The Properties and Multi-band Superconductivity of Magnesium Boride |
What is Magnesium Boride?
Magnesium boron diboride is an ionic complex with a hexagonal crystalline structure. It is an intercalation-type compound, with alternate layers of magnesium and boran.
Researchers discovered in the year 2001 that a seemingly ordinary compound, magnesium Diboride, becomes a Superconductor once it reaches a temperature slightly below 40K (ie. -233degC). Its working temperature ranges from 2030K, which is twice the temperature of other superconductors. You can use liquid neon, hydrogen or closed cycle refrigerators to reach this temperature. These methods are easier and cheaper than industrial cooling of niobium alloys (4K), which uses liquid helium. When magnesium boride is doped either with carbon or another impurity, it can be as superconducting as niobium or even better in the presence magnetic fields or currents. Applications include superconducting magnetic fields, power transmission cables, and sensitive magnet field detectors.
Superconductivity Research in Multi-Band
Metal materials are often characterized by multi-bands and multi-Fermi noodles. As the material becomes superconducting, the superconducting surface energy gap will be opened. This can lead to multiple energy band appearances. Due to extremely strong interband scattering, the multiband effect in superconducting materials is greatly diminished. However, in some superconducting materials with quasi-two-dimensional characteristics, multi-band and multi-gap effects will appear due to the orthogonality of the electron motion wave functions above different energy bands. Iron-based superconductors, which were recently discovered, also show this multiband phenomenon. It is a current important direction in superconducting material and physics research.
Magnesium diboride can be described as a superconductor with multiple bands. It has two electron-type-p bands, a hole-type-p band, and a hole-type-s band. Due to the special configuration of the Fermi surface (the p band is three-dimensional and the s band is quasi-two-dimensional), its The wave vectors of electrons in different energy bands are in an orthogonal state, so that the inter-band scattering is not very strong, which makes the superconductor's multi-band characteristics outstanding. Hall effect is an effective way to detect the scattering rate changes of electrons during cyclotron motion. Magnetoresistance can also detect the number of carriers. By combining magnetoresistance, and Hall effect we can calculate the scattering rate for electrons within different energy bands.
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