Andres Cano. European Synchrotron Radiation Facility, Grenoble, France. collaborator : Efim Kats (ILL, Grenoble)

Transcription

1 Théorie des electromagnons : histoire, préhistoire et quelques nouveaux résultats Andres Cano European Synchrotron Radiation Facility, Grenoble, France collaborator : Efim Kats (ILL, Grenoble)

2 PRÉHISTOIRE, subst. fém. Période de l'histoire de l'humanité comprenant l'ensemble des événements antérieurs à l'apparition de l'écriture et à l'emploi des métaux. centre national de ressources textuelles et lexicales CNRS, wikipédia : même si cette définition n est pas sans poser des problèmes.

3 PRÉHISTOIRE, subst. fém. Période de l'histoire de la théorie comprenant l'ensemble des événements antérieurs à l'apparition des expériences et à l'emploi des multiferroïques. wikipédia : même si cette définition n est pas sans poser des problèmes.

4 histoire BiFeO 3 -like(t FE T M ): desousa&moore PRB 77, (08); APL 92, (08); Zvezdin&Mukhin JETP Lett.89,328(09);... journées electromagnons - Institut Néel, Grenoble, 01/2011 TbMnO 3 -like(t FE =T M ): Katsura,Balatsky&Nagaosa, PRL 98, (07); Cano&Kats PRB 78, (08); Cano PRBNature 80, (R) Physics 2, 97 (09); (2006) Chenglong&Jamal EPL 85, (09); Mochizuki, Furukawa&Nagaosa PRL 104, (10);... See also: Room et al., PRB 70, (04) Cepas&Ziman PRB 70, (04) Golovenchits&Sanina in: Magnetoelectric Interaction Phenomena in Crystals [eds. Fiebig,Eremenko&Chupis, Dordrecht:Kluwer, p.139 (04)] préhistoire Bakay&Chupis, Fiz.NizkikhTemp. 3, 1153 (77) Savchenko&Khabakhpashev, Fiz.Tverd.Tela 18, 2699 (76) Plyushko&Chupis, Ukr.Fiz.Zh. 19, 826 (74) Akhiezer&Davydov, Fiz.Tverd.Tela 12, 3171 (70) Akhiezer&Akhiezer, Zh.Eksp.Teor.Fiz. 39, 1009 (70) Sov. Phys. Solid State 10, 2818 (69); 11, 2628 (70)

5 préhistoire

6 préhistoire Bar yakhtar&chupis, Sov.Phys. Solid State 10, 2818 (69); 11, 2628 (70) ferroelectric-ferromagnet (T FE T M ) with free energy: where

7 préhistoire ferroelectric-ferromagnet (T FE T M ) with Bar yakhtar&chupis, Sov.Phys. Solid State 10, 2818 (69); 11, 2628 (70) free energy: dynamics: (Ginzburg-Anderson) linear response: (Landau-Lifshitz)

8 préhistoire Bar yakhtar&chupis, Sov.Phys. Solid State 10, 2818 (69); 11, 2628 (70) ferroelectric-ferromagnet (T FE T M ) with external fields (static): phonons and magnons do not talk each other

9 préhistoire Bar yakhtar&chupis, Sov.Phys. Solid State 10, 2818 (69); 11, 2628 (70) ferroelectric-ferromagnet (T FE T M ) with external fields (static): phonons and magnons hybridize!

10 préhistoire ferroelectric-ferromagnet (T FE T M ) with Bar yakhtar&chupis, Sov.Phys. Solid State 10, 2818 (69); 11, 2628 (70) external fields (dynamic): ME resonance in μ(ω) at ω e? ME resonance in ε(ω) at ω s ε(ω) V(t) electromagnon

11 histoire

12 electromagnons: experimental data optical absorption TbMnO 3 (T FE = 28K) E a, H c Pimenov et al., Nature Phys.2, 97 (06)

13 electromagnons in spiral multiferroics Katsura, Balatsky & Nagaosa PRL 98, (07) Bar'yakhtar&Chupis is extended to complex orders like in TbMnO 3 : cycloidal-ferroelectric Mn 3+ O 2- key ingredient: Dzyaloshinskii-Moriya interaction -explains ferroelectricity (T FE = T N ) - hybridizes phonons and magnons

14 electromagnons in spiral multiferroics minimal model (microscopic): Katsura, Balatsky & Nagaosa PRL 98, (07) -Rota on of the cycloidal plane ME resonance in ε (ω) -Polar q = 0, ±Q modes ME resonances in μ (ω) - ME cross-coupling process: electric-field excitation of spin waves E (ω,q) m (ω,q) M (0,Q)

15 new results

16 electromagnons in spiral multiferroics Cano&Kats PRB 78, (08); Cano PRB 80, (R) (09) minimal model (phenomenological): Solving the equations for the dynamics of the system we find the constitutive equations: This reveals two different ME resonant processes: E (ω,q) H (ω,q) m (ω,q) p (ω,q) M (0,Q) M (0,Q) which are both important in optical experiments!

17 electromagnons in spiral multiferroics Raman (TbMnO 3 ) results from both αand β 0! Rovillain et al., PRB 81, (10)

18 electromagnons in spiral multiferroics Cano&Kats PRB 78, (08); Cano PRB 80, (R) (09) propagation of light (Maxwell's + constitutive equations) conditions for electromagnons (= ME resonances): genuine ME effect! andres.cano@esrf.fr

19 conclusions - in general, the dynamical ME response implies two different resonant processes: E (ω,q) H (ω,q) m (ω,q) p (ω,q) M (0,Q) M (0,Q) Bar yakhtar&chupis, Sov.Phys. Solid State 10, 2818 (69); 11, 2628 (70) -theycanshowupas MEresonancesineffectiveεand/orμ Katsura, Balatsky & Nagaosa PRL 98, (07) genuinemeeffectsαandβ Cano&Kats PRB 78, (08); Cano PRB 80, (R) (09) - we have developed a theoretical framework to deal with these processes in different experiments (absorption and inelastic scattering) that canreadilyappliedtoothersystemswithcomplexorders(e.g.,bifeo 3 )