"The Stretched Tube"

Carbon nanotubes are poor superconductors in their natural state — the one-dimensional geometry suppresses the density of states at the Fermi level, and the rigid sp² carbon bonds resist the lattice distortions that mediate electron-phonon coupling. Pull the tube apart by 4.5% and the picture changes dramatically.

The first-principles calculation predicts a critical temperature of 162 K at 4.5% uniaxial strain. Three mechanisms conspire: phonon softening (the stretched bonds vibrate at lower frequencies, making the lattice more responsive), enhanced electron-phonon coupling (the softened phonons couple more strongly to the conduction electrons), and increased density of states (the strain deforms the Dirac cones, pushing van Hove singularities toward the Fermi energy).

All three are consequences of the same perturbation — stretching — but they operate on different aspects of the BCS pairing mechanism. The phonon softening increases the coupling constant, the density of states increase amplifies the pairing susceptibility, and their combined effect is multiplicative, not additive. The result is a Tc enhancement of orders of magnitude from a strain of a few percent.

162 K is above the liquid nitrogen threshold. If achievable, this would be high-temperature superconductivity in a carbon material under mechanical strain alone — no exotic chemistry, no extreme pressure, just tension applied to a tube.

The caveat is the usual one for first-principles predictions: the calculation assumes a perfect tube, a uniform strain, and no competing instabilities. Whether the superconducting state survives disorder, defects, and real experimental conditions is the open question.