The description of excited state dynamics in multichromophoric systems constitutes both a theoretical and experimental challenge modern physical chemistry. An protocol which can systematically characterize coherent dissipative processes at the level evolving quantum chromophores is desired. In this article, we show that carefully chosen set polarization controlled two-color heterodyned photon-echo experiments be used to reconstruct time-evolving density matrix one-exciton manifold...

Long-lived exciton coherences have been recently observed in photosynthetic complexes via ultrafast spectroscopy, opening exciting possibilities for the study and design of coherent transport. Yet, ambiguity spectroscopic signals has led to arguments against interpreting them terms dynamics, demanding more stringent tests. We propose a novel strategy, quantum process tomography (QPT), spectroscopy apply it reconstruct evolving state excitons double-walled supramolecular light-harvesting...

We study effects of the oft-neglected cubic Dresselhaus spin-orbit coupling (i.e., directly proportional p3) in GaAs/AlGaAs quantum dots. Using a semiclassical billiard model, we estimate magnitude induced avoided crossings closed dot Zeeman field. previous analyses based on random matrix theory, calculate corresponding conductance through an open dot. Combining our results with experiment 8 microm2 [D. M. Zumbühl, Phys. Rev. B 72, 081305 (2005)10.1103/PhysRevB.72.081305] suggests that (1)...

We present a methodology for estimating the efficiency potential candidate impurity-band photovoltaic materials from empirical measurements. This employs both Fourier transform infrared spectroscopy and low-temperature photoconductivity to calculate “performance figure of merit” determine position bandwidth impurity band. evaluate material, silicon hyperdoped with sulfur; we find that merit is more than one order magnitude too low devices exceed thermodynamic limit single band gap materials.

Recent years have seen a number of candidate materials for intermediate band (IB) solar cells, but none has demonstrated high-efficiency device. We explain this deficit by means figure merit, which predicts the potential effectiveness IB in advance device fabrication. This merit captures single parameter inherent tradeoff between enhanced absorption and recombination within an material, it suggests path toward efficient materials. illustrate screening approach based on specific class...

Intermediate-band materials have the potential to be highly efficient solar cells and can fabricated by incorporating ultrahigh concentrations of deep-level dopants. Direct measurements ultrafast carrier recombination processes under supersaturated dopant not been previously conducted. Here, we use optical-pump/terahertz-probe study dynamics chalcogen-hyperdoped silicon with sub-picosecond resolution. The is described two exponential decay time scales: a fast scale ranges between 1 200 ps...

Silicon supersaturated with sulfur by ion implantation and pulsed laser melting exhibits broadband optical absorption of photons energies less than silicon's band gap. However, this metastable, hyperdoped material loses its ability to absorb sub-band gap light after subsequent thermal treatment. We explore deactivation process through electronic transport measurements sulfur-hyperdoped silicon subject anneals at a range durations temperatures. The is well described the...

We theoretically investigate the controlled dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. Three regimes long-term dynamics are identified, including buildup a large difference Overhauser fields across dots, saturation process associated with formation so-called ``dark states'', and elimination field. show that case unequal generally accompanies process, whereas for nearly identical competes dark states. The field does not, general,...

We report a conceptually straightforward witness that isolates coherent electronic oscillations from their vibronic counterparts in nonlinear optical spectra of molecular aggregates: Coherent as function waiting time broadband pump/broadband probe correspond to oscillations. Oscillations individual peaks 2D do not necessarily yield this conclusion. Our is simpler implement than quantum process tomography and potentially resolves long-standing controversy on the character ultrafast...

Intermediate band photovoltaics hold the promise of being highly efficient and cost effective photovoltaic cells. states in gap, however, are known to facilitate nonradiative recombination. Much effort has been dedicated producing metallic intermediate bands hopes lifetime recovery—an increase carrier as doping levels increase. We show that recovery induced by insulator-to-metal transition will not occur, because extended be localized phonons during recombination process. Only trivial forms...

