Is BCS theory still relevant for high-temperature superconductors?
That's an important question. BCS theory works beautifully for conventional superconductors, where phonons mediate pairing. But high-temperature superconductors, discovered in 1986, operate at much higher temperatures—sometimes above liquid nitrogen—and the mechanism is still debated. Some researchers argue that magnetic fluctuations, not phonons, drive pairing in these materials. However, the core idea of Cooper pairs remains central; experiments confirm that pairs exist in high-temperature superconductors. The challenge is that the simple BCS framework may need extensions, such as strong coupling or d-wave pairing symmetry. In physics, we are always approximating. BCS is not wrong—it's incomplete for these systems. The most profound insights often come from the simplest questions, and BCS gave us the language to ask them. So yes, it's relevant, but we're still refining the theory.
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