Novel Materials

Novel oxide materials such as manganites, nickelates, ruthenates, Invar and others with strongly correlated electrons and strong electron-phonon interactions are under theoretical and experimental investigation. The outstanding results include a theoretical description of orbital liquids, magnetopolarons and magnetoresistance in manganites and ruthenates, and electronic phase separation. The Kugel-Khomskii Hamiltonian originally introduced in the 1980s is playing a major role here. A highly cited novel theory of colossal magnetoresistance (CMR) in ferromagnetic oxides by Alexandrov and Bratkovsky (in collaboration with Hewlett-Packard Research Labs) is another remarkable achievement.

Alexandrov, Kabanov and Thomas are investigating how the de Haas-van Alphen and Shubnikov-de Haas magnetic oscillations are modified in nanostructures and other situations of reduced dimensionality. For details see the page on quantum oscillations in nanowires.

Ziebeck, Brown and Neumann are working on various applications of polarised neutron scattering to resolve complex magnetic structures in Invar and other spin-Peierls materials. Then work has attracted substantial interest as a possible solution to the 100-year old Invar problem. The ferromagnetic shape memory compound Ni₂MnGa, first reported by Ziebeck, is currently attracting significant interest world wide, particularly regarding its potential applications. The development of this material is now a major research theme at many centres.

Some recent and current PhD theses

• Tamsin Stephens, An investigation of the magnetic properties of heavy REPtIn alloys, 2005 (supervisor Ziebeck)
• Özhan Ünverdi, Investigations of SrRuO₃ and Sr₂RuO₄, 2005 (supervisor Ziebeck)
• Phil B Gamble, Strongly Correlated One Dimensional Systems and Applications to Super-Cooled Gases, 2006 (supervisor Kusmartsev)
• Michael G Banks, Investigation of frustrated one dimensional antiferromagnetic quantum chain systems and the rare earth intermetallic compound TmGa₃, 2007 (supervisor Neumann)
• Adrian P Gandy, The magnetic and structural properties of Ni₂Mn_1+xZ_1–x (Z=Ga, In, Sn, Sb) magnetic shape memory alloys, 2007 (supervisor Ziebeck)
• Douglas Green, Colossal Magnetoresistance, in progress (supervisor Alexandrov)

Contacts

• Sasha Alexandrov
• Joseph Betouras
• Alexander Boris
• Viktor Kabanov
• Daniel Khomskii
• Natalia Kovaleva
• Kliment Kugel
• Feo Kusmartsev
• Klaus Neumann
• Alexander Rakhmanov
• Kurt Ziebeck

For further information

T. H. Hewett and F. V. Kusmartsev , Geometrically enhanced extraordinary magnetoresistance in semiconductor-metal hybrids, Phys Rev B, 82 212404 (2010) (featured in PRB Kaleidoscope images: December 2010. )

M S Laad, I M Bradaric and F Kusmartsev, Orbital Non-Fermi-Liquid Behavior in Cubic Ruthenates, Phys Rev Lett, 100 096402 (2008)

I I Mazin, D I Khomskii, R Lengsdorf, J A Alonso, W G Marshall, R M Ibberson, A Podlesnyak, M . Martínez-Lope and M M Abd-Elmeguid, Charge Ordering as Alternative to Jahn-Teller Distortion, Phys Rev Lett 98 176406 (2007)

F Kusmartsev, Electronic molecules in semiconductors and other novel materials, Contemp Phys 453 237-250 (2004) (Review, on polarons and electronic phase separation, recommended for students)

F V Kusmartsev, Formation of Electron Strings in Polar  Narrow Band Semiconductors, Phys Rev Lett 84, 530 (2000)

A S Alexandrov and A M Bratkovsky, Carrier Density Collapse and Colossal Magnetoresistance in Doped Manganites, Phys Rev Lett 82 141 (1999)

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