Thermodynamics of designer quantum materials
Next Generation Magnetisation and Susceptibility Measurements
Artificial designer heterostructures of correlated electron systems, built atomic layer by atomic layer, allow the creation of new phases difficult to attain in bulk compounds [1]. Meanwhile, new bulk compounds from our solid-state chemistry collaborators typically arrive as powders or microcrystals; the layered osmate La₇Os₃O₁₈, which orders antiferromagnetically at 43 K yet releases only about half of its expected magnetic entropy down to 2 K, is a recent example [2].
The low thermal mass of such samples makes magnetisation and specific heat measurements at low temperatures and high magnetic fields a fundamental challenge. We have developed instrumentation specifically for this task: a membrane nanocalorimeter with self-calibrating, magnetic-field independent Coulomb blockade thermometers, resolving sub-nJ/K heat capacities on a µg-scale crystals [3], and capacitive dilatometry with a noise floor around 1 pm/√Hz [4]. Inside a uniaxial pressure cell, where conventional calorimetry is difficult to realise, a.c. elastocaloric measurements – used to map the strain phase diagram of Sr₂RuO₄ [5] – now yield absolute entropy and specific heat across the entire phase diagram [6].
A further development is the direct measurement of the chemical potential, and hence the Gibbs free energy, of quantum materials, following a concept from quantum Hall physics [7]. Extended to monolayers, heterostructures and membranes, this gives access to thermodynamic information on designer quantum materials that existing techniques cannot provide.
First prototypes have been built. You will join a team applying these techniques to novel quantum materials within the IMPRS; your work will span numerical modelling of setups, hands-on installation, low temperature instrumentation control, advanced data analysis and of course the physics of these new materials.
