Possible indicators for low dimensional superconductivity in the quasi-1D carbide Sc3CoC4

The transition metal carbide Sc3CoC4 consists of a quasi-one-dimensional (1D) structure with [CoC4]_{\inft} polyanionic chains embedded in a scandium matrix. At ambient temperatures Sc3CoC4 displays metallic behavior. At lower temperatures, however, charge density wave formation has been observed around 143K which is followed by a structural phase transition at 72K. Below T^onset_c = 4.5K the polycrystalline sample becomes superconductive. From Hc1(0) and Hc2(0) values we could estimate the London penetration depth ({\lambda}_L ~= 9750 Angstroem) and the Ginsburg-Landau (GL) coherence length ({\xi}_GL ~= 187 Angstroem). The resulting GL-parameter ({\kappa} ~= 52) classifies Sc3CoC4 as a type II superconductor. Here we compare the puzzling superconducting features of Sc3CoC4, such as the unusual temperature dependence i) of the specific heat anomaly and ii) of the upper critical field H_c2(T) at T_c, and iii) the magnetic hysteresis curve, with various related low dimensional superconductors: e.g., the quasi-1D superconductor (SN)_x or the 2D transition-metal dichalcogenides. Our results identify Sc3CoC4 as a new candidate for a quasi-1D superconductor.Comment: 4 pages, 5 figure

Unusual Single-Ion Non-Fermi Liquid Behavior in Ce_(1-x)La_xNi_9Ge_4

We report on specific heat, magnetic susceptibility and resistivity measurements on the compound Ce_(1-x)La_xNi_9Ge_4 for various concentrations ranging from the stoichiometric system with x=0 to the dilute limit x=0.95. Our data reveal single-ion scaling with the Ce-concentration and the largest ever recorded value of the electronic specific heat c/T approximately 5.5 J K^(-2)mol^(-1) at T=0.08K for the stoichiometric compound x=0 without any trace of magnetic order. While in the doped samples c/T increases logarithmically below 3K down to 50mK, their magnetic susceptibility behaves Fermi liquid like below 1K. These properties make the compound Ce_(1-x)La_xNi_9Ge_4 a unique system on the borderline between Fermi liquid and non-Fermi liquid physics.Comment: 4 pages, 5 figures; v2 contains additional resisitivity measurements; final version to appear in Phys. Rev. Let

14-19 education reform under New Labour : an exploration of how politics and the economy combine with educational goals to affect policy

The area of 14-19 education and training was a significant priority for the Labour Government of Tony Blair and New Labour. Reforms such as the 14-19 White Paper (Feb 2005) were seen as key to this government’s ‘third term’ agenda. This research has at its heart the desire to identify the true drivers for 14-19 education and training reform, and critically analyse the results against alternative ‘aims’ of education. Much of current policy for this phase of education mentions the economic imperative of providing young people with the skills which both they and businesses need to compete in the global economy. This research intends to question the fact that economic goals appear to be inexorably entwined with this area of education, and analyse if this is an appropriate philosophy on which to base reform of the 14-19 phase. To achieve this, document analysis was used to identify the drivers for education reform contained within five policy documents in an attempt to understand the goals of New Labour’s 14- 19 education and training reform policy between May 1997 and February 2005. The conclusions which came from this analysis point to a consistency in the 14-19 reform programme of New Labour around the theme of the economy, with much of the content of the reforms focusing on adapting the phase in order to promote economic objectives. It is argued that by accepting economic objectives as a basis for educational reform, New Labour confused the influence of the economy for an educational aim

Poly-MTO, {(CH_3)_{0.92} Re O_3}_\infty, a Conducting Two-Dimensional Organometallic Oxide

