March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14

Interplay of Superconductivity and Magnetism in Oxy-Chalcogen Cuprates YBaSrCu3OxSey

Armen Gulian, presenterChapman University, Institute for Quantum Studies,

Advanced Physics Laboratory, Burtonsville, MD 20866, USA

Vahan NikoghosyanChapman University, Institute for Quantum Studies,

Advanced Physics Laboratory, Burtonsville, MD 20866, USAAlso: Physics Research Institute, National Academy of Sciences, Ashtarak,

0203, Armenia

Vadim GrinenkoLeibniz Institute IFW-Dresden, PF 270116, Dresden D-01171, Germany

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March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 2

Motivation: Belief: Exploration of the oxychalcogens is a valuable step towards testing the proposed theories of HTSC

[Yee C.-H., Birol T., and Kotliar G. Guided design of copper oxysulfide superconductors. Europhys. Lett., 111, 17002 (2015).]

Intention:Replace in YBa2Cu3O7 superconductors: 1) one atom of Ba by Sr2) one oxygen atom by Se.

Outcome:This double substitution results in:1. two SC transitions: at 34K and and18K;2. the re-entrant Wohlleben effect;3. setting up of ferromagnetic interaction at 4K.

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 3

Standard Synthesis Routes

Y2O3, SrCO3, BaCO3, and SrSe in stoichiometric proportions for YBaSrCu3OxSe composition. Calcinating at 900oC for 100 min. Re-grinding, pelletizing, baking at 950oC for 30 min. Continued at 650oC for 80 minutes.

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 4

Initial Findings: Doubly Re-entrant Magnetization

While resistive transition takes place at ~35K, diamagnetic transition which started at the same T is suppressed by the re-entrant paramagnetism at cooling down, which itself is suppressed by the re-entrant diamagnetism at further cooling down!

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 5

What is going on?

1) How many phase transitions?2) What is causing the jumps?3) Any effect on resistivity?4) Crystalline structure5) Composition

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 6

Surface morphology and Structure

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 7

Wohlleben Effect (PME)

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 8

Two SC transitions as indicated by heat capacity

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 9

Two SC phases in resistivity?

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 10

Two SC phases in resistivity?

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 11

Fitting by the Curie-Weiss law

• µeff∼2/3 µB per Cu atom

• Enhanced correlations are responsible for magnetism.

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 12

• Various magnetic fields: H=0, 100 Oe, 1000 Oe

• f=3333Hz ; measurements at other frequencies yielded similar results.

Upturn in the AC-susceptibility

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 13

In some samples only

Re-entrant resistive state

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 14

Does Se stay in composition?

TEM analysis (Hitachi-USA)

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 15

Quantitatively?

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 16

In the lattice?

Kikkuchi pattern with simultaneous EDX

March Meeting of the American Physical Society, Baltimore, March 14-18, 2016 . Session B25, March 14 17

• This work is supported in part by the US Office of Naval Research• Collaborative support of Hitachi-USA (S. Nozaki, A. Muto,

J. Clark, and J. Kilcrease) is very appreciated

Acknowledgement

Many thanks for your attention!