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Your search keyword '"Forgan, E.M."' showing total 152 results
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152 results on '"Forgan, E.M."'

8. Observation of square flux-line lattice in the unconventional superconductor Sr(sub2)RuO(sub4)

Author

Riseman, T.M., Kealey, P.G., Forgan, E.M., Mackenzie, A.P., Galvin, L.M., Tyler, A.W., Lee, S.L., Ager, C., McK. Paul. D., Aegerter, C.M., Cubitt, R., Mao, Z.Q., Akima, T., and Maeno, Y.

Subjects
Perovskite -- Research, Superconductors -- Research, Magnetic flux -- Research, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Superconductivity is of considerable scientific and practice interest and to gain further information about the properties of the superconductor, the intensity of the flux-line lattice (Fll) signal must be understood, or the magnitude of the Fourier components. A small-angle neutron-scattering measurement of magnetic flux lines in the Sr(sub2)RuO(sub4) perovskite superconductor was taken. Magnetic flux lines were found to form a square lattice over broad field and temperature fields.

Published
1998

10. Observations of the effect of strong Pauli paramagnetism on the vortex lattice in superconducting CeCu2Si2

Author

Campillo, E., Riyat, R., Pollard, S., Jefferies, P., Holmes, A.T., Cubitt, R., White, J.S., Gavilano, J., Huesges, Z., Stockert, O., Forgan, E.M., and Blackburn, E.

Subjects
Condensed Matter::Superconductivity, no topic specified
Abstract

We present the results of a study of the vortex lattice in the heavy fermion superconductor CeCu2Si2, using small angle neutron scattering SANS . In this material at temperatures well below Tc amp; 8764;0.6 K, the value of the upper critical field Bc2 amp; 8764;2.2 T is strongly limited by the Pauli paramagnetism of the heavy fermions. In this temperature region, our SANS data show an increase in the magnetization of the flux line cores with field, followed by a rapid fall near Bc2. This behavior is the effect of Pauli paramagnetism and we present a theory based model, which can be used to describe this effect in a range of materials. The pairing in CeCu2Si2 appears to arise from the effect of magnetic fluctuations, but the evidence for a d wave order parameter is rather weak. We find that the vortex lattice structure in CeCu2Si2 is close to regular hexagonal. There are no phase transitions to square or rhombic structures; such transitions are expected for d wave superconductors and observed in CeCoIn5; however, the temperature dependence of the SANS intensity indicates that both large and small gap values are present, most likely due to multiband s wave superconductivity, rather than a nodal gap structure

Published
2021

11. Small-angle neutron scattering study of the flux-line lattice in a single crystal of Bi2.15Sr1.95CaCu2O(8 + x) (invited)

Author

Yethiraj, M., Mook, H.A., Forgan, E.M., Cubitt, R., Wylie, M.T., Paul, D.M., Lee, S.L., Ricketts, J., Kes, P.H., and Mortensen, K.

Subjects
Superconductors -- Magnetic properties, Neutrons -- Scattering, Crystal lattices -- Research, Physics
Abstract

Small-angle neutron scattering analysis of a flux-line lattice (FLL) in a single crystal of Bi2.15Sr1.95CaCu2O(8 + x) (BSCCO) reveals that the disappearance of diffraction intensity with respect to temperature rise above a field-sensitive melting temperature and to the vortex lattice and an applied field increase causes FLL melting. The Bragg intensity of the FLL peak varies inversely to the fourth power of the London penetration depth. The temperature dependence of the order parameter is linear in BSCCO, with an applied field of 50 mT.

Published
1994

12. Direct observation of magnetic flux lattice melting and decomposition in the high-Tc superconductor Bi2.15Sr1.95CaCu2O8+x

Author

Cubitt, R., Forgan, E.M., Yang, G., Lee, S.L., Paul, D. McK., Mook, H.A., Yethiraj, M., Kes, P.H., Li, T.W., Menovsky, A.A., Tarnawski, Z., and Mortensen, K.

