Interacting electron physics

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 a focused-ion-beam/scanning-electron microscope dual-beam system (FEI Helios Nanolab G3).

Figure 1: The clean room (left) and the Focused Ion Beam system (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.

Thermodynamic and transport measurements on interacting electron systems 

Although thermodynamic and thermal transport measurements are well-established techniques, they remain vitally important in the study of modern materials. This is particularly the case when interacting electrons form subtle new low temperature phases, or cause breakdowns from the standard Fermi liquid picture of metals.  We concentrate on making high-resolution measurements of the magneto-caloric effect, specific heat, thermopower, thermal conductivity and thermal Hall effect in different thermal regimes, from dilution refrigerators at 20 mK and below to 4He cryostats working at much higher temperatures. Current projects of interest are phase formation in Sr3Ru2O7, magnetothermal transport in Weyl semimetals and the study of quasi-1D materials which are postulated to show Luttinger liquid behavior.  A technical goal is to merge the two main activities of the group, and extend our capabilities for thermal measurement to the micro- and mesoscopic regimes.

Figure 3: The setup used for thermal conductivity measurements in which high resolution thermometers and a heat source are thermally anchored to a single crystal sample.  One end of the sample is tightly coupled to an external heat bath, from which the thermometers and heater are simultaneously decoupled.
Go to Editor View