Observation of 0–π transition in SIsFS Josephson junctions

The 0–π transition in Superconductor-Insulator-superconductor-Ferromagnet-Superconductor (SIsFS) Josephson junctions (JJs) was investigated experimentally. As predicted by theory, an s-layer inserted into a ferromagnetic SIFS junction can enhance the critical current density up to the value of an SIS tunnel junction. We fabricated Nb′ | AlOx | Nb | Ni60Cu40 | Nb JJs with wedge-like s (Nb) and F (Ni60Cu40) layers and studied the Josephson effect as a function of the s- and F-layer thickness, ds and dF, respectively. For ds = 11 nm, π-JJs with SIFS-type jc(dF) and critical current densities up to jcπ=60 A/cm2 were obtained at 4.2 K. Thicker ds led to a drastic increase of the critical current decay length, accompanied by the unexpected disappearance of the 0–π transition dip in the jc(dF) dependence. Our results are relevant for superconducting memories, rapid single flux quantum logic circuits, and solid state qubits.

[1]  M. Weides,et al.  Memory cell based on a $\varphi$ Josephson junction , 2013, 1306.1683.

[2]  M. Weides,et al.  High quality ferromagnetic 0 and π Josephson tunnel junctions , 2006, cond-mat/0604097.

[3]  O. Mielke,et al.  Improved operation range of digital superconductive electronics by implementing passive phaseshifters , 2010 .

[4]  V. V. Ryazanov,et al.  Magnetic Josephson Junctions With Superconducting Interlayer for Cryogenic Memory , 2013, IEEE Transactions on Applied Superconductivity.

[5]  L. B. Ioffe,et al.  Quiet SDS Josephson Junctions for Quantum Computing , 1998 .

[6]  B. Dimov,et al.  Phase engineering techniques in superconducting quantum electronics , 2008 .

[7]  O. Mielke,et al.  Reduced Probability of Noise Introduced Malfunction in RSFQ Circuits by Implementing Intrinsic $\pi$-Phaseshifter , 2009, IEEE Transactions on Applied Superconductivity.

[8]  H. Kohlstedt,et al.  The role of surface roughness in the fabrication of stacked Nb/Al–AlOx/Nb tunnel junctions , 1996 .

[9]  D. Koelle,et al.  Combinatorial sputtering in planetary type systems for alloy libraries with perpendicular gradients of layer thickness and composition realised by a timing approach , 2014 .

[10]  V. Oboznov,et al.  Superconductor—Ferromagnet—Superconductor π-junctions , 2004 .

[11]  E. Terzioglu,et al.  Complementary Josephson junction devices and circuits: a possible new approach to superconducting electronics , 1998, IEEE Transactions on Applied Superconductivity.

[12]  Lev B. Ioffe,et al.  Environmentally decoupled sds -wave Josephson junctions for quantum computing , 1999, Nature.

[13]  J Aarts,et al.  Coupling of two superconductors through a ferromagnet: evidence for a pi junction. , 2001, Physical review letters.

[14]  V. V. Ryazanov,et al.  Theoretical model of superconducting spintronic SIsFS devices , 2013, 1305.0836.

[15]  J. Aarts,et al.  Coupling of Two Superconductors through a Ferromagnet , 2001 .

[16]  N. V. Klenov,et al.  Theory of supercurrent transport in SIsFS Josephson junctions , 2013, 1310.0142.

[17]  V. V. Ryazanov,et al.  Implementation of superconductor/ferromagnet/ superconductor [pi]-shifters in superconducting digital and quantum circuits , 2010, 1005.1581.

[18]  A. I. Buzdin Proximity effects in superconductor-ferromagnet heterostructures , 2005 .

[19]  T. Kontos,et al.  Josephson junction through a thin ferromagnetic layer: negative coupling. , 2002, Physical review letters.

[20]  Igor V. Vernik,et al.  Magnetic Josephson Junction Technology for Digital and Memory Applications , 2012 .

[21]  A. Marx,et al.  Josephson coupling and Fiske dynamics in ferromagnetic tunnel junctions , 2010, 1008.3341.

[22]  V. V. Ryazanov,et al.  Ferromagnetic Josephson switching device with high characteristic voltage , 2012 .