First-Principles Method to Study Near-Field Radiative Heat Transfer

Significance 

Near-field radiative heat transfer remains vital in the development of alternative technologies, particularly involving: thermophotovoltaics, thermal rectification, noncontact refrigeration and thermal transistors – among others. At present, both theoretical and experimental studies have shown that thermal radiation in systems with distances comparable to or smaller than the thermal wavelength λT = 2πhc/(kBT) exceeds the black body limit by several orders of magnitude. There exists a vacuum gap whereby the heat flux crossing it is given by a Landauer-type expression with a transmission function that consists of contributions from both propagating and evanescent waves. Research has shown that the dramatic increase of thermal radiation in the near field is due to the tunneling of evanescent waves that decay exponentially with the gap size. On the other hand, research has also shown that from a microscopic quantum mechanical point of view, thermal radiation can be attributed to both Coulomb interactions between charge fluctuations and photonic interactions between transverse current fluctuations. To date, several methods to study the contribution of Coulomb interactions to the energy transfer between two closely separated bodies have been proposed.

Looking carefully at these approaches reveals that despite using different notations and physical quantities, similarities in the results obtained persist. To address this, researchers from the National University of Singapore: Tao Zhu, Dr. Zu-Quan Zhang, Zhibin Gao and Led by Professor Jian-Sheng Wang, developed a new first-principles method to investigate this NFRHT problem. Their work is currently published in the research journal, Physical Review Applied.

In their approach, a random phase approximation was used to calculate the response function. The research team then computed the heat transfer in three systems: graphene, molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN). Their goal was to prove that the transmission functions from microscopic quantum mechanical models can be expressed by a formula of a frequency- and wave-vector-dependent macroscopic dielectric function, consistent with the results of fluctuational electrodynamics.

The authors reported that the Landauer-like expression of heat flux could be expressed in terms of a frequency, while as the wave-vector-dependent macroscopic dielectric function could be obtained from the linear response density functional theory. Interestingly, the results presented also showed that the near-field heat flux exceeded the black body limit by up to 4 orders of magnitude. Further, it was seen that with an increase of the distances between two parallel sheets, a 1/d2 dependence of heat flux was consistent with Coulomb’s law.

In summary, the study presented an in-depth investigation of the near-field radiative heat transfer of vacuum-gapped 2D crystal lattices using a first-principles method. The researchers showed that the transmission function could be expressed in a form of macroscopic dielectric functions with summation over all parallel wave vectors in the first Brillouin zone. In a statement to Advances in Engineering, the authors said that their innovative method can be applied to a wide range of materials including systems with inhomogeneities, which provides solid references for applications of both physics and engineering.

Reference

Tao Zhu, Zu-Quan Zhang, Zhibin Gao, Jian-Sheng Wang. First-Principles Method to Study Near-Field Radiative Heat Transfer. Physical Review Applied: Volume 14, Issue 2.

Go To Physical Review Applied

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