Most solids compress when squeezed, though the effect isn’t very large for most technologically important materials (metals, ceramics, and so forth). A few rare materials exhibit negative compressibility: they expand in the direction the force is exerted, though again the effect is small. However, researchers figured out a way to produce extraordinarily large negative compressibility, by fabricating a material with a folding wine-rack structure. (This was a fun story to write, and I got to refer to caecilians. Which are breaking my heart. Which are shaking my confidence daily.)

No material can exhibit negative compressibility in all dimensions at once: if it expands in one direction, then it will contract in the two directions perpendicular to the expansion. The researchers’ insight was to realize that they could maximize negative compressibility in one dimension by simultaneously maximizing positive compressibility in the other two. This kind of “wine rack” configuration (their words) is similar to an example found in nature: tendon structures in the legless amphibians known as caecilians. [Read more…]