Experimental Condensed Matter Physics

Research Interests

Novel materials synthesis; high-field, low-temperature, high-pressure material properties; physics of transition metal oxides

Cao Lab Webpage

Director, Center for Advanced Materials CAM.aspx

2009-2010 University Research Professor 

 (Author of more than 140 articles in refereed journals. For a complete publication list, please go to http://www.pa.uky.edu/~cao/ or nph-abs_connect )

• "Giant Magneto-electric Effect in the J_eff=1/2 Mott Insulator, Sr_2,IrO₄", S. Chikara, O. Korneta, W.P. Crumett, L.E. DeLong, P. Schlottmann and G. Cao, Phys. Rev. B 80, 140407(R) (2009)
• "Bandwidth-Controlled Insulator-Metal Transition and Correlated Metallic State in 5d Sr_n+1Ir_nO_3n+1 (n=1, 2, and 1)", 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, 226401 ( 2008)
• (Ivited Review) "Ca₃Ru₂O₇: A New Paradigm for Spintronics", G. Cao, and P. Schlottmann, Modern Physics Letters B 22, 1785-1813( 2008)
• "Novel Jeff 1=2 Mott State Induced by Relaivistic Spin-Orbit Coupling in Sr₂IrO₄", 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)
• "Observation of Strong Spin Valve Effect in bulk Ca₃ (Ru_1-x Cr_x )₂ O₇", G. Cao, V. Durairaj, S. Chikara, and L.E. DeLong, Phys. Rev. Lett. 100, 016604 (2008).
• "Non-Fermi-Liquid behavior in nearly ferromagnetic metal SrIrO₃ single crystals", G. Cao, V. Duarairaj, S. Chikara, L.E. DeLong, S. Parkin, and P. Schlottmann, Phys. Rev. B 76, 100402(R) ( 2007)
• "Partial Antiferromagnetism in Spin-Chain Sr₅Rh₄O₁₂, Ca₅Ir₃O₁₂ and Ca₄IrO₆ Single Crystals" G. Cao, V. Durairaj, S. Chikara, S. Parkin and P. Schlottmann, Phys. Rev. B 75,134402 (2007)
• "Studies on the Weak Itinerant Ferromagnet SrRuO₃ under High Pressure to 34 GPa", J.J. Hamilin, S. Deemyad, J.S. Schilling, M.K. Jacobsen, R.S. Kumar, A.L. Cornelius, G. Cao and J.J. Neumeier, Phys. Rev. B 76, 014432 (2007)
• "Anomalous Itinerant Magnetism in Single-Crystal Sr₄Ru₃O₁₀: A Thermodynamic and Transport Investigation" G. Cao, S. Chikara, J. W. Brill, and P. Schlottmann, Phys. Rev. B 75 024429 (2007)
• "Electronic Structures of Layered Perovskite Sr₂MO₄ (M=Ru, Rh, and Ir)",S. J. Moon, M. W. Kim, K. W. Kim, Y. S. Lee, J.-Y. Kim, J.-H. Park, B. J. Kim, S.-J. Oh, S. Nakatsuji, Y. Maeno, I. Nagai, S. I. Ikeda, G. Cao, and T. W. Noh, Phys. Rev. B 74, 113104 (2006)
• "Borderline Magnetism in Sr₄Ru₃O₁₀: Impact of Dilute La and Ca Doping on Itinerant Ferromagnetism and Metamagnetism", S. Chikara , V. Durairaj, W.H. Song, Y.P. Sun, X.N. Lin, A. Douglass, G. Cao, P. Schlottmann, and S. Parkin, Phys. Rev. B 73, 224420 (2006)
• "Field- and Pressure-Induced Phases in Sr₄Ru₃O₁₀: A Spectroscopic Investigation" Rajeev Gupta, M. Kim, H. Barath, S.L. Cooper and G. Cao, Phys. Rev. Lett. 96, 067004 (2006)
