe this discrete spectrum. Now, in principle the detailed spectrum depends on the exact arrangement of metal atoms, but in practice one can look at the statistical distribution of levels and compare that distribution with a theory (in this case, "random matrix theory") that averages in some way over possible configurations. This paper is a beautiful example of fabrication skill and measurement technique. There are no big physics surprises here, but the data are extremely pretty.

Xiao et al., "Flexible, stretchable, transparent carbon nanotube thin film loudspeakers"
This is just damned cool. The authors take very thin films of carbon nanotubes and are able to use them as speakers even without making the films vibrate directly. The idea is very simple: convert the acoustic signal into current (just as you would to send it through an ordinary speaker) and run that current through the film. Because of the electrical resistance of the film (low, but nonzero), the film gets hot when the current is at a maximum. Because the film is so impressively low-mass, it has a tiny heat capacity, meaning that small energy inputs result in whopping big temperature changes. The film locally heats the air adjacent to the film surface, launching acoustic waves. Voila. A speaker with no moving parts. This is so simple it may well have real practical implementation. Very clever.

To quell speculation....

Yes, if asked, I would serve as President Obama's science advisor. (Come on - you would, too, right? Of course, it's easy for me to joke about this since it's about as probable as me being asked to serve as head of the National Science Board.)

This one's easy.

Has Bush been good for science? I agree with ZapperZ: No. How Marburger can argue that research funding has kept pace with inflation is beyond me, given the last three years of continuing resolutions, unless one (a) fudges the definition of research to include a lot of military development, and (b) fudges the definition of inflation to ignore things like food, fuel, and health care costs.

Could Bush have been even worse? Yes.

Statistical physics

This fall I'm teaching Statistical and Thermal Physics, a senior (in the most common Rice physics curriculum, anyway) undergraduate course, and once again I'm struck by the power and profundity of the material. Rather like quantum, stat mech can be a difficult course to teach and to take; from the student perspective, you're learning a new vocabulary, a new physical intuition, and some new mathematical tools. Some of the concepts are rather slippery and may be difficult to absorb at a first hearing. Still, the subject matter is some of the best intellectual content in physics: you learn about some of the reasons for the "demise" of classical physics (the Ultraviolet Catastrophe; the heat capacity problem), major foundational issues (macroscopic irreversibility and the arrow of time; the precise issue where quantum mechanics and general relativity are at odds (or, as I like to call it, "Ultraviolet Catastrophe II: Electric Boogaloo")), and the meat of some of the hottest topics in current physics (Fermi gases and their properties; Bose Einstein condensation). Beyond all that you also get practical, useful topics like thermodynamic cycles, how engines and refrigerators work, chemical equilibria, and an intro to phase transitions. Someone should write a popular book about some of this, along the lines of Feynman's QED. If only there were enough hours in the day (and my nano book was further along). Anyway, I bring this up because over time I'm thinking about doing a series of blog posts at a popular level about some of these topics. We'll see how it goes.

Ahh, Texas, again.

Stories like this one depress me. Is it really any wonder that our state has a difficult time attracting large high-tech companies from, e.g., California and Illinois, even though corporate taxation policies are very friendly here?

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".

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.

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.

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.

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?

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.