Download presentation
Presentation is loading. Please wait.
Published bySilvia Bryant Modified over 9 years ago
1
Confinement of spin diffusion to single molecular layers in layered organic conductor crystals András Jánossy 1 Ágnes Antal 1 Titusz Fehér 1 Richard Gaál 2 Bálint Náfrádi 1,2 László Forró 2 Crystal growth: Erzsébet Tátrainé Szekeres 1, Ferenc Fülöp 1 special thanks to Natasha Kushch 1 Budapest University of Technology and Economics, Institute of Physics 2 Ecole Polytechnique Federale de Lausanne I.F. Schegolev Memorial Conference “Low-Dimensional Metallic and Superconducting Systems” October 11–16, 2009, Chernogolovka, Russia
2
Quasi 2D molecular layered compounds: Independent currents in each layer? Uncoupled magnetic order in each layer? A or M A B or M B A B A B
3
ac =0° ac =90° - ET 2 -X, layered organic crystal X = Cu[N(CN) 2 ]Cl, Br 2D polymer c a b A B 1 hole / ET 2 dimer X
4
c a b A B X t II ac =45° tt t 0.1 meV t // 100 meV - ET 2 -X, layered organic crystal X = Cu[N(CN) 2 ]Cl, Br 2D polymer
5
Phase diagram -(BEDT-TTF) 2 CuN(CN) 2 Cl, Br 5110 Mott transition
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
9.4 GHz BRUKER E500 420 GHz, Lausanne 222.4 GHz, Budapest High frequency ESR spectrometer high resolution same sensitivity 0-12 kbar pressure
8
Phase diagram -(BEDT-TTF) 2 CuN(CN) 2 Cl, Br ET-Cl ET-Br 2. Conduction electron spin resonance 5110 1. Antiferromagnetic resonance
9
D y z B M1M1 M2M2 F = H Zeeman + H exchange + H DM + H anisotropy F = - B(M 1 + M 2 ) + M 1 M 2 + D(M 1 x M 2 ) + ½K b (M 1y 2 +M 2y 2 )+½K(M 1z 2 + M 2z 2 ) Antiferromagnetic resonance 2 magnetizations 2 oscillation modes First AFMR work: Ohta et al, Synth. Met, 86, (1997), 2079-2080
10
DADA M A1 M A2 DBDB M B2 M B1 Magnetic structure D. F. Smith and C. P. Slichter, Phys. Rev. Let. 93, 167002, 2004 A B AB =? J = 600 T F = F A + F B + AB M A M B
11
Antiferromagnetic resonance calculation -(BEDT-TTF) 2 CuN(CN) 2 Cl 4 magnetizations : 4 modes: ω αA, ω A ω αB, ω A F = F A + F B + AB M A M B Antal et al., Phys. Rev. Lett. 102, 086404 (2009) 111.2 GHz ωω ωω Magnetic field [T] Frequency [GHz] B // b
12
Antiferromagnetic resonance experiment -(BEDT-TTF) 2 CuN(CN) 2 Cl 4 magnetizations : 4 modes: ω αA, ω A ω αB, ω A F = F A + F B + AB M A M B AFMR, 111.2 GHz, 4 K, H//b Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
13
A B A and B modes do not cross! intra-layer exchange: J = 600 T inter-layer coupling: AB =1x 10 -3 T AB = AB exchange + AB dipole (same order of magnitude) AB Antiferromagnetic resonance measured and calculated b a B, magnetic field ab Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
14
ET-Cl ET-Br Conduction electron spin resonance 5110 Conduction electron spin resonance in the metallic phase
15
A B 2D spin diffusion interlayer hopping rate T 1 spin life time < 1/T 1 2D spin diffusion
16
Expectation (300 K) : ħ / t ≈ 10 -11 s, // ≈ 10 -14 s T 1 ≈ 10 -9 s ≈ 2x10 8 s < 1/T 1 2D spin diffusion 2D spin diffusion v F // = 1 nm spin ≈ 250 nm A B = (2t 2 // ) / ħ 2 blocked by short // N. Kumar, A. M. Jayannavar, Phys. Rev. B 45, 5001 (1992) tt
17
A B A = g A B B/h B = g B B B/h Measurement of interlayer hopping ESR of 2 coupled spins g A ≠ g B
18
A B A B A B ESR < I A – B I ≈ I A – B I > I A – B I Measurement of interlayer hopping interlayer hopping frequency
19
B A 2 resolved ESR lines P=0, T=45-300 K A B < I A – B I < 3 x 10 8 Hz Ref. Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
20
ESR g- factor anisotropy 45 -250 K -(BEDT-TTF) 2 CuN(CN) 2 Cl A B b a B, magnetic field Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
