Photocarrier injection and the I-V characteristics of La0.8Sr0.2MnO3/SrTiO3:Nb heterojunctions

Oxide heterojunctions made of p-type L0.8Sr0.2MnO3 (LSMO) and niobium-doped n-type SrTiO3 (STO:Nb) have been fabricated by the pulsed laser deposition (PLD) technique and are characterized under UV light irradiation by measuring the current-voltage, photovoltaic properties and the junction capacitance. It is shown that the heterojunctions work as an efficient UV photodiode, in which photogenerated holes in the STO:Nb substrate are injected to the LSMO film. The maximum surface hole density Q/e and external quantum efficiency gamma are estimated to be 8.3x1012 cm-2 and 11 % at room temperature, respectively. They are improved significantly in a p-i-n junction of LSMO/STO/STO:Nb, where Q/e and gamma are 3.0x1013 cm-2 and 27 %, respectively

Efficient Migration of Large-memory VMs Using Private Virtual Memory

Recently, Infrastructure-as-a-Service clouds provide virtual machines (VMs) with a large amount of memory. Such large-memory VMs can be migrated to other hosts on host maintenance, but it is costly to always preserve hosts with sufficient free memory as the destination of VM migration. Using virtual memory in destination hosts is a possible solution, but the performance of VM migration largely degrades because traditional general-purpose virtual memory causes frequent paging during the migration. This paper proposes VMemDirect, which achieves efficient migration of large-memory VMs using private virtual memory. VMemDirect creates private swap space for each VM on fast NVMe SSDs. Then it transfers likely accessed memory data to physical memory and the other data to the private swap space directly. This direct memory transfer can completely avoid paging during VM migration. We have implemented VMemDirect in KVM and showed that the performance of VM migration and the migrated VM was improved dramatically.11th International Conference on Intelligent Networking and Collaborative Systems(INCoS 2019), September 5-7, 2019, Oita, Japa

Erratum to Three Papers on the beta-Pyrochlore Oxide Superconductors

The magnitude of magnetic fields given in the three papers that report on the superconductivity of the beta-pyrochlore oxides is corrected.Comment: 2 pages, 1 figure. to be published in J. Phys. Soc. Jp

Crystal structure of the pyrochlore oxide superconductor KOs2_2O6_6

We report the single-crystal X-ray analysis of the structure of the pyrochlore oxide superconductor KOs$_2$O$_6$. The structure was identified as the $\beta$-pyrochlore structure with space group $Fd\bar{3}m$ and lattice constant $a$ = 10.089(2)~\AA at 300 K: the K atom is located at the 8$b$ site, not at the 16$d$ site as in conventional pyrochlore oxides. We found an anomalously large atomic displacement parameter $U_\mathrm{iso}$ = 0.0735(8)~\AA$^2$ at 300 K for the K cation, which suggests that the K cation weakly bound to an oversized Os$_{12}$O$_{18}$ cage exhibits intensive rattling, as recently observed for clathrate compounds. The rattling of A cations is a common feature in the series of $\beta$-pyrochlore oxide superconductors AOs$_2$O$_6$ (A = Cs, Rb and K), and is greatest for the smallest K cation.Comment: 5 pages, 5 figures, to appear in J. Solid. State. Che

Magnetic-field-induced insulator-metal transition in W-doped VO2 at 500 T

Metal-insulator (MI) transitions in correlated electron systems have long been a central and controversial issue in material science. Vanadium dioxide (VO2) exhibits a first-order MI transition at 340 K. For more than half a century, it has been debated whether electronic correlation or the structural instability due to dimerised V ions is the more essential driving force behind this MI transition. Here, we show that an ultrahigh magnetic field of 500 T renders the insulator phase of tungsten (W)-doped VO2 metallic. The spin Zeeman effect on the d electrons of the V ions dissociates the dimers in the insulating phase, resulting in the delocalisation of electrons. Because the Mott-Hubbard gap essentially does not depend on the spin degree of freedom, the structural instability is likely to be the more essential driving force behind the MI transition.Comment: 9 pages, 9 figures (including the supplementary information