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Confinement of spin diffusion to single molecular layers in layered organic conductor crystals

Confinement of spin diffusion to single molecular layers in layered organic conductor crystals. I.F. Schegolev Memorial Conference “Low-Dimensional Metallic and Superconducting Systems” October 11–16, 2009, Chernogolovka, Russia. András Jánossy 1 Ágnes Antal 1 Titusz Fehér 1

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Confinement of spin diffusion to single molecular layers in layered organic conductor crystals

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  1. Confinement of spin diffusion to single molecular layers in layered organic conductor crystals I.F. Schegolev Memorial Conference “Low-Dimensional Metallic and Superconducting Systems” October 11–16, 2009, Chernogolovka, Russia András Jánossy1 Ágnes Antal1 Titusz Fehér1 Richard Gaál2 Bálint Náfrádi1,2 László Forró2 Crystal growth: Erzsébet Tátrainé Szekeres1, Ferenc Fülöp1 special thanks to Natasha Kushch 1Budapest University of Technology and Economics, Institute of Physics 2Ecole Polytechnique Federale de Lausanne

  2. Quasi 2D molecular layered compounds: Independent currents in each layer? Uncoupled magnetic order in each layer? IAor MA A IBor MB B A B

  3. - ET2-X, layered organic crystal X = Cu[N(CN)2]Cl, Br 2D polymer b 1 hole / ET2 dimer c A X B a ac=90° ac=0°

  4. - ET2-X, layered organic crystal X = Cu[N(CN)2]Cl, Br 2D polymer b 1 hole / ET2 dimer c A tII t X B a t// 100 meV ac=45° t 0.1 meV

  5. Phase diagram-(BEDT-TTF)2CuN(CN)2Cl, Br Mott transition 1 5 10

  6. Goal: Determine: 1. interlayer magnetic interaction in antiferromagnet 2. interlayer electron hopping frequency,  in metallic phase Method: high frequency ESR 1. Antiferromagnetic resonance, AFMR 2. Conduction electron spin resonance, CESR

  7. High frequency ESR spectrometer high resolution same sensitivity 0-12 kbar pressure 420 GHz, Lausanne 222.4 GHz, Budapest 9.4 GHz BRUKERE500

  8. Phase diagram-(BEDT-TTF)2CuN(CN)2Cl, Br ET-Cl ET-Br 2. Conduction electron spin resonance 1 5 10 1. Antiferromagnetic resonance

  9. Antiferromagnetic resonance F = HZeeman + Hexchange + HDM + Hanisotropy F = - B(M1 + M2 ) +  M1 M2 + D(M1 x M2) + ½Kb(M1y2 +M2y2)+½K(M1z2 + M2z2) D z y M1 M2 B 2 magnetizations  2 oscillation modes First AFMR work: Ohta et al, Synth. Met, 86, (1997), 2079-2080

  10. Magnetic structure DA J = 600 T MA1 A MA2 lAB =? B DB MB2 D. F. Smith and C. P. Slichter, Phys. Rev. Let. 93, 167002, 2004 F = FA + FB+ lABMAMB MB1

  11. Antiferromagnetic resonance calculation-(BEDT-TTF)2CuN(CN)2Cl B // b F = FA + FB+ lABMAMB ωb ωa 4 magnetizations : 4 modes: ωαA , ωbA ωαB , ωbA Frequency [GHz] 111.2 GHz Magnetic field [T] Antal et al., Phys. Rev. Lett. 102, 086404 (2009)

  12. Antiferromagnetic resonance experiment-(BEDT-TTF)2CuN(CN)2Cl AFMR, 111.2 GHz, 4 K, H//b F = FA + FB+ lABMAMB 4 magnetizations : 4 modes: ωαA , ωbA ωαB , ωbA Antal et al., Phys. Rev. Lett. 102, 086404 (2009)

  13. Antiferromagnetic resonance measured and calculated b B, magnetic field A ab a lAB B A and B modesdonotcross! intra-layerexchange: J = 600 T inter-layercoupling:AB =1x 10-3 T  AB =  AB exchange+  ABdipole (sameorder of magnitude) Antal et al., Phys. Rev. Lett. 102, 086404 (2009)

  14. Conduction electron spin resonance in the metallic phase ET-Cl ET-Br Conduction electron spin resonance 1 5 10

  15. 2D spin diffusion A  B interlayer hopping rate T1spin life time < 1/T1 2D spin diffusion

  16. 2D spin diffusion spin ≈ 250 nm vF//= 1 nm A  t B  = (2t2 //)/ ħ 2blocked by short // N. Kumar, A. M. Jayannavar, Phys. Rev. B 45, 5001 (1992) Expectation (300 K) : ħ / t≈10-11 s, //≈ 10-14 s T1≈ 10-9 s  ≈ 2x108 s < 1/T1 2D spin diffusion

  17. Measurement of interlayer hopping ESR of 2 coupled spins A= gABB/h A  B= gBBB/h B gA ≠ gB

  18. Measurement of interlayer hopping ESR  > I A – BI B A interlayer hopping frequency  ≈ I A – BI B A  < I A – BI B A

  19. 2 resolved ESR lines P=0, T=45-300 K A A B  Ref. B < I A – BI < 3 x 108 Hz Antal et al., Phys. Rev. Lett. 102, 086404 (2009)

