How does BCS theory explain superconductivity?
Let's be precise. In a normal metal, electrons scatter off impurities and lattice vibrations, creating resistance. But below a critical temperature, something remarkable happens. An electron moving through the lattice attracts positive ions, creating a slight distortion—a region of higher positive charge. A second electron is drawn to that region, and the two become correlated as a Cooper pair. Though each electron is a fermion, the pair behaves as a boson, allowing them to condense into a single quantum state. This condensate flows without resistance because scattering would require breaking the pair, which costs energy. The theory predicts a gap in the energy spectrum, which we confirmed experimentally. It's a beautiful example of how collective behavior emerges from simple interactions. The beauty of a theory is not a guarantee of its truth, but in this case, the predictions matched.
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