Robert J. Cava
In our research group, we search for and synthesize non-molecular solids with the goal of finding new materials with exotic electronic and magnetic properties. We find new compounds, grow crystals from the melt and vapor transport, determine their crystal structures, and characterize their electronic and magnetic properties. The choice of chemical systems to be studied is informed by understanding how chemistry and structure combine to yield the electronic properties of solids; understanding what the important forefront areas of research are in condensed matter physics is always an important part of the equation. When a new compound appears to be particularly interesting, we work closely with colleagues in theoretical and experimental condensed matter physics at Princeton, Johns Hopkins and Penn State Universities, Brookhaven, and many other laboratories around the world to study the properties in detail and alter them through chemical and structural manipulation. We work closely with experts in high resolution electron microscopy to determine the crystal structures of complex materials and learn about their nanometer scale structure. We perform temperature dependent neutron diffraction measurements with collaborators at the National Institute of Standards and Technology and the Spallation Neutron Source at Oak Ridge National Laboratory, and synchrotron x-ray diffraction at Brookhaven and Argonne National Laboratories to determine the crystal and magnetic structures of the new materials we make. The detailed structural information obtained in these experiments is correlated with the measured physical properties of the materials. Elementary electronic structure calculations are performed to help direct our exploratory research program and to interpret the properties we observe. Students and postdoctoral fellows are trained in the connections between structure, bonding, and electronic and magnetic properties of non-molecular solids.
A major part of our research is in exploring the properties and structures of ternary and quaternary 4d and 5d transition metal oxides – materials that fall at the border between magnetic and non-magnetic low temperature electronic states. Such materials often display unexpected electronic properties. Other major areas of research are new superconductors, new thermoelectrics, and new geometrically frustrated magnets. With a group of researchers in Princeton’s MRSEC program we have played a significant role in the recent discovery and characterization of a new kind of electronic state of matter - topological metallic surface states on the surfaces of certain bulk insulating crystals with strong spin-orbit coupling, known as topological insulators. In all our work, we employ the principles and synthetic and analytical methods of solid state chemistry to find new materials with exceptional physical properties in the hope of driving the study of the electronic properties of solids in new directions through new materials.
Selected Recent Publications
- “Superconductivity in CuxBi2Se3 and its Implications for Pairing in the Undoped Topological Insulator ”, Y.S. Hor, A.J. Williams, J.G. Checkelsky, P. Roushan, J. Seo, Q. Xu, H.W. Zandbergen, A. Yazdani, N.P. Ong, and R.J. Cava, Phys. Rev. Lett. 104 057001 (2010).
- “Multiple electronic transitions and superconductivity in PdxTiSe2 ”, E. Morosan, K.E. Wagner, Liang L. Zhao, Y. Hor, A.J. Williams, J. Tao, Y. Zhu, and R.J. Cava, Phys. Rev. B 81 094524 (2010).
- “Topological surface states protected from backscattering by chiral spin texture”, Pedram Roushan, Jungpil Seo, Colin V. Parker, Y.S. Hor, D. Hsieh, Dong Qian, Anthony Richardella, M. Z.Hasan, R.J. Cava, Ali Yazdani, Nature 460 1106 (2009).
- “Tetragonal-to-Orthorhombic Structural Phase Transition at 90 K in the Superconductor Fe1.01Se”, T.M. McQueen, A.J. Williams, P.W. Stephens, J. Tao, Y. Zhu, V. Ksenofontov, F. Casper, C. Felser, and R.J. Cava, Phys. Rev. Lett. 103 057002 (2009).
- “Electronic and magnetic phase diagram of beta-Fe1.01Se with superconductivity at 36.7 K under pressure”, S. Medvedev, T.M. McQueen, I. A. Troyan, T. Palasyuk, M. I. Eremets, R. J. Cava, S. Naghavi, F. Casper, V. Ksenofontov, G. Wortmann, C. Felser, Nature Materials 8 630 (2009).
- “Observation of a large-gap topological-insulator class with a single Dirac cone on the surface”, Y. Xia, D. Qian, D. Hsieh, L. Wray, A. Pal, H. Lin, A. Bansil, D. Grauer, Y. S. Hor, R. J. Cava, M. Z. Hasan, Nature Physics 5 398 (2009).
- “p-type Bi2Se3 for topological insulator and low-temperature thermoelectric applications”, Y. S. Hor, A, Richardella, P. Roushan, Y. Xia, J.G. Checkelsky, A. Yazdani, M.Z. Hasan, N.P. Ong, and R.J. Cava, Phys Rev. B79 195208 (2009).
- “Insulator to correlated metal transition in V1-xMoxO2”, K.L. Holman, T.M. McQueen, A.J. Williams, T. Klimczuk, P.W. Stephens, H.W. Zandbergen, Q. Xu, F. Ronning, R. J. Cava, Phys. Rev. B 79 245114 (2009).
- “Stoichiometry, spin fluctuations, and superconductivity in LaNiPO”, T.M. McQueen, T. Klimczuk, A.J. Williams, Q. Huang, R.J. Cava, Phys. Rev. B 79 172502 (2009).
- “The A2+Mn5(SO4)6 family of triangular lattice, ferromagnetic sulfates”, D. V. West, T.M. McQueen, I.D. Posen, X. Ke, Q. Huang, H.W. Zandbergen, A.J. Williams, P. Schiffer, R.J. Cava, J. Sol. St. Chem. 182 1343 (2009).
- “Extreme sensitivity of superconductivity to stoichiometry in Fe1+δSe”, T.M. McQueen, Q. Huang, V. Ksenofontov, C. Felser, Q. Xu, H.W. Zandbergen, Y.S. Hor, J. Allred, A.J. Williams, D. Qu, J.G. Checkelsky, N.P. Ong, R.J. Cava, Phys. Rev. B 79 014522 (2009).
- “Lattice collapse and the magnetic phase diagram of Sr1-xCaxCo2P2”, S. Jia, A.J. Williams, P.W. Stephens and R.J. Cava, Phys. Rev. B 80 165107 (2009).
- “Structural disorder, octahedral coordination and two-dimensional ferromagnetism in anhydrous alums”, D.V. West, Q. Huang, H.W. Zandbergen, T.M. McQueen, and R.J. Cava, J. Sol. St. Chem. 181 2768 (2008).
- “Long- and short-range order in stuffed titanate pyrochlores”, G.C. Lau, T.M. McQueen, Q. Huang, H.W. Zandbergen and R.J. Cava, J. Sol. St. Chem. 181 45 (2008).