Some of these things are so basic it is embarrassing.
Tony Wright had the nice idea that at the UQ condensed matter theory group meeting each member should have a turn saying a topic they don't understand and feel they should. Speakers will be in order of decreasing seniority. Hopefully, then the junior people will not feel so bad. I guess the ultimate goal is to help one another understand these things. It is also to create a culture where people are comfortable asking basic questions.
So here is a list for me in order of increasing profoundness:
- Why are metals shiny?
- How do p-n junctions and transistors work?
- What is the origin of hysteresis in ferromagnets?
- Why do extremal areas of the Fermi surface determine the frequency of quantum oscillations?
- How does a Fano resonance between a bound state in the continuum lead to an asymmetric spectral lineshape?
- Why does the Kondo effect lead to unitary scattering and a phase shift of pi/2?
- How do you derive Hund's rules?
- How do you derive Goldstone's theorem?
- What is the chiral anomaly in quantum field theory? How is it related to edge states and topological order in condensed matter?
What are some questions on your list?