Laboratory of Superconducting Nanoelectronics

It is planned to observe the suppression of the critical current and the 0-pi transition in Josephson structures with a barrier based on normal metals and normal metal-ferromagnetic bilayers at different values of the injection current of normal particles. It is planned to obtain the dependence of the 0-π transition on the injection current, temperature, as well as the thicknesses of the superconductor and normal metal layers. One of the interesting effects in Josephson SNS junctions is the control of the critical current of the SNS junction up to its complete suppression and further transition to the π-state. The creation of critical current control capabilities in Josephson SNS structures opens up new possibilities for superconducting electronics based on such structures. Obtaining a 0-π junction without using ferromagnets greatly simplifies the process of obtaining a 0-π state, since it requires only the manufacture of a conventional SNS junction with additional contacts made of normal metal. Production by the classical method [1] requires high precision of sample manufacturing, since due to the large exchange field of ferromagnets, the penetration length of electrical conductivity into a ferromagnet is very small [2]. 0-π junctions have a significant number of applications in promising superconducting electronics, increasing its compactness. For example, in superconducting single-quantum logic (RSFQ), the use of rings with 0-π junctions makes it possible to reduce the number of supply lines and expand the boundaries of the element parameters, which makes the circuits less sensitive to deviations in production [3]. Adding the 0-π junction to the SFQ circuit makes it possible to reduce the magnetic flux stored in this circuit, and hence the size of the circuit (and, consequently, the entire circuit) [4]. It is also possible to create compact circuits in which coding is carried out by the direction of the current flowing through the circuit [5]. There are other ways to miniaturize RSFQ circuits using 0-π junctions [6]. [1] Ryazanov V. V. et al. Coupling of two superconductors through a ferromagnet: Evidence for a π junction //Physical review letters. – 2001. – Vol. 86. – No. 11. – p. 2427. [2] T. Karminskaya. Theory of Josephson effect in junctions with complex ferromagnetic/normal metal weak link region. PhD thesis, University of Twente, The Netherlands, 2011. [3] Ortlepp T. et al. Flip-flopping fractional flux quanta //Science. – 2006. – Vol. 312. – No. 5779. – pp. 1495-1497. [4] Feofanov A. K. et al. Implementation of superconductor/ferromagnet/superconductor π-shifters in superconducting digital and quantum circuits //Nature Physics. – 2010. – Vol. 6. – No. 8. – pp. 593-597. [5] Kamiya T. et al. Energy/space-efficient rapid single-flux-quantum circuits by using π-shifted Josephson junctions //IEICE Transactions on Electronics. – 2018. – Vol. 101. – No. 5. – pp. 385-390. [6] Ustinov A.V., Kaplunenko V. K. Rapid single-flux quantum logic using π-shifters //Journal of Applied Physics. – 2003. – Vol. 94. – No. 8. – pp. 5405-5407.