Subjects
Magnetic flux -- Analysis, Superconductors -- Magnetic properties, Heat resistant materials -- Analysis, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

The flux line structures in the high-Tc superconductor Bi2+xSr2-xCaCu2O8+x (BSCCO) are explored by using small-angle neutron scattering which was previously used to elucidate the spatial alignment of flux lines in YBa2Cu3O7-y (YBCO). The clear diffraction signal which vanishes on raising temperature at constant field, is evident at low fields and temperatures. The signal is absent at fields over 0.1 T, even at the lowest temperatures, possibly because the pinning of individual pancakes distorts straight flux lines.

Published
1993

13. Neutron measurements of the vortex lattice in YBa2Cu3O7

Author

Mook, M.A., Yethiraj, M., Wignall, G.D., Forgan, E.M., Lee, S.J., Cubitt, R., McK. Paul, D., and Armstrong, T.

Subjects
Superconductors -- Research, Yttrium barium copper oxides -- Research, Neutrons -- Diffraction, Physics
Abstract

Vortex lattice scattering in YBa2Cu3O7 was investigated using neutron diffraction measurements. The results showed that the application of a field along the c axis produces a square pattern. However, the application of a similar field some distance from the c axis produced a triangular pattern. The square pattern featured a vortex lattice with long-range orientational order but only short-range positional order.

Published
1993

33. The microscopic structure of charge density waves in underdoped YBa2Cu3O6.54 revealed by X-ray diffraction

Author

Forgan, E.M., Blackburn, E., Holmes, A.T., Briffa, A.K.R., Chang, J., Bouchenoire, L, Brown, S.D., Liang, Ruixing, Bonn, D., Hardy, W.N., Christensen, Niels Bech, Zimmermann, M V, Hücker, M., Hayden, S.M., Forgan, E.M., Blackburn, E., Holmes, A.T., Briffa, A.K.R., Chang, J., Bouchenoire, L, Brown, S.D., Liang, Ruixing, Bonn, D., Hardy, W.N., Christensen, Niels Bech, Zimmermann, M V, Hücker, M., and Hayden, S.M.

Abstract

Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa2Cu3O6.54 at its superconducting transition temperature ∼60 K. We find that the CDWs in this material break the mirror symmetry of the CuO2 bilayers. The ionic displacements in the CDWs have two components, which are perpendicular and parallel to the CuO2 planes, and are out of phase with each other. The planar oxygen atoms have the largest displacements, perpendicular to the CuO2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For instance, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states with broken symmetry observed in scanning tunnelling microscopy and soft X-ray measurements.

Published
2015

36. Exploring the Fragile Antiferromagnetic Superconducting Phase in CeCoIn5

Author

Blackburn, E., Das, P., Eskildsen, M.R., Forgan, E.M., Laver, Mark, Niedermayer, C., Petrovic, C., Blackburn, E., Das, P., Eskildsen, M.R., Forgan, E.M., Laver, Mark, Niedermayer, C., and Petrovic, C.

Abstract

CeCoIn5 is a heavy fermion type-II superconductor showing clear signs of Pauli-limited superconductivity. A variety of measurements give evidence for a transition at high magnetic fields inside the superconducting state, when the field is applied either parallel to or perpendicular to the c axis. When the field is perpendicular to the c axis, antiferromagnetic order develops on the high-field side of the transition. This order remains as the field is rotated out of the basal plane, but the associated moment eventually disappears above 17°, indicating that anomalies seen with the field parallel to the c axis are not related to this magnetic order. We discuss the implications of this finding. © 2010 The American Physical Society

Published
2010

37. Fermi Surface and Order Parameter Driven Vortex Lattice Structure Transitions in Twin-Free YBa2Cu3O7

Author

White, J.S., Hinkov, V., Heslop, R.W., Lycett, R.J., Forgan, E.M., Bowell, C., Strässle, S., Abrahamsen, Asger Bech, Laver, M., Dewhurst, C.D., Kohlbrecher, J., Gavilano, J.L., Mesot, J., Keimer, B., Erb, A., White, J.S., Hinkov, V., Heslop, R.W., Lycett, R.J., Forgan, E.M., Bowell, C., Strässle, S., Abrahamsen, Asger Bech, Laver, M., Dewhurst, C.D., Kohlbrecher, J., Gavilano, J.L., Mesot, J., Keimer, B., and Erb, A.

