March 2005 SNS 2006 8 HFIR SNS picture
- Slides: 13
March 2005 SNS 2006 -8, HFIR SNS picture “Recent Developments in the Study of Strongly Correlated Electronic Systems” E. Dagotto, UT-ORNL Joint Institutes (JIAM, JINS) Nanocenter (CNMS)
Organization • Strong correlation in nanoscopic systems: transport in molecules and quantum dots. • Manganites: recent simulations of realistic models. Cuprates: recent simulations of phenomenological models. Strong Interaction UT Nano systems UT Bulk (Mn, Cu UT oxides)
C. Sen G. Alvarez + A. Moreo, M. Mayr, and S. Yunoki A. Feiguin K. Al-Hassanieh G. Martins
(1) Molecular conductors and quantum dots Key role of phonons in molecular conductors Kondo effect observed in molecules with net spin via enhancement in conductance (Coulombic effects cannot be neglected in small molecules)
DMRG/Lanczos for Transport in SCES systems (Al-Hassanieh et al. , PRB B 73, 195304 (2006); Schneider and Schmitteckert, preprint. ) Non interacting One Dot Current vs. time
New results: quantum interferences Anomalous cancellation of conductance in arrays of quantum dots, Center of Mass phonons in molecules, and in T-geometries. In progress: finite bias -> currents in Mott insulators, etc. G. Martins et al. , PRL 05 K. Al-Hassanieh et al. , PRL 05 G. Martins et al. , PRL 06 +A. Feiguin, C. Busser, et al.
(2, 3) Complex materials, phase competition Mitchell, Raveau et al. Manganites Cava et al. ORNL group + vast evidence of inhomogeneous states in manganites and cuprates (Cheong, De Teresa, Fernandez-Baca, Dusenhofer, Hennion, Fischer, , Zheng, Khomskii, Argyriou, Perring, Radaelli, …) Intrinsic softness!! E. D. , Science 2005 Cobaltites
Colossal Magneto Resistance (CMR) Big Dreams: Potential applications in read sensors. GMR already in computers. Critical temperatures must be raised. Resistivity of Mn-oxides changes by 10 orders of magnitude at low T (1994)
Special Case: CMR (1) Phase competition FM Metal vs. CO/AF Insulator is the basis of the phenomenon. (2) Simulations of simple models (resistor networks) show CMR. (3) Both strong Hund coupling and JT phonons needed. T* T mixed CO FM W SG S. Yunoki et al. , PRL 98, A. Moreo et al. Science 99; E. D. et al. , Phys. Rep. 01 Very recent effort at UT/ORNL aims to observe CMR in double exchange models of Mn oxides. It exploits (i) ORNL computers facilities with thousands of processors for parallel computing, (ii) new algorithms TPEM.
Final attack: realistic models, one- and two-orbital DE with phonons (C. Sen, G. Alvarez, et al. , PRB, to appear) Large MR Importance of Coulomb, phonons, and disorder! Large peak even in clean limit at low n Two orbitals
Recent results, involving two phases with different spin/charge order. One-orbital model, realistic density, FM metal vs. CO/AF competition.
Origin of glassy state? Patches of SC above Tc? (Alvarez et al. , PRB 71, 014514 (2005); M. Mayr et al. , PRB 06). T* SC AF Coulombic centers, as in Sr++. Each provides 1 h. D=|D| eif Giant responses? Giant proximity effect Strain?
Conclusions • Strong interactions are important in transport in small molecules and dots. Bulk Nano? • Interesting physics arises from a combination of Coulombic, phononic, and disordering effects. We need a ``Theory of Everything’’. • Electronic softness, self-organization, several d. of f. simultaneously active: Cause of CMR? Yes. Cause of high-Tc?
