Recently, the Danish Institute for Advanced Study cooperated with Beijing University of Technology, Japan National Institute of Materials Science and Technology, University of Leuven in Belgium, Central South University, University of Bristol in the United Kingdom, University of Ghent in Belgium, etc., using chemical vapor deposition and micro-nano processing technology to prepare Nanoscale "diamond rings" were discovered, and metal-Bose semiconductor phase transitions and unconventional "giant magnetoresistance" effects were discovered in these "diamond rings". These findings provide new ideas for the design of superconducting quantum devices.
The results of the research paper entitled Unconventional Giant [Magnetoresistance" in Bosonic Semiconductor Diamond Nanorings have been published in the scientific journal Advanced Materials.
Materials can be roughly divided into insulators, semiconductors, conductors and superconductors according to their electrical properties. As the temperature decreases, the resistance of insulators and semiconductors tends to increase due to their non-zero bandgap. Metals are good conductors, and their electrical resistance usually decreases with decreasing temperature. Superconductors generally exhibit metal-like electrical properties at higher temperatures. At low temperatures, when the free electrons in a superconductor combine into Cooper pairs and quantum condense, their electrical resistance plummets to zero. At present, in addition to the familiar superconducting maglev trains, superconductors are also used to develop advanced quantum devices, such as single-photon detectors and quantum computers.
A question that has plagued the physics and materials science community for a long time is: Does the formation of Cooper pairs necessarily lead to a phase transition from a metallic state to a superconducting state? This question was answered in collaboration with the above-mentioned international research team. The team selected boron-doped artificial diamond (diamond) as the raw material, and used advanced micro-nano processing technology to prepare a nanoscale diamond ring structure ("diamond ring"). These nano "diamond rings" exhibit metal-like electrical properties at relatively high temperatures, and their electrical resistance spikes rather than drops when cooled to the superconducting phase transition temperature of their raw materials. The occurrence of the anomalous phase transition is caused by the confinement of the Cooper pair by the nano "diamond ring". The formation of Cooper pairs is at the cost of the consumption of free single electrons. When the nano-"diamond ring" effectively acts as a quantum well for the Cooper pairs, the system will have "no electrical conduction", so the resistance soars. Because this phase transition is closely related to the formation and dynamics of Cooper pairs (bosons), the team defines it as a metal-Bose semiconductor phase transition. This discovery is fundamentally different from the traditional metal-insulator phase transition, which is often caused by the localization of single electrons (fermions).
Accompanied by the occurrence of the metal-Bose semiconductor phase transition, the nano-"diamond ring" exhibits an unconventional "giant magnetoresistance" effect. The conventional giant magnetoresistance effect is caused by spin-related electron scattering, and is now widely used in computer hard disk data reading. The multilayer film structure composed of magnetic and non-magnetic materials is a key component of the hard disk read head. When the structure is placed in the magnetic field generated by the magnetic domain of the hard disk, the spin-related electron scattering will be suppressed, resulting in a significant reduction in the structure resistance. , so as to realize the identification and reading of data. Different from the conventional giant magnetoresistance effect, the "giant magnetoresistance" effect in the nanometer "diamond ring" is caused by the annihilation of Cooper pairs. In an external magnetic field, the Cooper pairs in the nanometer "diamond ring" are split into single electrons, and the release of these single electrons makes the system "electrically conductive", resulting in a sudden drop in resistance.
This research reveals a series of novel quantum phenomena, expands the understanding of the traditional classification of materials, and provides a new physical basis, material platform and design ideas for the development of superconducting quantum devices. Professor Zhang Gufei from the Danish Institute for Advanced Study initiated the research and led the main research work with Professor Ke Xiaoxing from Beijing University of Technology, Chairman Liao Meiyong from the National Institute of Materials Science and Technology of Japan, Dr. Liu Liwang from the University of Leuven in Belgium, and Professor Li Yejun from Central South University. .
Bohong sharing--Advanced Materials:Nanoscale "diamond ring" provides new ideas for the design of superconducting quantum devices
2023 03/10