• "Highly Anisotropic Magnetism in Cr Doped Perovskite Ruthenates", V. Durairaj, S. Chikara, X.N. Lin, A. Douglass, G. Cao, P. Schlottmann, E.S.Choi and R.P. Guertin, Phys. Rev. B 73, 214414 (2006)
• "Observation of Quantum Oscillations Periodic in 1/B and B in Bilayered Ca₃Ru₂O₇ ", V. Durairaj, X. N. Lin, Z.X. Zhou, S Chikara, E. Elhami, P. Schlottmenn and G. Cao, Phys. Rev. B 73, 054434 (2006)
• "Spectroscopic Study of the Field- and Pressure-Induced Phases of the Bilayered Ruthenate Ca₃Ru₂O₇", J. F. Karpus, C. S. Snow, R. Gupta, H. Barath, S. L. Cooper, and G. Cao, Phys. Rev. B 73, 134407 (2006)
• "Colossal Magnetoresistance by Avoiding a Ferromagnetic State in Mott System Ca₃Ru₂O₇", X. N. Lin, Z.X. Zhou, V. Durairaj, P. Schlottmenn and G. Cao, Phys. Rev. Lett. 95, 017203 (2005)
• "Thermal and magnetic Properties of Spin-Chain Material, Pr₃Ru₂O₇", M. Fremat, X.N. Lin, V. Durairaj, S.Chikara, G. Cao, and J.W. Brill, Phys. Rev. B 72, 014458 (2005)
• "From Itinerant Ferromagnetism to Insulating Antiferromagnetism: a Magnetic and Transport Study of Single Crystal SrRu_1-xMn_xO₃ (0≤x<0.60)", G. Cao, S. Chikara, E. Elhami, X.N. Lin and P. Schlottmann, Phys. Rev. B 71, 035104 (2005)
• "Angle-resolved de Hass-van Alphen Study of SrRuO₃", C. S. Alexander, S. McCall, P. Schlottmann, J. E. Crow and G. Cao, Phys. Rev. B 72, 24415 (2005)
• "Field-Induced Orbital and Magnetic Phases in Ca₃Ru₂O₇ : Light Scattering Studies", J.F. Karpus, R. Gupta, Barath, S.L. Cooper and G. Cao, Phys. Rev. Lett.93, 167205 (2004)
• (Invited Paper) Orbitally-driven Behavior: Mott Transition, Quantum Oscillations and Colossal Magnetoresistance in Bilayered Ca₃Ru₂O₇", G. Cao, X.N. Lin, L. Balicas, S. Chikara, J.E. Crow and P. Schlottmann, a special issue on Orbital Physics, New Journal of Physics 6, 159 (2004). http://www.iop.org/EJ/news/-topic=842 or http://www.iop.org/EJ/abstract/1367-2630/6/1/159/ (This paper was selected as IOP Select (IOP=Institute of Physics in Europe))
• "Transport and Thermodynamic Properties of Sr₃Ru₂O₇ Near the Quantum Critical Point", Z.X Zhou, S. McCall, C.S. Alexander, J.E. Crow, P.Schlottmann, A. Bianchi, C. Capan, R. Movshovich, K.H. Kim, M. Jaime, and N. Harrison, M. Haas, R. Cava and G. Cao, Phys. Rev B 69, 140409 (2004)
• "High-temperature Weak Ferromagnetism on the Verge of a Metallic State: Impact of Dilute Sr-doping on BaIrO3 ", G. Cao, S. Chikara, X.N. Lin, E. Elhami and V. Durairaj, Phys. Rev. B 69, 174418 (2004)
• "Field-Tuned Collapse of an Orbital Ordered and Spin-polarized State: Colossal Magnetoresistance in Bilayered Ruthenate", G. Cao, L. Balicas, X.N. Lin, S. Chikara, V. Durairaj, E. Elhami, J.W. Brill, R.C. Rai and J. E. Crow, Phys. Rev. B 69, 014404 (2004)
• “Dimer Liquid State in the Quantum Antiferromagnetic Compound LiCu₂O₂” S. Zvyagin S, G. Cao, Y. Xin, S. McCall, T. Caldwell, W. Moulton, L.C. Brunel, A. Angerhofer, J.E. Crow, Phys. Rev. B 69, 189901 (2004)
