We report the observation of the intrinsic magnetic susceptibility of highly purified SWCNT samples prepared by a combination of acid treatment and density gradient ultracentrifugation (DGU). We observed that the diamagnetic susceptibility of SWCNTs
increases linearly with increasing nanotube diameter. We found that the magnetic susceptibility divided by the diameter is a universal function of the scaled temperature. Furthermore, the estimated magnetic susceptibilities of pure semiconducting and pure metallic SWCNT samples suggest that they respond differently to changes in carrier density, which is consistent with theory. These findings provide experimental verification of the theoretically predicted diameter, temperature, and metallicity dependence of the magnetic susceptibility.
We found a giant Seebeck effect in semiconducting single-wall carbon nanotube (SWCNT) films, which exhibited a performance comparable to that of commercial Bi2Te3 alloys. Carrier doping of semiconducting SWCNT films further improved the thermoelectri
c performance. These results were reproduced well by first-principles transport simulations based on a simple SWCNT junction model. These findings suggest strategies that pave the way for emerging printed, all-carbon, flexible thermoelectric devices.
$^{75}$As and $^{139}$La NMR results of LaFeAs(O$_{1-x}$F$_x$) ($x$=0, 0.025, and 0.04) were reported. Upon F-doping, the tetragonal-to-orthorhombic structural phase transition temperature $T_S$, antiferromagnetic transition temperature $T_N$ and int
ernal magnetic field $mu_0H_{rm int}$ are gradually reduced for $x<0.04$. However, at $x=0.04$, $T_N$ is abruptly suppressed to be 30 K along with a tiny $mu_0H_{rm int}$, which is distinct from the continuous disappearance of the ordered phases in the Ba122 systems of Ba(Fe,Co)$_2$As$_2$ and BaFe$_2$(As,P)$_2$. The anisotropy of the spin-lattice relaxation rate $T_1^{-1}$, $(T_1)^{-1}_{Hparallel ab}/(T_1)^{-1}_{Hparallel c}$, in the paramagnetic phase of $x = 0$ and 0.025 is constant ($sim 1.5$), but increases abruptly below $T_S$ due to the enhancement of $(T_1)^{-1}_{Hparallel ab}$ by the slowing down of magnetic fluctuations. This indicates that the tetragonal-to-orthorhombic structural distortion enhances the anisotropy in the spin space via magnetoelastic coupling and/or spin-orbit interaction.
^{31}P and ^{75}As NMR measurements were performed in superconducting BaFe_2(As_{0.67}P_{0.33})_2 with T_c = 30 K. The nuclear-spin-lattice relaxation rate T_1^{-1} and the Knight shift in the normal state indicate the development of antiferromagneti
c fluctuations, and T_1^{-1} in the superconducting (SC) state decreases without a coherence peak just below T_c, as observed in (Ba_{1-x}K_{x})Fe_2As_2. In contrast to other iron arsenide superconductors, the T_1^{-1} propto T behavior is observed below 4K, indicating the presence of a residual density of states at zero energy. Our results suggest that strikingly different SC gaps appear in BaFe_2(As_{1-x}P_{x})_2 despite a comparable T_c value, an analogous phase diagram, and similar Fermi surfaces to (Ba_{1-x}K_{x})Fe_2As_2.
We report experimental results of nuclear magnetic resonance (NMR) at the La site and nuclear quadrupole resonance (NQR) at the Sb site in the filled skutterudite LaOs$_4$Sb$_{12}$. We found that the nuclear spin-lattice relaxation rate divided by te
mperature $1/T_1T$ at the La site exhibits a different temperature dependence from that at the Sb site. Although $1/T_1T$ at the Sb site is explained by the Korringa mechanism, $1/T_1T$ at the La site exhibits a broad maximum around 50 K, showing the presence of an additional contribution at the La site. The additional low-lying excitations observed at the La site can be understood with the relaxation from anharmonic phonons due to the rattling motion of the La atoms.
