superfluid density

A thin layer of indium arsenide lies hidden under a superconducting film, like a voice beneath the noise of a crowd. In such a hybrid, current takes the path of least resistance and flows almost entirely through the metal, leaving the semiconductor inaudible to standard probes.

In the depths of sub-Neptunes, the most common type of planet in the Galaxy, though not one you could stand on, silicate magma and hydrogen mix into a single supercritical cocktail. Previously, it was thought that beneath the dense hydrogen atmosphere lay a sharp boundary with molten silicate, like oil on water.

A film sliver thinner than a human hair was placed between diamond anvils and squeezed. The pressure climbed — a hundred thousand atmospheres, half a million, a million… Yet the material kept conducting electricity without resistance.

Water is not just a wet substance. On a picosecond scale, it resembles a dance floor where molecules continuously break and form bonds with each other. Usually, this dance is described by one main movement — collective relaxation, as if the whole crowd simultaneously slows down after the music stops.

A superfluid flows without friction, like water that never stops. But when you spin it, it doesn't just rotate: each tiny vortex remembers exactly how it was spun. This 'trace' is not a metaphor but a real geometric imprint, which physicists call the Berry phase (the phase acquired by a wave as it travels along a closed path).

Spintronics promises to transmit information not by charge but by spin, ridding microelectronics of its main enemy — Joule heating.

In the crystal CsV3Sb5-xSnx, which becomes a superconductor at low temperatures, current does not flow as a uniform stream but along narrow, winding paths. A scanning microscope with a sensitive magnetic field sensor helped reveal these paths: it picks up the faintest currents, much like a sonar probes the seafloor.

In the 1930s, Fritz Zwicky first noticed that galaxies in clusters were moving too fast — something invisible was holding them. Later, Vera Rubin measured the rotation of spiral galaxies, confirming that space is permeated by dark matter.

A stone falls into a pond, and ripples spread across the water. Long waves and short ones travel at the same speed: that's how ordinary sound behaves in almost any medium. But in quantum liquids, things can be different. Physicists considered a superfluid where particles move along a "flat" energy band.

Imagine a packed dance floor where dancers glide without any friction — passing through each other without a touch. That's a superfluid. In a neutron star's crust, neutrons could behave this way, but a rigid lattice of ions gets in the way, like suddenly sticking the dance floor full of pillars.

A crowd of people who can move freely but suddenly start acting as one: that's how a superconductor carries current without resistance.

Spread a handful of coins on the table. Each coin is a possible outcome: heads, tails, or something else. If we know how chaotic this set is (its entropy), which combinations of probabilities will we encounter more often? It turns out the answer depends on how much chaos we allow.

In superfluid helium, friction disappears — the liquid flows like a mountain stream, but without a single eddy. A short laser pulse rippled this smooth surface, and scientists using spectroscopy captured the spreading ripples — quantum waves with many speeds.

In helium cooled to near absolute zero, the liquid stops rubbing against itself and begins to flow without any resistance.

A frictionless liquid that flows forever: that's superfluidity. Helium-3 only achieves it at thousandths of a degree above absolute zero. The theory of this state was developed by Lev Landau and Richard Feynman.

A sheet of graphene one atom thick is twisted at a small angle, and it starts behaving like a layered pie with layers slightly rotated relative to each other. At a certain twist angle, this material becomes a superconductor: electrons begin to move in pairs, like dancers in a waltz, without losing energy. But what exactly happens inside has remained a mystery.

In a protoplanetary disk, a cloud of gas and dust around a young star, dust grains don't just fly in circles. They are carried by the gas flow, like sand by the wind, and in turn alter that flow. Layers emerge, sliding past each other, and at their boundaries an instability arises — waves and vortices.

The quantum Hall effect has long been suspected of superfluidity — the ability to flow without friction. Imagine a cook following a recipe: for each unit of magnetic flux, he must add exactly a certain number of electrons.

A liquid that flows without friction is superfluid helium-4, a strange state of matter at temperatures below two kelvins. In a large volume, the transition to superfluidity occurs at the lambda-point temperature, but in narrow channels everything changes.

In the macroscopic world we know, any motion inevitably decays: friction, a dissipative process that scatters energy, intervenes. But quantum reality has surprises in store.

Liquid helium cooled to near absolute zero behaves like two fluids at once: a normal viscous part and a superfluid part that flows without friction. When such a flow hits a cylinder, vortices are born behind it. But sometimes vortices appear in front of the cylinder — where classical laws say they shouldn't be.

In a superconductor, electric current flows without loss, like water through a perfectly smooth pipe. But if you place such a material in a magnetic field, vortices appear inside — tiny whirlpools where superconductivity is destroyed. As long as these whirlpools stay put, current flows freely.

A superconductor is like a city where electrons stop jostling and start moving in pairs, like people strolling arm in arm. In neodymium-strontium nickelate (Nd₀.₈Sr₀.₂NiO₂), this 'parade' kicks in at around 10 kelvin (minus 263 degrees Celsius), but not uniformly.

Inside giant planets like Jupiter and Saturn, heat doesn't always rise freely. Heavy elements, which are more abundant in some layers than others, prevent hot fluid from floating up. This creates semiconvection — a type of mixing where heat and composition spread at different rates.

Helium on graphite behaves like an acrobat who simultaneously slides along a tightrope and holds a pose.

All bodies in vacuum fall with the same acceleration: this principle, formulated by Einstein in general relativity, underpins our understanding of gravity. Yet so far it has been experimentally confirmed only for particles of ordinary matter.

A supersolid is ice that flows. Think of a pond with a frozen crust, but beneath it, a liquid depth without friction. Usually, creating that crust means changing the liquid's properties throughout its entire volume.

According to Einstein's theory, Earth's rotation drags space-time itself along — like a spoon dragging thick honey. This effect is incredibly weak: about one revolution in billions of years. But it can be caught.