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Allowing current to flow for a long time without hindrance

In a superconductor, current can flow for infinitely long time without any hindrance. Normally, superconductivity is destroyed by a magnetic field but researchers at IISc, Bangalore in collaboration with NPL, Delhi and IIT, Kharagpur have shown that magnetic fields can generate a superconducting state.

Current flowing through any material, such as a wire, produces heat because of the resistance which arises due collision of electrons (particles which are responsible for current flow) with impurities. A superconductor is a material which has zero electrical resistance; this implies, charge carriers can flow unimpeded. Current can flow in a superconductor without producing any heat and hence transmission is lossless. This aspect has been used to provide electricity to residents though only for test purposes due to the high cost involved. Other common technological applications of superconductivity include magnetic resonance imaging (MRI), which is widely used for medical diagnosis purposes, and Maglev transportation where an object (say a train) can be transported for long distances using magnets, without the need for wheels or any physical contact with rails. Currently, a lot of research is being carried out across the world to use superconductors in the field of quantum computation.

The material used in experiments in this study are Lanthanum aluminate and Strontium titanate which are by themselves insulators (which do not carry current). However, high quality Lanthanum aluminate grown on top of Strontium titanate leads to a layer of electrons which can be both superconducting and magnetic. Prof. Aveek Bid from the Department of Physics, IISc and his group found that the resistance at the interface of these materials can be made zero by the application of a magnetic field, something which is contrary to the usual scenario where an external magnetic field kills superconductivity. The zero resistance lasts for a few seconds, after which the resistance increases back to its normal value.

Prof. Bid said, “Our work describes the observation of a novel transient superconducting state which is assisted by an external magnetic field. This effect may be used to develop magnetic field controlled ultra-fast superconducting switches.” Of course, this effect has been observed at extremely low temperatures (around -273 C!), but this provides a starting point to search for materials with tunable superconductivity at normal room temperatures.

The unique transient superconductivity has been explained by the reduction of the inherent magnetization of LaAlO3-SrTiO3 by the external magnetic field and for a short time of about 10 seconds the resistance reduces to exactly zero. The tunabiltiy of transient superconductivity with external magnetic field has potential for device applications.

About the authors:

Aveek Bid is an Assistant Professor at the Department of Physics, Indian Institute of Science, Bangalore. Shelender Kumar and Gopi Nath Daptary work in his lab. The paper has collaborators from other institutes: National Physical Laboratory, New Delhi and Indian Institute of Technology Kharagpur.

Contact:Aveek Bid aveek.bid@physics.iisc.ernet.in; 080-22933340; 23605265