Abstract Intermediate band solar cells hold the promise of ultrahigh power conversion efficiencies using a single semiconductor junction. Many current implementations use materials with bandgaps too small to achieve maximum efficiency or cost-prohibitive substrates. Here we demonstrate material system for intermediate InGaN/GaN quantum-dot-in-nanowire heterostructures grown directly on silicon provide lower cost, large-bandgap cell platform. We sequential two-photon generation sub-bandgap...

InAlGaAs tunnel diodes, lattice-matched to InP and grown by molecular beam epitaxy, are demonstrated with peak tunneling current densities exceeding 1200 A/cm2. This was achieved a 20 °C reduction in growth temperature for the p-type diode layers, resulting up two orders of magnitude improvement density. Secondary ion mass spectrometry measurements reveal that lower reduces unwanted segregation Be dopants, improving dopant incorporation within active layers. The diodes transparent...

Time-resolved spectroscopy is commonly used to study diverse phenomena in chemistry, biology, and physics. Pump-probe experiments coherent two-dimensional (2D) have resolved site-to-site energy transfer, visualized electronic couplings, much more. In both techniques, the lowest-order signal, a perturbative expansion of polarization, third order electric field, which we call one-quantum (1Q) signal because 2D it oscillates coherence time with excitation frequency. There also two-quantum (2Q)...

The efficiency of GaAs nanowire (NW) solar cells can be significantly improved with no new processing steps or material requirements. We report coupled optoelectronic simulations a NW cell vertical p-i-n junction and high-bandgap AlInP passivating shell. Our frequency-dependent model facilitates calculation quantum for the first time in cells. For passivated NWs, we find that short-wavelength photons most effectively harnessed by using thin emitter, while long-wavelength are best utilized...

We present a multijunction detailed-balance model that includes the effects of luminescent coupling, light trapping, and nonradiative recombination, suitable for treatment solar cells photonic power converters—photovoltaic devices designed to convert narrow-band light. The both specular Lambertian reflections using ray-optic formalism treats processes an internal radiative efficiency. Using this model, we calculate optimize efficiency converters range material qualities light-trapping...

An unpolarized charge current passing through a chaotic quantum dot with spin-orbit coupling can produce spin-polarized exit without magnetic fields or ferromagnets. We use random matrix theory to estimate the typical spin polarization as function of number channels in each lead limit large coupling. find rms polarizations up 45% one input channel and two output channels. Finite temperature dephasing both suppress effect, we include effects using variation third model. If there is only lead,...

Undergraduate coursework familiarizes us with heat engines---but not like these. This study identifies an innovative type of radiative engine and derives its fundamental efficiency power bounds. The findings include the surprising possibility that certain classes engines, such as thermoradiative diodes, can exceed Landsberg limit approach Carnot limit. Conventional engines have a converter coupled to cold reservoir absorbing external hot (e.g. solar) radiation produce work, but here...

Waste heat is a free and abundant energy source, with 15% of global total use existing as waste above 600 K. For 600–900 K temperature range, near-field thermophotovoltaics (NFTPVs) are theorized to be the most effective technology recycle into electrical power. However, date, experimental efficiencies have not exceeded 1.5%. In this work, we optimize efficiency three modeled InAs/InAsSbP-based room-temperature NFTPV devices positioned 0.1 μm from 750 p-doped Si radiator. We couple...

Intermediate band (IB) materials are promising candidates for realizing high efficiency solar cells. In IB photovoltaics, photons absorbed in one of three possible electronic transitions—valence to conduction band, valence intermediate or band. With fully concentrated sunlight, when the gaps have been chosen appropriately, highest cells require that these absorptions be non-overlapping, so fixed energy contribute only transition. The realistic case overlapping absorptions, where transitions...

Perturbative nonlinear optical spectroscopies are powerful methods to understand the dynamics of excitonic and other condensed phase systems. Feynman diagrams have long provided essential tool interpret experimental spectra organize calculation for model When pulses strictly time ordered, only a small number contribute, but in many experiments, pulse-overlap effects important interpreting results. overlap, contributing can increase rapidly, especially with higher order spectroscopies, human...