Thursday, November 29, 2012

Ionic liquid gating - amazing results

I've mentioned ionic liquid gating a couple of times (here, here) before.  Ionic liquids are basically organic salts (molecular anion; molecular cation, though there are some that use, e.g., alkaline metal ions instead) that are liquid at room temperature.  The concept is simple enough:  use the ionic liquid as an electrolyte in a capacitor comprising a wire employed as a gate electrode and the surface of a sample of interest as the counterelectrode (helpfully contacted by source and drain electrodes).   Setting the bias of the gate relative to the surface drives the ions to move, building up (ionic) surface charge densities at the sample surface.   The material responds to screen what would otherwise be an enormous electric field penetrating the surface by accumulating mobile charge carriers of the appropriate species in a layer at the interface.  This approach, adopted by multiple groups, has been pushed hardest by the group of Iwasa.  The real advantage of this approach is that it allows access to electrostatically gated charge densities comparable to what can be achieved in chemical doping - on the order \( 10^{15} \) per cm2 in that top layer of material.  (This is the regime that He Who Shall Not Be Named fraudulently claimed to access, but this time it's real!)

Particular highlights have included:
A new paper appears in Science this week with yet another impressive result.  Iwasa's team has used ionic liquid gating to push an exfoliated flake of MoS2 into superconductivity.  Indeed, they see what looks a lot like a superconducting "dome" as a function of gated charge, with \(T_{c}\) actually decreasing above an optimal gated carrier density.   Wild.

The results just keep coming.  There are some real subtleties to the technique, though.  It's extremely important to make sure that the ionic liquid is really acting as a chemically inert electrolyte, and not inducing electrochemistry at the material surface or any other kind of chemical doping.

Anyway, this whole area is clearly one to watch in condensed matter.  Anytime you can push into a previously inaccessible regime, Nature tends to offer up surprises.

Wednesday, November 21, 2012


Now that a couple of papers are in and the never-ending list of tasks is getting shorter, hopefully blogging will pick back up. Here are a few interesting links for the (American) Thanksgiving holiday.


This is a paper about the subtleties and challenges of computational physics, meant to be very conversational and pedagogical for students. It was a fun read, and we should have more resources like this.

The Bad Astronomer has relocated to He did this just in time for the rampant speculation about NASA's pending chemistry results from the Curiosity rover. I don't think Curiosity actually killed a cat, but you never know.

The University of Houston just had a one-day symposium in honor of the twenty-fifth anniversary of the discovery of YBCO, the first superconductor with a transition temperature greater than the boiling point of liquid nitrogen. I wish I could've been there, but I had other commitments. My colleague tells me it was a very nicely done affair with many interesting talks and panel discussions. Now if only we could figure this out definitively....

It's always interesting to see a very thought-provoking paper from someone you take seriously. Miles Blencowe, a condensed matter/quantum measurement theorist at Dartmouth, argues that perturbative quantum gravity (a general approach to extending general relativity a bit into the quantum regime) can be a major source of decoherence of quantum superpositions of massive objects. This implies that the very quantum structure of spacetime acts dynamically to "collapse wavefunctions" in the language of the Copenhagen take on quantum mechanics. I need to read this more carefully.



Monday, November 12, 2012

Physics education, again.

This video is great at pointing out much of what is wrong with high school physics education in the US.  However, I find the implication that this is not that hard to fix to be a bit tough to swallow.  More later....

Wednesday, November 07, 2012

Things no one teaches you as part of your training.

Over the last couple of months I've been reflecting about some aspects of being an academic physicist, particularly what skills are important and what aspects of the job are never explicitly taught.  The training system that has evolved in the post-WWII US research universities is one that, when it works well, instills critical thinking, experimental or calculational design, and a large amount of (often rather narrow) scientific expertise.  Ancillary to this, doctoral students often (but not always) get indirect training in written and oral communications through the various papers and theses they write and the presentations that are made at conferences and dissertation defenses.  Often students gain some teaching experience, though many times this is in the form of the kind of TA work (running a lab section, grading problem sets) that is a far cry from actually planning out and lecturing a course.  Sometimes in the course of graduate or postdoctoral work, scholars are taught a bit about mentoring of younger students, but this is almost entirely informal.

However, there are many critical skills (relevant to eventual careers in both academia and industry) that get by-passed.   I'm not sure how you would actually teach these things in practice, and setting up courses to do so would widely be viewed as a waste of student time.  Still, it's interesting how much of being a good faculty member (or valued employee with managerial responsibilities) is never taught; it's just assumed that you pick this stuff up along the way somehow, or you are innately skilled.  Examples:
  • Managing students.  This includes: motivating students; determining what level of guidance is best suited to a particular student to instill independence and creativity yet avoid either aimless floundering or complete micromanagement; how to deal with personal, physical health or mental health problems; how to assess whether a student really has strong potential or an affinity for a particular project or set of skills.
  • Managing money.  No one ever tells you how to run a research group's finances.  No one ever explicitly sits you down and explains how the university's finances really work, what indirect costs really mean, how to deal with unanticipated financial issues, how to write a budget justification, how to stretch money as far as possible, how to negotiate with vendors, how the university accounting system works, how much responsibility to delegate to students/postdocs, how you may interact with the office of research accounting, how to do effort reporting.
  • Working with colleagues within the department and the university.  (actually, my department does a decent job at this through faculty mentoring, but most of that was put in place after I had been promoted already.)  How does university decision making work, what can the chair do, what do the deans do, what does the provost do.  Why are there so many university committees?  Do any of them do anything useful?  Are they just a refuge for people with too much free time, who like to argue for hours about whether "could" or "should" is the appropriate language for a policy?
  • Writing.  The only way people learn to write all of the really critical documents (papers, grant proposals, white papers, little blurbs for the department web page, group websites, etc.) is by doing.
  • Teaching.  At the modern research university, there is an assumption that you can pick up teaching.  This is widely considered insulting by serious education professionals, though there is truth to it - most people who are highly successful, communicative, organized scientists tend to be pretty good in the classroom, since good teaching requires good communications and organization capabilities (though also considerably more).
  • Time management.  No one teaches you how to budget your time, but if you can't do it reasonably well, you're really in trouble.  (For example, I should be writing three other things right now....)
Thoughts?  Anyone have any other examples of things we're expected to know but are never taught?  Suggested solutions to this problem?