Interplay between magnetism and superconductivity in 2D van der Waals heterostructures

超导态和时间反转对称性破缺的态之间的相互作用使得非常规超导成为可能。我们建议探索由超导和非超导范德华体系组合而成的各种二维范德华异质结构中近邻诱导超导电性的本质。特别令人感兴趣的是新形式的库珀配对，特别是三重态配对，它是由传统的S波超导体与磁性系统或更一般的具有空间和时间反转对称性的系统的邻近耦合产生的。我们建议同时制备由范德华异质结形成的垂直和横向约瑟夫森结。最近，我们已经证明了这类系统可以表现出新的性质，包括约瑟夫森二极管效应，在这种效应中，电流反向流动的临界超流密度可以变化高达80%。我们已经在约瑟夫森结(JJ)中证明了这种效应，其中势垒是由van der Waals半金属NiTe2、PtTe2和WTe2形成的，使用由2D Ising超导体2H-NbSe2和传统Nb形成的超导电极。二极管效应的详细来源仍有待确定。我们计划通过探索二极管效应与使用各种2D材料形成的异质结构的详细电子和磁性结构之间的关系来解决这个问题。我们还建议探索由2D磁性系统形成的异质结构中的邻近感应超导电性，这些异质结构具有拓扑性的非共线自旋织构(例如Skyrmions)，并与2D超导材料相结合。我们将使用磁输运技术以及超导隧道显微镜(STM)和超导隧道谱(STS)来探索这些系统中出现的超导态，以探索它们的空间范围。一个重要的目标是理解和控制三重态对邻近诱导超导态的贡献。范德华异质结构将使用分子束外延和机械剥离技术来形成。我们已经证明了高质量的范德华薄膜的分子束外延生长，它表现出几种铁性性质，如单原子层和横向单分子层异质结构。我们的建议直接针对SP 2244-2DMP中的“集体和相关现象(包括自旋、磁性和超导邻近效应、Mott绝缘体)以及在2D VDW[异质]结构中出现的新拓扑态”的研究领域。设想与SPP内的几个小组在理论和实验方面进行强有力的合作。

The interplay between superconducting states and states with broken time-reversal symmetry allows for unconventional superconductivity. We propose to explore the nature of proximity induced superconductivity in various 2D van der Waals heterostructures formed from combinations of superconducting and non-superconducting van der Waals systems. Of particular interest are novel forms of Cooper pairing, especially triplet pairing, engendered by proximity coupling of a conventional s-wave superconductor with magnetic systems or, more generally, systems with broken space and time reversal symmetries. We propose to prepare both vertical and lateral Josephson junctions formed from van der Waals heterostructures. Recently we have demonstrated that such systems can exhibit novel properties including a Josephson Diode Effect in which the critical supercurrent density for current flowing in opposite directions can vary by up to 80%. We have demonstrated such effects in Josephson Junctions (JJs) where the barrier is formed from the van der Waals semimetals NiTe2, PtTe2 and WTe2 using superconducting electrodes formed from both the 2D Ising superconductor 2H-NbSe2 as well as conventional niobium. The detailed origin of the diode effect remains to be determined. We plan to address this by exploring the relationship of the diode effect to the detailed electronic and magnetic structures of heterostructures formed using a wide variety of 2D materials. We also propose to explore proximity induced superconductivity in heterostructures formed using 2D magnetic systems that exhibit topological non-collinear spin textures (e.g. skyrmions) in combination with 2D superconducting materials. The emergent superconducting states in these systems will be explored using both magneto-transport techniques as well as superconducting tunneling microscopy (STM) and superconducting tunneling spectroscopy (STS) to explore their spatial extent. An important goal is to both understand and control the contribution of triplet pairing to the proximity induced superconducting states. Van der Waals heterostructures will be formed using both molecular beam epitaxy and mechanical exfoliation techniques. We have demonstrated the MBE growth of high-quality van der Waals films displaying several ferroic properties as thin as a single atomic layer and also as lateral monolayer heterostructures. Our proposal directly addresses the research area on “collective and correlated phenomena (including spin, magnetic and superconducting proximity effects, Mott insulators) and novel topological states emerging in 2D vdW [hetero]structures” in the SP 2244-2DMP. Strong collaborations with several groups within the SPP in both theory and experiment are envisaged.