Entropy-driven inductance on the surface of a topological insulator

New opportunities for energy harvesting can be found in a century-old thought experiment known as Maxwell's demon, which suggests that energy can be extracted from information. Although systems resembling Maxwell's demon have been experimentally realized, scalability remains a challenge. A scalable solution can be found in the interfacial states of topological insulators, which could resemble Maxwell's demon due to the interaction between spin-momentum locked electrons and nuclear spins. In these systems, information - nuclear spin polarization - can be directly used to store and harvest energy. In this thesis, we focused on thin films of the three-dimensional topological insulator (Bi1-xSbx)2Te3 (BST), which can act as an ‘information engine’ to extract electrical work.
Theoretical predictions reveal that the interaction between surface states and nuclear spins in BST leads to an inductive effect, directly coupled to the entropy of the system. This ‘entropic inductance’ has potential applications in microelectronics. Experiments with Hall bar devices fabricated from molecular beam epitaxy (MBE)-grown BST were conducted to investigate this phenomenon under various source-drain bias voltages and temperatures.
Despite challenges with high current densities and Joule heating, the study demonstrated finite current-induced nuclear polarization in BST, but the expected inductive signal was small. To enhance the inductive signal, the study explored magnetic doping using vanadium-doped BST (VBST), and searched for the quantum spin Hall effect in ultrathin BST where diffusive losses would be reduced. In future research, the principle of the information engine can be applied to other material systems such as Fermi arc surface states, and future developments in electronic materials could therefore provide the key to a scalable information engine.