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New Paradigms for Spintronics in Complex Oxides

Oct. 6, 2010 (past)
12:10 p.m. to 1:30 p.m.
60 St. George Street, MP 606
Gang Cao speaker details
Gang Cao

Abstract:

The 4 d - and 5 d -transition metal oxides exhibit nearly every collective state known for solids. It is commonly expected that 4d -based ruthenates and 5d -based iridates are more metallic and less magnetic than their 3 d and 4 f counterparts because the extended nature of electron orbitals leads to a broad 4d - and 5d -bandwidth and a reduced Coulomb interaction such that the Stoner criterion anticipates a metallic, paramagnetic state. In marked contrast, many layered ruthenates and iridates are magnetic insulators with a wide range of exotic properties. This talk reviews underlying properties of these materials with an emphasis on a few intriguing issues: (1) an unusual colossal magnetoresistance and a spin-valve effect existing in bulk single crystals of bilayered Ca3Ru2O7 [1-3], and (2) a novel Jeff = ½ Mott insulator, Sr2IrO4, and its unstable ground state that readily swings between highly insulating and metallic state via only slight perturbations [4-7] . These novel phenomena bring to light the importance of spin-orbit coupling that rigorously competes with other energies, thus setting a new balance between various degrees of freedom in this class of materials.

References:

[1] G. Cao, S. McCall, J.E. Crow and R.P. Guertin, Phys. Rev. Lett. 78 , 1751(1997)

[2] X. N. Lin, Z.X. Zhou, V. Durairaj, P. Schlottmenn and G. Cao, Phys. Rev. Lett. 95, 017203 (2005)

[3] G. Cao, V. Durairaj, S. Chikara, and L.E. DeLong and P. Schlottmenn, Phys. Rev. Lett. 100 , 016604 (2008)

[4] B . J. Kim, Hosub Jin, S. J. Moon, J.-Y. Kim, B.-G. Park, C. S. Leem, Jaejun Yu, T. W. Noh, C.Kim, S.-J. Oh, V. Durairai, G. Cao , and J.-H. Park, Phys. Rev. Lett. 101 , 076402 (2008)

[5] S.J. Moon, H. Jin, K.W. Kim, W.S. Choi, Y.S. Lee, J. Yu, G. Cao, A. Sumi, H. Funakubo, C. Bernhard, and T.W. Noh, Phys. Rev. Lett. 101 , 226402(2008)

[6] S. Chikara, O.Korneta, W. P. Crummett, L.E. DeLong, P. Schlottmann and G. Cao, Phys. Rev. B 80 , 140407 ( R ) (2009)

[7] O.B. Korneta, Tongfei Qi, S. Chikara, S. Parkin, L. E. De Long, P. Schlottmann and G. Cao, to appear in Phys. Rev. B 82 (2010) (15 September issue)