Graphene zigzag ribbons: hidden multiferroic order and (spin polarized) transport SPAIN J. Fernández-Rossier, F. Muñoz, J. J. Palacios Electronic structure.

Presentación del tema: "Graphene zigzag ribbons: hidden multiferroic order and (spin polarized) transport SPAIN J. Fernández-Rossier, F. Muñoz, J. J. Palacios Electronic structure."— Transcripción de la presentación:

1 Graphene zigzag ribbons: hidden multiferroic order and (spin polarized) transport SPAIN J. Fernández-Rossier, F. Muñoz, J. J. Palacios Electronic structure graphene zigzag ribbons= Magnetic edges, S=0, P=0, spin resolved ferroelectricity + + + www.ua.es/personal/jfrossier H29-00010 = +

2 Bands of graphene zigzag ribbons Magnetic edges Non interacting bandsDFT LSDA bands 2 gaps Y. Son, Phys. Rev. Lett. 97, 216803 (06) Flat edge bands Joaquín Fernández-Rossier H29-00010

3 DFT results and questions Origin of the 2 gaps? What kind of electronic order? Relation with Spin resolved dipole? H29-00010 Y. Son, Phys. Rev. Lett. 97, 216803 (06) Joaquín Fernández-Rossier H29-00010

4 Methodology: Mean field Hubbard Mean Field Hubbard model M. Fujita et al.,J. Phys. Soc. Jpn., 65, 1920 (1996) K. Wakabayashi, M. Sigrist, M. Fujita, J. Phys. Soc. Jpn. 67, 2089 (1998) JFR, J. J. PalaciosPhys. Rev. Lett. 99, 177204 (2007) JFR, Phys. Rev. B. 77, 075430 (08) M. Wimmer, I. Adagideli, S. Berber, D. Tomanek, K.Richter, arXiv:0709.3244 Joaquín Fernández-Rossier H29-00010

5 Methodology: Mean field Hubbard vs DFT Mean Field Hubbard model MF Hubbard JFR, PRB. 77, 075430 (08) Joaquín Fernández-Rossier H29-00010

6 Crucial remark about mean field Hubbard in ZZ JFR, Phys. Rev. B 77, 075430 (2008) Joaquín Fernández-Rossier H29-00010

7 Crucial remark about mean field Hubbard in ZZ JFR, Phys. Rev. B 77, 075430 (2008) Joaquín Fernández-Rossier H29-00010

8 Crucial remark about mean field Hubbard in ZZ JFR, Phys. Rev. B 77, 075430 (2008) Joaquín Fernández-Rossier H29-00010

9 Crucial remark about mean field Hubbard in ZZ JFR, Phys. Rev. B 77, 075430 (2008) Joaquín Fernández-Rossier H29-00010

10 Spontaneous generation of eh pairs Joaquín Fernández-Rossier H29-00010 Non interacting ground state Interacting ground state

11 Interband coherence, phase Locking, Spin dipole Excitonic Insulator Joaquín Fernández-Rossier H29-00010 Spin dipole Phase Locking

12 Origin of the 2 gaps JFR, Phys. Rev. B 77, 075430 (2008) Joaquín Fernández-Rossier H29-00010 Pairing gap (inter-band exchange) Diagonal exchange BCS dispersion

13 Origin of the 2 gaps Joaquín Fernández-Rossier H29-00010 JFR,Phys. Rev. B 77, 075430 (2008) Diagonal exchange Magnetism in edges Pairing gap (inter-band exchange)

14 Spin state vs conduction properties FM: conducting AF: insulator No dipole No pairing gap Joaquín Fernández-Rossier H29-00010

15 Graphene Ribbon Spin Valve (CIP) Armchair conducting Short Zigzag Joaquín Fernández-Rossier H29-00010

16 Graphene Ribbon Spin valve (CIP) Joaquín Fernández-Rossier H29-00010

17 Summary J. Fernandez-Rossier, Phys. Rev. B 77, 075430 (2008) JFR, F. Muñoz-Rojas, J. J. Palacios, in preparation. DFT= MF Hubbard MF Hubbard=BCS Excitonic Insulator BCS= Spin Hidden Ferroelectricity BCS: intraband vs interband gapsAll Graphene SPIN VALVE