Polymeric methyltrioxorhenium, {(CH_{3})_{0.92}ReO_{3}}_{\infty} (poly-MTO), is the first member of a new class of organometallic hybrids which adopts the structural pattern and physical properties of classical perovskites in two dimensions (2D). We demonstrate how the electronic structure of poly-MTO can be tailored by intercalation of organic donor molecules, such as tetrathiafulvalene (TTF) or bis-(ethylendithio)-tetrathiafulvalene (BEDT-TTF), and by the inorganic acceptor SbF$_3$. Integration of donor molecules leads to a more insulating behavior of poly-MTO, whereas SbF$_3$ insertion does not cause any significant change in the resistivity. The resistivity data of pure poly-MTO is remarkably well described by a two-dimensional electron system. Below 38 K an unusual resistivity behavior, similar to that found in doped cuprates, is observed: The resistivity initially increases approximately as $\rho \sim$ ln$(1/T$) before it changes into a $\sqrt{T}$ dependence below 2 K. As an explanation we suggest a crossover from purely two-dimensional charge-carrier diffusion within the \{ReO$_2$\}$_{\infty}$ planes at high temperatures to three-dimensional diffusion at low temperatures in a disorder-enhanced electron-electron interaction scenario (Altshuler-Aronov correction). Furthermore, a linear positive magnetoresistance was found in the insulating regime, which is caused by spatial localization of itinerant electrons at some of the Re atoms, which formally adopt a $5d^1$ electronic configuration. X-ray diffraction, IR- and ESR-studies, temperature dependent magnetization and specific heat measurements in various magnetic fields suggest that the electronic structure of poly-MTO can safely be approximated by a purely 2D conductor.Comment: 15 pages, 16 figures, 2 table

Antiferroelectricity Driven by Cluster Jahn-Teller Effect in the Lacunar Spinel GaNb4_4S8_8

We report the observation of an antiferroelectric (AFE) transition in cubic GaNb$_4$S$_8$ driven by an unconventional microscopic mechanism, the Jahn-Teller effect of Nb$_4$S$_4$ clusters. At T$_\mathrm{JT}$ = 31 K, we observed a strong drop of the dielectric constant, a clear signature of frst-order AFE transitions. The frst-order character is also verifed by specifc heat and magnetic susceptibility measurements. Below T$_\mathrm{JT}$, the combination of single-crystal and high-resolution powder X-ray dffraction revealed a violation of the previously reported space-group $P\bar{4}21m$, in favor of a lower-symmetric distortionpattern of the Nb$_4$S$_4$ clusters. In addition, weak ferroelectric polarization was found below T$_\mathrm{JT}$, likely emerging due to the presence of polar domain walls within the otherwise AFE bulk structure

Pressure-induced excitations in the out-of-plane optical response of the nodal-line semimetal ZrSiS

The anisotropic optical response of the layered, nodal-line semimetal ZrSiS at ambient and high pressure is investigated by frequency-dependent reflectivity measurements for the polarization along and perpendicular to the layers. The highly anisotropic optical conductivity is in very good agreement with results from density functional theory calculations and confirms the anisotropic character of ZrSiS. Whereas the in-plane optical conductivity shows only modest pressure-induced changes, we found strong effects on the out-of-plane optical conductivity spectrum of ZrSiS, with the appearance of two prominent excitations. These pronounced pressure-induced effects can neither be attributed to a structural phase transition according to our single-crystal x-ray diffraction measurements, nor can they be explained by electronic correlation and electron-hole pairing effects, as revealed by theoretical calculations. Our findings are discussed in the context of the recently proposed excitonic insulator phase in ZrSiS.Comment: 6 pages, 3 figures, accepted for publication in Phys. Rev. Let

Pressure-Induced Excitations in the Out-of-Plane Optical Response of the Nodal-Line Semimetal ZrSiS

The anisotropic optical response of the layered, nodal-line semimetal ZrSiS at ambient and high pressure is investigated by frequency-dependent reflectivity measurements for the polarization along and perpendicular to the layers. The highly anisotropic optical conductivity is in very good agreement with results from density-functional theory calculations and confirms the anisotropic character of ZrSiS. Whereas the in-plane optical conductivity shows only modest pressure-induced changes, we found strong effects on the out-of-plane optical conductivity spectrum of ZrSiS, with the appearance of two prominent excitations. These pronounced pressure-induced effects can neither be attributed to a structural phase transition according to our single-crystal x-ray diffraction measurements, nor can they be explained by electronic correlation and electron-hole pairing effects, as revealed by theoretical calculations. Our findings are discussed in the context of the recently proposed excitonic insulator phase in ZrSiS

Elucidation of the bonding in Mn(η²-SiH) complexes by charge density analysis and T₁ NMR measurements: asymmetric oxidative addition and anomeric effects at silicon

The bonding in Mn(η2-SiH) complexes is interpreted in terms of an asymmetric oxidative addition whose extent is controlled by the substitution pattern at the hypercoordinate silicon centre, and especially by the ligand trans to the η2-coordinating SiH moiety