Mesoscopic fluctuations of the ground state spin of a small metal particle

We study the statistical distribution of the ground state spin for an ensemble of small metallic grains, using a random-matrix toy model. Using the Hartree Fock approximation, we find that already for interaction strengths well below the Stoner criterion there is an appreciable probability that the ground state has a finite, nonzero spin. Possible relations to experiments are discussed.Comment: 4 pages, RevTeX; 1 figure included with eps

Photocurrent generation in artificial light-harvesting protein matrices

Global interest in solar energy utilization is driving the search for new materials that allow light harvesting and photocurrent generation under a light stimulus. Light harvesting is also one of the most important natural phenomena, of which photosynthesis is an example, and such natural systems have been as well for photocurrent generation. Inspired by natural light-harvesting complexes, we present here a synthetic and artificial solid-state protein-based biopolymer that facilitates the formation of a photocurrent in a wide range of wavelengths upon the molecular doping of the natural light-harvesting chlorophyll molecules. Interfacing of the doped protein matrix with electrodes yielded a photocurrent in the order of a few microamperes when the matrix was exposed to light. We show a switchable (flipping in the) photocurrent behavior when: 1) the magnitude of the applied bias is changed, 2) the location of the irradiated area is changed with respect to the electrodes, and 3) a gradient doping, enabled by the facile molecular doping approach, is formed. Finally, the synthetic artificial nature of the protein matrix allows the exploration of several light-harvesting cofactors not used in natural systems, where we further show photocurrent generation by doped metal-free porphyrins

Light-Modulated Cationic and Anionic Transport Across Protein Biopolymers

Light is a convenient source of energy and the heart of light-harvesting natural systems and devices. Here, we show light-modulation of both the chemical nature and ionic charge carrier concentration within a protein-based biopolymer that was covalently functionalized with photoacids or photobases. Using steady-state and time-resolved fluorescence, we explore the capability of the biopolymer-tethered photoacids and photobases to undergo excited-state proton transfer and capture (ESPT and ESPC), respectively. Various electrical measurements show that both the photoacid- and photobase-functionalized biopolymers exhibit an impressive increase in ionic conductivity upon light irradiation, which can be modulated by the light intensity. Whereas ESPT-induced cationic protons are the charge carriers for the photoacid-functionalized biopolymer, ESPC-induced water-derived anionic hydroxides are the suggested charge carriers for the photobase-functionalized biopolymer. Our work introduces a versatile toolbox to light?modulate charge carriers in polymers and taking together the attractive environmental nature of our new light-modulated ionic-conductive biopolymers, they can be considered for various photoelectrochemical applications. <br /