Modern Physics Letters B

Elastic properties of iron-based superconductor Ba(Fe_1-xCo_x)₂As₂ with various Co concentrations x were reviewed. Among all elastic constants, C₆₆ shows remarkable softening associated with the structural transition from tetragonal to orthorhombic. The amount of anomaly in C₆₆ is 90% for the underdoped samples of x < 0.07 For the overdoped samples, the anomalies in C₆₆ gradually disappear with the increasing of Co concentration. The elastic compliance S₆₆ (= 1/C₆₆) shows a quantum critical behavior, which behaves just like the magnetic susceptibility of unconventional superconductors. There exists a clear correlation between the superconducting transition temperature and the amount of anomaly in S₆₆. It was suggested that the structural fluctuation, which is measured by S₆₆, plays an important role in the emergence of superconductivity. The elastic anomaly of Ba(Fe_1-xCo_x)₂As₂ is characterized by a strong electron–lattice coupling, which would be originated from the 3d orbitals of iron. This might be a universal phenomenon not only in iron-based superconductors but also d-electron based superconductors. The results on Ba(Fe_1-xCo_x)₂As₂ would reveal relevant roles of the structural fluctuations due to the orbitals, which should be taken into account for the understanding of a whole picture of the superconductivity in iron-based superconductors and related materials.

Intercalation of hydrogen phosphate (HPO₄) into Mg/Al-Layered Double Hydroxides (LDH) with DodecylBenzeneSulfonate (DBS) was investigated with regard to anion exchange, rehydration and a combination of delamination and anion exchange. HPO₄ could not be intercalated into the interlayer space of LDH with DBS when using either anion exchange or rehydration methods. However, HPO₄ was successfully intercalated into the Mg/Al-LDH using a combination of delamination and anion exchange methods.

Conventional local and semilocal density functionals cannot predict correct bandgap energy for semiconductors especially the indium compounds. By employing the density functional theory calculations with a hybrid functional, we studied the bandgap energy and structure properties of AlN and InN compounds as well as their ternary AlInN alloys. We showed that by adjusting the screening parameter in the hybrid functional, the bandgaps calculated are in good agreement with the experimental data. A 2.54 eV natural valence band offset between AlN and InN is found with the hybrid density functional study. Furthermore, we studied the bandgap and band bowing parameter for AlInN alloys by using the hybrid density functional. The bandgap and band bowing parameters obtained are consistent with experimental and other theoretical results. Our results revealed that, although the PBE functional underestimates the bandgap energy for binary compound and ternary AlInN alloy, their band bowing parameters are still reasonable and valid. Our results should be useful for experiment and optoelectronic device applications.

Studies have shown that numerous operating parameters affecting the proton exchange membrane fuel cell (PEMFC) performance, such as fuel cell operating temperature, operating pressure, anode/cathode humidification temperatures, anode/cathode stoichiometric flow ratios. In order to improve performance of fuel cell systems, it is advantageous to have an accurate model with which one can predict fuel cell behavior at different operating conditions. In this paper, a model using support vector regression (SVR) approach combining with particle swarm optimization (PSO) algorithm for its parameter optimization was developed to modeling and predicting the electrical power of proton exchange membrane fuel cell. The accuracy and reliability of the constructed support vector regression model are validated by leave-one-out cross-validation. Prediction results show that the maximum absolute percentage error does not exceed 5%, the mean absolute percentage error (MAPE) reached 0.68% and the correlation coefficient (R²) as high as 0.998. This implies that one can estimate an available combination of controller parameters by using support vector regression model to get suitable electrical power of proton exchange membrane fuel cell system.

This paper contains experimental results of the direct current breakdown voltage curves in nitrogen, hydrogen, oxygen and dry air discharges formed between parallel-plane electrodes placed at distances ranging from 2.5 μm to 100 μm. Experimental results presented here clearly show that electrical breakdown across micron size gap may occur at voltages below the minimum predicted by the conventional scaling law. The observed breakdown voltage reduction maybe attributed to the long path breakdown. Experimental results satisfactorily agree with the available simulation results and can be useful for microelectronic devices in localized diagnostics of ICs during their manufacture, in choosing appropriate conditions for electromechanical micro systems which may eventually lead to nano-machining in localized treatment of materials and assembly of nano-structures and in micro- and nano-biological processing and diagnostics.

The transport of electrons through TiO₂ anatase and rutile thin films synthesized via sol–gel route has been investigated using electronic and optical spectroscopic studies. Mesoporosity of the films is confirmed by poroellipsometry. A smaller electron effective mass in anatase can be accounted for larger effective Bohr radius of trap electrons observed in anatase than in rutile. Further, the smaller effective mass in anatase favors high mobility. A mott transition is observed in anatase with change in temperature but not in rutile. Luminescence of self-trapped excitons is observed in anatase thin films, that implies a strong lattice relaxation.

In this paper, we study the Aharonov–Bohm (A–B) effect and Anderson–Higgs mechanism in Ginzburg–Landau model of superconductors from the perspective of the decomposition of U(1) gauge potential. By the Helmholtz theorem, we derive exactly the expression of the transverse gauge potential A_⊥ in A–B experiment, which is gauge-invariant and physical. For the case of a bulk superconductor, we find that the gradient of the total phase field θ provides the longitudinal component A_‖, which reflects the Anderson–Higgs mechanism. For the case of a superconductor ring, the gradient of the longitudinal phase field θ₁ provides the longitudinal component A_‖, while the transverse phase field θ₂ produces new physical effects such as the flux quantization inside a superconducting ring.

We study the effects of spin-antisymmetric interactions on the stability of a Landau–Fermi liquid on the square lattice, using the generalized Pomeranchuk method for two-dimensional lattice systems. In particular, we analyze interactions that could induce instabilities of the so-called spin-split type, that is when spin-up and spin-down Fermi surfaces are displaced with respect to each other. The phase space is studied as a function of the strength of the interaction V, the electron chemical potential μ and an external magnetic field h. We find that such interactions produce in general an enhancement of the instability region of the Landau–Fermi liquid. More interestingly, in certain regions of the V–μ phase space, we find a reentrant behavior as a function of the magnetic field h, similar to that found in recent experiments, e.g. in URu₂Si₂ and Sr₃Ru₂O₇.