2,031 research outputs found
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
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