  20. ESR g- factor anisotropy 45 -250 K -(BEDT-TTF)2CuN(CN)2Cl b B, magnetic field a a B  A Antal et al., Phys. Rev. Lett. 102, 086404 (2009)

  21. Measurement of interlayer hopping ESR  > I A – BI B A interlayer hopping frequency pressure  ≈ I A – BI B A  < I A – BI B A

  22. Measurement of interlayer hopping Motional narrowing under pressure 210 GHz T=250 K, B in (a,b) plane -ET2-Cl Ref. Instr.  > I A – BI  ≈ I A – BI pressure < I A – BI

  23. Measurement of interlayer hopping Motional narrowing under pressure 420 GHz T=250 K, A ESR spectral intensity B  = I A – BI = 1.0 x109 s-1

  24. Measurement of interlayer hopping pressure dependence T=250 K = (2t2 //)/ħ2 blocked interlayer hopping   // parallel d.c. conductivity

  25. Summary (P, T) interlayer hopping frequency ET-Cl ET-Br 2x108 s-1 5x109 s-1 1 5 10

  26. Measurement of interlayer hopping temperature dependence 111.2 GHz P=0 metal temperature Interlayer hopping frequency antiferromagnet

  27. Measurement of interlayer hopping temperature dependence 111.2 GHz P=4 kbar metal temperature Interlayer hopping frequency superconductor

  28. 2D spin diffusion confinement ≈ 350 nm A vF//= 1 nm  B  = (2t2 //)/ ħ 2blocked by short // Measurement 250 K, P=0 :  ≈ 2x108 s-1 < 1/T1 2D spin diffusion Electrons are confined to single molecular layers in regions of 350 nm radius // = 10-14 - 10-13 s t= 0.1 meV - 0.03 meV

  29. Anisotropy of resistivity t// 100 meV t 0.1 meV H. Ito et al J. Phys. Soc. Japan 65 2987 (1996) •  / // nearly independent of T •  100 cm •  / //  102 - 103

  30. Anisotropy of resistivity -(BEDT-TTF)2CuN(CN)2Br -(BEDT-TTF)2CuN(CN)2Cl Buravov et al. J. Phys. I 2 1257(1992) H. Ito et al J. Phys. Soc. Japan 65 2987 (1996)  = (2t2 //)/ ħ 2 blocking of interlayer tunnelling  1 /   1 / //, // 1 / //  / //  ( t// / t )2 (a/d)2 independent of T

  31. Perpendicular dc resistivity:  = 1/( e2 g(EF)  d) g(EF) = two dimensinal density of states d: interlayer distance -(BEDT-TTF)2CuN(CN)2Cl at 250 K, P=0: Calculated:  = 80 -300 cm Typical measured: 100 cm

  32. Anisotropy of resistivity t  0.1 meV, t// 100 meV  / //  ( t// / t )2 (a/d)2 expected anisotropy:  / //  106 measured:  / //  102 - 103 : dc resistivity and DoS agree with CESR // : measured is much less than calculated ?? unsolved

  33. -(BEDT-TTF)2[Mn2Cl5(H2O)5]† Mn Layer B Mn Layer A Zorina et al CrystEngComm, 2009, 11, 2102

  34. ESR in (ET)2CuMn[N(CN)2]4, a radical cation salt with quasi two dimensional magnetic layers in a three dimensional polymeric structure K. L. Nagy1, B. Náfrádi2, N. D.Kushch3, E. B. Yagubskii3, Eberhardt Herdtweck4, T. Fehér1, L. F. Kiss5, L. Forró2, A. Jánossy1 Phys. Rev. B (2009) ESR spectrum in the a* direction at 420 GHz and 300 K. Resolved lines correspond to the Mn2+ ions and the ET molecules.

  35. Me-3.5-DIP)[Ni(dmit)2]2 PS3-7 Yamamoto bi functional conductor PHYSICAL REVIEW B 77, 060403R 2008 PS3-10 Hazama transport under pressure

  36. Summary (P, T) interlayer hopping frequency ET-Cl ET-Br 2x108 s-1 5x109 s-1 1 5 10

  37. Antiferromagnet lAB = lAB exchange + lAB dipolesame order of magnitude Maybe lAB changes sign at Mott transition ? A B lAB

  38. Measurement of interlayer hopping Motional narrowing under pressure 420 GHz T=250 K, B in (a,b) plane -ET2-Cl Instr. Ref.  > I A – BI  ≈ I A – BI  1< I A – BI

  39. Antiferromagnetic resonance Calculated B in (a,b) plane B ab A ωa ωb „A” layers only

  40. Antiferromagnetic resonance Calculated B in (a,b) plane A B Independent A and B layers A and B modes cross!

  41. Antiferromagnetic resonance-(BEDT-TTF)2CuN(CN)2Cl B // b A. Antal et al 2008 (present work) Ohta et al, Synth. Met, 86, (1997), 2079-2080

  42. ’-(BEDT-TTF)2CuN(CN)2Clresistivity Zverev et al, Phys. Rev. B. 74, 104504 (2006)

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