Colossal Thermopower Beyond the Boltzmann Limit (20/08/26)
Speaker and Affliation:
Prof. Bivas Saha
Associate Professor, International Center for Materials Science (ICMS), Chemistry and Physics of Materials Unit (CPMU),
School of Advanced Materials (SAMat),
Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR)
When?
20th August, 2026 (Thursday), 4.00 PM (India Standard Time)
Where
KPA Auditorium, Dept. of Materials Engineering, IISc, Bangalore
Abstract:
The Seebeck effect converts a temperature gradient into an electrical voltage and underpins technologies ranging from thermocouples and thermopiles to thermoelectric generators and other energy-conversion devices. In crystalline materials, conventional transport theories typically constrain the Seebeck coefficient to a few millivolt-per-kelvin range, establishing a widely accepted upper limit for thermopower.
We show experimental evidence of a colossal Seebeck coefficient exceeding -124 mV K⁻1 near room temperature in heavily doped, highly compensated (HDHC) epitaxial scandium nitride (ScN) thin films. Random distribution of charged dopants in HDHC ScN generate potential fluctuations that distort the electronic bands, giving rise to percolative transport governed by a power-law scaling between thermopower and electrical conductivity. At moderate doping, the Seebeck coefficient reverses sign as a function of temperature. Moreover, in ultrathin films, the Rytova-Keldysh modifications of the Coulomb potential further amplify the potential fluctuations and enhance the Seebeck response. The observed thermopower behavior, including the sign reversal, the weak temperature dependence at elevated temperatures, and its evolution from large to colossal magnitudes, can all be qualitatively explained within the framework of a narrow-band Hubbard model. Our findings reveal a solid-state analogue of electrolyte-like thermopower in a crystalline semiconductor, offering a new paradigm for thermoelectrics, ultrasensitive temperature sensing, and quantum-precision metrology.
References:
R. Karanje#, D. Rao#, D. Dadhich, S. Rudra, A. I. K. Pillai, M. Garbrecht, S. Mukerjee and B. Saha, “Heavily doped, highly compensated epitaxial ScN thin films exceed Boltzmann thermopower limits” Science 393, 611-614 (2026).
D. Rao, D.P. Panda, A.I.K. Pillai, A. Tayal, M. Garbrecht, and B. Saha, “Quasiclassical Anderson transition and thermally activated percolative charge transport in single-crystalline ScN” Phys. Rev. B, 109, 155307 (2024).
Bio:
Bivas Saha is an Associate Professor at the International Centre for Materials Science and the Chemistry and Physics of Materials Unit at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bangalore, India. He received his Ph.D. from Purdue University (2014), M.S. from JNCASR (2010), and B.Sc. from Jadavpur University (2007), and was a postdoctoral scholar at UC Berkeley (2014–2017). His research group focuses on epitaxial heterostructures, plasmonics, phase-change materials, topological physics, and thermoelectrics. He has published over 86 peer-reviewed papers and holds five patents, including one US and four Indian patents. Five Ph.D. and five M.S. students have completed their theses under his supervision. His honors include the Sheikh Saqr Senior Career Award Fellowship, BRNS Young Scientist Research Award, and Purdue Outstanding Graduate Student Award. He currently serves as an Editor of Solid State Communications journal.