The threshold at which superconductivity is obliged to disappear helped to overcome ... graphene and gallium.
Physicists have shown that superconductivity can be stored in a much stronger magnetic field than thought possible for such materials. To do this, they did not take the usual compounds with heavy elements, but built a very thin three-layer structure with glelium, graphene and silicon carbide. It was at the boundaries between these layers that quantum effects arose that helped the Gallium to hold superconducting properties where a regular superconductor would have stopped working.
The work was carried out by an interdisciplinary team from the University of Pennsylvania. They grew a hallium film with a thickness of only three atomic layers, placed it on a substrate of silicon carbide and covered with a graphene on top. The resulting structure retained superconductivity in a magnetic field directed along the surface of the material. Moreover, the field was much stronger than the limit, which is usually considered critical for the destruction of the superconducting state.
To understand the meaning of the result, you need to remember how superconductivity works at all. In the usual conductor, the current is faced with resistance, so part of the energy inevitably goes into heat. In the superconductor, the resistance disappears, and the current flows without loss. This mode occurs at a very low temperature, when electrons cease to behave as separate particles and combine into Cooper pairs. In this state, the pairs move in concert and do not lose energy for scattering.
Most superconductors have a serious restriction. A strong magnetic field destroys the couper pairs, and the material loses its superconducting properties. For this, there is a well-known landmark, which is called the Paramagnetic limit of Pauli. When the field becomes too strong, the spins of the electrons in the pair are no longer held in the desired configuration, the bond breaks down, and the superconductivity disappears. That is why superconductors are difficult to use in conditions where without strong magnetic fields can not do.
Previously, scientists have already found exceptions, but almost always they were associated with materials that make up heavy elements. In such compounds, the spin-orbital interaction is noticeably more proliferated. This is called the quantum effect, in which the movement of the electron is associated with the direction of its spin. If the material in this case passes into a superconducting state, the spin-orbital interaction can form an unusual mode known as the superconductivity of the Iinging type. In this case, the orientation of the spins of the electrons is rigidly fixed perpendicular to the plane of the crystal, and it becomes more difficult for the magnetic field to destroy the vapors. Due to this, the superconductivity lasts longer than usual, even beyond Pauli.
In the new work, not a heavy, but a light element, galley was used. No one expected such a steady behavior in a magnetic field. According to the usual logic, superconductivity had to weaken as the field grew and disappeared in the expected range. But the experiment showed something else. In the three-layer design, the gallium retained superconducting properties in a magnetic field that has more than three times exceeded the Pauli limit. For an easy element, the result looks especially unusual.
The key role was played not only by the film of the gallium itself, but also by the entire geometry of the structure. The lower layer of silicon carbide served as a substrate on which ultra-thin gallium was grown. The upper layer of graphene protected the metal from air, oxidation and contamination. But the most important thing happened at the boundaries of the division between the layers. It was there that special quantum conditions arose, which changed the behavior of the electrons. The researchers believe that the interfaces between gallium, graphene and silicon carbide created an environment where the lightweight element began to exhibit properties that were previously characteristic mainly for systems with heavy atoms.
Work changes the very approach to the search for unusual superconductors. Until now, the superconductivity of the Ising type was almost automatically associated with heavy elements, because it is they who have a strong spin-orbit interaction that arises naturally. Now it turned out that a similar effect can be obtained in a system with a light element, if you properly construct the boundaries between the layers. In other words, it’s not necessarily a heavy chemical composition. Sometimes decisive is how the material is collected at the atomic level.
The practical significance of the work is also quite clear. Superconductors are needed for new generation electronics, where high efficiency and very fast transmission of the signal without energy loss are important. But the weakness for magnetic fields remained a serious limitation for a long time. If it is possible to reliably create lightweight materials that retain superconductivity in a strong field, engineers will have more freedom in designing quantum devices, sensitive sensors and other components, where conventional superconductors quickly get out of the working mode.
Researchers are not going to stop at one gallia. Then the team wants to check whether it is possible to get the same way to get unusual superconductivity in other light metals, for example, in India and tin, if you choose suitable substrates for them and properly configure interfaces. In fact, the work offers not a single trick with one material, but a more general principle. If it is confirmed, physicists will be able to assemble a whole family of new superconductors not at the expense of heavy elements, but due to fine engineering on the boundaries of atomic layers.
To look more broadly, the work shows well where the condensed state physics is now moving. Researchers are increasingly looking for new properties not in “pure” matter, but in a properly assembled structure of several layers, where the boundaries between the materials give effects that each component does not have individuality.
