Cuprate Materials' Fluctuating Stripes May Be Linked to High-temp Superconductivity

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Scientists at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have shown that copper-based superconductors, or cuprates – the first class of materials found to carry electricity with no loss at relatively high temperatures – contain fluctuating stripes of electron charge and spin that meander like rivulets over rough ground.

Image caption: An animation based on computer simulations shows stripes of electron charge (white atoms) and spin (red and blue atoms) in a copper-based superconducting material. The stripes are zones where electrons either pile up, creating bands of negative charge, or align their spins (arrows) in a particular pattern to create bands of magnetism. A computational study by researchers at SLAC and Stanford shows these stripes are present in a subtle, fluctuating form at high temperatures. The results will help researchers test theories about how stripes may be related to high-temperature superconductivity. (Farrin Abbott/SLAC National Accelerator Laboratory)

The stripes are zones where electrons either pile up, creating bands of negative charge, or align their spins to create bands of magnetism. They were previously known to exist in cuprate superconductors at temperatures near absolute zero, although in this deep chill the stripes did not move around and their exact role in superconductivity – do they boost or squelch it? – has been unclear.

Now the researchers have computationally demonstrated for the first time that these stripes also exist at high temperatures, but they are subtle and fluctuate in a way that could only be discovered through numerical computer simulations of a precision and scale not done before.

“There’s reason to think that stripes of charge and spin may be intimately tied to the emergence of high-temperature superconductivity in these materials, which was discovered 30 years ago but so far is not understood or explained,” said Edwin Huang, a physics graduate student at Stanford and at the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC.

“This discovery of fluctuating stripes in a realistic computer model will give us a way to test the many theories about how stripes are related to superconductivity,” Huang said. “We think our results will be useful for scientists doing experimental studies of these materials, and they’ll also help develop and refine the computational techniques that go hand in hand with theory and experiments to push the field forward.”

The results also apply to other novel materials, said SIMES Director Thomas Devereaux. “Materials that spontaneously develop this sort of non-uniform structure are quite commonplace, including magnets and ferroelectrics,” he said. “It can even be thought of as a signature of ‘quantum’ materials, whose surprising properties are produced by electrons that cooperate in unexpected ways. Our numerical results demonstrate that this phenomenon can generally be related to strong interactions between electron charges and spin.”

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