Browsing by Department "Oak Ridge National Laboratory"

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    Atomic-Scale Andreev Probe of Unconventional Superconductivity
    (American Chemical Society, 2023-09-13) Ko, Wonhee; Song, Sang Yong; Yan, Jiaqiang; Lado, Jose; Maksymovych, Petro; Oak Ridge National Laboratory; Correlated Quantum Materials (CQM); Department of Applied Physics
    Recent emergence of low-dimensional unconventional superconductors and their exotic interface properties calls for new approaches to probe the pairing symmetry, a fundamental and frequently elusive property of the superconducting condensate. Here, we introduce the unique capability of tunneling Andreev reflection (TAR) to probe unconventional pairing symmetry, utilizing the sensitivity of this technique to specific Andreev reflections. Specifically, suppression of the lowest-order Andreev reflection due to quantum interference but emergence of the higher-order Andreev processes provides direct evidence of the sign-changing order parameter in the paradigmatic FeSe superconductor. TAR spectroscopy also reveals two superconducting gaps, points to a possibility of a nodal gap structure, and directly confirms that superconductivity is locally suppressed along the nematic twin boundary, with preferential and near-complete suppression of the larger energy gap. Our findings therefore enable new, atomic-scale insight into microscopic, inhomogeneous, and interfacial properties of emerging quantum materials.
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    Cellulose-lignin composite fibres as precursors for carbon fibres. Part 1 – Manufacturing and properties of precursor fibres
    (ELSEVIER SCI LTD, 2020-09-28) Trogen, Mikaela; Le, Nguyen-Duc; Sawada, Daisuke; Guizani, Chamseddine; Vergara Lourencon, Tainise; Pitkänen, Leena; Sixta, Herbert; Shah, Riddhi; O'Neill, Hugh; Balakshin, Mikhail; Byrne, Nolene; Hummel, Michael; Biopolymer Chemistry and Engineering; Deakin University; Wood Material Science; Department of Bioproducts and Biosystems; Biorefineries; Oak Ridge National Laboratory; Lignin Chemistry; Department of Bioproducts and Biosystems
    Cellulose-lignin composite fibres were spun from ionic liquid (IL) solutions by dry-jet wet spinning. Birch pre-hydrolysed Kraft (PHK) pulp and organosolv beech (BL) or spruce lignin (SL) were dissolved in the IL 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) to prepare spinning dopes. Fibres with lignin concentrations of up to 50% were spun successfully. The fibres were analysed focusing on important properties for the production of carbon fibres (CF). Due to the higher molar mass of the SL compared to the BL, SL showed higher stability in the spinning process, giving higher lignin content in the final fibres. The CF yield after carbonization increased with increasing lignin content. The higher carbon content of SL compared to BL, resulted in moderately higher CF yield of the SL fibres, compared to fibres with BL. Overall, the produced cellulose-lignin composite fibres show great potential as precursors for CF production.
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    Crack roughness in the two-dimensional random threshold beam model
    (2008-10-13) Nukala, Phani K.V.V.; Zapperi, Stefano; Alava, Mikko J.; Šimunović, Srdan; Oak Ridge National Laboratory; CNR-INFM; Department of Applied Physics
    We study the scaling of two-dimensional crack roughness using large scale beam lattice systems. Our results indicate that the crack roughness obtained using beam lattice systems does not exhibit anomalous scaling in sharp contrast to the simulation results obtained using scalar fuse lattices. The local and global roughness exponents (ζloc and ζ, respectively) are equal to each other, and the two-dimensional crack roughness exponent is estimated to be ζloc =ζ=0.64±0.02. Removal of overhangs (jumps) in the crack profiles eliminates even the minute differences between the local and global roughness exponents. Furthermore, removing these jumps in the crack profile completely eliminates the multiscaling observed in other studies. We find that the probability density distribution p [Δh (l)] of the height differences Δh (l) = [h (x+l) -h (x)] of the crack profile obtained after removing the jumps in the profiles follows a Gaussian distribution even for small window sizes (l).
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    Role of disorder in the size scaling of material strength
    (2008-02-05) Alava, Mikko J.; Nukala, Phani K.V.V.; Zapperi, Stefano; Department of Applied Physics; Oak Ridge National Laboratory; INFM-CNR
    We study the sample-size dependence of the strength of disordered materials with a flaw, by numerical simulations of lattice models for fracture. We find a crossover between a regime controlled by the disorder and another controlled by stress concentrations, ruled by continuum fracture mechanics. The results are formulated in terms of a scaling law involving a statistical fracture process zone. Its existence and scaling properties are revealed only by sampling over many configurations of the disorder. The scaling law is in good agreement with experimental results obtained from notched paper samples.