Using a magnetic Frederiks transition technique, we measure the temperature and concentration dependences of splay K1, twist K2, and bend K3 elastic constants for the lyotropic chromonic liquid crystal sunset yellow formed through noncovalent reversible aggregation of organic molecules in water. K1 and K3 are comparable to each other and are an order of magnitude higher than K2. At higher concentrations and lower temperatures, K1 and the ratios K1/K3 and K1/K2 increase, which is attributed to elongation of self-assembled lyotropic chromonic liquid crystal aggregates, a feature not found in conventional thermotropic and lyotropic liquid crystals formed by covalently bound units of a fixed length.

High-T c superconductors confined to two dimension exhibit novel physical phenomena, such as superconductor-insulator transition. In the Bi 2 Sr 2 CaCu 2 O 8 þ x (Bi2212) model system, despite extensive studies, the intrinsic superconducting properties at the thinness limit have been difficult to determine. Here, we report a method to fabricate high quality single-crystal Bi2212 films down to half-unit-cell thickness in the form of graphene/Bi2212 van der Waals heterostructure, in which sharp superconducting transitions are observed. The heterostructure also exhibits a nonlinear current-voltage characteristic due to the Dirac nature of the graphene band structure. More interestingly, although the critical temperature remains essentially the same with reduced thickness of Bi2212, the slope of the normal state T-linear resistivity varies by a factor of 4-5, and the sheet resistance increases by three orders of magnitude, indicating a surprising decoupling of the normal state resistance and superconductivity. The developed technique is versatile, applicable to investigate other two-dimensional (2D) superconducting materials.

The novel binuclear neutral nickel(II) complex [((2, 2 C 6 H 3 )NCH)C 6 H 3 ONi(PPh 3 )Ph] 2 (5), based on the 3,3′-bisalicylaldimine ligand, has been synthesized in high yield, and its structure has been confirmed by X-ray crystallography, elemental analysis, and 1 H NMR and 13 C NMR spectra. Used in the polymerization of ethylene as an active single-component catalyst, the complex exhibited a high catalytic activity of up to 4.55 × 10 5 g of PE/((mol of Ni) h), and polyethylenes with a weight-average molecular weight (M h w ) of up to 487.7 kg/ mol and relatively broad molecular weight distribution (M h w /M h n ) 2.8-3.8) were produced.

Resistivity, magnetization and microscopic 75 As nuclear magnetic resonance (NMR) measurements in the antiferromagnetically ordered state of the iron-based superconductor parent material CaFe2As2 exhibit anomalous features that are consistent with the collective freezing of domain walls. Below T * ≈ 10 K, the resistivity exhibits a peak and downturn, the bulk magnetization exhibits a sharp increase, and 75 As NMR measurements reveal the presence of slow fluctuations of the hyperfine field. These features in both the charge and spin response are strongly field dependent, are fully suppressed by H * ≈ 15 T, and suggest the presence of filamentary superconductivity nucleated at the antiphase domain walls in this material.

The 12442-type Fe-based superconductor is the only system that possesses two FeAs layers between neighboring insulating layers, which is worth the in-depth investigations. In this work, millimeter-sized single crystals of KCa2Fe4As4F2 were grown using a self-flux method. The chemical compositions and crystal structure were characterized carefully. Superconductivity with the critical transition T c = 33.5 K was confirmed by both the resistivity and magnetic susceptibility measurements. Moreover, the upper critical field H c2 was studied by the resistivity measurements under different magnetic fields, where an anisotropy of 8 was revealed near the superconducting transition. Importantly, a rather steep increase for the in-plane H c2 ab with cooling, dμ0 H c2 ab /dT| T c = −50.9 T/K, was observed. This value is several times higher than that of other systems of Fe-based superconductor and indicates an extremely high upper critical field. Possible origins for this behavior were discussed. The finding in our work is a great promotion both for understanding the physical properties and for the high-field applications of 12442-type Fe-based superconductors.

