Field-induced quantum breakdown of superconductivity in magnesium diboride

The quantum breakdown of superconductivity (QBS) is the reverse, comprehensive approach to the appearance of superconductivity. A quantum phase transition from superconducting to insulating states tuned by using nonthermal parameters is of fundamental importance to understanding the superconducting (SC) phase but also to practical applications of SC materials. However, the mechanism of the transition to a nonzero resistive state deep in the SC state is still under debate. Here, we report a systematic study of MgB2 bilayers with different thickness ratios for undamaged and damaged layers fabricated by low-energy iron-ion irradiation. The field-induced QBS is discovered at a critical field of 3.2 Tesla (=Hc), where the quantum percolation model best explains the scaling of the magnetoresistance near Hc. As the thickness of the undamaged layer is increased, strikingly, superconductivity is recovered from the insulating state associated with the QBS, showing that destruction of quantum phase coherence among Cooper electron pairs is the origin of the QBS. Superconducting islands play a role in the breakdown of superconductivity in thin films according to researchers in South Korea and China. Superconductors offer no resistance to the flow of electricity below a critical temperature. Researchers try to create new superconducting materials by reducing temperature, but insulator properties can re-emerge even at low temperatures. Soon-Gil Jung and Tuson Park from Sungkyunkwan University in Suwon, South Korea, and co-workers have systematically investigated this so-called quantum breakdown of superconductivity in thin films of magnesium diboride. The researchers studied bilayers comprising a damaged film and an undamaged film. They found that the superconductivity suppressed by the damaged film was gradually restored as the thickness of the undamaged film was increased. This supports the hypothesis that quantum breakdown is caused by the loss of quantum-mechanical links between superconducting islands. The significance of our results is related to “the quantum breakdown of superconductivity (QBS) and the role of superconducting islands in disordered superconducting systems”. Study on the QBS uses a reverse, comprehensive approach to the appearance of superconductivity, which is of utmost importance not only to understanding the superconducting phase but also to practical applications of superconductors. However, the mechanism underlying the transition to the nonzero resistive state deep in the superconducting state is still under debate. In this work, we have successfully achieved the field-induced QBS in disordred MgB2 thin films via a unique technique of low-energy ion irradiation.