Interacting electron mesoscopics
 

While strongly correlated systems in general are being studied quite extensively, relatively little work has been done to explore the mesoscopic regime in which one or more sample dimensions are reduced to be the same as, or smaller than, characteristic length scales of the states being studied. Examples of these scales include the mean free path in metals, the coherence length and penetration depth in superconductors, and characteristic domain dimensions in many forms of exotic order. For such studies, extremely high purity materials are paramount. Optimising the conditions for high purity thin film growth of complex materials can be difficult and time-consuming, so our goal is to begin with high purity single crystals and develop techniques for preparing micron-sized samples from them. To this end, we have built a dedicated clean room and installed - among other equipment - an electron beam lithography instrument (Raith150TWO) and two focused-ion-beam (FIB)/scanning-electron microscope dual-beam systems (FEI Helios). The Ga-FIB offers highest resolution and minimum feature sizes of a few 100 nm have been achieved. The Xe-Plasma FIB can provide significantly higher beam currents of up to 2.5 µA, which makes it highly suitable for preparing larger devices where ultimate resolution is not required. Using noble-gas ions also eliminates any residual risk of chemical doping.

Figure 1: The clean room (left) and one of our Focused Ion Beam systems (FEI Helios G3 Ga-FIB, right).

The available techniques enable us to customise the design of our samples. Thus, the relevant questions can be addressed directly and in an optimised geometry.

Figure 2: (left) PdRh02 microstructure (blue) with precise alignment to the crystal axes extracted and prepared from a macroscopic single crystal (inset) of the delafossite material. (right) Long narrow wire (L x W ≈ 18 mm x 10 µm) fabricated from an YbRh2Si2 crystal.
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