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We report on the upper critical field B c2 of a superconducting LiFeAs single crystal with T c $ 16 K, determined from magnetic torque measurements in dc-magnetic fields up to 35 T and at temperatures down to 0.3 K. B c2 at 0.3 K is obtained to be 26.4 and 15.5 T for the applied field B a k ab and B a k c, respectively. The anisotropy parameter À ¼ B ab c2 =B c c2 is $3 at T c and decreases to 1.7 as T ! 0, showing rather isotropic superconductivity. While B c2 is orbitally-limited for B a k c, the spin-paramagnetic effect is evident in the temperature dependence of B c2 for B a k ab. KEYWORDS: iron-based superconductor, LiFeAs, upper critical field, anisotropySince the discovery of superconductivity in LaFeAs(O,F) with T c ¼ 26 K, 1) a variety of related compounds containing FeAs-layers has been found to exhibit superconductivity.2)The parent compounds RFeAsO (R = rare earth, ''1111'' system) and AFe 2 As 2 (A = alkaline earth or Eu, ''122'' system) with the ZrCuSiAs-and ThCr 2 Si 2 -type structures, respectively, undergo antiferromagnetic and structural transitions. The transitions can be suppressed by several kinds of doping effects 1,[3][4][5][6] or application of pressure, [7][8][9] and T c reaches $56 K in some compounds. [10][11][12] The magnetic long range order usually competes with superconductivity, but the fluctuation likely plays a crucial role in the pairing mechanism of the Fe-based high-T c systems. It is also of interest that, around the optimal condition where T c shows its maximum, deviation from conventional Fermi-liquid behavior has been observed such as $ T , 13,14) anomalous Hall angle, 13) an enhancement of effective masses, 15) etc. These superconducting and normal-state features bear resemblance with those widely reported for strongly-correlated electron systems including cuprates and heavy fermion compounds.The title compound LiFeAs, categorized as the ''111'' system with the CeFeSi-type structure, has distinctive characteristics: (i) the stoichiometric superconductivity with T c as high as $17 K, 16) (ii) no experimental evidence for the magnetic/structural transitions, 17,18) and (iii) single crystals with high quality (residual resistivity ratio up to 50). 19,20) Therefore, LiFeAs provides a unique opportunity to probe the intrinsic properties of Fe-based high-T c superconductivity.Up to now, there are few reports on systematic measurements of the upper critical field B c2 of Fe-based superconductors to address the issue of the pair-breaking mechanism. This is mainly due to the fact that high-T c superconductors including Fe-based systems generally have extremely high B c2 . In many cases, accordingly, the lowtemperature behavior is extrapolated from the high temperature data around T c , which may lead to misleading conclusions. A precise determination of B c2 over the whole temperature range could provide important clues to the pairbreaking mechanism of high-T c superconductivity.Here, we present the first report on the whole temperature dependence of B c2 and its angular variatio...

Single-walled carbon nanotubes were dispersed in an aqueous medium using surfactants and filtered to make entangled networks, called buckypaper (BP), and the Raman spectra of BP samples revealed the degree of entanglement and residual surfactant content. The temperature dependence of the G-band peak shift in the BP was found to depend on the reduction in residual surfactant and nanotube oxidation. The electrical conductivity was improved after removing the surfactant and increasing the nanotube alignment, although the temperature dependence of electrical resistivity still followed a variable range hopping conduction behavior. The mechanical properties were affected by the degree of entanglement, alignment, and residual surfactant content, and tensile properties were found to improve with the reduction in surfactant and enhancement of alignment.