Modern Physics Letters B

Effects of the order parameter symmetries on the cutoff parameter ξ_h (determining the magnetic field distribution) in the mixed state are investigated in the framework of quasiclassical Eilenberger theory for isotropic s^±, s₊₊ and anisotropic d_x²-y²-wave superconducting pairings. These symmetries are proposed for the pairing state of the Fe-pnictides. In s^± pairing symmetry, the gap function has opposite sign at the electron and hole pockets of the Fermi surface, it is connected with interband antiferromagnetic spin fluctuations. In s₊₊ pairing symmetry, the gap function has the same sign at the Fermi surface, it is mediated by moderate electron–phonon interaction due to Fe-ion oscillation and the critical orbital fluctuation. The d_x²-y² pairing symmetry can rise from intraband antiferromagnetic spin fluctuation in strongly hole overdoped iron pnictide KFe₂As₂ and ternary chalcogenides. The s^± pairing symmetry results in different effects of intraband (Γ₀) and interband (Γ_π) impurity scattering on ξ_h. It is found that ξ_h/ξ_c2 value decreases with Γ₀ leading to the values much less than those predicted by the analytical Ginzburg–Landau (AGL) theory for high Γ₀. At very high Γ₀, the interband scattering suppresses ξ_h/ξ_c2 considerably below one in the whole field range making it flat for both s^± and s₊₊ pairing symmetries. Scaling of the cutoff parameter with the electromagnetic coherence length shows the importance of the nonlocal effects in mixed state. The small values of ξ_h/ξ_c2 were observed in μSR measurements of Co-doped BaFe₂As₂. If Γ₀ and Γ_π are small and equal than the ξ_h/ξ_c2(B/B_c2) dependence for s^± symmetry behaves like that of the AGL model and shows a minimum with value much more than that obtained for s₊₊ superconductors. With high Γ_π, the ξ_h/ξ_c2(B/B_c2) dependence resides above the AGL curve for s^± pairing symmetry, as observed in SANS measurements of stoichiometrical LiFeAs compound. In d-wave superconductors, ξ_h/ξ_c2 always increases with Γ similar to the s^± symmetry case with Γ₀ = Γ_π.

The equivalent circuit of the p-i-n structure has been considered and developed for the quantum dot intermediate band solar cells where the nanoparticles are inserted in the active region of the diode. The admittance of the circuits are calculated consisting of frequency dependent capacitance and conductance. The presence of quantum dot layers in the active region of the diode increases the capacitance and conductance of the cell in lower frequencies. However, the number of QD cannot be increased and has an optimum.

The phase diagram of a quantum Hall bilayer at total filling ν = 1 contains an incompressible superfluid for small distances d between the layers, as well as the compressible phase corresponding to two uncoupled Fermi liquids for large d. Using exact diagonalization on the sphere and torus geometry, we investigate a long-standing question of the nature of the transition between the two regimes, and the possibility for the existence of a paired phase in the transition region. We find considerable evidence for a direct transition between the superfluid and the Fermi liquid phase, based in particular on the behavior of the ground state energy on the sphere (including appropriate finite-size corrections) as a function of d. At the critical distance d_C ≈ 11.6ℓ_B the topological number ("shift") of the ground state changes, suggesting that tuning the layer separation d in experiment likely leads to a direct transition between the superfluid and the Fermi liquid phase.

The collision efficiency of Brownian coagulation for monodisperse nanoparticles is considered. A new expression for friction coefficient of particle pair is proposed based on an assumption from a statistical point of view and the relative diffusion coefficient is thus be modified in order to take into account this influence as well as the effects of slip. The modified diffusion coefficient increases the collision efficiency to some extent as expected whether van der Waals interparticle potential is considered or not. A comparison with experimental measurements shows the accuracy of the results predicted by modified theory and the necessity of considering the decrease of friction coefficient due to the random motion of nanoparticles as well as the slip effects arising from the finite mean free path of gas molecules.

We present a model to understand the effect of temperature on the electrical resistance of individual semiconducting single wall carbon nanotubes (s-SWCNTs) of various diameters under various electric fields. The temperature dependence of the resistance of s-SWCNTs and metallic SWCNTs (m-SWCNTs) are compared. These results help us to understand the temperature dependence of the resistance of SWCNTs network. We experimentally examine the temperature dependence of the resistance of random networks of SWCNTs, prepared by dispersing CNTs in ethanol and drop-casting the solution on prefabricated metallic electrodes. Examining various samples with different electrode materials and spacings, we find that the dominant resistance in determination of the temperature dependence of resistance of the network is the resistance of individual tubes, rather than the tube–tube resistance or tube–metal contact resistance. It is also found that the tube–tube resistance depends on the electrode spacing and it is more important for larger electrode spacings. By applying high electric field to burn the all-metallic paths of the SWCNTs network, the temperature dependence of the resistance of s-SWCNTs is also examined. We also investigate the effect of acid treatment of CNTs on the temperature dependence of the resistance of SWCNTs and also multi-wall CNTs (MWCNTs) networks.

In living cells, molecular motors convert chemical energy into mechanical work. Its thermodynamic energy efficiency, i.e. the ratio of output mechanical work to input chemical energy, is usually high. However, using two-state models, we found the motion of molecular motors is loosely coupled to the chemical cycle. Only part of the input energy can be converted into mechanical work. Others are dissipated into environment during substeps without contributions to the unidirectional movement.

In the present work, we consider a quantum LC circuit under a constant magnetic field. In particular, we derive a new discretized form of the Schrödinger equation, which is equivalent to introducing a potential in the pseudo-flux representation. We discuss the physical assumptions leading to our results, and using a direct numerical approach we calculate the energy spectrum of the LC quantum circuit as a function of a constant external magnetic flux. The results are compared with the spectrum obtained using the Li–Chen potential [Y. Q. Li and B. Chen, Phys. Rev. B 53 (1996) 4027]. Our results indicate that the energy spectra from both models are numerically different, hence they may be clearly distinguished under appropriate experimental conditions.

We theoretically study Zitterbewegung behavior of electrons in graphene system when the external perpendicular magnetic field exists. The initial state is assumed as a wave packet shape which is the superposition of the positive and negative LLs. The evolution of the dipole moments and the excited electric fields are calculated for the localized and extended wave packets which exhibit different behavior. We further analyze their Fourier spectrum and study which factors affect the excited electric field as it can be directly detected in experiment. The results are analyzed and discussed.