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Found a new superconducting material


Japanese physicists have found a way to translate the familiar material KTaO3 superconducting.
Usually task of making semiconductors and insulators into metals or superconductors solve chemical doping – replacing atoms of one element of the other atoms of the parent compound to increase the concentration of free charge carriers. Unfortunately, chemical methods are not always possible to achieve the desired.
Sometimes used in the experiments electrostatic doping, which also makes it possible to increase the concentration of carriers? For example, in 2008, a joint team of scientists from Switzerland, France and Germany showed that the superconductivity of the interface between two dielectrics (LaAlO3/SrTiO3) in the structure of conventional MOSFET easily “controlled” by the electric field. Restriction on n is given by the field strength (~ 106 V / cm) at which the dielectric breakdown.

Higher strength values ​​achieved in the scheme, which is called the transistor with an electric double layer (electric double-layer transistor, ​​EDLT). This device is a lot like the FET, but the role of the gate dielectric in the document is reserved liquid electrolyte. When placed in a liquid sample is prepared, the ions from the electrolyte accumulate at the surface of a semiconductor channel and form a double layer, which acts like a capacitor at the interface between the solid and liquid phases. In this configuration, physics, experiments are performed with a dielectric SrTiO3, were able to increase the carrier concentration up to ~ 1014 cm-2 and registered SrTiO3 superconducting state at T = 0.4 K. KTaO3 is very similar to SrTiO3: materials have the perovskite structure and similar band structures. At a temperature of about 10 K in the conventional field effect transistor circuit KTaO3 can be translated into a metallic state, but make it a superconductor nobody has been able, while trying to lower the temperature even up to 10 mK.

Constructed by the authors using single crystal KTaO3 samples EDLT under normal conditions show excellent transistor characteristics, and carrier concentration, achieved by cooling, an order of magnitude greater than the value which has limited the possibility of chemical doping. When the temperature dropped to 70 mK, the researchers noted a reduction in layer resistance, and after a while, at 35 mK, it became zero. Like any other superconductor, KTaO3 left the state with no resistance if the experimenters applied the magnetic field (in our case, its intensity was less than 5 Oe).

Perhaps using an experimental technique to be opened several superconducting materials.