Natural Regulation of Energy Flow in a Green Quantum Photocell

Manipulating the flow of energy in nanoscale and molecular photonic devices is of both fundamental interest and central importance for applications in light harvesting optoelectronics. Under erratic solar irradiance conditions, unregulated power fluctuations in a light harvesting photocell lead to inefficient energy storage in conventional solar cells and potentially fatal oxidative damage in photosynthesis. Here, we show that regulation against these fluctuations arises naturally within a two-channel quantum heat engine photocell, thus enabling the efficient conversion of varying incident solar spectrum at Earth's surface. Remarkably, absorption in the green portion of the spectrum is avoided, as it provides no inherent regulatory benefit. Our findings illuminate a quantum structural origin of regulation, provide a novel optoelectronic design strategy, and may elucidate the link between photoprotection in photosynthesis and the predominance of green plants on Earth.Comment: 17 pages, 4 figure

Quieting a noisy antenna reproduces photosynthetic light harvesting spectra

Photosynthesis is remarkable, achieving near unity light harvesting quantum efficiency in spite of dynamic light conditions and noisy physiological environment. Under these adverse conditions, it remains unknown whether there exists a fundamental organizing principle that gives rise to robust photosynthetic light harvesting. Here, we present a noise-canceling network model that relates noisy physiological conditions, power conversion efficiency, and the resulting absorption spectrum of photosynthetic organisms. Taking external light conditions in three distinct niches - full solar exposure, light filtered by oxygenic phototrophs, and under sea water - we derive optimal absorption characteristics for efficient solar power conversion. We show how light harvesting antennae can be finely tuned to maximize power conversion efficiency by minimizing excitation noise, thus providing a unified theoretical basis for the experimentally observed wavelength dependence of light absorption in green plants, purple bacteria, and green sulfur bacteria

Intervalley coherence and intrinsic spin-orbit coupling in rhombohedral trilayer graphene

Rhombohedral graphene multilayers provide a clean and highly reproducible platform to explore the emergence of superconductivity and magnetism in a strongly interacting electron system. Here, we use electronic compressibility and local magnetometry to explore the phase diagram of this material class in unprecedented detail. We focus on rhombohedral trilayer in the quarter metal regime, where the electronic ground state is characterized by the occupation of a single spin and valley isospin flavor. Our measurements reveal a subtle competition between valley imbalanced (VI) orbital ferromagnets and intervalley coherent (IVC) states in which electron wave functions in the two momentum space valleys develop a macroscopically coherent relative phase. Contrasting the in-plane spin susceptibility of the IVC and VI phases reveals the influence of graphene's intrinsic spin-orbit coupling, which drives the emergence of a distinct correlated phase with hybrid VI and IVC character. Spin-orbit also suppresses the in-plane magnetic susceptibility of the VI phase, which allows us to extract the spin-orbit coupling strength of $\lambda \approx 50\mu$eV for our hexagonal boron nitride-encapsulated graphene system. We discuss the implications of finite spin-orbit coupling on the spin-triplet superconductors observed in both rhombohedral and twisted graphene multilayers

The Condensation of Electrons, Holes and Data: Imaging Non-Equilibrium Dynamics at the Microscopic, Mesoscopic, and Statistical Scales

Physical systems driven out of thermal equilibrium may exhibit complex behavior before eventually relaxing to thermal equilibrium. The prototypical non-equilibrium state in quantum materials is the photoexcited electron, where an electron is imparted excess energy and may exhibit a variety of interesting phenomena before eventually recombining with a hole. In nanoscale systems, quantum confinement makes the behavior of non-equilibrium electrons more complex and experimentally accessible. To measure non-equilibrium dynamics, we develop a technique for data-intensively imaging photoresponse that efficiently samples phenomenological parameter space. The result is a large set of images which we condense down to dynamical parameters that can be visualized and physically interpreted. Using this data intensive methodology, we explore the non-equilibrium physics of photoexcited electrons on multiple scales. Firstly, on the microscopic scale we study the interactions of excitons and electron-phonon coupling in TMD heterostructures. Then, zooming out to the mesoscopic scale, we observe an electron-hole liquid phase in MoTe2 and hot carrier regime in graphene heterostructures. Finally, at the statistical scale we explore how a simple model for quieting a noisy antenna can decrease noise in the non-equilibrium states that power photosynthesis. In sum, we demonstrate that data intensive imaging is a powerful and versatile tool for exploring non-equilibrium dynamics of quantum materials and biophysical systems