Abstract

We report on small-angle neutron scattering studies of the intrinsic vortex lattice (VL) structure in detwinned YBa2Cu3O7 at 2 K, and in fields up to 10.8 T. Because of the suppressed pinning to twin-domain boundaries, a new distorted hexagonal VL structure phase is stabilized at intermediate fields. It is separated from a low-field hexagonal phase of different orientation and distortion by a first-order transition at 2.0(2) T that is probably driven by Fermi surface effects. We argue that another first-order transition at 6.7(2) T, into a rhombic structure with a distortion of opposite sign, marks a crossover from a regime where Fermi surface anisotropy is dominant, to one where the VL structure and distortion is controlled by the order-parameter anisotropy.

Published
2009

38. Structure and degeneracy of vortex lattice domains in pure superconducting niobium: A small-angle neutron scattering study

Author

Laver, M., Bowell, C.J., Forgan, E.M., Abrahamsen, Asger Bech, Fort, D., Dewhurst, C.D., Mühlbauer, S., Christen, D.K., Kohlbrecher, J., Cubitt, R., Ramos, S., Laver, M., Bowell, C.J., Forgan, E.M., Abrahamsen, Asger Bech, Fort, D., Dewhurst, C.D., Mühlbauer, S., Christen, D.K., Kohlbrecher, J., Cubitt, R., and Ramos, S.

Abstract

High-purity niobium exhibits a surprisingly rich assortment of vortex lattice (VL) structures for fields applied parallel to a fourfold symmetry axis, with all observed VL phases made up of degenerate domains that spontaneously break some crystal symmetry. Yet a single regular hexagonal VL domain is observed at all temperatures and fields parallel to a threefold symmetry axis. We report a detailed investigation of the transition between these lush and barren VL landscapes, discovering new VL structures and phase transitions at high fields. We show that the number and relative population of VL domains is intrinsically tied to the underlying crystal symmetry. We discuss how subtle anisotropies of the crystal may generate the remarkable VLs observed.

Published
2009

39. Uncovering flux line correlations in superconductors by reverse monte carlo refinement of neutron scattering data

Author

Laver, M., Forgan, E.M., Abrahamsen, Asger Bech, Bowell, C., Geue, T., Cubitt, R., Laver, M., Forgan, E.M., Abrahamsen, Asger Bech, Bowell, C., Geue, T., and Cubitt, R.

Abstract

We describe the use of reverse Monte Carlo refinement to extract structural information from angle-resolved data of a Bragg peak. Starting with small-angle neutron scattering data, the positional order of an ensemble of flux lines in superconducting Nb is revealed. We discuss the uncovered correlation functions in the light of topical theories, in particular, the "Bragg glass" paradigm.

Published
2008

42. μSR studies of the flux vortex phases in a BEDT-TTF superconductor

Author

Pratt, F.L., primary, Lee, S.L., additional, Aegerter, C.M., additional, Ager, C., additional, Lloyd, S.H., additional, Blundell, S.J., additional, Ogrin, F.Y., additional, Forgan, E.M., additional, Keller, H., additional, Hayes, W., additional, Sasaki, T., additional, Toyota, N., additional, and Endo, S., additional

Published
2001
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44. Measurements of the penetration depth of an YBa2Cu3O7−δ thin film with low-energy muons

Author

Riseman, T.M, primary, Jackson, T.J, additional, Long, M.W, additional, Forgan, E.M, additional, Morenzoni, E, additional, Glückler, H, additional, Prokscha, T, additional, Weber, H.-P, additional, Niedermayer, Ch, additional, Hofer, A, additional, Pleines, M, additional, Schatz, G, additional, Litterst, J, additional, Luetkens, H, additional, and Schatz, A, additional

Published
2000
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49. Muon-spin rotation studies of the flux lattice in κ-(BEDT-TTF)2Cu(ScN)2

Author

Lee, S.L., primary, Blundell, S.J., additional, Pratt, F.L., additional, Pattenden, P.A., additional, Forgan, E.M., additional, Sasaki, T., additional, Aegerter, C.M., additional, Hunt, M., additional, Chow, K.H., additional, Hayes, W., additional, Singleton, J., additional, Keller, H., additional, and Savic, I.M., additional

Published
1997
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