Thermoelectricity is the direct conversion of temperature differences into electric voltage and vice versa. This phenomenon is utilized in thermoelectric generators (TEGs) to convert waste heat into electricity and in thermoelectric coolers to create temperature gradients. Key applications include waste heat recovery, remote power generation, and precise temperature control in various industries. The efficiency of thermoelectric materials continues to improve, opening new possibilities for sustainable energy solutions.

Topological insulators are unique materials that act as insulators in their bulk but have conductive states on their surfaces or edges. These surface states are protected by time-reversal symmetry and remain conductive even in the presence of non-magnetic impurities. Topological insulators are classified into two types: 2D topological insulators, which have edge states with dissipationless transport, and 3D topological insulators, which have surface states forming a Dirac cone. These materials have potential applications in spintronics, quantum computing, and other advanced technologies due to their robust and distinctive properties.