Fabrication of Josephson junctions with nano-injectors and investigation of fractional flux quanta.

人工相位不连续允许创建携带磁通量的约瑟夫森涡旋，磁通量是单个通量量子的任意分数。我们和其他研究小组已经报道了几个关于这些分数约瑟夫森涡旋的实验。然而，人工相位不连续产生的涡旋尺寸相当大，并且迄今为止还不可能对涡旋分子或一维晶体等多涡旋系统进行研究。一个限制因素是用于产生相位不连续的电流注入器的宽度和约瑟夫森结的临界电流密度jc。通过使用电子束光刻，我们将制造纳米注入器（理想情况下，两个宽度为100 nm的注入器之间的间隙为200 nm），并将约瑟夫森结宽度减小到300 nm。这将允许安全地将jc增加到几个kA/cm 2，以减小涡流尺寸μ 1/μ jc。利用新技术，我们将研究温度T ≥ 0.3时经典域中的多涡旋分子和一维涡旋晶体。. . 6 K.本项目的成功实施将把Nb/Al-AlOx/Nb约瑟夫森结技术推向纳米领域，也将有助于其他应用，例如，在量子域中（由于较高的jc和较小的结宽，经典到量子的交叉温度较高）。

Artificial phase discontinuities allow to create Josephson vortices carrying a magnetic flux, whichis an arbitrary fraction of a single flux quantum. Few experiments with these fractional Josephsonvortices were already reported by our and other groups. However, vortices created by artificialphase discontinuities are rather large in size and investigation of multi-vortex systems such asvortex molecules or 1D crystals was not possible up to now. A limiting factor is the width ofthe current injectors used to produce a phase discontinuity and the critical current density jc ofthe Josephson junction. By using e-beam lithography we are going to fabricate nano-injectors(ideally two injectors of the width ∼ 100 nm with a gap of ∼ 200 nm in between), and reduce theJosephson junction width down to ∼ 300 nm. This will allow to safely increase the jc to a fewkA/cm2 to decrease the vortex size ∝ 1/√jc. Using the new technology we will investigate multivortexmolecules and 1D vortex crystals in the clasical domain at temperatures T ∼ 0.3 . . . 6K.The successful implementation of this project will push forward the Nb/Al-AlOx/Nb Josephsonjunction technology into the nanometer domain and will also be useful for other applications, e.g.,in the quantum domain (higher classical-to-quantum crossover temperature due to higher jc andsmaller junction width).