Thermoelectric (TE) materials directly transform thermal into electrical energy and vice versa, making them promising for applications in power generation or cooling. However, state-of-the-art semiconductors that are the focus of current research have not made the leap into broad applications due to poor mechanical properties and low power density. Metallic materials would be superior in this regard but have remained largely neglected over the past decades due to their small Seebeck coefficient S. Here we realize ultrahigh TE performance in metals via tuning of electronic interband scattering, an innovative enhancement principle fundamentally different from those applied in semiconductors so far. In particular, we boost S by selectively reducing the mobility of holes as they scatter off localized states, leveraged by electronic bandwidth tuning. Using this paradigm, we recently discovered record-high power factors (PF) of 34 mW m−1 K−2 in binary NixAu1−x alloys [1]. Despite this unprecedented TE performance, with the highest zT ≈ 0.5 among all metals [1], metastability and the high cost of NixAu1−x pose difficulties for applications. We have therefore continued our quest for metallic TE with superior functional properties based on more abundant elements. Utilizing an automated materials screening approach, we discover ultrahigh PF values up to 11 mW m−1 K−2 near room temperature in the textbook metal Ni3Ge [2]. In our search for novel physical mechanisms to tailor electronic scattering, we identify topological flat bands induced by geometrical frustration as a powerful tool to boost the performance of metallic TE [3]. References [1] Garmroudi, F.; Parzer, M.; Riss, A.; Bourgès, C.; Khmelevskyi, S.; Mori, T.; Bauer, E.; Pustogow, A., Sci. Adv. 9, eadj1611 (2023). [2] Garmroudi, F.; Di Cataldo, S.; Parzer, M.; Coulter, J.; Iwasaki, Y.; Grasser, M.; Stockinger, S.; Pázmán, S.; Witzmann, S.; Riss, A.; Michor, H.; Podloucky, R.; Khmelevskyi, S.; Georges, A.; Held, K.; Mori, T.; Bauer, E.; Pustogow, A., Sci. Adv. 11, eadv7113 (2025). [3] Garmroudi, F.; Serhiienko, I.; Parzer, M.; Riss, A.; Grasser, M.; Stockinger, S.; Khmelevskyi, S.; Pryga, K.; Wiendlocha, B.; Held, K.; Mori, T.; Bauer, E.; Pustogow, A., Phys. Rev. X 15, 021054 (2025).