A supersolid is a phase of matter that behaves like a rigid crystal and a frictionless fluid at the same time. Its atoms lock into a repeating, organized structure the way atoms in any solid do, yet they can also flow through that structure without losing any energy. For decades this was purely theoretical, but in 2019 three independent research teams created supersolids in the lab, and experiments have been advancing rapidly since.
Two Properties That Shouldn’t Coexist
In everyday experience, solids and fluids are opposites. A solid holds its shape because its atoms are fixed in a lattice. A fluid flows because its atoms move freely past one another. A supersolid does both. Its atoms arrange themselves into a repeating crystalline pattern, yet a fraction of those atoms simultaneously participate in a collective, frictionless flow called superfluidity. Think of it as a scaffolding of atoms that stays rigid while a ghostly current of matter streams through the gaps without resistance.
Physicists describe this in terms of two types of order breaking at once. In a normal crystal, the regular spacing of atoms breaks what’s called translational symmetry: the material looks different depending on where you sample it, because atoms sit at specific positions. In a superfluid, a different kind of symmetry (related to the quantum phase of the particles) breaks, allowing the entire collection of atoms to behave as one coherent wave that flows without friction. A supersolid breaks both symmetries simultaneously, which is what makes it so unusual and so difficult to produce.
How a Supersolid Actually Looks
In laboratory supersolids, the structure isn’t a perfect, rigid block like an ice cube. Instead, clouds of atoms organize into a row of tiny, dense clusters (often called droplets) separated by thin regions of lower density. Each droplet is like a node in a chain. Crucially, a quantum wave function stretches continuously across the entire chain, linking all the droplets together. That shared wave function is what carries the superfluid flow from one droplet to the next.
The depth of the density dips between droplets matters. If the dips are shallow, the superfluid connection between clusters is strong and matter flows easily across the whole structure. If the dips are deep, more of the wave function stays trapped inside each cluster and the superfluid fraction drops. A 2024 study published in Nature measured this superfluid fraction directly for the first time, confirming that it decreases as the density contrast between clusters grows, matching a prediction made decades earlier by physicist Anthony Leggett.
The Helium-4 False Start
The idea of a supersolid dates back to the 1960s and 1970s, when theorists proposed that solid helium-4 might support frictionless flow at extremely low temperatures. In 2004, physicists Eunseong Kim and Moses Chan at Penn State seemed to find evidence for it. They packed solid helium into a tiny can mounted on a thin shaft and set it twisting. When cooled below 0.2 kelvin, the twisting frequency suddenly increased, as if about 1% of the helium had decoupled from the container and was standing still while the rest of the crystal rotated around it. The implication was striking: solid helium appeared to flow freely through itself.
The excitement didn’t last. Follow-up experiments showed that the effect depended on defects in the helium crystal. When researchers gently heated the crystal just below its melting point and slowly cooled it again (a process called annealing that smooths out flaws), the signal vanished. The unusual behavior turned out to be an elastic quirk of imperfect crystals, not true supersolidity. The helium-4 chapter is a cautionary tale, but it sharpened the criteria physicists use to identify a genuine supersolid.
The 2019 Breakthrough With Magnetic Atoms
Confirmed supersolids finally arrived in 2019, not in solid helium but in ultracold gases of highly magnetic atoms. Three teams announced results nearly simultaneously: two using dysprosium-162 (led by Giovanni Modugno at the University of Florence and Tilman Pfau at the University of Stuttgart) and one using erbium (at the University of Innsbruck). These atoms have unusually strong magnetic properties, which turns out to be the key ingredient.
The recipe starts with laser beams suspending a cloud of atoms inside a vacuum chamber, then cooling them to around 50 nanokelvin, roughly a billionth of a degree above absolute zero. At these temperatures the atoms form a Bose-Einstein condensate (BEC), a state in which all the atoms collapse into a single quantum wave and behave as one entity. A standard BEC is a superfluid but has no crystal structure. To push it into supersolid territory, the researchers tuned the balance between two competing forces: a short-range repulsion that wants to spread the atoms out evenly, and a long-range magnetic attraction that wants to pull them into clumps. By carefully dialing down the repulsion using a technique called a Feshbach resonance, they tipped the balance just enough for the atoms to spontaneously organize into a chain of droplets while keeping the superfluid wave function intact across the whole system.
What Makes It Different From a Regular BEC
A standard Bose-Einstein condensate is already exotic: it’s a superfluid with atoms moving in lockstep as a single quantum wave. But its density is essentially uniform. There’s no repeating pattern, no lattice, no crystal structure. A supersolid adds that missing ingredient. The atoms self-organize into a periodic arrangement of high-density and low-density regions, giving the system a spatial order that a plain BEC lacks. In physics terminology, a BEC breaks only one symmetry (the gauge symmetry responsible for superfluidity), while a supersolid breaks two (adding the translational symmetry that produces a lattice).
You can also force a BEC into a lattice by shining crisscrossing laser beams through it, creating an artificial egg-carton pattern that traps atoms at regular intervals. But that structure is imposed from outside. In a true supersolid, the periodic structure arises spontaneously from the interactions between the atoms themselves. That self-organization is what distinguishes the supersolid phase.
Why Neutron Stars Care
Supersolids aren’t just a laboratory curiosity. Neutron stars, the ultra-dense remnants of collapsed massive stars, spin extremely fast and are among the most magnetic objects in the universe. Occasionally their rotation speed abruptly jumps in events called glitches, then slowly relaxes back. The leading explanation involves a superfluid layer inside the star: swirling vortices in this superfluid get pinned against the star’s rigid crystalline crust, and when many vortices suddenly unpin at once, they dump angular momentum into the crust, speeding it up.
Researchers at the University of Innsbruck and the Gran Sasso Science Institute have shown that rotating supersolids in the lab can mimic this glitch behavior. In their dipolar supersolid, vortices pin in the low-density gaps between droplets and then abruptly release, reproducing the same dynamics believed to occur inside neutron stars. Because you can control every parameter in a lab experiment (temperature, rotation speed, interaction strength), supersolids offer a way to test theories about neutron star interiors that would otherwise be completely inaccessible.
Where the Field Stands Now
Most supersolids created so far are one-dimensional: a single line of droplets. The next major goal is extending supersolidity into two dimensions, creating a flat sheet of self-organized clusters with superfluid flow in every direction. Early ETH Zurich experiments placed atoms inside optical resonators to coax them into two-dimensional crystalline patterns while preserving superfluidity, and several groups are working toward fully two-dimensional dipolar supersolids. Achieving this would open the door to studying phenomena like partially quantized vortices, which are predicted to exist in supersolids but have never been observed.
Meanwhile, a parallel line of research explores supersolid-like behavior in magnetic crystals. A 2025 study in npj Quantum Materials identified a “spin supersolid” phase in a triangular-lattice magnet made of potassium, cobalt, and selenium. In these materials, it isn’t atoms flowing but rather magnetic spin orientations that simultaneously form a crystal-like pattern and a superfluid-like coherent state. These solid-state analogs operate at higher temperatures (a few kelvin rather than nanokelvin) and could eventually make supersolid physics more accessible outside specialized ultracold labs.