Identifying Potential Problems and Risks in GQM+Strategies Models Using Metamodel and Design Principles

Although GQM+Strategies®1 assures that business goals and strategies are aligned throughout an organization and at each organizational unit based on the rationales to achieve the overall business goals, whether the GQM+Strategies grid is created correctly cannot be determined because the current definition of GQM+Strategies allows multiple perspectives when aligning goals with strategies. Here we define modeling rules for GQM+Strategies with a metamodel specified with a UML class diagram. Additionally, we create design principles that consist of relationship constraints between GQM+Strategies elements, which configure GQM+Strategies grids. We demonstrate that the GQM+Strategies grids can be automatically determined with the help of design principles described in OCL. In fact, an experiment is implemented using these approaches in order to show that this method helps identify and improve potential problems and risks. The results confirm that our approaches help create a consistent GQM+Strategies grid

Longitudinal spin fluctuations driving field-reinforced superconductivity in UTe2_2

Our measurements of $^{125}$Te NMR relaxations reveal an enhancement of electronic spin fluctuations above $\mu_0H^*\sim15$ T, leading to their divergence in the vicinity of the metamagnetic transition at $\mu_0H_m\approx35$ T, below which field-reinforced superconductivity appears when a magnetic field ($H$) is applied along the crystallographic $b$ axis. The NMR data evidence that these fluctuations are dominantly longitudinal, providing a key to understanding the peculiar superconducting phase diagram in $H\|b$, where such fluctuations enhance the pairing interactions.Comment: 7 pages, 4 figure

First Observation of de Haas-van Alphen Effect and Fermi Surfaces in Unconventional Superconductor UTe2

We report the first observation of the de Haas-van Alphen (dHvA) effect in the novel spin-triplet superconductor UTe2 using high quality single crystals with the high residual resistivity ratio (RRR) over 200. The dHvA frequencies, named alpha and beta, are detected for the field directions between c and a-axes. The frequency of branch beta increases rapidly with the field angle tilted from c to a-axis, while branch alpha splits, owing to the maximal and minimal cross-sectional areas from the same Fermi surface. Both dHvA branches, alpha and beta reveal two kinds of cylindrical Fermi surfaces with a strong corrugation at least for branch alpha. The angular dependence of the dHvA frequencies is in very good agreement with that calculated by the generalized gradient approximation (GGA) method taking into account the on-site Coulomb repulsion of U = 2 eV, indicating the main Fermi surfaces are experimentally detected. The detected cyclotron effective masses are large in the range from 32 to 57 m0 . They are approximately 10-20 times lager than the corresponding band masses, consistent with the mass enhancement obtained from the Sommerfeld coefficient and the calculated density of states at the Fermi level. The local density approximation (LDA) calculations of ThTe2 assuming U4+ with the 5f^2 localized model are in less agreement with our experimental results, in spite of the prediction for two cylindrical Fermi surfaces, suggesting a mixed valence states of U4+ and U3+ in UTe2.Comment: 7 pages, 8 figures, submitted to J. Phys. Soc. Jp

Low-temperature Magnetic Fluctuations Investigated by 125^{125}Te-NMR on the Uranium-based Superconductor UTe2_{2}

To investigate the static and dynamic magnetic properties on the uranium-based superconductor UTe$_{2}$, we measured the NMR Knight shift $K$ and the nuclear spin-lattice relaxation rate $1/T_{1}$ in $H \parallel a$ by $^{125}$Te-NMR on a $^{125}$Te-enriched single-crystal sample. $1/T_1T$ in $H \parallel a$ is much smaller than $1/T_1T$ in $H \parallel b$ and $c$, and magnetic fluctuations along each axis are derived from the $1/T_1T$ measured in $H$ parallel to all three crystalline axes. The magnetic fluctuations are almost identical at two Te sites and isotropic at high temperatures, but become anisotropic below 40 K, where heavy-fermion state is formed. The character of magnetic fluctuations in UTe$_2$ is discussed with the comparison to its static susceptibility and the results on other U-based superconductors. It is considered that the magnetic fluctuations probed with the NMR measurements are determined by the magnetic properties inside the two-leg ladder formed by U atoms, which are dominated by the $q_a$ = 0 ferromagnetic fluctuations.Comment: 10 pages, 6 figures

125Te-NMR Study on a Single Crystal of Heavy Fermion Superconductor UTe2

We report 125Te-NMR studies on a newly discovered heavy fermion superconductor UTe2. Using a single crystal, we have measured the 125Te-NMR Knight shift K and spin-lattice relaxation rate 1/T1 for fields along the three orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for both the static (K) and dynamical susceptibilities (1/T1) in the paramagnetic state above about 20 K. Around 20 K, however, we have observed a sudden loss of NMR spin-echo signal due to sudden enhancement of the NMR spin-spin relaxation rate 1/T2, when the field is applied along the easy axis of magnetization (=a axis). This behavior suggests the development of longitudinal magnetic fluctuations along the a axis at very low frequencies below 20 K.Comment: 5 pages, 7 figures, accepted for publication in J. Phys. Soc. Jp

Large Reduction in the aa-axis Knight Shift on UTe2_2 with TcT_{\rm c} = 2.1 K

Spin susceptibility in the superconducting (SC) state was measured in the higher-quality sample of uranium-based superconductor UTe$_2$ by using Knight-shift measurements for a magnetic field $H$ along all three crystalline axes. In the higher-quality sample, the SC transition temperature $T_{\rm c}$ is about 2.1 K, and the residual electronic term in the specific heat is almost zero. The NMR linewidth becomes narrower and is almost half of that in the previous sample with $T_{\rm c} \sim 1.6$ K when $H \parallel a$ and $c$. Although the Knight-shift behavior was not so different from the previous results for $H \parallel b$, and $c$, a large reduction in Knight shift along the $a$ axis was observed, in contrast with the previous $a$-axis Knight shift result. We discuss the origin of the difference between the previous and present results, and the possible SC state derived from the present results.Comment: 7 pages, 6 figures, including supplemental material