What Is a High-Temperature Superconductor?

Published June 28, 2026

Part 1 of our five-part Superconductor 101 series. The other parts cover the main superconductor materials, how a superconducting cable is built, how the tape itself is manufactured, and where superconductors are used today.

In short: below a certain temperature, superconductors carry electric current with zero resistance, so a superconducting cable can move several times the power of a copper cable the same size. The materials discovered from 1986 onwards superconduct at temperatures reachable with liquid nitrogen, one of the cheapest and safest coolants in industry. More power in less space, with practical cooling: that is what every project in our tracker is built on.

This article explains what zero resistance means in practice, what the catches are, and why the word high-temperature in “high-temperature superconductor” (HTS) refers to temperatures around −200 °C (−328 °F).

Resistance, and why zero resistance matters

In an ordinary metal like copper, electric current is a flow of electrons through a lattice of metal atoms. The electrons constantly collide with vibrating atoms and impurities, and every collision converts a little electrical energy into heat. This is electrical resistance. It is why cables get warm, why transmission lines lose a share of the power fed into them, and why every copper wire has a current limit. The only cure copper allows is more copper: thicker conductors, wider trenches, bigger transformers, more cooling. A large share of the cost and bulk of an electricity grid is, at root, the cost of resistance.

In 1911 the Dutch physicist Heike Kamerlingh Onnes cooled mercury with liquid helium and watched its resistance drop abruptly to zero at 4.2 kelvin (−269 °C / −452 °F). Not roughly zero: a current started in a closed superconducting loop keeps circulating with no power source, and experiments have run such persistent currents for years without measurable decay.

For the grid, that is the whole point. Below its critical temperature a superconductor carries current with no loss and no heating, so a far smaller conductor carries far more current, and more power fits through the same duct, trench or substation.

The catch: staying cold

Superconductivity comes with conditions, and the one that matters most in practice is the critical temperature: warm the material past it and superconductivity disappears. Each material has its own, about 9 K (−264 °C / −443 °F) for the niobium-titanium alloy in MRI machines, and about 90 K (−183 °C / −298 °F) for the REBCO compounds used in most modern HTS projects. There are also limits on current and on magnetic field, and the three trade off: the colder a superconductor runs below its critical temperature, the more current it carries. That is why some projects in the tracker operate REBCO, which superconducts up to 90 K, at 20 K (−253 °C / −424 °F) instead.

Crossing any of these limits switches the material abruptly back into an ordinary, and rather poor, conductor. That event is called a quench. In a large magnet a quench must be detected and managed within moments. But the same sharp transition doubles as a built-in safety mechanism. If a fault slams too much current through a superconductor, it instantly turns resistive and throttles the very surge that triggered it, then recovers as it cools back down. Superconducting fault current limiters are built around exactly this self-limiting behaviour.

Superconductors have striking magnetic properties too: they expel magnetic fields from their interior (the Meissner effect, the physics behind every photo of a magnet floating above a cooled black disc), and superconducting magnets levitate Japan’s record-setting maglev trains. This website’s focus, though, is the electrical story: loss-free current, and more of it.

Why 1986 changed everything

For 75 years after Onnes, every known superconductor needed extreme cold. Critical temperatures sat below about 23 K (−250 °C / −418 °F), reachable in practice only with liquid helium at 4.2 K (−269 °C / −452 °F). Helium is scarce and expensive, and it demands complex refrigeration plants and specialist skills. Superconductivity worked, but only where the application, like MRI machines, was valuable enough to justify a helium habit.

Then in 1986, Georg Bednorz and Alex Müller at IBM Zurich found superconductivity in a copper-oxide ceramic at around 35 K (−238 °C / −397 °F), smashing the old ceiling and earning a Nobel Prize within a year. Researchers pushed the new family further within months, and in early 1987 yttrium barium copper oxide (YBCO) was shown to superconduct at about 93 K (−180 °C / −292 °F).

That number was the revolution, because of a mundane fact of cryogenics: liquid nitrogen boils at 77 K (−196 °C / −321 °F). Any superconductor that works above 77 K can be cooled with it, and as coolants go, liquid nitrogen is hard to beat:

  • Abundant and cheap. Nitrogen makes up 78% of air. Liquid nitrogen is produced industrially by the tanker-load and costs less per litre than milk.
  • Safe. It does not burn and cannot explode. Liquid hydrogen is a serious fire and explosion hazard; helium is inert but scarce and expensive.
  • A dense, effective coolant. Each litre soaks up far more heat than a litre of ultra-light liquid helium or hydrogen, so it stores compactly and can be pumped through kilometres of cable.
  • Routinely handled. Food plants, hospitals and workshops use it every day. Cooling with liquid nitrogen is industrial refrigeration, not exotic laboratory cryogenics.

So a high-temperature superconductor is one that superconducts at temperatures reachable with liquid nitrogen rather than liquid helium. By everyday standards it is still brutally cold (“high-temperature” is physicist humour), but it is a kind of cold industry already knows how to buy, store and pump. One hard problem remained: the new materials are brittle ceramics, and making them into kilometre-long flexible conductors took two more decades of engineering. Part 4 of this series tells that story.

What zero resistance makes possible

Combine zero resistance with practical cooling and you get capabilities copper cannot match:

  • Far more power through the same space. An HTS cable can carry several times the power of a conventional cable of the same duct size. In Shenzhen, China, a 400-metre HTS cable operating at just 10 kV delivers the capacity of a conventional 110 kV line. It is one of several such projects in our tracker.
  • Magnets stronger than iron and copper allow. Superconducting coils carry currents that would vaporize copper windings, producing the 20-tesla-class fields behind compact fusion reactor designs like SPARC.
  • Smaller, lighter machines. A superconducting wind turbine generator (the EcoSwing project in Denmark) came out roughly 40% lighter than its permanent-magnet equivalent.
  • Self-resetting grid protection. Superconducting fault current limiters use the quench described above as a passive, self-resetting circuit breaker, a device with no conventional equivalent.

Where to go next

The rest of this series builds up the practical picture:

And for the state of the industry right now, the project tracker lists real HTS installations worldwide, with sources for every row.

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