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FUNMAT research
activities on
Superconductivity
Contents • Short description of research
fields
• Relevant publications
Short description of research fields and
plans Strong, focused activities exist within experimental and theoretical
fields. These activities in solid state physics at UiO and NTNU interact with
materials science groups for materials synthesis and characterization. The
latter aspect will be strengthened by the FUNMAT collaboration. The involved
groups are highly specialized and are attractive partners for international
collaboration. The traditions go far back, e.g. to studies of superconductivity
in aluminum in the 60’s and 70’s. Most of the present research is on
high Tc materials. Recently a revived interest has been taken also in low-Tc
superconductors. The activities listed below are described historically and
hence according to teams. These teams define within FUNMAT common research
fields where the integrated knowledge will add further dimensions to the work
carried out individually by the groups.
With respect to excellence and critical mass, FUNMAT will point at
the following fields (web-links will be established to the mentioned
topics):
Space and time resolved MO studies (Oslo team). The experimental
work focuses on the use of magneto-optical (MO) imaging to study the
space-resolved magnetic behavior of superconducting materials. A large number
of materials, both high- and low-Tc as well as the newly discovered MgB2 have
been investigated. Effects related to magnetic granularity in films, tapes and
bulk material, flux instabilities of various kinds (macroturbulence, dendritic
penetration), coexistence of SC and FM, flux avalanches and SOC in vortex
matter, are but a few of the phenomena studied. A major breakthrough was made
in our laboratory in January of last year, when for the first time it was shown
possible to make MO imaging of the individual magnetic vortices. This became
possible since we also have the ability to grow the highly specialized ferrite
garnet films that are used as sensor for MO imaging. Due to the specific
know-how needed for the LPE growth of these in-plane magnetization garnet
films, we are still the only laboratory in the world being able to visualize
the behavior of vortex matter in real-time. Our work has also a large component
of theoretical analysis and simulations, mainly related to the experiments, but
also as an independent activity. More details are found on the homepage
http://www.fys.uio.no/faststoff/ltl/index.htm
One near future goal is to harvest from the tremendous
possibilities that lie open by having the unique MO imaging facility. Another
is to optimize the LPE growth so that even more sensitive garnet films of high
optical quality can be made available. In addition to the basic research, which
involves collaborating partners at numerous universities and research centers
worldwide, there is some industrial collaboration on magnetic sensor films.
Research on thin films, and critical properties (Trondheim team).
Patterning of, and research on high-Tc thin film structures is now starting
again after a break of several years. Nanostructured thin film superconductor
properties will be the main focus. 1D superconductors will be created and
studied with respect to transport properties in zero field, and in magnetic
fields under conditions of single and multiple vortex penetration.
Magnetization properties are to be studied in low dimensional structures and
thin films, including also low-Tc superconductors like Pb, and alternating
layers of Pb, Al, and Al2O3.
A larger activity has for many years centred
on the properties of the flux line system, in particular flux line dynamics as
measured by ac susceptibility, magnetisation relaxometry, and ultrasound.
Thermodynamics, in particular critical properties, will be investigated by
measurements of specific heat and resonant ultrasound in magnetic fields up to
9 tesla. Superconducting fluctuations above Tc will be studied in LASCCO. In
particular the relation between such fluctuations and the T*(x) line will be
sought, where x is doping. Electron doped Nd-based superconductors will be
investigated similarly.
Theoretical activities (Trondheim team). The
theoretical research focuses on the breakdown of the Fermi-liquid picture in
strongly correlated systems such as cuprate perovskites. Large-scale Monte
Carlo simulations are performed with the aim of understanding the universality
class of the quantum phase transition from Fermi-liquid metallic systems to
singular Fermi-liquids, as well from Mott-Hubbard insulators to
charge-fractionalized insulators. The Monte Carlo simulations utilize
descriptions of strongly correlated systems in terms of effective lattice gauge
theories capable of sustaining so-called confinement-deconfinement transitions.
The connection between the confinement-deconfinement transitions that exists in
these effective theories, phenomena such as breakdown of Fermi-liquid theory
and spin-charge separation and charge-fractionalization will be investigated in
detail. These issues are incidentally closely related to the experimental study
of the superconducting fluctuations above Tc described above.
Materials chemistry and physics (Oslo team). Chemical modification of
superconducting oxides (hole doing by means of heterovalent substitution or
monitoring of oxygen content) falls into a larger activity on advanced oxides.
In progress are ALCVD approaches towards thin film growth of high Tc oxides.
Furthermore, chemical transport reactions are utilized for growth of single
crystals of low-dimensional chalcogenides.
The electronic structure of complex oxides, their relationship to
physical properties, and structure-property connections, are part on broad
activities on oxides. Concerning high-Tc materials, recent studies of the
electronic structure and physical properties of compounds like MgB2 have been
carried out by DFT methods. These studies add fundamental understanding in
addition to provide hints for development of novel materials with potentially
interesting properties.
Relevant publications
Space and time resolved MO studies • T.H. Johansen, J.
Lothe and H. Bratsberg: “Shape Distortion by Irreversible
Flux-Pinning-Induced Magnetostriction”, Phys. Rev. Lett. 80, 4757
(1998).