We show results on the vortex core dissipation through current-voltage measurements under applied pressure and magnetic field in the superconducting phase of CeCoIn5. We find that as soon as the system becomes superconducting, the vortex core resistivity increases sharply as the temperature and magnetic field decrease. The sharp increase in flux flow resistivity is due to quasiparticle scattering on critical antiferromagnetic fluctuations. The strength of magnetic fluctuations below the superconducting transition suggests that magnetism is complimentary to superconductivity and therefore must be considered in order to fully account for the low-temperature properties of CeCoIn5.PACS numbers: 71.10. Hf, 71.27.+a, 74.70.Tx Unconventional superconductivity in heavy-fermion material CeCoIn 5 is a complex state of matter involving magnetic and conduction degrees of freedom strongly coupled with each other [1][2][3][4][5]. Superconductivity emerges at a temperature T c ≃ 2.3 K with the order parameter most likely having d-wave symmetry [6][7][8][9]. The magnitude of the specific heat jump at the superconducting transition temperature [1, 6] indicates the mass enhancement of conduction electrons by several orders of magnitude. Normal state resistivity shows nonFermi liquid linear temperature dependence at low temperatures (< 20 K). Approximately at a temperature T * ≃ 45 K [1, 11], the heavy electrons begin to form due to the strong hybridization between the conduction electrons and localized Ce f -electrons. Despite the significant enhancement of the electronic mass, the magnetic susceptibility shows a Curie-Weiss behavior down to moderately low temperatures [1, 2,12,13] signaling the absence of the fully quenched magnetic moments.The pronounced non-Fermi liquid behavior in the normal state and unconventional superconductivity in CeCoIn 5 are thought to arise from the proximity of the system to a quantum critical point (QCP) separating paramagnetic and antiferromagnetic phases. Specifically, it was recently proposed that the transport and thermodynamic properties of CeCoIn 5 in the normal phase are controlled by an antiferromagnetic QCP at an inaccessible negative pressure [14]. The recovery of a Fermi liquid state at low temperatures and high magnetic fields was reported in Ref.[1], pointing to a field-induced QCP at the zero-temperature upper critical field H c2 (0). However, the location of the field-induced QCP exactly at H c2 (0) seems to be just a coincidence, since, with increasing pressure, this QCP moves inside the superconducting dome to lower fields. In fact, high sensitivity Hall effect measurements have revealed that the field induced QCP is located at H ≃ 4.1 T < H c2 (0), which suggest a possible antiferromagnetic ground state superseded by superconductivity [16]. In addition, low temperature thermal expansion data [17] on identification of the quantum critical line can be consistently interpreted within the same set of ideas as the Hall effect data. Thus, all these observations seem to favor the ant...

The strongly correlated electron fluids in high temperature cuprate superconductors demonstrate an anomalous linear temperature (T) dependent resistivity behavior, which persists to a wide temperature range without exhibiting saturation. As cooling down, those electron fluids lose the resistivity and condense into the superfluid. However, the origin of the linear-T resistivity behavior and its relationship to the strongly correlated superconductivity remain a mystery. Here we report a universal relation , which bridges the slope of the linear-T-dependent resistivity (dρ/dT) to the London penetration depth λ L at zero temperature among cuprate superconductor Bi2Sr2CaCu2O8+δ and heavy fermion superconductors CeCoIn5, where μ 0 is vacuum permeability, k B is the Boltzmann constant and ħ is the reduced Planck constant. We extend this scaling relation to different systems and found that it holds for other cuprate, pnictide and heavy fermion superconductors as well, regardless of the significant differences in the strength of electronic correlations, transport directions, and doping levels. Our analysis suggests that the scaling relation in strongly correlated superconductors could be described as a hydrodynamic diffusive transport, with the diffusion coefficient (D) approaching the quantum limit D ~ ħ/m*, where m* is the quasi-particle effective mass.

A series of novel vanadium(III) complexes bearing iminopyrrolide chelating ligands [2-(RN=CH)C4H3N]V(THF)2Cl2 (2a: R = cyclohexyl; 2b: R = Ph; 2c: R = 2,6-iPr2C6H3; 2d: R = p-CF3C6H4; 2e: R = C6F5) have been synthesized and characterized. Single-crystal X-ray diffraction revealed that complexes 2a, 2c and 2e adopt an octahedral geometry around the vanadium center. In the presence of Et2AlCl as a co-catalyst, these complexes displayed high catalytic activities up to 48.6 kg PE mmol(V)(-1) h(-1) bar(-1) for ethylene polymerization, and produced high molecular weight polymers. 2a-e/Et2AlCl catalytic systems were tolerant to elevated temperature (70 degrees C) and yielded unimodal polyethylenes, indicating the single site behaviour of these catalysts. By pre-treating with equimolar amounts of alkylaluminums, functional alpha-olefin 10-undecen-1-ol can be efficiently incorporated into polyethylene chains. 10-Undecen-1-ol incorporation can easily reach 15.8 mol% under the mild conditions. When compared with VCl3(THF)3 or rac-Et[Ind]2ZrCl2, these vanadium(III) complexes exhibited higher activities towards the copolymerization, and can incorporate more 10-undecen-1-ol into polymer chains under the similar conditions.