Emilia Morosan Physics and Astronomy Chemistry

1. Tailoring the crystal structure towards optimal electronic and spin properties Emilia Morosan Physics and Astronomy Chemistry NASA Johnson Space Center, May 18th 2010

2. OUTLINE: • Who we are • What do we do • Methods and facilities for materials synthesis and characterization • Areas of interest Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

3. Who we are: We are part of the Condensed Matter group in Physics and Astronomy at Rice University in Houston Professor Emilia Morosan Physics and Astronomy, and Chemistry Rice University, Houston, TX, USA Email: emorosan@rice.edu Phone: +1-713-348-2529 www.ruf.rice.edu/~morosan/group • 3-4 graduate students • 1-2 undergraduate students • 1 visiting student (high school) • 2 summer visiting science teachers Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

4. What do we do? • Design and synthesize new compounds with desired properties • Identify novel materials and crystal structures • Use different tuning parameters (doping, pressure, magnetic field) to tailor properties Our “ingredients” Things I wouldn’t touch Things I thought I wouldn’t touch Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

5. Why do we prefer single crystals? • Often have better quality than the polycrystalline analogues (fewer defects, no grain boundaries, superior transport properties) • Allow for anisotropic measurements (magnetization, resistance, etc.) LuFe6Ge6 Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

6. The recipes: how we make compounds 1. Single crystal growth • Liquid solution decant excess flux 10 mm TbIn3 Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

7. The recipes: how we make compounds 1. Single crystal growth • Vapor transport Thot Tcold Convection (transport, usually from hot to cold) Reactant powders + transport agent Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

8. The recipes: how we make compounds 2.Polycrystalline synthesis • Solid state reactions • Arc-melting Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

9. Why do this? • Want to discover, synthesize and measure properties of novel or known compounds with interesting properties We study: • Superconductivity • Magnetism (Itinerant, Local Moment) • Density Waves • Heavy Fermions, Quantum Criticality Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

10. TbSn2 Examples of materials we look at: Intermetallic compounds • Rare earth based (local moment) magnetic systems - RSn2: metamagnetism - Gd5Pb3: high ferromagnetic ordering around 300 K • Itinerant ferromagnets • - Sc3In: quantum phase transition (T = 0) with doping Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

11. Examples of materials we look at: • Transition metal compounds • - search for new layered iron superconductors • new Fe-As superconductors discovered recently • Tc > 50 K • - for practical superconductors • high Tc is not enough • more important: high carrier density, low anisotropy Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

12. Fe - As B Search for new superconductors Opportunities for discovery • Use “Fe-As” + B building layers • Doping: enhance (control) carrier density Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

13. As Fe Ca Search for new superconductors Opportunities for discovery • Routes to reduced anisotropy: - doping, pressure: push layers together - coupled Fe-As layers  less 2D crystal structure? CaFe4As3– new compound recently discovered in my lab Zhao et al., PRB 80 020404(R) (2009) Todorov et al., JACS 131 5405 (2009) Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

14. Search for new superconductors CaFe4As3 • Infinitely long Fe-Asribbons • Infinite Fe-As planes in layered superconductors Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

15. As Fe Ca CaFe4As3 • Fe-As ribbons form 3D channels – reduced anisotropy • Ca atoms inside Fe-As channels – can “rattle”  potential for good thermoelectric materials Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

16. M(T) H = 0.1 T Magnetic ordering (antiferromagnetic) TN = 88 K Second phase transition around T2 = 26 K Slight upturn in low-T M(T)  FM ? No hysteresis is observed Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

17. CaFe4As3 – resistivity • (T) i||b Metallic above TN = 89 K Local minimum around TN SDW Second phase transition around T2 = 26 K 0 = 45 μΩ cm A = 0.25 μΩ cm/K2 Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

18. CaFe4As3 – specific heat •  = 20 mJ/(molFe K2) • A = 0.25 μΩ cm/K2  Enhanced electronic correlations Morosan Laboratory • www.ruf.rice.edu/~morosan/group Moo Sung Kim et al. (unpublished) Tailoring the crystal structure towards optimal electronic and spin properties

19. Other interesting problems - Charge Density Wave to Superconductivity transition: CuxTiSe2 Morosan et al., Nature Physics 2 (2006) Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

20. Sample characterization • Powder x-ray diffraction to confirm or identify structure • Magnetic susceptibility (temperatures between 2 – 300 K), magnetization (applied magnetic fields up to 9 T) • Resistivity, specific heat, Hall coefficient (T = 0.4 K to 400 K, H = 0 - 9 T) • Angle-dependent magnetization, resistivity Morosan Laboratory • www.ruf.rice.edu/~morosan/group Tailoring the crystal structure towards optimal electronic and spin properties

21. Summary • Numerous possibilities to try and design of new, practical materials: • superconductors: layered structures close to magnetic instabilities; reduce anisotropy by pressure, doping, coupled layers, “locally layered” structures (e.g. CaFe4As3- type) • thermoelectrics: CaFe4As3- type (large, empty volumes) • Doping as tuning parameter between competing ground states, to change charge carrier density (insulator to metal) • New compounds discovered in the process