We have developed a technique to fabricate quantum dot (QD) solar cells with direct doping of Si into InAs QDs in GaNAs strain-compensating matrix in order to control the quasi-Fermi level of intermediate QD states. The Si atoms were evenly incorporated into QDs during the assembling stage of growth such that a uniform array of partially filled QDs has been obtained. Nonradiative recombination losses were also reduced by Si doping and a photocurrent increase due to two-step photon absorption was clearly measured at room temperature detected under filtered air-mass 1.5 solar spectrum.

A combination of density functional theory calculations, many-body model considerations, magnetization and electron spin resonance measurements shows that the multiferroic FeTe2O5Br should be described as a system of alternating antiferromagnetic S = 5/2 chains with strong Fe-O-Te-OFe bridges weakly coupled by two-dimensional frustrated interactions, rather than the previously reported tetramer models. The peculiar temperature dependence of the incommensurate magnetic vector can be explained in terms of interchain exchange striction being responsible for the emergent net electric polarization.

BiFeO 3 is one of most celebrated multiferroic compounds with both ferroelectric and magnetic transition temperatures both above room temperature. 1) Furthermore, it exhibits one of highest electric polarization values, including archetypal ferroelectric materials such as PbTiO 3 , with a reported value of polarization, 100 C/cm 2 . 2) As such, there have been enormous studies that went into basic understanding of its physical properties. 3) However, one of the most notable properties from the viewpoint of magnetism is that it undergoes an antiferromagnetic transition at 650 K with an extremely large period of 630A. 4) The nature of this unusual incommensurate antiferromagnetic structure is believed to lie in a microscopic competition between exchange interactions of neighboring Fe moments and DzyaloshinskiiMoriya (DM) interaction.According to recent bulk studies, both magnetization and magnetoelectric current measurements exhibit a drastic metamagnetic transition around 20 T, above which the magnetization shows a pronounced increase while the magnetoelectric current displays a drop of about 40 nC/cm 2 of electric polarization. 5-7) Thus the incommensurate magnetic order produces additional electric polarization in the magnetically ordered phase, a very evidence of magnetoelectric coupling. This transition is conjectured to be due to a metamagnetic transition, above which the magnetic structure becomes collinear. However, we ought to stress that this conjecture has never been tested experimentally by neutron diffraction studies, which would provide the ultimate answer regarding the question of the magnetic structure.Therefore, the nature of the metamagnetic transition is expected to hold some essential information to the microscopic interaction of this interesting multiferroic material. However, the fact that it occurs at as high as 20 T has hampered experimental efforts. Here we report on our recent works, wherein we were able to measure the magnetic peaks above the reported metamagnetic transition by taking advantage of a state-of-the-art miniature home-made set-up as shown in the insert of Fig. 1 and a high quality single crystal with a total mass of 94 mg grown by a flux method. Our experiments were carried out at the NOBORU beam line of MLF, J-PARC.In Fig. 1(a), we plotted the data (line) of nuclear (006) Bragg peaks taken at zero field without magnetic pulses while the symbols represent the data taken at zero field during the pulsed magnetic field experiments. All our data were taken at 77 K with enough intervals between the magnetic pulses, which allowed sufficient cooling of the setup we used after each repetition of magnetic pulses. That there is no visible change in the peak position as well as width of the nuclear peaks ensures that there has been no change to the experimental setting during the pulsed magnetic field experiments. Figure 1(b) shows the data for the magnetic (003) Bragg peak taken at zero and 22 T. The zero field data were accumulated for 15 min, whereas we had to spend as much as roughl...

When an electronic system has strong correlations and a large spin-orbit interaction, it often exhibits a plethora of mutually competing quantum phases. How a particular quantum ground state is selected out of several possibilities is a very interesting question. However, equally fascinating is how such a quantum entangled state breaks up due to perturbation. This important question has relevance in very diverse fields of science from strongly correlated electron physics to quantum information. Here we report that a quantum entangled dimerized state or valence bond crystal (VBC) phase of Li2RuO3 shows nontrivial doping dependence as we perturb the Ru honeycomb lattice by replacing Ru with Li. Through extensive experimental studies, we demonstrate that the VBC phase melts into a valence bond liquid phase of the RVB (resonating valence bond) type. This system offers an interesting playground where one can test and refine our current understanding of the quantum competing phases in a single compound.

We have developed highly crystallized n-type microcrystalline Si layers as window layers for rear emitter Si heterojunction solar cells. We introduce a seed layer between an n-type microcrystalline Si layer and an intrinsic amorphous Si layer to improve the crystallinity of the n-type microcrystalline Si layer. By using this stacked layer instead of an n-type amorphous Si layer, the contact resistance between the n-type thin layer and In2O3:H is reduced without Al-doped ZnO. As a result, we obtain a high short-circuit current and a high fill factor simultaneously, and achieve a solar cell efficiency of 23.43%.