Emil S. Bozin

Understanding the insulating phase in colossal magnetoresistance manganites: shortening of the Jahn-Teller long-bond across the phase diagram of La1-xCaxMnO3.

The detailed evolution of the magnitude of the local Jahn-Teller (JT) distortion in La(1-x)Ca(x)MnO3 is obtained across the phase diagram for 0< or =x< or =0.5 from high-quality neutron diffraction data using the atomic pair distribution function method. A local JT distortion is observed in the insulating phase for all Ca concentrations studied. However, in contrast with earlier local structure studies, its magnitude is not constant, but decreases continuously with increasing Ca content. This observation is at odds with a simple small-polaron picture for the insulating state.

Superconductivity, Magnetism and Stoichiometry of Single Crystals of Fe1+y(Te1−xSx)z

We report synthesis of high quality Fe1+y(Te1-xSx)z single crystals and a comprehensive study of structural, magnetic and transport properties. There is high sensitivity to material stoichiometry which includes vacancies on the Te(S) site. Our results reveal competition and coexistence of magnetic order and percolative superconductivity for x >= 0.03, while zero resistivity is acheived for x >= 0.1.

Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductors

Understanding the role played by broken-symmetry states such as charge, spin and orbital orders in the mechanism of emergent properties, such as high-temperature superconductivity, is a major current topic in materials research. That the order may be within one unit cell, such as nematic, was only recently considered theoretically, but its observation in the iron-pnictide and doped cuprate superconductors places it at the forefront of current research. Here, we show that the recently discovered BaTi2Sb2O superconductor and its parent compound BaTi2As2O form a symmetry-breaking nematic ground state that can be naturally explained as an intra-unit-cell nematic charge order with d-wave symmetry, pointing to the ubiquity of the phenomenon. These findings, together with the key structural features in these materials being intermediate between the cuprate and iron-pnictide high-temperature superconducting materials, render the titanium oxypnictides an important new material system to understand the nature of nematic order and its relationship to superconductivity.

Magnetism in La₂O₃(Fe₁₋xMnx)₂Se₂ tuned by Fe/Mn ratio

We report the evolution of structural and magnetic properties in La₂O₃(Fe₁₋xMnx)₂Se₂. Heat capacity and bulk magnetization indicate an increased ferromagnetic component of the long-range magnetic order and possible increased degree of frustration. Atomic disorder on Fe(Mn) sites suppresses the temperature of the long-range order whereas intermediate alloys show a rich magnetic phase diagram.

Synthesis, Crystal Structure, and Magnetism of β-Fe1.00(2)Se1.00(3) Single Crystals

Understanding iron-based superconductors requires high-quality impurity-free single crystals. So far they have been elusive for {beta}-FeSe and extraction of intrinsic materials properties has been compromised by several magnetic-impurity phases. Here, we report synchrotron-clean {beta}-FeSe superconducting single crystals grown via LiCl/CsCl flux method. Phase purity yields evidence for a defect-induced weak ferromagnetism that coexists with superconductivity below T{sub c}. In contrast to Fe{sub 1+y}Te-based superconductors, our results reveal that the interstitial Fe(2) site is not occupied and that all contribution to density of states at the Fermi level must come from in-plane Fe(1).

Spin-glass Behavior of Semiconducting KxFe2−yS2

We report the discovery of K{sub x}Fe{sub 2-y}S{sub 2} single crystals, isostructural to K{sub x}Fe{sub 2-y}S{sub 2} superconductors. The sulfide compound is a small gap semiconductor and shows spin-glass behavior below 32 K. Our results indicate that stoichiometry, defects, and the local environment of FeCh (Ch = S,Se) tetrahedra have important effects on the physical properties of isostructural and isoelectronic K{sub x}Fe{sub 2-y}S{sub 2} compounds.

Synthesis, crystal structure, and magnetism of β -Fe 1.00(2) Se 1.00(3) single crystals

Understanding iron-based superconductors requires high-quality impurity-free single crystals. So far they have been elusive for {beta}-FeSe and extraction of intrinsic materials properties has been compromised by several magnetic-impurity phases. Here, we report synchrotron-clean {beta}-FeSe superconducting single crystals grown via LiCl/CsCl flux method. Phase purity yields evidence for a defect-induced weak ferromagnetism that coexists with superconductivity below T{sub c}. In contrast to Fe{sub 1+y}Te-based superconductors, our results reveal that the interstitial Fe(2) site is not occupied and that all contribution to density of states at the Fermi level must come from in-plane Fe(1).

Local Structural Evidence for Strong Electronic Correlations in Spinel LiRh2O4

The local structure of the spinel LiRh

Spin glass behavior of insulating K0.8Fe2-xS2

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Thermoelectric studies of Ir1−xRhxTe2 (0≤x≤0.3)

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