Abstract: Thermodynamic probes, such as heat capacity measurements, are a well-established tool for characterising phase properties of complex bulk materials, such as spin-ice, 2D electron gas or baro- or magnetocaloric materials. However, the standard techniques can not be used for microscopic systems due to the requirement for increasingly precise heat flow measurements with the decreasing system size. To solve this issue, in the last few years several methods have been proposed to directly measure entropy in nanodevices through electrical (charge state or charge transport) measurements.
These have two benefits. On a practical side, entropy in a system with few degrees of freedom in strongly linked to its microscopic dynamics, and knowing it can reveal the system's quantum states, such as energy levels and their degeneracies, number of spatial localisation sites, spin, etc.
The system-universality of thermodynamics, one of the strongest features of the theory, allows for such methods to be used on a variety of materials, from molecules to qubits, Majorana fermions and magic-angle graphene, making thermodynamic methods a promising avenue for many currently active fields of research in condensed matter physics. More fundamentally, the ability to measure thermodynamic parameters of an electric nanodevice allows it to be used for quantum thermodynamic research, building on the existing technology and opening up a new avenue of easily experimentally accessible devices in a notoriously challenging experimental field.
