Traditional superconductivity is limited by the masses of atoms vibrating in the lattice, which sets an upper temperature threshold because thermal noise acts like a phase change that returns the superconductor to being an ordinary conductor or insulator above its critical temperature.
Electrons are fermions with half-integer spin, meaning that their total quantum wave function must be antisymmetric. Swapping any two electrons flips the sign of their wave function, meaning that they can't overlap with the same spin, by the Pauli exclusion principle. But two electrons with opposite spin form a spin-singlet state where their spatial wave functions can overlap. Which is why two electrons with opposite spin can be in the same atomic orbital forever.
For larger quantum wave functions in molecules, electrons occupy larger molecular orbitals forming covalent bonds, and in conductors form what's known as a Fermi sea. If many electrons spontaneously align their spins via the exchange force which arises from exclusion and electrostatic repulsion (the same effect which causes Fermi holes, conceptually analogous to electron vacancies in semiconductors), their magnetic moments become large enough to be observed at the macro-scale as ferromagnetism.
At low temperatures, electrons have restricted momentum states at the sharp edge of the Fermi sea, so by the Heisenberg uncertainty principle, their spatial wave function uncertainty (coherence length) expands, causing them to overlap. Below the critical superconducting temperature, they pair up to become composite bosons. Bosons have integer spin and symmetric wave functions, so they aren't bound by the exclusion principle and undergo Bose-Einstein condensation.
In Bardeen-Cooper-Schrieffer (BCS) theory, these composite bosons are known as Cooper pairs. They share a wide coherence length and act as a unified macroscopic quantum state that flows around atomic nuclei without scattering, even in the presence of atomic vibrations (phonons) or imperfections in the lattice. In effect, this makes the superconductor a macro-scale orbital, similarly to how a permanent magnet is macro-scale spin.
BCS theory explains superconductivity from the bottom up like an engineering approximation. More foundational frameworks like Ginzburg-Landau (GL) theory use spontaneous symmetry breaking to explain it from the top down.
Using GL theory and going back to first principles, instead of avoiding phonons/vibrations to raise the critical temperature, we can manipulate lightweight electron clouds. To do this, we use electron-hole pairs (excitons) in semiconductors to dynamically polarize the electron clouds. This electronic framework leads to orbital fluctuation theory and excitonic superconductivity.
It was recently discovered that graphene layers twisted at a 1.1-degree magic angle create superconductivity. The overlapping atomic lattices form a Moiré superlattice that slows electrons down in places to restrict their momentum and expand their spatial uncertainty. This mimics the effects of low temperatures spatially instead of thermally, and is known as twistronic superconductivity.
Note that I wrote this summary by hand after doing a deep dive with AI, which also helped me edit it. While it's notable that AI can explore large problem spaces and find solutions independently, I'm at least as fascinated that it can now help us tackle complex topics in an approachable manner, which should lead to new insights and hopefully inspire future researchers.