Sunday, February 05, 2023

Some interesting links - useful lecture notes, videos

Proposal writing, paper writing, and course prep are eating a lot of my bandwidth right now, but I wanted to share a few things:

  • David Tong at Cambridge is a gifted educator and communicator who has written lecture notes that span a wide swath of the physics curriculum, from introductory material on mechanics through advanced graduate-level treatments of quantum field theory.  Truly, these are a fantastic resource, made freely available.  The link above goes to a page with links to all of these.
  • In a similar vein, Daniel Arovas at UC San Diego has also written up lecture notes on multiple components of physics, though usually aimed at the graduate level and not all linked in one place.  These include (links to pdf files) mechanics, thermodynamics and statistical mechanics, condensed matter physics, nonlinear dynamics, the quantum Hall effect, and group theory (unfinished).
  • I long ago should have mentioned this youtube channel (Kathy Loves Physics and History), by Kathy Joseph.  Her videos are a great blend of (like it says on the label) physics and history of science.  As a great example, check out the story of Ohm's Law.  I had never heard about the dispute between Ohm and Ampère (who didn't know about the internal resistance of batteries, and thus thought his experiments disproved Ohm's law).  
  • This twitter thread pointing out that current in quantum Hall and related systems is not, in fact, purely carried by states at the sample edges, is thought-provoking.  


darovas said...

Thanks Doug! Could you please update the links to the most recent versions?


Nonlinear dynamics:


Condensed Matter:

Group Theory (unfinished):


Douglas Natelson said...

Done, and thank you for making these great resources available!

Anonymous said...

So what *is* the correct way to understand the Quantum Hall Effect? I have a hard time understanding the quantization without topology. Or did many of us just drink the topological Kool-aid without thinking?

Any resources you recommend reading for those of us bothered by that Twitter thread?

Nicholas Sedlmayr said...

I think if you read David Tong's lecture notes on the Quantum Hall Effect this is explained quite clearly.

Anonymous said...

No, those notes go through the usual explanation of the QHE in terms of chiral edge modes. Where does it address the questions brought up in the Twitter thread or experimentally in current distribution measurements in IQHE systems?

Anonymous said...

As far as I recall he explains there that the current is not just carried by the edge states, but by all states. Even so the topological protection /does/ require the edge states, even if the current can be carried by bulk states as well.

Anonymous said...

Well the experimental data they show says a different story - current flows on the edge for small bias voltages, but becomes increasingly bulk with higher bias. See cartoon Figure 3 of this

Jonah said...

I seem to agree with the last anonymous. The current not carried by edge states arises from a combination of disorder, which generates compressible puddles in the bulk, and voltage bias, which allows edge current to tunnel into these puddles, thereby causing a bulk voltage drop and current that is detected. It doesn't seem to change the basic picture of quantum Hall transport, or am I missing something?