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Dive into the research topics where Kenneth E. Gray is active.

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Featured researches published by Kenneth E. Gray.


Nature Materials | 2004

Full bulk spin polarization and intrinsic tunnel barriers at the surface of layered manganites

J. W. Freeland; Kenneth E. Gray; Lutfi Ozyuzer; Peter Berghuis; Elvira Badica; J.J. Kavich; Hong Zheng; John F. B. Mitchell

Transmission of information using the spin of the electron as well as its charge requires a high degree of spin polarization at surfaces. However, at surfaces this degree of polarization can be quenched by competing interactions. Using a combination of surface-sensitive X-ray and tunnelling probes, we show for the quasi-two-dimensional bilayer manganites that only the outermost Mn–O bilayer is affected: it is a 1-nm-thick insulator that exhibits no long-range ferromagnetic order, whereas the next bilayer displays the full spin polarization of the bulk. Such an abrupt localization of the surface effects is due to the two-dimensional nature of the layered manganite, and the loss of ferromagnetism is attributed to weakened double exchange in the reconstructed surface bilayer and a resultant antiferromagnetic phase. The creation of a well-defined surface insulator atop a fully spin-polarized bulk demonstrates the ability of two of the most demanding components of an ideal magnetic tunnel junction to self-assemble naturally.


Physical Review Letters | 2013

Chiral phase transition in charge ordered 1T-TiSe2

John-Paul Castellan; Stephan Rosenkranz; Ray Osborn; Qing’an Li; Kenneth E. Gray; X. Luo; U. Welp; G. Karapetrov; Jacob P. C. Ruff; Jasper van Wezel

It was recently discovered that the low-temperature, charge-ordered phase of 1T-TiSe(2) has a chiral character. This unexpected chirality in a system described by a scalar order parameter could be explained in a model where the emergence of relative phase shifts between three charge density wave components breaks the inversion symmetry of the lattice. Here, we present experimental evidence for the sequence of phase transitions predicted by that theory, going from disorder to nonchiral and finally to chiral charge order. Employing x-ray diffraction, specific heat, and electrical transport measurements, we find that a novel phase transition occurs ~7 K below the main charge ordering transition in TiSe(2), in agreement with the predicted hierarchy of charge-ordered phases.


Physical Review B | 1998

Evidence of d{sub x{sup 2}{minus}y{sup 2}} symmetry in the tunneling conductance density of states of Tl{sub 2}Ba{sub 2}CuO{sub 6}

Lutfi Ozyuzer; Z. Yusof; J. F. Zasadzinski; Radion Mogilevsky; D. G. Hinks; Kenneth E. Gray

Tunnel junctions have been made on single crystals of Tl{sub 2}Ba{sub 2}CuO{sub 6} with a T{sub c}{approximately}91 K using a mechanical point-contact method. Both superconductor{endash}insulator{endash}normal-metal (SIN) and superconductor-insulator-superconductor (SIS) junctions were obtained using Au and Nb tips, respectively. The tunneling conductances obtained are reproducible, with sharp, well-defined energy gap structures and are characterized by a cusplike feature at zero bias. These conductances can be fit to a simple, momentum-averaged density of states (DOS) obtained from a superconducting order parameter with d{sub x{sup 2}{minus}y{sup 2}} symmetry. The SIS data display a weak Nb gap feature which is consistent with the subgap DOS observed in the SIN data. {copyright} {ital 1998} {ital The American Physical Society}


Physical Review B | 1998

Evidence of d{sub x}{sup 2}{sub -y}{sup 2} symmetry in the tunneling density of states of Tl{sub 2}Ba{sub 2}CuO{sub 6}.

Lutfi Ozyuzer; Z. Yusof; J. F. Zasadzinski; Radion Mogilevsky; D. G. Hinks; Kenneth E. Gray

Tunnel junctions have been made on single crystals of Tl{sub 2}Ba{sub 2}CuO{sub 6} with a T{sub c}{approximately}91 K using a mechanical point-contact method. Both superconductor{endash}insulator{endash}normal-metal (SIN) and superconductor-insulator-superconductor (SIS) junctions were obtained using Au and Nb tips, respectively. The tunneling conductances obtained are reproducible, with sharp, well-defined energy gap structures and are characterized by a cusplike feature at zero bias. These conductances can be fit to a simple, momentum-averaged density of states (DOS) obtained from a superconducting order parameter with d{sub x{sup 2}{minus}y{sup 2}} symmetry. The SIS data display a weak Nb gap feature which is consistent with the subgap DOS observed in the SIN data. {copyright} {ital 1998} {ital The American Physical Society}


Physical Review B | 1987

Energy gap in La_{1.85}Sr_{0.15}CuO_{4-y} from point-contact tunneling

M. E. Hawley; Kenneth E. Gray; D. W. Capone; David G. Hinks


Physical Review B | 2004

Unexpected in-plane canting and metallic behavior in the A-type antiferromagnetic layered manganite La2-2xSr1+2xMn2O7

E. Badica; Kenneth E. Gray; J. F. Mitchell; H. Zheng


Physical Review B | 1989

Electron tunneling study of the normal and superconducting states of Bi_{1.7}Pb_{0.3}Sr_{2}CaCu_{2}O_{x}

Qiang Huang; J. F. Zasadzinski; Kenneth E. Gray; Jing-Zhou Liu; H. Claus


Physical Review B | 2008

Charge/orbital ordered phases of La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7-{delta}}.

H. Zheng; Qing’An Li; Kenneth E. Gray; J. F. Mitchell


Archive | 2002

Probing the phase diagram of BiSrCaCuO{sub 8+delta} with tunneling spectroscopy.

Lutfi Ozyuzer; J. F. Zasadzinski; Kenneth E. Gray; David G. Hinks; N. Miyakawa


Archive | 2002

Pairing Symmetry in Electron Doped Nd-Ce-Cu-O from Quasiparticle Tunneling

J. F. Zasadzinski; Kenneth E. Gray

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J. F. Zasadzinski

Illinois Institute of Technology

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David G. Hinks

Argonne National Laboratory

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Lutfi Ozyuzer

University of Erlangen-Nuremberg

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C. L. Kendziora

State University of New York System

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N. Miyakawa

Tokyo University of Science

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Z. Yusof

Argonne National Laboratory

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D. G. Hinks

Argonne National Laboratory

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J. F. Mitchell

Argonne National Laboratory

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Prasenjit Guptasarma

University of Wisconsin–Milwaukee

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Lutfi Ozyuzer

University of Erlangen-Nuremberg

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