Quantum Transfer Energy and Nonlocal Correlation in a Dimer with Time-Dependent Coupling Effect

The presence of coherence phenomenon due to the interference of probability amplitude terms, is one of the most important features of quantum mechanics theory. Recent experiments show the presence of quantum processes whose coherence provided over suddenly large interval-time. In particular, photosynthetic mechanisms in light-harvesting complexes provide oscillatory behaviors in quantum mechanics due to quantum coherence. In this work, we investigate the coherent quantum transfer energy for a single-excitation and nonlocal correlation in a dimer system modelled by a two-level atom system with and without time-dependent coupling effect. We analyze and explore the required conditions that are feasible with real experimental realization for optimal transfer of quantum energy and generation of nonlocal quantum correlation. We show that the enhancement of the probability for a single-excitation transfer energy is greatly benefits from the combination of the energy detuning and time-dependent coupling effect. We investigate the presence of quantum correlations in the dimer using the entanglement of formation. We also find that the entanglement between the donor and acceptor is very sensitive to the physical parameters and it can be generated during the coherent energy transfer. On the other hand, we study the dynamical behavior of the quantum variance when performing a measurement on an observable of the density matrix operator. Finally, an interesting relationship between the transfer probability, entanglement and quantum variance is explored during the time evolution in terms of the physical parameters.     

Chemical approach to the realization of electronic devices in epitaxial graphene

We have shown that nitrophenyl groups may be added to the surface of few‐layer epitaxial graphene (EG) by the formation of covalent carbon–carbon bonds thereby changing the electronic structure and transport properties of EG from near‐metallic to semiconducting. In the present Letter we discuss the opportunities afforded by such chemical processes to engineer device functionality in graphene by modification of the electronic properties without physical patterning.

     

A note on the mean circulation in standing waves

We consider the time-mean motion in two dimensions induced by small-amplitude standing waves on liquid of finite depth. We obtain solutions, by numerical integration, of the Navier-Stokes equations at finite values of an appropriately defined Reynolds number, from which we infer the nature of the solution at infinite Reynolds number.     

Synthesis, structure and physical properties of the first one-dimensional phenalenyl-based neutral radical molecular conductor

We report the preparation, crystallization, and solid-state characterization of a benzyl-substituted spirobiphenalenyl radical. The crystal structure shows that the radical is monomeric in the solid state, with the molecules packed in an unusual one-dimensional (1-D) fashion that we refer to as a pi-step stack. This particular mode of 1-D stacking is forced on the lattice arrangement by the presence of the orthogonal phenalenyl units that were specifically incorporated to prevent the crystallization of low-dimensional structures. The structure shows that this strategy is effective, and neighboring molecules in the stack can only interact via the overlap of one pair of active (spin-bearing) carbon atoms per phenalenyl unit, leading to the pi-step structure in which the remaining four active carbon atoms per phenalenyl unit do not interact with nearest neighbor molecules. The magnetic susceptibility data in the temperature range 4-360 K may be fit to an antiferromagnetic Heisenberg S = 1/2 linear chain model with intrachain spin coupling J = -52.3 cm(-1). Despite the uniform stacking, the material has a room temperature conductivity of 1.4 x 10(-3) S/cm and is best described as a Mott insulator.     

Phenalenyl-based neutral radical molecular conductors: substituent effects on solid-state structures and properties

We report the preparation, crystallization, and solid-state characterization of cycloheptyl and cyclooctyl-substituted spirobiphenalenyl radicals and the corresponding sigma-dimer of the cyclooctyl derivative. The crystal structure shows that the cycloheptyl radical (9) is monomeric in the solid state, with the molecules packed in an unusual one-dimensional (1-D) fashion that we refer to as a pi-chain structure, whereas the cyclooctyl variant exists both as pi-dimer 10 and sigma-dimer 10d. The neutral radical 9 shows the temperature-independent Pauli paramagnetism characteristic of a metal with a magnetic susceptibility, chip approximately 4.5x10(-4) emu/mol and is assigned a resonating valence bond (RVB) ground state. We highlight the relationship between the magnetic properties of the Heisenberg antiferromagnet and the RVB ground state in 1-D and further elucidate the electronic structure of this new class of compounds. Magnetic susceptibility measurements show that 10 is a diamagnetic pi-dimer, whereas 10d is a diamagnetic sigma-dimer. Extended Hückel calculations for 9 indicate that the solid is a one-dimensional organic metal with a bandwidth of about 0.4 eV. Pressed pellet conductivity measurements indicate values of sigmaRT=1.5x10(-3) S/cm for compound 9 and sigmaRT=1.0x10(-6) S/cm for compound 10. The structural results and transport properties are discussed in the light of extended Hückel theory band structure calculations and DFT investigations of the electronic structure of related compounds.     

Solution properties of graphite and graphene

Covalent derivatization of the acidic functional groups in oxidized graphite with octadecylamine renders graphite soluble in common organic solvents. Atomic force microscopic characterization of the soluble species supports the idea that the solutions consist of single and few layer graphene sheets, and we report the first solution properties of graphite.