Ideal near-field thermophotovoltaic cells

We ask the question, what are the ideal characteristics of a near-field thermophotovoltaic cell? Our search leads us to a reformulation of near-field radiative heat transfer in terms of the joint density of electronic states of the emitter-absorber pair in the thermophotovoltaic system. This form reveals that semiconducting materials with narrowband absorption spectra are critical to the energy conversion efficiency. This essential feature is unavailable in conventional bulk semiconductor cells but can be obtained using low dimensional materials. Our results show that the presence of matched van Hove singularities resulting from quantum-confinement in the emitter and absorber of a thermophotovoltaic cell boosts both the magnitude and spectral selectivity of radiative heat transfer; dramatically improving energy conversion efficiency. We provide a model near-field thermophotovoltaic system design making use of this idea by employing the van Hove singularities present in carbon nanotubes. Shockley-Queisser analysis shows that the predicted heat transfer characteristics of this model device are fundamentally better than existing thermophotovoltaic designs. Our work paves the way for the use of quantum dots, quantum wells, two-dimensional semiconductors, semiconductor nanowires and carbon nanotubes as future materials for thermophotovoltaic cells.Comment: 9 pages, 5 figure

Dirac-Maxwell correspondence: Spin-1 bosonic topological insulator for light

Fundamental differences between fermions and bosons are revealed in their spin and distribution statistics as well as the discrete symmetries they obey (charge, parity and time). While significant progress has been made on fermionic topological phases of matter with time-reversal symmetry, the bosonic counterpart still remains elusive. We present here a spin-1 bosonic topological insulator for light by utilizing a Dirac-Maxwell correspondence. Departing from structural photonic approaches which mimic the pseudo-spin-\textonehalf{} behavior of electrons, we exploit the integer spin and discrete symmetries of the photon to formulate a distinct bosonic topological phase of matter. We introduce a bosonic Kramers theorem and the photonic equivalent of topological quantization, which arises solely from photon spin. Our continuum field theory predicts that photons acquire a mass in the presence of a spatio-temporally dispersive degenerate chirality, a unique form of magneto-electric coupling inside matter fundamentally different from well-known chirality, magneto-electricity, gyrotropy or bi-anisotropy. We predict that this unique dispersive (non-local) degenerate chiral medium has anomalous parity and time-reversal symmetries and if found in nature will exhibit a gapped Quantum spin-1 Hall bosonic phase. Photons do not possess a conductivity transport parameter which can be quantized (unlike electronic systems), but we predict that photon spin quantization of symmetry-protected edge states is amenable to experimental isolation leading to a new bosonic phase of matter.Comment: 13 pages, 4 figure