At school we learn about three states of matter: solid, liquid and gas. Physicists know of many more, from plasmas in the Sun to superconductors that carry electricity with no resistance.

Now a team in Austria and France says it has found another one.

Physicists report a new state of matter, created by repeatedly switching how ultracold atoms interact. They call it a fractional Fermi sea.

There’s an important catch: the experiment hasn’t yet passed peer review. If it holds up, it’s a genuine breakthrough.

Two papers predict and report the new state

The work comes in two papers by the same team, led by Hanns-Christoph Nägerl and Manuele Landini at the University of Innsbruck and theorist Alvise Bastianello of CNRS and Université Paris-Dauphine.

  • A theory paper, published in Physical Review Letters in June 2026, predicts the new state.
  • An experimental paper, posted as a preprint, reports creating it with cesium atoms. It is still under review.

Four ideas explain the experiment

Ultracold atoms

The atoms were cooled to a tiny fraction of a degree above absolute zero, the coldest possible temperature. At that point they barely move, and their strange quantum behaviour takes over.

One dimension

The atoms were trapped in extremely thin tubes so they could only move along a line, like beads on a string. Physics in a line is very different from physics in open space, because particles can’t go around each other.

Bosons and fermions

All particles come in two families, and the difference is about sharing.

Think of a cinema. Fermions, like electrons, never share: one per seat. Bosons, like the cesium atoms here, happily pile into the same seat.

This “no sharing” rule for fermions is called the Pauli exclusion principle, and it’s why atoms have structure and why you don’t fall through the floor.

The Fermi sea

When fermions fill up the available “seats”, which are really energy levels, they fill from the lowest up, one per seat, leaving a neatly packed block. Physicists call this block a Fermi sea: imagine a cinema filled solidly from the front row to some point, with every seat taken.

In the new state, every seat is only partly filled

In the new state, the seats are filled evenly, but only partly. Instead of every seat taken in the occupied block, it’s as if each seat were, say, half or a third occupied, uniformly across the block.

That’s impossible for ordinary particles. But in the 1990s, physicist Duncan Haldane suggested that under some conditions particles could follow in-between rules: neither fully sharing like bosons nor never sharing like fermions.

The team’s atoms seem to behave like this. Nägerl says they are not yet sure what to call these new collective particles, suggesting “super-fermions” as one option.

Shaking the atoms produced order instead of chaos

Normally, shaking a system makes it hot and messy. Think of shaking a box of marbles: they end up scattered randomly.

Here, the team switched the atoms’ interactions back and forth, from strongly pushing each other away to strongly pulling together, over and over.

Instead of becoming a random mess, the atoms settled into a highly excited but highly ordered state. As lead author Yi Zeng puts it: “Instead of simply heating the system, the interaction cycle reorganises the atoms into a new many-body state.”

Ripples in how the atoms spread out are the telltale sign

They looked for Friedel oscillations: regular ripples in how the atoms are spread out, a bit like the evenly spaced ripples around a stone dropped in a pond.

These ripples have a specific pattern for a fractional Fermi sea, and the experimental paper describes them as “smoking-gun” signatures of the new state.

The state breaks the standard theory of one-dimensional systems

For decades, almost every one-dimensional quantum system has been described by one theory: the Tomonaga–Luttinger liquid.

Think of single-lane traffic. Cars can’t overtake, so any jam or gap spreads down the line as a wave. The Luttinger theory describes particles in a line in a similar collective way.

The new state’s correlations, meaning how the behaviour of atoms at one point relates to atoms elsewhere, don’t match that theory. That’s what makes it a candidate for a genuinely new phase of matter.

Driving a system hard can create order

There’s a bigger idea here. We usually expect that pumping energy into a system destroys order: heat ice and it melts; shake a jigsaw and it falls apart.

This work suggests that, in the right conditions, driving a system hard can create a new kind of order rather than wiping it out. It works partly because this one-dimensional gas is special: its atoms can’t fully scramble their motion, so some order survives the shaking.

What we don’t know yet

  • The experiment isn’t peer reviewed. It needs independent checks before the claim is confirmed.
  • The theory says “suggesting”. The authors describe a novel critical phase as suggested by their predictions, not proven.
  • It’s not brand new news. The theory paper and press release appeared in June 2026.
  • Very special conditions. It needs near absolute zero, one-dimensional traps and a particular kind of gas.
  • No everyday uses yet. The team mentions possible uses in quantum information and sensing, but these are speculative.

New states of matter are rare discoveries

Discovering a new state of matter is rare. Each one, from superconductors to the quantum states behind modern electronics, has deepened our understanding of nature, and sometimes led to technology decades later.

If confirmed, the fractional Fermi sea would show that particles can follow rules in between the two families we know, and that even violent shaking can produce order.

If it holds up, physicists have found a new way for matter to be.