Superconductivity more common than previously thought

Superconductivity is not confined to certain classes of exotic compounds, says a study that investigated the underlying mechanisms responsible for variation of superconducting temperature threshold (TC) in Titanium-Vanadium (Ti-V) alloys.

The critical temperature for superconductors is the temperature at which the electrical resistivity drops to zero.

Local magnetic fluctuation or spin fluctuation, an intrinsic property of Ti-V alloys, influences superconductivity in a way that is more widespread than previously thought, says the study done by M. Matin from the Raja Ramanna Center for Advanced Technology in Indore, India.

They found that it is the competition between local magnetic fluctuations and the interaction between electrons and collective excitations, referred to as phonons, which determine the superconductivity.

The researchers measured the temperature and magnetic field dependency of several physical characteristics including resistivity, heat capacity and magnetisation.

They also used a microscopic theoretical technique - called density functional theory - to study the density of states at each energy level available for electrons to occupy.

Theoretical predictions provided by the Bardeen Cooper Schrieffer (BCS) theory suggest a high TC on the order of 20 Kelvin (K) for these alloys. By comparison, the authors' experimental value of TC was less than 10 K.

They attribute the difference to spin fluctuations in these alloys, which, the authors found, are inherent to the Ti-V alloys.

The authors deduced that these spin fluctuations are reflected in the properties of the normal state of electrons.

They therefore influence the superconductivity of the alloys in a similar way to that observed in high temperature oxide and iron-based superconductors, as such the influence of spin fluctuations on superconductivity is not necessarily confined to certain classes of exotic compounds as previously thought.

The findings appeared in the European Physical Journal B (EPJB).