• D.V. Shantsev, M.R. Koblischka, Yu. Galperin, T.H.
Johansen, P. Nalevka and M. Jirsa: “Central Peak Position in Magnetization
Loops of High-Tc Superconductors”, Phys. Rev. Lett. 82, 2947 (1999).
• T.H. Johansen: “Flux-Pinning-Induced Stress and
Magnetostriction in Bulk Superconductors”, Topical Review in Supercond.
Sci. Technol. 13, R121 (2000).
• L.M. Fisher, P.E. Goa, M.
Baziljevich, T.H. Johansen, A.L. Rakhmanov and V.A. Yampol'skii:
“Hydrodynamic Instability of the Flux-antiflux Interface in Type-II
Superconductors”, Phys. Rev. Lett. 87, 247005 (2001).
• L.
Y. Gorelik, A. Isacsson, Y.M. Galperin, R.I. Shekhter, M. Jonson: "Coherent
transfer of Cooper pairs by a movable grain", Nature 411, 454 (2001).
• T.H. Johansen, M. Baziljevich, D.V. Shantsev, P.E. Goa, Y.M. Galperin,
W.N. Kang, H.J. Kim, E.M. Choi, M.-S. Kim and S.-I. Lee: “Dendritic Flux
Instability in Superconducting MgB2 Films”, Europhys. Lett. (in press)
Thin films; critical properties • K. Fossheim, N.T.
Opheim, and H. Bratsberg. Transverse Phonon Scattering in s-Wave
Superconductors: The Role of BCS Coherence Factors and Meissner Screening Near
Tc. Superconductor Science and Technology 2002
• Nyhus J,
Thisted U, Kikugawa N, et al. Elastic and specific heat critical properties of
La1.85Sr0.15CuO4. Physica C 369 (1-4): 273-277 2002
• Zhilyaev
IN, Boronin SG, Fossheim K Step-like oscillations in the resistance of two
weakly linked aluminum rings. Physica C 332 (1-4): 422-425 2000
• Fossheim K, Tuset ED, Ebbesen TW, et al. Enhanced flux-pinning in
Bi2Sr2CaCu2O8+x superconductor with embedded carbon nanotubes. Physica C 248
(3-4): 195-202 1995
• Z.H. Gong, A. Rønnekleiv, and J.K.
Grepstad Performance of a surface acoustic wave filter with YBa2Cu3O7-?
superconducting electrodes Physica C 282-287, 2521-2522 (1997)
•
R. Fagerberg, H.E. Stokke, and J.K. Grepstad Impact of a normally conducting
surface layer on attenuation in high -Tc superconducting microstrip
transmission lines
IEEE Transactions on Applied Superconductivity 6,
167-171 (1996)
• Z.H. Gong, J.K. Grepstad, and R. Fagerberg The
YBCO(001)/Ag interface, correlation between specific contact resistence and
interfacial microstructure IEEE Transactions on Applied Superconductivity 5,
2412-2415 (1995)
• Z.H. Gong, F. Vassenden, R. Fagerberg, J.K.
Grepstad, A. Bardal, and R. Høier Processing dependence of the
interfacial microstructure of Ag contacts to YBa2Cu3O7-? thin films.
Applied Physics Letters 63, 836-838 (1993)
Theoretical activities • J. Hove and A. Sudbø,
Anomalous scaling dimension and stable charged fixed point in type-II
superconductors, Phys. Rev. Lett., 84, 3426 (2000).
• J. Hove, S.
Mo, and A. Sudbø, Hausdorrf-dimension of critical fluctuations in
abelian gauge theories, Phys. Rev. Lett., 85, 2368 (2000).
• S.
Mo, J. Hove, and A. Sudbø, Order of the metal-to-superconductor
transition, Phys. Rev. B 65, 104501 (2002).
• H. Kleinert, F. S.
Nogueira, and A. Sudbø, Confinement transition in three-dimensional
compact U(1) gauge theories coupled to matter fields, Phys. Rev. Lett., 88,
232001 (2002).
• J. B. Marston, J. O. Fjærestad, and A.
Sudbø, Staggered flux-phase in a model of strongly correlated electron
systems, Phys. Rev. Lett., 89, xxxxxx (2002).
• A. Sudbø,
F. S. Nogueira, and J. Hove, Z(q) universality in three-dimensional compact
U(1) abelian Higgs model and fractionalized insulators, submitted to Phys. Rev.
Lett. (2002)
• Ravindran, P, Vajestoon, P., Vidya, R., Kjekshus,
A. and Fjellvåg, H.”Detailed electronic structure studies on
superconducting MgB2 and related compounds” Phys. Rev. B. 6422 (2001) 4509
Materials chemistry • Hosomi, T., Suematsu, H.,
Fjellvåg, H., Karppinen, M. and Yamauchi, H., ”Identification of
Superconducting Phases in the Ba-Ca-Cu-O system: an Unstable Phase with Tc =
126 K and its
Derivative with Tc = 90 K” J. Mater. Chem. 9 (1999)
1141 – 1148.
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