The noncentrosymmetric superconductor (NCS) AuBe is investigated using a variety of thermodynamic and resistive probes in magnetic fields of up to 65 T and temperatures down to 0.3 K. Despite the polycrystalline nature of the samples, the observation of a complex series of de Haasvan Alphen (dHvA) oscillations has allowed the calculated bandstructure for AuBe to be validated. This permits a variety of BCS parameters describing the superconductivity to be estimated, despite the complexity of the measured Fermi surface. In addition, AuBe displays a nonstandard field dependence of the phase of dHvA oscillations associated with a band thought to host unconventional fermions in this chiral lattice. This result demonstrates the power of the dHvA effect to establish the properties of a single band despite the presence of other electronic bands with a larger density of states, even in polycrystalline samples. In common with several other NCSs, we find that the resistive upper critical field exceeds that measured by heat capacity and magnetization by a considerable factor. We suggest that our data exclude mechanisms for such an effect associated with disorder, implying that topologically protected superconducting surface states may be involved. arXiv:1812.02830v2 [cond-mat.supr-con]

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The molecular coordination complex NiI2(3,5-lut)4 [where (3,5-lut) = (3,5-lutidine) = (C7H9N)] has been synthesized and characterized by several techniques including synchrotron X-ray diffraction, ESR, SQUID magnetometry, pulsed-field magnetization, inelastic neutron scattering and muon spin relaxation. Templated by the configuration of 3,5-lut ligands the molecules pack in-registry with the Ni-I· · · I-Ni chains aligned along the c-axis. This arrangement leads to through-space I· · · I magnetic coupling which is directly measured for the first time in this work. The net result is a near-ideal realization of the S = 1 Haldane chain with J = 17.5 K and energy gaps of ∆ = 5.3 K ∆ ⊥ = 7.7 K, split by the easy-axis single-ion anisotropy D = −1.2 K. The ratio D/J = −0.07 affords one of the most isotropic Haldane systems yet discovered, while the ratio ∆0/J = 0.40(1) (where ∆0 is the average gap size) is close to its ideal theoretical value, suggesting a very high degree of magnetic isolation of the spin chains in this material. The Haldane gap is closed by orientation-dependent critical fields µ0H c = 5.3 T and µ0H ⊥ c = 4.3 T, which are readily accessible experimentally and permit investigations across the entirety of the Haldane phase, with the fully polarized state occurring at µ0H s = 46.0 T and µ0H ⊥ s = 50.7 T. The results are explicable within the so-called fermion model, in contrast to other reported easy-axis Haldane systems. Zero-field magnetic order is absent down to 20 mK and emergent end-chain effects are observed in the gapped state, as evidenced by detailed low-temperature measurements. arXiv:1909.07900v1 [cond-mat.str-el]