nickel

A tiny black hole flies through a hydrogen cloud and stretches atoms like taffy. That is what a superconductor looks like when it traps a persistent current: a material in which electricity flows without losses turns into a miniature permanent magnet.

Old treasure maps were drawn from hearsay: someone found gold by a river, someone else in the mountains, and each person dug in their own spot. High-temperature superconductors went the same way: cuprates were found in some compounds, iron pnictides in others, nickelates in yet others, and there was no common map.

In a thin layer of liquid crystal, molecules usually lie like matches in a box — aligned in one direction but randomly oriented: some point up, others down. To make all the matches point the same way, you need a special molecular architecture. Scientists have found a chemical trick that does this almost automatically.

A metal made of five different atoms is like a soup with bits of carrot, peas, potato, onion, and meat floating in it. Each bit is its own element: chromium, vanadium, titanium, niobium, and tantalum. Such an alloy is called high-entropy: there is no single order, and the atoms are mixed almost randomly.

Current in an ordinary metal flows like a crowd of people down a straight street: each electron is on its own, and if you turn on a magnetic field, the whole crowd shifts slightly sideways. This shift is called the Hall effect.

A tiny sandwich of oxides, grown layer by layer, becomes perfectly conducting at about minus 200 degrees Celsius. This is not a magic trick but a new chapter in the search for high-temperature superconductors.

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.

Many materials behave like finicky ice: at one pressure they melt, at another they turn harder. Superconductors in the cuprate family are no exception. Their ability to carry current without loss depends on how tightly the crystal lattice is squeezed. In a new study, physicists traced this dependence for the compound Bi-2223.

A ceramic plate as thin as a soap film, and through it flows current with zero resistance. That's the superconductivity achieved in nickelates, relatives of the famous cuprate superconductors. Previously, this required enormous pressure, comparable to that at the ocean floor.

Lossless current is the dream of energy technology. Some materials become superconductors, but usually only at extreme cold. Recently, in the family of nickelates, compounds based on nickel, candidates were found that work at higher temperatures.

A layered cake where each tier conducts electricity differently: that's the structure of the crystal La3Ni2O7, a compound of nickel, lanthanum, and oxygen. Current flows differently along the layers than across them.

A piece of metal is cooled to minus two hundred degrees, and electric current begins to flow through it without the slightest friction, like water in a pipe flowing without touching the walls. This behavior is called superconductivity.

Some crystals behave like a switch: nudge the temperature or pressure, and they turn from a conductor into an insulator. This is called a metal–insulator transition (a change in the ability to conduct electricity).

The nickelate family consists of layered crystals, like a stack of pancakes: nickel and oxygen layers alternate with lanthanum spacers. Two years ago, superconductivity was discovered in them — the ability to conduct electricity without resistance when cooled.

Usually, superconductivity is a story about cold. The lower the temperature, the easier it is for electrons to pair up and flow without resistance. But in a new study, physicists grew thin films of nickelates doped with europium and saw the opposite picture.

In murky mud, between two electrodes, long chains of bacteria line up: each one as thin as a microscopic cable. Every such filament conducts current over a full centimeter, a true marathon for a microbe.

Using laser spectroscopy — a method akin to listening to the echo from a crystal — physicists examined the layered material. They found regions where electrons move freely (Fermi pockets) and noticed that each such region behaves in its own way.

Electrons in a conductor are like a chaotic crowd: colliding, they lose energy, and resistance arises. In a superconductor, however, they move in unison, like partners in a well-coordinated dance, without touching each other. This state has reduced энтропией — meaning disorder. Such behavior is rare for gold and copper.

Imagine a sandwich where the bread is made of copper oxide layers and the filling is a thin layer of strontium ions. That's the infinite-layer cuprate, the simplest version of superconducting ceramics, conceived nearly 40 years ago.

Hot gas settles on a substrate, building up a transparent film layer by layer. But instead of a perfect mirror, the surface sometimes gets covered with tiny bumps, like frost patterns on glass in severe cold. Usually, people try to remove them because they get in the way of making smooth components. Physicists from Oxford and their colleagues did the opposite: they looked inside the bumps.

A swarm of fireflies rarely collides, yet they synchronously change color by exchanging signals. This is how neutrinos behave in dense streams from collapsing stars: they collectively transform from one type to another, even though individually they interact extremely weakly.

