D 2h D 3d /D 5d T 400K hindered rotationquasi-isotropic rotation T 350 K bcobct ordered anionsmolecular axis nonparallel with c staggered static distortion static JTEor dynamic JTE potential field of molecular JTE counterions dominatesdominates 87 K 300 K Rb 4 C K 300 K K 4 C 60 Linewidth (cm -1 ) Temperature dependence of K 4 C 60 Temperature dependence of Rb 4 C 60 Cs 4 C K 96 K 475 K Temperature dependence of Cs 4 C 60 Transition temperature: KTransition temperature: KTransition temperature: K, 400 K IR(this work)D 2h D 3d /D 5d K 4 C 60 T K Rb 4 C 60 T K NMR [6,8]hindered rotationaxial rotation K 4 C 60 T < 250 K250 K < T < 580 K XRD [7,3]bct ordered axis ornonparallel with c merohedral staggered static distortion static JTE or dynamic JTE potential field of molecular JTE counterions dominatesdominates Distortions of C 60 studied by infrared spectroscopy Distortions of C 60 studied by infrared spectroscopy G. Klupp, F. Borondics, G. Oszlányi, K. Kamarás, N. M. Nemes*, J. E. Fischer*, A. F. Hebard**, D. B. Tanner** Research Institute for Solid State Physics and Optics, P. O. Box 49, Budapest, H 1525, Hungary, *Laboratory on the Research of the Stucture of Matter, University of Pennsylvania, Philadelphia, PA 19104, USA **Department of Physics, University of Florida, Gainesville, FL 32611, USA 4- Funding: Hungary OTKA T , T US NSF-INT K 4 C 60, Rb 4 C 60, Cs 4 C 60 Mott-Jahn-Teller insulator [1] JTE: p n  h  I h  D 5d / D 3d / D 2h [2] Detected molecular distortions: Cs 4 C 60 neutron diffraction: D 2h at 5 K, 293 K [3] K 4 C 60 IR: D 2h at K, D 3d / D 5d at 300 K[4] Na 4 C 60 CiCi [5] Introduction A 4 C 60 (A = Na, K, Rb, Cs) are air sensitive  preparation and KBr pellet pressing in dry box measurements in dynamic vacuum Sample characterization: XRD, Raman, IR  purity > 95 % IR measurements: LN2 cooled cryostat Bruker IFS28 FT-IR transmittance measurements while warming up Measurements Preparation 4 Na + C 60 4 K + C 60 4 Rb + C 60 4 Cs + C 60 Na 4 C 60 K 4 C 60 Rb 4 C 60 Cs 4 C o C 10 d 1 regrind 350 o C 10 d 1 regrind 350 o C 20 d 1 regrind 350 o C 10 d 1 regrind [1] M. Fabrizio and E. Tosatti, Phys. Rev. B 55, (1997). [2] C. C. Chancey and M. C. M. O’Brien, The Jahn-Teller effect in C 60 and Other Icosahedral Complexes (Princeton University Press, Princeton, 1997). [3] P. Dahlke and M. J. Rosseinsky, J. Mater. Chem. 14, 1285 (2002). [4] K. Kamarás, G. Klupp, D. B. Tanner, A. F. Hebard, N. M. Nemes and J. E. Fischer, Phys. Rev. B 65, (2002). [5] G. Oszlányi, G. Baumgartner, G. Faigel and L. Forró, Phys. Rev. Lett. 78, 4438 (1997). [6] V. Brouet, H. Alloul, S. Garaj and L. Forró, Phys. Rev. B 66, (2002). [7] R. M. Fleming, M. J. Rosseinsky, A. P. Ramirez, D. W. Murphey, J. C. Tully, R. C. Haddon, T. Siegrist, R. Tycko, S. H. Glarum, P. Marsh, G. Dabbagh, S. M. Zahurak, A. V. Makhija and C. Hampton, Nature 352, 701 (1991). [8] C. Goze, F. Rachdi and M. Mehring, Phys. Rev. B 54, 5164 (1996). References Staggered static distortion Correlation table Na 4 C 60 C i 4A u + 4A u + 4A u every T 1u splitmany strong new modes  covalent bonding cm -1 mode (typicalstrong distortion of single bonded fullerene polymers) Cs 4 C 60 D 2h 4B 1u + 4B 2u + 4B 3u Rb 4 C 60 D 3d / D 5d 4E u + 4A 2u only T 1u (3) & (4) splitting observedfew, weak new modes  weak distortion K 4 C 60 D 3d / D 5d 4E u + 4A 2u C 60 I h 4T 1u * / cm -1 IR Absorbance (a.u., baseline corrected) Comparison at room temperature Conclusion