• "Competing Ground State in Triple-layered Sr₄Ru₃O₁₀: Verging on Itinerant Ferromagnestism with Critical Fluctuations”, G. Cao, L. Balicas, W. H. Song, Y.P. Sun, Y. Xin, V.A. Bondarenko, J.W. Brill, S. Parkin, and X.N. Lin, Phys. Rev. B 68 174409 (2003)
• "Coloassal Magnetoresistance, Quantum Oscillations and Magnetoelastic Interactions in Bilayered Ca₃Ru₂O₇”, G. Cao, L. Balicas, Y. Xin, J.E. Crow, and C.S. Nelson, Phys. Rev. B 67, 184405 (2003)
• "Impact of Magnetic Fields on Anisotropy in Ca₃Ru₂O₇”, S. McCall, G. Cao, and J.E. Crow, Phys. Rev. B 67, 094427 (2003)
• "Mean Field Behavior with Gaussian Fluctuations at the Ferromagnettic Phase Transition of SrRuO₃”, D. Kim, B.L. Zink, F. Hellman, S. McCall, G. Cao, and J.E. Crow, Phys. Rev. B 67, 100406 (R) (2003)
• “Tunneling Magnetoresistance and Quantum Oscillations in Bilayered Ca₃Ru₂O₇”, G. Cao, L. Balicas, Y. Xin,  E. Dagotto, J.E. Crow, C.S. Nelson, and D.F. Agterberg, Phys. Rev. B 67 060406(R) (2003)
• "Pressure-Tuned Collapse of the Mott-like State in Ca_n+1Ru_nO_3n+1 (n=1,2): Raman Spectroscopic Stduies”, C.S. Snow, S.L. Cooper, G. Cao, J.E. Crow, S. Natatsuji, and Y. Maeno, Phys. Rev. Lett. 89, 226401 (2002)
• “Temperature-dependent Raman Spectroscopy in BaRuO₃ Systems”, Y.S. Lee, T.W. Noh, J.H. Park, K.-B. Lee, G. Cao, J.E. Crow, M.K. Lee, C. B. Eom, E.J. Oh and In-Sang Yang, Phys. Rev. B 65, 235113 (2002)
• "Sensitivity to Disorder of the Metallic State in the Ruthenates”, L. Capogna, A. P. Mackenzie, R. S. Perry, S. A. Grigera, L. M. Galvin, P. Raychaudhuri, A. J. Schofield, C. S. Alexander, G. Cao, S. R. Julian, and Y. Maeno, Phys. Rev Lett. 88, 76602 (2002)
• "Dimer Liquid State in the Quantum Antiferromagnet LiCu₂O₂: ESR Studies”, S. Svyagin, G. Cao, A. Angerhofer, Y. Xin, T. Caldwell, W. Moulton, L.-C. Brunel, and J.E. Crow, Phys. Rev. B 66, 064424 (2002)
• "Structure and Magnetism of Single Crystal Sr₄Ru₃O₁₀: A Ferromagnetic Triple-Layered Ruthenates” M.K. Crawford, R.L. Harlow, W. Marshall, Z. Li, G. Cao, R.L. Lindstrom, Q. Huang, and J.W. Lynn. Phys. Rev. B 65, 214412 (2002)
• "Anomalous Magnetic and Transport Properties in Magnetic Insulator Sr₃Ir₂O₇”, G. Cao, Y. Xin, C. S. Alexander, J.E. Crow and P. Schlottmann, Phys. Rev. B 66, 214412 (2002)
• "Weak Ferromagnetism and Spin-Charge Coupling in Single Crystal Sr₂YRuO₆”, G. Cao, C.S. Alexander, Y Xin and J.E. Crow, Phys. Rev. B 63,184432 (2001)
• "Pseudogap Formation in 4d-transition Metal Oxide BaRuO₃”, Y.S. Lee, T.W. Noh, Jaejun Yu, J.S. Lee, K.W. Kim, E.J. Choi, G. Cao, and J.E. Crow, Europhys. Lett. 55, 280 (2001)
• "Magnetic Ordering and Enhanced Specific Heat in Insulating Ln₂RuO₅ (Ln=Nd, Pr, Sm, Gd and Tb)”, G. Cao, S. McCall, Z.X. Zhou, C.S. Alexander, and J.E. Crow, Phys. Rev. B 63, 144427 (2001)
• "Spin-Charge Coupling for Dilute La-doped Ca₃Ru₂O₇”, G. Cao, K. Abbound, S. McCall, J.E. Crow and R.P.Guertin, Phys. Rev. B 62, 998 (2000)
