Radiation transport simulations were used to analyse neutron imaging with the current-biased kinetic inductance detector (CB-KID). The PHITS Monte Carlo code was applied for simulating neutron, $^{4}$He, $^{7}$Li, photon and electron transport, $^{10
}$B(n,$alpha$)$^{7}$Li reactions, and energy deposition by particles within CB-KID. Slight blurring in simulated CB-KID images originated $^{4}$He and $^{7}$Li ions spreading out in random directions from the $^{10}$B conversion layer in the detector prior to causing signals in the $X$ and $Y$ superconducting Nb nanowire meander lines. 478 keV prompt gamma rays emitted by $^{7}$Li nuclei from neutron-$^{10}$B reactions had negligible contribution to the simulated CB-KID images. Simulated neutron images of $^{10}$B dot arrays indicate that sub 10 $mu$m resolution imaging should be feasible with the current CB-KID design. The effect of the geometrical structure of CB-KID on the intrinsic detection efficiency was calculated from the simulations. An analytical equation was then developed to approximate this contribution to the detection efficiency. Detection efficiencies calculated in this study are upper bounds for the reality as the effects of detector temperature, the bias current, signal processing and dead-time losses were not taken into account. The modelling strategies employed in this study could be used to evaluate modifications to the CB-KID design prior to actual fabrication and testing, conveying a time and cost saving.
We developed an interface program between a program suite for an automated search of chemical reaction pathways, GRRM, and a program package of semiempirical methods, MOPAC. A two-step structural search is proposed as an application of this interface
program. A screening test is first performed by semiempirical calculations. Subsequently, a reoptimization procedure is done by ab initio or density functional calculations. We apply this approach to ion adsorption on cellulose. The computational efficiency is also shown for a GRRM search. The interface program is suitable for the structural search of large molecular systems for which semiempirical methods are applicable.
We theoretically investigate the applied magnetic field-angle dependence of the flux-flow resistivity $rho_{rm f}(alpha_{rm M})$ for an uniaxially anisotropic Fermi surface. $rho_{rm f}$ is related to the quasiparticle scattering rate $varGamma$ insi
de a vortex core, which reflects the sign change in the superconducting pair potential. We find that $rho_{rm f}(alpha_{rm M})$ is sensitive to the sign-change in the pair potential and has its maximum when the magnetic field is parallel to the gap-node direction. We propose the measurement of the field-angle dependent oscillation of $rho_{rm f}(alpha_{rm M})$ as a phase-sensitive field-angle resolved experiment.
We numerically investigate the effect of in-plane anisotropic Fermi surface (FS) on the flux-flow resistivity $rho_{rm f}$ under rotating magnetic field on the basis of the quasiclassical Greens function method. We demonstrate that one can detect the
phase in pairing potential of Cooper pair through the field-angular dependence of $rho_{rm f}$ even if the FS has in-plane anisotropy. In addition, we point out one can detect the gap-node directions irrespective of the FS anisotropy by measuring $rho_{rm f}$ under rotating field.
We theoretically study the dependence of the quasiparticle (QP) scattering rate $varGamma$ on the uniaxial anisotropy of a Fermi surface with changing the magnetic field angle $alpha_{rm M}$. We consider the QP scattering due to the non-magnetic impu
rities inside a single vortex core. The field-angle dependence of the quasiparticle scattering rate $varGamma(alpha_{rm M})$ is sensitive to the sign-change of the pair potential. We show that with increasing the two dimensionality of the system, $varGamma(alpha_{rm M})$ reflects more clearly whether there is the sign-change in the pair potential.
We theoretically investigate the magnetic-field-angle dependence of the flux-flow resistivity $rho_{rm f}$ in unconventional superconductors. Two contributions to $rho_{rm f}$ are considered: one is the quasiparticle (QP) relaxation time $tau(bm{k}_{
rm F})$ and the other is $omega_0(bm{k}_{rm F})$, which is a counterpart to the interlevel spacing of the QP bound states in the quasiclassical approach. Here, $bm{k}_{rm F}$ denotes the position on a Fermi surface. Numerical calculations are conducted for a line-node s-wave and a d-wave pair potential with the same anisotropy of their amplitudes, but with a sign change only for a d-wave one. We show that the field-angle dependence of $rho_{rm f}$ differs prominently between s-wave and d-wave pairs, reflecting the phase of the pair potentials. We also discuss the case where $tau$ is constant and compare it with the more general case where $tau$ depends on $bm{k}_{rm F}$.
We theoretically investigate the quasiparticle scattering rate $varGamma$ inside a vortex core in the existence of non-magnetic impurities distributed randomly in a superconductor. We show that the dependence of $varGamma$ on the magnetic field direc
tion is sensitive to the sign of the pair potential. The behavior of $varGamma$ is quite different between an s-wave and a d-wave pair potential, where these are assumed to have the same amplitude anisotropy, but a sign change only for the d-wave one. It is suggested that measurements of the microwave surface impedance with changing applied-field directions would be used for the phase-sensitive identification of pairing symmetry.
We study hydrogen doping effects in an iron-based superconductor LaFeAsO_(1-y) by using the first-principles calculation and explore the reason why the superconducting transition temperature is remarkably enhanced by the hydrogen doping. The present
calculations reveal that a hydrogen cation stably locating close to an iron atom attracts a negatively-charged FeAs layer and results in structural distortion favorable for further high temperature transition. In fact, the lattice constant a averaged over the employed supercell shrinks and then the averaged As-Fe-As angle approaches 109.74 degrees with increasing the hydrogen doping amount. Moreover, the calculations clarify electron doping effects of the solute hydrogen and resultant Fermi-level shift. These insights are useful for design of high transition-temperature iron-based superconductors.
We calculate electronic structures of a high-Tc iron-based superconductor Sr2VFeAsO3 by LDA+U method. We assume a checker-board antiferromagnetic order on blocking layers including vanadium and strong correlation in d-orbits of vanadium through the H
ubbard U. While the standard LDA brings about metallic blocking layers and complicated Fermi surface as in the previous literatures, our calculation changes the blocking layer into insulating one and the Fermi surface becomes quite similar to those of other iron-based superconductors. Moreover, the appearance of the insulating blocking layers predicts high anisotropy on quasi-particle transports and new types of intrinsic Josephson effects.
Performing the first-principles calculations, we investigate the anisotropy in the superconducting state of iron-based superconductors to gain an insight into their potential applications. The anisotropy ratio $gamma_lambda$ of the c-axis penetration
depth to the ab-plane one is relatively small in BaFe2As2 and LiFeAs, i.e., $gamma_lambda sim 3$, indicating that the transport applications are promising in these superconductors. On the other hand, in those having perovskite type blocking layers such as Sr2ScFePO3 we find a very large value, $gamma_lambda sim 200$, comparable to that in strongly anisotropic high-Tc cuprate Bi2Sr2CaCu2O{8-delta}. Thus, the intrinsic Josephson junction stacks are expected to be formed along the c-axis, and novel Josephson effects due to the multi-gap nature are also suggested in these superconductors.