A superconductor is like a perfect electron dance: electrons move in pairs without losing energy, like dancers who never miss a beat. But add a few magnetic impurities, and strangers crash into the dance, disrupting the synchronized motion. The temperature at which this dance begins drops.

A bridge made of two rows of planks bends under the feet of pedestrians, and each step gets a boost from the elastic motion of the deck. A similar principle underlies superconductivity: electrons glide without resistance because the atomic lattice itself adapts to them. In nickel-based materials, this picture has long been elusive.

A packed stadium: fans mill about chaotically, creating jostling and resistance. That's how electrons behave in an ordinary conductor. In superconductivity, they pair up and move in sync, like spectators holding hands and calmly leaving the stands, without losing energy.

A metal bar suddenly becomes stiff when heated, and at the same time loses or gains magnetic properties. In alloys based on nickel and manganese, such transformations occur not smoothly but abruptly — atoms rearrange into a new order, and the material changes its behavior.

The La3Ni2O7 crystal resembles a layered pie, where the filling of nickel and oxygen atoms alternates with lanthanum layers. At ambient pressure, it does not conduct without resistance, but squeeze it or grow it as a thin film, and high-temperature superconductivity emerges.

If you change not the composition but only the arrangement of atoms, you can make the same material conduct electricity or absorb light differently. That's exactly what the authors did with nickel and cobalt oxides. In one case, atoms are stacked like balls in a cubic box: each metal atom is surrounded by six oxygen atoms (rock salt structure).

A layered cake of atomic planes of nickel and oxygen: that's how bilayer nickelates are built. Two such planes are separated by a spacer layer. If an oxygen atom sits in that spacer, it acts as a bridge: it links the layers and triggers a state in which electrons move without resistance.

In familiar metals like copper, electrons move almost independently, like cars on an open highway. Resistance arises from rare collisions and can be described by simple formulas.

A superconductor does not let a magnetic field penetrate its interior. But if the field is strong enough, it does get in — not as a continuous flux, but as individual vortex filaments, like tiny tornadoes. Inside each filament, superconductivity is destroyed, and around it flows a persistent current.

An ordinary kitchen knife made of niobium would suddenly start conducting electricity with zero loss at −258 °C. That's how superconductivity works, and you can "switch it on" right at the metal's surface by blasting it with a laser in a nitrogen atmosphere.

A superconductor is a material that, when strongly cooled, loses its electrical resistance: current flows through it without losses. Scientists took a layered crystal of PdTe2, similar to a stack of sheets of paper, and cooled it to temperatures below 1.8 kelvin (that's about -271°C).

A superconductor is a material through which current flows without loss, like water through a perfectly smooth pipe. But to make the pipe perfect, you have to cool it to very low temperatures. Physicists have long been looking for ways to make such a pipe at warmer temperatures, and one clue is the quantum critical point.

Inside copper-based superconductors, materials that carry current without loss at unexpectedly high temperatures, there is a hidden phase. It behaves like an ordinary metal, but it's invisible in standard measurements.

A compass needle turns slowly, but inside some materials, tiny magnetic moments can flip over timescales that are hard to imagine. A team of physicists has calculated how to make them change direction in a quadrillionth of a second — faster than a lightbulb blinks.

In a molecule resembling chlorophyll and built from carbon, a metal atom at the center acts as a toggle. Shifting it by fractions of a nanometer can make the molecule glow, quench, or boost its brightness a hundredfold.

An alloy of palladium and tellurium with a small amount of gold added behaves like a wire that loses its resistance when cooled. At ambient pressure, the three samples with different gold contents had superconducting transition temperatures of 2.7, 4.1, and 4.6 kelvin — colder than a freezer, roughly like deep space.

Niobium is a metal that, when cooled to a few degrees above absolute zero, conducts electricity without resistance. In labs, it is deposited as thin strips onto a substrate, like frosting on a cake. But during deposition, oxygen from the special mask seeps into the metal, and it spoils the superconducting properties.

Electric current in a superconductor is like a crowd running down a frictionless corridor. But in type-II superconductors there are obstacles, tiny vortices of magnetic field, that the current shoves out of place. Once a vortex moves, resistance appears and the current drops.

A piece of silver antimony telluride is like a sponge: it readily soaks up heat and turns it into electricity. Such materials are called thermoelectrics, and they already work in space probes and car refrigerators. But if you squeeze this sponge, it starts behaving like a superconductor — current flows with zero resistance.