Physicists have shown that superconductivity can be stored in a much stronger magnetic field than thought possible for such materials. To do this, they did not take the usual compounds with heavy elements, but built a very thin three-layer structure with glelium, graphene and silicon carbide. It was at the boundaries between these layers that quantum effects arose that helped the Gallium to hold superconducting properties where a regular superconductor would have stopped working.
The work was carried out by an interdisciplinary team from the University of Pennsylvania. They grew a hallium film with a thickness of only three atomic layers, placed it on a substrate of silicon carbide and covered with a graphene on top. The resulting structure retained superconductivity in a magnetic field directed along the surface of the material. Moreover, the field was much stronger than the limit, which is usually considered critical for the destruction of the superconducting state.
To understand the meaning of the result, you need to remember how superconductivity works at all. In the usual conductor, the current is faced with resistance, so part of the energy inevitably goes into heat. In the superconductor, the resistance disappears, and the current flows without loss. This mode occurs at a very low temperature, when electrons cease to behave as separate particles and combine into Cooper pairs. In this state, the pairs move in concert and do not lose energy for scattering.
Most superconductors have a serious restriction. A strong magnetic field destroys the couper pairs, and the material loses its superconducting properties. For this, there is a well-known landmark, which is called the Paramagnetic limit of Pauli. When the field becomes too strong, the spins of the electrons in the pair are no longer held in the desired configuration, the bond breaks down, and the superconductivity disappears. That is why superconductors are difficult to use in conditions where without strong magnetic fields can not do.
Previously, scientists have already found exceptions, but almost always they were associated with materials that make up heavy elements. In such compounds, the spin-orbital interaction is noticeably more proliferated. This is called the quantum effect, in which the movement of the electron is associated with the direction of its spin. If the material in this case passes into a superconducting state, the spin-orbital interaction can form an unusual mode known as the superconductivity of the Iinging type. In this case, the orientation of the spins of the electrons is rigidly fixed perpendicular to the plane of the crystal, and it becomes more difficult for the magnetic field to destroy the vapors. Due to this, the superconductivity lasts longer than usual, even beyond Pauli.
In the new work, not a heavy, but a light element, galley was used. No one expected such a steady behavior in a magnetic field. According to the usual logic, superconductivity had to weaken as the field grew and disappeared in the expected range. But the experiment showed something else. In the three-layer design, the gallium retained superconducting properties in a magnetic field that has more than three times exceeded the Pauli limit. For an easy element, the result looks especially unusual.
The key role was played not only by the film of the gallium itself, but also by the entire geometry of the structure. The lower layer of silicon carbide served as a substrate on which ultra-thin gallium was grown. The upper layer of graphene protected the metal from air, oxidation and contamination. But the most important thing happened at the boundaries of the division between the layers. It was there that special quantum conditions arose, which changed the behavior of the electrons. The researchers believe that the interfaces between gallium, graphene and silicon carbide created an environment where the lightweight element began to exhibit properties that were previously characteristic mainly for systems with heavy atoms.
Work changes the very approach to the search for unusual superconductors. Until now, the superconductivity of the Ising type was almost automatically associated with heavy elements, because it is they who have a strong spin-orbit interaction that arises naturally. Now it turned out that a similar effect can be obtained in a system with a light element, if you properly construct the boundaries between the layers. In other words, it’s not necessarily a heavy chemical composition. Sometimes decisive is how the material is collected at the atomic level.
The practical significance of the work is also quite clear. Superconductors are needed for new generation electronics, where high efficiency and very fast transmission of the signal without energy loss are important. But the weakness for magnetic fields remained a serious limitation for a long time. If it is possible to reliably create lightweight materials that retain superconductivity in a strong field, engineers will have more freedom in designing quantum devices, sensitive sensors and other components, where conventional superconductors quickly get out of the working mode.
Researchers are not going to stop at one gallia. Then the team wants to check whether it is possible to get the same way to get unusual superconductivity in other light metals, for example, in India and tin, if you choose suitable substrates for them and properly configure interfaces. In fact, the work offers not a single trick with one material, but a more general principle. If it is confirmed, physicists will be able to assemble a whole family of new superconductors not at the expense of heavy elements, but due to fine engineering on the boundaries of atomic layers.
To look more broadly, the work shows well where the condensed state physics is now moving. Researchers are increasingly looking for new properties not in “pure” matter, but in a properly assembled structure of several layers, where the boundaries between the materials give effects that each component does not have individuality.
