hyper-efficient solar cells that aren’t actually efficient! or, giving good science a bad title
It’s ironic (or perhaps siliconic since this is about solar cells) to find a takedown article (which is otherwise OK) that says things like “relaxed momentum conservation” and explain it like this:
These strange little beasties are tiny bits of semiconductor material — tiny enough that lots of strict physical laws (like conservation of momentum) get to relax in some ways, making all sorts of fantastic things possible.
The phrase show up in a few places on the net, but the context there is not that the law is relaxed, but that the conditions are. Silicon is an indirect-bandgap material, meaning that the bands on either side of the bandgap do not line up if you lot energy vs. momentum, as you can see here. This requires a “phonon assist” for an excitation — you need the right vibration, with the right momentum at the time the photon arrives in order to promote the election. In other words, it’s harder to meet the conditions of momentum conservation.
But that’s in a crystal. So what I suspect is that in a quantum dot, the conditions are easier to meet, because it looks more like a direct bandgap material. Not that the law itself is more relaxed.
Conserved quantities and symmetries are 1:1 united by Noether’ theorems. Time is locally homogeneous, energy is locally conserved. The vacuum is isotropic, angular momentum is conserved. Locally reduce symmetry, as inside a chiral crystal lattice, and locally clean equations suddenly get footnotes from the boundary conditions. Render the material disordered and the naughtiness dissipates.
Physics deeply assumes the vacuum is isotropic. Massless boson photons agree to 14 significant figures. The interesting part of the universe (e.g., sit on a thumbtack sharp end up) is massed fermions. Is the vacuum isotropic toward massed fermions? Do enantiomorphic space group alpha-quartz single crystals vacuum free fall non-identically? Nobody has looked. Physical theory, by choice (e.g., Calabi-Yau manifolds), is mirror-symmetric. Physics contains massed chirality from manually inserted symmetry breakings (e.g., Chern-Simmons), empirical reality not being mirror-symmetric
http://www.mazepath.com/uncleal/erotor1.jpg
Somebody should look.
If the vacuum were trace anisotropic toward matter, conservation of angular momentum would be trace violated. Milgrom acceleration in MOND would be sourced, ending dark matter. Who wants to replace hectacres of untestable theory with one reproducible experiment in existing apparatus? No tenure for youuuu!