• "Charge Density Wave Formation Accompanying Ferromagnetic Ordering in Quasi-one-dimensional BaIrO₃”, G. Cao, J.E. Crow, R.P. Guertin, P. Henning, C.C. Homes, M. Strongin, D.N. Basov, and E. Lochner, Solid State Comm. 113, 657 (2000)
•  "Ground-State Instability of Mott Insulator Ca₂RuO₄: Impact of Slight La-doping on Metal-Insulator Transition and Magnetic Ordering”, G. Cao, S. McCall, V. Dobrosavljevic, S.C. Alexander, and J.E. Crow, and R.P. Guertin, Phys. Rev. B 61, R5053 (2000)
• "Raman Scattering Study of the Charge and Spin Dynamics of the Layered Ruthenium Oxide Ca₃Ru₂O₇”, H.L. Liu, S. Yoon, S.L. Cooper and G. Cao, Phys. Rev. B 60, R6980, (1999)
• "Destruction of the Mott Insulating Ground State of Ca₂RuO₄ by a Structural Transition,” C.S. Alexander, G. Cao, V. Dobrosavljevic, E. Lochner, S. McCall, J.E. Crow and P.R. Guertin, Phys. Rev. B 60, R8422 (1999)
• "Weak Ferromagnetism, Metal-to-Nonmetal Transition and Negative Differential Resistivity in Single Crystal Sr₂IrO₄”, G. Cao, J. Bolivar, S. McCall, J.E. Crow, and R.P. Guertin, Phys. Rev. B, 57, R11039 (1998)
• "Layered Ruthenium Oxides: From Band Metal to Mott Insulator”, A.V. Puchkov, M.C. Schabel, D.N Basov, T. Startseva,  G. Cao, T. Timusk, and Z.-X. Shen, Phys. Rev. Lett. 81, 2747 (1998)
• "High-field Electron Spin Resonance of Cu_1-xZn_xGeO₃”, A.K. Hassan, L.A. Pardi, G.B. Martins, G. Cao, and L-C. Brunnel, Phys. Rev. Lett. 80, 1984 (1998)
• "Magnetic and Transport Properties of Single Crystal Ca₂RuO₄: Relationship to Superconducting Sr₂RuO₄”, G. Cao, S. McCall, M. Shepard, J.E. Crow and R.P. Guertin, Phys. Rev. B 56, R2916 (1997)
• "Thermal, Magnetic and Transport Properties of Single Crystal Sr_1-xCa_xRuO₃ (0 £ x£ 1.0)”, G. Cao, S. McCall, M. Shepard, J. E. Crow, and R. P. Guertin, Phys. Rev. B 56, 321 (1997)
• "Observation of a Metallic Antiferroamgnetic Phase and Metal-Nonmetal Transition in Ca₃Ru₂O₇”, G. Cao, S. McCall, J.E. Crow and R.P. Guertin,  Phys. Rev. Lett. 78, 1751  (1997)
• "Observation of Pr Magnetic Order in PrBa₂Cu₃O₇”, S. Skanthakumar, J.W. Lynn,  N. Rosov, G. Cao, and J.E. Crow, Phys. Rev. B 55, R3406 (1997)
• "Itinerant-to-Localized Electron Transition in Peroviskites CaRu_1-xSn_xO₃ and SrRu_1-xPb_xO₃”, G. Cao, S. McCall, J. Bolivar, M. Shepard, F. Freibert J.E. Crow, Phys. Rev. B 54, 15144 (1996)
• "Observation of an Anomalous Quasi-One-Dimensional Behavior in Na2Ru4O9 Single Crystals”, G. Cao, S. McCall, M. Shepard, and J. E. Crow, Phys. Rev. B 53, 12215 (1996)
• "High Dielectric Permittivity of Ceramic and Single Crystal PrBa2Cu3Ox", P. Mazzara, S. Skirus, G. Cao, J.W. O'Reilly, J.E.  Crow, and L.R. Testardi, Phys. Rev. B 47, 8119 (1993)
• "Enhanced Electric Polarizability at Magnetic Ordering Temperature of La2CuO4+x", G. Cao, J.W. O'Reilly, J.E. Crow, and L.R. Testardi, Phys. Rev. B 47, 11510 (1993)