Another crack at the high-temperature superconductor walnut
- 著者:Ella Cai
- 公開：:2017-07-28
Scientists from the US Brookhaven National Laboratory and Yale University have discovered surprising behaviour amongst electrons in high-temperature superconductors (HTS).
“Our discovery challenges a corner-stone of condensed matter physics,” said Brookhaven Lab physicist Jie Wu. “These electrons seem to spontaneously ‘choose’ their own paths through the material – a phenomenon in direct opposition to expectations.”
The crystals in this study are layered with four-fold rotational symmetry, with electrons expected to flow uniformly parallel to these layers.
But this is not what the Brookhaven group observed, and the symmetry-breaking persists up to room temperature, across a range of chemical compositions.
“The electrons somehow co-ordinate their movement through the material, even after the superconductivity fails,” said Wu.
Unlike classical superconductivity, which is well-understood, HTS has puzzled scientists for more than three decades.
Strong electron-electron interactions may help explain the preferential direction of current flow, according to Brookhaven, and, in turn, these intrinsic electronic quirks may share a relationship with HTS phenomena and offer a hint to decoding its unknown mechanism.
This work is part of a 12 year project that includes the synthesis and study of more than lanthanum strontium copper oxide superconductor films.
To ensure observed effects are intrinsic, the films are as pure as the researchers can make them – created one layer at a time using molecular beam epitaxy (MBE) with electron diffraction characterisation added to asses defects.
The most difficult part of the whole work is the meticulous material synthesis, said scientist Xi He. It helps set the Brookhaven work apart.
The findings suggest, said Brookhaven that what looks like normal metallic conduction in the materials above their critical temperature, where superconductivity breaks down, might also be extraordinary.“Looking carefully, the scientists observed that as external current flowed through the samples, a spontaneous voltage unexpectedly emerged perpendicular to that current.” – something that had previously been discounted as experimental error.
The cuprates seem to be acting as electronic liquid crystals.
“We need to understand how this electron behaviour fits into the HTS puzzle as a whole,” said researcher Anthony Bollinger. “This study gives us new ideas to pursue and ways to tackle what may be the biggest mystery in condensed matter physics.”
Image: Brookhaven Lab scientists, from the left: Ivan Bozovic, Xi He, Jie Wu and Anthony Bollinger, and their atomic layer-by-layer molecular beam epitaxy system.
“Our discovery challenges a corner-stone of condensed matter physics,” said Brookhaven Lab physicist Jie Wu. “These electrons seem to spontaneously ‘choose’ their own paths through the material – a phenomenon in direct opposition to expectations.”
The crystals in this study are layered with four-fold rotational symmetry, with electrons expected to flow uniformly parallel to these layers.
But this is not what the Brookhaven group observed, and the symmetry-breaking persists up to room temperature, across a range of chemical compositions.
“The electrons somehow co-ordinate their movement through the material, even after the superconductivity fails,” said Wu.
Unlike classical superconductivity, which is well-understood, HTS has puzzled scientists for more than three decades.
Strong electron-electron interactions may help explain the preferential direction of current flow, according to Brookhaven, and, in turn, these intrinsic electronic quirks may share a relationship with HTS phenomena and offer a hint to decoding its unknown mechanism.
This work is part of a 12 year project that includes the synthesis and study of more than lanthanum strontium copper oxide superconductor films.
To ensure observed effects are intrinsic, the films are as pure as the researchers can make them – created one layer at a time using molecular beam epitaxy (MBE) with electron diffraction characterisation added to asses defects.
The most difficult part of the whole work is the meticulous material synthesis, said scientist Xi He. It helps set the Brookhaven work apart.
The findings suggest, said Brookhaven that what looks like normal metallic conduction in the materials above their critical temperature, where superconductivity breaks down, might also be extraordinary.“Looking carefully, the scientists observed that as external current flowed through the samples, a spontaneous voltage unexpectedly emerged perpendicular to that current.” – something that had previously been discounted as experimental error.
The cuprates seem to be acting as electronic liquid crystals.
“We need to understand how this electron behaviour fits into the HTS puzzle as a whole,” said researcher Anthony Bollinger. “This study gives us new ideas to pursue and ways to tackle what may be the biggest mystery in condensed matter physics.”
Image: Brookhaven Lab scientists, from the left: Ivan Bozovic, Xi He, Jie Wu and Anthony Bollinger, and their atomic layer-by-layer molecular beam epitaxy system.
