Professor Stephen Blundell: Publications

Soft chemical control of superconductivity in lithium iron selenide hydroxides Li1–xFex(OH)Fe1–ySe

Inorganic Chemistry American Chemical Society 54:4 (2015) 1958-1964

Authors:

H Sun, Dn Woodruff, Sj Cassidy, Gm Allcroft, Sj Sedlmaier, Amber Thompson, Pa Bingham, Sd Forder, S Cartenet, N Mary, S Ramos, Fr Foronda, Bh Williams, X Li, Stephen Blundell, Simon Clarke

Abstract:

Hydrothermal synthesis is described of layered lithium iron selenide hydroxides Li_1–xFe_x(OH)Fe_1–ySe (x ∼ 0.2; 0.02 < y < 0.15) with a wide range of iron site vacancy concentrations in the iron selenide layers. This iron vacancy concentration is revealed as the only significant compositional variable and as the key parameter controlling the crystal structure and the electronic properties. Single crystal X-ray diffraction, neutron powder diffraction, and X-ray absorption spectroscopy measurements are used to demonstrate that superconductivity at temperatures as high as 40 K is observed in the hydrothermally synthesized samples when the iron vacancy concentration is low (y < 0.05) and when the iron oxidation state is reduced slightly below +2, while samples with a higher vacancy concentration and a correspondingly higher iron oxidation state are not superconducting. The importance of combining a low iron oxidation state with a low vacancy concentration in the iron selenide layers is emphasized by the demonstration that reductive postsynthetic lithiation of the samples turns on superconductivity with critical temperatures exceeding 40 K by displacing iron atoms from the Li_1–xFe_x(OH) reservoir layer to fill vacancies in the selenide layer.

Anisotropic Local Modification of Crystal Field Levels in Pr-Based Pyrochlores: A Muon-Induced Effect Modeled Using Density Functional Theory

Physical Review Letters American Physical Society (APS) 114:1 (2015) 017602

Authors:

FR Foronda, F Lang, JS Möller, T Lancaster, AT Boothroyd, FL Pratt, SR Giblin, D Prabhakaran, SJ Blundell

40 Years of Berezinskii–Kosterlitz–Thouless Theory, edited by Jorge V. José

Contemporary Physics Taylor & Francis 56:1 (2015) 99-100

Magnetostructural relationship in the tetrahedral spin-chain oxide CsCoO2

Physical Review B American Physical Society (APS) 91:2 (2015) 024419

Authors:

NZ Ali, RC Williams, F Xiao, SJ Clark, T Lancaster, SJ Blundell, DV Sheptyakov, M Jansen

Transverse field muon-spin rotation signature of the skyrmion lattice phase in Cu2OSeO3

Physical Review A American Physical Society 91:22 (2015) 224408

Authors:

T Lancaster, RC Williams, IO Thomas, F Xiao, FL Pratt, Stephen J Blundell, Thorsten Hesjedal, SJ Clark, PD Hatton, MC Hatnean, DS Keeble, G Balakrishnan, JC Loudon

Abstract:

We present the results of transverse field (TF) muon-spin rotation (μ+SR) measurements on Cu2OSeO3, which has a skyrmion-lattice (SL) phase. We measure the response of the TF μ+SR signal in that phase along with the surrounding ones, and suggest how the phases might be distinguished using the results of these measurements. Dipole field simulations support the conclusion that the muon is sensitive to the SL via the TF line shape and, based on this interpretation, our measurements suggest that the SL is quasistatic on a time scale τ>100 ns.

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