Browsing by Author "Maljuk, Andrey"
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- ItemEvidence for a percolative Mott insulator-metal transition in doped Sr2IrO4(College Park, MD : APS, 2021) Sun, Zhixiang; Guevara, Jose M.; Sykora, Steffen; Pärschke, Ekaterina M.; Manna, Kaustuv; Maljuk, Andrey; Wurmehl, Sabine; van den Brink, Jeroen; Büchner, Bernd; Hess, ChristianDespite many efforts to rationalize the strongly correlated electronic ground states in doped Mott insulators, the nature of the doping-induced insulator-to-metal transition is still a subject under intensive investigation. Here, we probe the nanoscale electronic structure of the Mott insulator Sr2IrO4−δ with low-temperature scanning tunneling microscopy and find an enhanced local density of states (LDOS) inside the Mott gap at the location of individual defects which we interpret as defects at apical oxygen sites. A chiral behavior in the topography for those defects has been observed. We also visualize the local enhanced conductance arising from the overlapping of defect states which induces finite LDOS inside of the Mott gap. By combining these findings with the typical spatial extension of isolated defects of about 2 nm, our results indicate that the insulator-to-metal transition in Sr2IrO4−δ could be percolative in nature.
- ItemFloating zone growth of Bi2Sr2Ca2Cu3Oy superconductor(Basel : MDPI, 2016) Maljuk, Andrey; Lin, C.T.The crystal growth of high-temperature oxide superconductors has been hampered by the complexities of these materials and the lack of knowledge of corresponding phase diagrams. The most common crystal growth technique adopted for these materials is the so-called “Flux” method. This method, however, suffers from several drawbacks: (i) crystals are often crucible and flux contaminated; (ii) crystals are difficult to detach from solidified melt; and (iii) crystals are rather small. In most cases, these drawbacks can be overcome by the crucible-free floating zone method. Moreover, this technique is suitable for crystal growth of incongruently melting compounds, and has been thus successfully used to make large single crystals of Bi2Sr2Ca2Cu3Oy superconductor. In this review, the authors summarize the published and their own growth efforts as well as detailed characterization of as-grown and post-growth annealed samples. The optimal growth conditions that allowed one to obtain the large-size, almost single phase and homogeneous in composition Bi2Sr2Ca2Cu3Oy single crystals are presented. The effect of long lasting post-growth heat treatment on both crystal quality and superconducting properties has also been demonstrated.
- ItemGrowth of LiCoO2 Single Crystals by the TSFZ Method(Washington, DC : ACS Publ., 2018) Nakamura, Shigenobu; Maljuk, Andrey; Maruyama, Yuki; Nagao, Masanori; Watauchi, Satoshi; Hayashi, Takeshi; Anzai, Yutaka; Furukawa, Yasunori; Ling, Chris D.; Deng, Guochu; Avdeev, Maxim; Büchner, Bernd; Tanaka, IsaoWe have grown LiCoO2 single crystals by the traveling solvent floating zone (TSFZ) growth with Li-rich solvent, having observed the incongruent melting behavior of LiCoO2 between 1100 and 1300 °C. The optimum growth conditions in terms of atmosphere and solvent composition were determined to be Ar flow and an atomic ratio Li/Co 85:15, respectively. The crystals grown using a conventional-mirror-type furnace contained periodic inclusions of a Co-O phase due to the influence of Co-O phase segregation on the stability of the molten zone during growth. By using a tilted-mirror FZ furnace, inclusion-free LiCoO2 crystals of about 5 mm in diameter and 70 mm long were obtained at a tilting angle Î = 10°. The grown crystals were confirmed to be single-domain by neutron Laue diffraction. © 2018 American Chemical Society.
- ItemHidden Charge Order in an Iron Oxide Square-Lattice Compound(College Park, Md. : APS, 2021) Kim, Jung-Hwa; Peets, Darren C.; Reehuis, Manfred; Adler, Peter; Maljuk, Andrey; Ritschel, Tobias; Allison, Morgan C.; Geck, Jochen; Mardegan, Jose R. L.; Bereciartua Perez, Pablo J.; Francoual, Sonia; Walters, Andrew C.; Keller, Thomas; Abdala, Paula M.; Pattison, Philip; Dosanjh, Pinder; Keimer, BernhardSince the discovery of charge disproportionation in the FeO2 square-lattice compound Sr3Fe2O7 by Mössbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained “hidden” to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe K-edge resonant x-ray scattering to demonstrate checkerboard charge order in the FeO2 planes that vanishes at a sharp second-order phase transition upon heating above 332 K. Stacking disorder of the checkerboard pattern due to frustrated interlayer interactions broadens the corresponding superstructure reflections and greatly reduces their amplitude, thus explaining the difficulty of detecting them by conventional probes. We discuss the implications of these findings for research on “hidden order” in other materials.
- ItemLaser-Assisted Floating Zone Growth of BaFe2S3 Large-Sized Ferromagnetic-Impurity-Free Single Crystals(Basel : MDPI, 2021) Amigó, Maria Lourdes; Maljuk, Andrey; Manna, Kaustuv; Stahl, Quirin; Felser, Claudia; Hess, Christian; Wolter, Anja U.B.; Geck, Jochen; Seiro, Silvia; Büchner, BerndThe quasi-one-dimensional antiferromagnetic insulator BaFe2S3 becomes superconducting under a hydrostatic pressure of ∼10 GPa. Single crystals of this compound are usually obtained by melting and further slow cooling of BaS or Ba, Fe, and S, and are small and needle-shaped (few mm long and 50–200 μm wide). A notable sample dependence on the antiferromagnetic transition temperature, transport behavior, and presence of superconductivity has been reported. In this work, we introduce a novel approach for the growth of high-quality single crystals of BaFe2S3 based on a laser-assisted floating zone method that yields large samples free of ferromagnetic impurities. We present the characterization of these crystals and the comparison with samples obtained using the procedure reported in the literature.
- ItemTSFZ Growth of Eu-Substituted Large-Size LSCO Crystals(Basel : MDPI, 2022) Voloshyna, Olesia; Romaka, Vitaliy V.; Karmakar, Koushik ;Seiro, Silvia; Maljuk, Andrey; Büchner, BerndThe travelling solvent floating zone (TSFZ) growth of Eu-substituted LSCO (La1.81−xEuxSr0.19CuO4, with nominal x = 0 ÷ 0.4) single crystals was systematically explored for the first time. The substitution of La with Eu considerably decreased the decomposition temperature. Optimal growth parameters were found to be: oxygen pressure 9.0–9.5 bars; Eu-free CuO-poor solvent (66 mol% CuO) with a molar ratio of La2O3:SrCO3:CuO = 4:4.5:16.5 and growth rate 0.6 mm/hour. The obtained single crystals were characterized with optical polarized microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy analysis. The solubility of Eu in LSCO appeared to be limited to x~0.36–0.38 under the used conditions. The substitution of La3+ with smaller Eu3+ ions led to a structural transition from tetragonal with space group I4/mmm for La1.81Sr0.19CuO4 (x = 0) to orthorhombic with space group Fmmm for La1.81−xSr0.19EuxCuO4 (x = 0.2, 0.3, 0.4), and to a substantial shrinking of the c-axis from 13.2446 Å (x = 0.0) to 13.1257 Å (x = 0.4). Such structural changes were accompanied by a dramatic decrease in the superconducting critical temperature, Tc, from 29.5 K for x = 0 to 13.8 K for 0.2. For x ≥ 0.3, no superconductivity was detected down to 4 K.