21
A B A B A B ESR < I A – B I ≈ I A – B I > I A – B I Measurement of interlayer hopping pressure interlayer hopping frequency
22
-ET 2 -Cl < I A – B I ≈ I A – B I > I A – B I Measurement of interlayer hopping Ref. Motional narrowing under pressure 210 GHz T=250 K, B in (a,b) plane Instr. pressure
23
B A Measurement of interlayer hopping Motional narrowing under pressure 420 GHz T=250 K, = I A – B I = 1.0 x10 9 s -1 ESR spectral intensity
24
= (2t 2 // )/ħ 2 blocked interlayer hopping // parallel d.c. conductivity pressure dependence T=250 K Measurement of interlayer hopping
25
(P, T) interlayer hopping frequency ET-Cl ET-Br 5110 2x10 8 s -1 5x10 9 s -1 Summary
26
Measurement of interlayer hopping temperature dependence 111.2 GHz P=0 temperature Interlayer hopping frequency antiferromagnet metal
27
temperature dependence 111.2 GHz P=4 kbar Measurement of interlayer hopping temperature Interlayer hopping frequency metal superconductor
28
Measurement 250 K, P=0 : ≈ 2x10 8 s -1 < 1/T 1 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 2D spin diffusion = (2t 2 // ) / ħ 2 blocked by short // v F // = 1 nm A B confinement ≈ 350 nm
29
t 0.1 meV t // 100 meV Anisotropy of resistivity H. Ito et al J. Phys. Soc. Japan 65 2987 (1996) - / // nearly independent of T - 100 cm - / // 10 2 - 10 3
30
= (2t 2 // ) / ħ 2 blocking of interlayer tunnelling 1 / 1 / //, // 1 / // / // ( t // / t ) 2 (a/d) 2 independent of T H. Ito et al J. Phys. Soc. Japan 65 2987 (1996) Anisotropy of resistivity Buravov et al. J. Phys. I 2 1257(1992) -(BEDT-TTF) 2 CuN(CN) 2 Br -(BEDT-TTF) 2 CuN(CN) 2 Cl
31
Perpendicular dc resistivity: = 1/( e 2 g(E F ) d) g(E F ) = two dimensinal density of states d: interlayer distance -(BEDT-TTF) 2 CuN(CN) 2 Cl at 250 K, P=0: Calculated: = 80 -300 cm Typical measured: 100 cm
32
t 0.1 meV, t // 100 meV / // ( t // / t ) 2 (a/d) 2 expected anisotropy: / // 10 6 measured: / // 10 2 - 10 3 : dc resistivity and DoS agree with CESR // : measured is much less than calculated ?? unsolved Anisotropy of resistivity
33
-(BEDT-TTF) 2 [Mn 2 Cl 5 (H 2 O) 5 ] † Zorina et al CrystEngComm, 2009, 11, 2102 Mn Layer A Mn Layer B
34
ESR spectrum in the a* direction at 420 GHz and 300 K. Resolved lines correspond to the Mn 2+ ions and the ET molecules. ESR in (ET) 2 CuMn[N(CN) 2 ] 4, a radical cation salt with quasi two dimensional magnetic layers in a three dimensional polymeric structure K. L. Nagy 1, B. Náfrádi 2, N. D. Kushch 3, E. B. Yagubskii 3, Eberhardt Herdtweck 4, T. Fehér 1, L. F. Kiss 5, L. Forró 2, A. Jánossy 1 Phys. Rev. B (2009)
36
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
37
(P, T) interlayer hopping frequency ET-Cl ET-Br 5110 2x10 8 s -1 5x10 9 s -1 Summary
38
Antiferromagnet AB = exchange + AB dipole same order of magnitude Maybe AB changes sign at Mott transition ? AB A B
39
-ET 2 -Cl 1 < I A – B I ≈ I A – B I > I A – B I Measurement of interlayer hopping Ref. Motional narrowing under pressure 420 GHz T=250 K, B in (a,b) plane Instr.
40
A ωω ωω „A” layers only B ab Antiferromagnetic resonance Calculated B in (a,b) plane
41
A B Independent A and B layers A and B modes cross! Antiferromagnetic resonance Calculated B in (a,b) plane
42
Ohta et al, Synth. Met, 86, (1997), 2079-2080 Antiferromagnetic resonance -(BEDT-TTF) 2 CuN(CN) 2 Cl A. Antal et al 2008 (present work) B // b
43
’-(BEDT-TTF) 2 CuN(CN) 2 Cl resistivity Zverev et al, Phys. Rev. B. 74, 104504 (2006)
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.