Research
Thermal radiation and Renewable energy
Can we generate renewable energy by pointing a semiconductor cell at the sky? How about at night? Yes, and yes! The clear, cold night sky is a vast, unrealized renewable energy resource. Our research explores the fundamental, thermodynamic limits of renewable energy extraction from the cold night sky.
- W Li, S Buddhiraju, and S Fan. Thermodynamic limits for simultaneous energy harvesting from the hot sun and cold outer space. Light: Science and Applications 9(68), 2020. [Open Access]
- S Buddhiraju, P Santhanam, and S Fan. Thermodynamic Limits of Energy Harvesting from Outgoing Thermal Radiation. Proceedings of the National Academy of Sciences 115 (16), 2018. [Open Access]
The second law of thermodynamics prescribes that in passive, time-independent systems, heat must flow from hot to cold. But what about time-dependent systems? We show that a time-varying refractive index enables a "photonic" refrigerator, allowing a cold object to pump heat towards a hot object. Check out our PRL and popular science coverage!
- S Buddhiraju, W Li, and S Fan. Photonic Refrigeration from Time-Modulated Thermal Emission. Physical Review Letters 124(7), 2020. [PDF]
- Phys.org: A possible new way to cool computer chips
- APS Focus: Emitting Photons Is One Way to Be Cool
High-school physics taught us that thermal radiation from any hot object is capped by the Stefan-Boltzmann law. But this is true only in the "far-field", where hot objects are far away from each other - like the Sun and Earth. When hot objects are sufficiently close to each other, or in the "near-field", the Stefan-Boltzmann law can be overcome by orders of magnitude! This can enable future renewable energy technologies such as thermal photovoltaics (TPVs) with high efficiency and power density.
- GT Papadakis, S Buddhiraju, Z Zhao, B Zhao, and S Fan. Broadening Near-Field Emission for Performance Enhancement in Thermophotovoltaics. Nanoletters 20(3) 2020. [PDF]
- B Zhao, S Buddhiraju, P Santhanam, K Chen, and S Fan. Self-sustaining thermophotonic circuits. Proceedings of the National Academy of Sciences 116 (24), 2019. [Open Access]
- GT Papadakis, B Zhao, S Buddhiraju, and S Fan. Gate-tunable near-field heat transfer. ACS Photonics 6 (3), 2019. [PDF]
- B Zhao, P Santhanam, K Chen, S Buddhiraju, and S Fan. Near-field thermophotonic systems for low-grade waste-heat recovery. Nano letters 18 (8), 2018. [PDF]
- B Zhao, K Chen, S Buddhiraju, G Bhatt, M Lipson, and S Fan. High-performance near-field thermophotovoltaics for waste heat recovery. Nano Energy 41, 2017. [PDF]
Time-Dependent photonic systems
The second law of thermodynamics prescribes that in passive, time-independent systems, heat must flow from hot to cold. But what about time-dependent systems? We show that a time-varying refractive index enables a "photonic" refrigerator, allowing a cold object to pump heat towards a hot object. Check out our PRL and popular science coverage!
- S Buddhiraju, W Li, and S Fan. Photonic Refrigeration from Time-Modulated Thermal Emission. Physical Review Letters 124(7), 2020. [PDF]
- Popular science: (1) A possible new way to cool computer chips (2) Emitting Photons Is One Way to Be Cool
- Computational tool: GitHub
optical metamaterials
Metamaterials are artificial materials that exhibit new behaviors not found in natural materials. Over the years, dozens of strange and exciting properties have been discovered in these artificial materials. Here, we ask: is it possible to construct an artificial material that breaks Lorentz reciprocity while still effectively appearing to be time-reversal symmetric? What cool properties would such a material have?
- S. Buddhiraju, AY Song, GT Papadakis, and S Fan. Nonreciprocal Metamaterial obeying Time-Reversal Symmetry. Physical Review Letters 124(25), 2020. [PDF]
plasmonics
Plasmonics is the study of hybrid electron-light oscillations at metallic interfaces. These oscillations can have wavelengths much, much smaller than the wavelength of light at the same frequency. Here, we consider a peculiar problem: what happens when a plasmonic system breaks Lorentz reciprocity? It turns out that quantum mechanical effects become very important, and ignoring them can lead to thermodynamic paradoxes!
- S Buddhiraju, Y Shi, AY Song, C Wojcik, M Minkov, IAD Williamson, A Dutt, and S Fan. Absence of unidirectionally propagating surface plasmon-polaritons at nonreciprocal metal-dielectric interfaces. Nature Communications 11(1), 2020. [Open Access]
solid-state high-harmonic generation
- H Liu, G Vampa, JL Zhang, Y Shi, S Buddhiraju, S Fan, J Vuckovic, PH Bucksbaum, and DA Reis. Overcoming the absorption limit in high-harmonic generation from crystals. arXiv:1905.02821, 2019. [Open Access]
nanoelectronics
- S Buddhiraju and B Muralidharan. Optimal single quantum dot heat-to-pure-spin-current converters. Physica B: Condensed Matter 478, 2015. [PDF]
- S Buddhiraju and B Muralidharan. Role of dual nuclear baths on spin blockade leakage current bistabilities. Journal of Physics: Condensed Matter 26 (48), 2014. [PDF]