PILLAR: Electron dynamics in laterally confined quasi-two-dimensional metals

强层状材料提供了丰富的令人兴奋的物理现象和新颖的应用。这些准2D晶体(Q2D)由强的面内键和弱的面外键定义。剥离通常导致原子薄的薄片，其电、磁、光和化学特性与大块显著不同。他们新奇行为的关键是将有效维度降低到平面内的两个维度。剥离概念最突出的例子无疑是石墨/石墨烯和过渡金属二卤化物(TMD)。如果一个三维晶体可以被机械塑造成类似2D系统的行为，那么它也一定有可能从它产生准1D状态(3D=q2D+q1D)。我们称这种极限为“柱”，无限堆叠的介观(&lt；1微米)q2D薄片。就像它们更熟悉的q2D表亲一样，降维预计会导致与整体截然不同的电子行为。柱子的每一个平面都可以看作是一个独立的岛屿，与其上下相邻的岛屿弱耦合，从而形成一种新的q1D岛链。在这里，我们建议通过打破强键而保留弱键来实现和探索这种状态。虽然剥离很容易制备Q2D薄片，但柱子与自然键的各向异性相反，因此很难用传统方法获得。我们建议使用聚焦离子束加工作为一种温和的动力学技术来从大块晶体中雕刻这种柱子。我们计划基于q1D柱子的独特性质探索三个主要的科学主题：1)在介观柱子中的一种新的量子输运机制，其中面内驻波在堆积层之间相干地传输。Itshallmark是一种新的磁导振荡，类似于我们最近在FIB雕刻的PdCoO2柱子上演示的Aharonov-Bohm效应。这是这种氟磷矿金属的一个独特案例，还是一种普遍的属性？它是否经受住了强关联并与超导电性相互作用，例如在Sr2RuO4中？在大块晶体金属中从未观察到(至今)Bloch振荡。我们提出，柱子中的朗道量子化产生了浅(平)朗道带，这非常适合于实现Bloch振荡。这两个问题都将通过运输和建造光学微谐振器来解决。3)层状金属的极端电导各向异性为透明导体的技术研究提供了一种新的途径。我们计划在衬底平面上制备具有原子-夹层方向的Sr2RuO4独特的柱状和片状结构。这种材料应该是一种很好的面内导体，当垂直于平面极化时，它可以传输可见光。

Strongly layered materials have offered a wealth of exciting physical phenomena andnovel applications. These quasi-2D crystals (q2D) are defined by strong in-plane bondsand weak out-of-plane bonding. Exfoliation leads to often atomically thin flakes withelectronic, magnetic, optical and chemical properties that are strikingly different fromthe bulk. The key to their novel behavior is the reduction of the effective dimensionalityto the two in-plane dimensions. The most prominent examples of the concept ofexfoliating are undoubtedly graphite/graphene and the transition-metaldichalcogenides (TMD).If a crystal in three dimensions can be mechanically shaped to behave akin to a 2Dsystem, it must also be possible to generate quasi-1D states from it (3D = q2D + q1D).We call this limit "pillar", an infinite stack of mesoscopic (<1 micron) q2D flakes. Justlike their more familiar q2D cousins, dimensional reduction is expected to lead toelectronic behavior that is strikingly different to the bulk. Each plane of the pillar canbe viewed as an individual island that is weakly coupled to its upper and lowerneighbors, hence forming a new kind of q1D island chain. Here we propose to realizedand explore this state, by breaking the strong bonds while preserving the weak ones.While q2D sheets are easily prepared by exfoliation, pillars oppose the natural bondanisotropy and hence are difficult to obtain by conventional methods. We propose touse Focused Ion Beam machining as a gentle kinetic technique to carve such pillarsfrom bulk crystals.We plan to explore three main scientific topics based on the unique properties of q1Dpillars:1) A new regime of quantum transport in mesoscopic pillars in whichin-plane standing waves are coherently transported between the stacked sheets. Itshallmark is a novel magnetoconductance oscillation akin to the Aharonov-Bohm-effect,which we recently demonstrated in FIB-carved pillars of PdCoO2. Is this a unique caseof this delafossite metal, or a general property? Does it survive strong correlations and interact with superconductivity, e.g.in Sr2RuO4?2) Bloch-oscillations have never been observed (yet) in bulk crystalline metals. Wepropose that Landau-quantization in pillars induces shallow (flat) Landau-bands,which are ideally suited to realize Bloch oscillations. This will both be tackled viadc-transport and by building optical micro-resonators. If successful, it woulddemonstrate a field-tunable, solid-state frequency source in the THz range.3) Extreme conductivity anisotropy in layered metals provides a new approach to thetechnologically relevant field of transparent conductors. We plan to fabricate uniquepillar and slab structures of Sr2RuO4 with their atomic-interlayer direction in theplane of the substrate. Such material should be an excellent in-plane conductor whiletransmitting visible light when polarized perpendicular to the planes.