Spectroscopic Imaging Scanning Tunneling Microscopy (SI-STM)
Spectroscopic Imaging Scanning Tunneling Microscopy has become a key part of the toolset available to experimental condensed matter physics. The atomically resolved direct imaging of local density of states variations has applications to a range of problems including electronic self organisation on the nanoscale, the study of the quasiparticle excitation spectrum of unconventional superconductors, surface states of topological insulators and 3D Dirac electron systems. A recent focus has become the study of designer heterostructures of thin film materials leading to the combination of MBE and STM techniques. In our group we have three key instruments working on these topics as well infrastructure for thin film research.
Our first instrument is a 4K UHV compatible SI-STM capable of studying both bulk and thin film samples (see below). The key current purpose is the study of 3D Dirac electron and topological insulator materials.
We recently installed a new UHV compatible 9T/3T+3T vector magnet system currently operating at 1 K and to be upgraded to sub-K temperatures. The lab space decoration is the result of an outreach program with the local kindergarten.
In collaboration with Hiro Nakamura at the MPI for Solid State Research we are developing and setting up infrastructure for STM studies of MBE and PLD grown samples. For this we have installed a Unisoku STM / q-plus AFM system directly mounted on the MBE chamber for sample characterisation and have developed infrastructure to transfer thin film samples under UHV conditions to our low temperature SI-STMs (see figure below).
Thin film designer heterostructures grown by molecular beam epitaxy (MBE) or pulsed laser deposition (PLD) are a key research field both for the fundamental questions that new classes of materials are posing as well as the potential for being a key part of future technologies due to the possible integration of the properties of different functional materials.
However, while such systems can be readily studied by charge transport and modern spectroscopies, measurements of fundamental thermodynamic properties pose a substantial experimental challenge. The key problem is the small intrinsic 'thermal mass' of such systems which are often less than 100 nm thick. In our group we are pushing existing technologies to their limits to access a very small number of such materials. In parallel we very recently started to explore new technologies to build bespoke thermodynamic apparatus tailored to the demands of thin films. As a 'side product' such techniques will also be suitable for the study of nanogram bulk crystals.