Experimental observation of the crystallization of a paired holon state

A new excitation is observed at 201 meV in the doped-hole ladder cuprate Sr$_{14}$Cu$_{24}$O$_{41}$, using ultraviolet resonance Raman scattering with incident light at 3.7 eV polarized along the direction of the rungs. The excitation is found to be of charge nature, with a temperature independent excitation energy, and can be understood via an intra-ladder pair-breaking process. The intensity tracks closely the order parameter of the charge density wave in the ladder (CDW$_L$), but persists above the CDW$_L$ transition temperature ($T_{CDW_L}$), indicating a strong local pairing above $T_{CDW_L}$. The 201 meV excitation vanishes in La$_{6}$Ca$_{8}$Cu$_{24}$O$_{41+\delta}$, and La$_{5}$Ca$_{9}$Cu$_{24}$O$_{41}$ which are samples with no holes in the ladders. Our results suggest that the doped holes in the ladder are composite bosons consisting of paired holons that order below $T_{CDW}$.Comment: Accepted for publication in Physical Review Letters (4 figures

Evidence for phase formation in potassium intercalated 1,2;8,9-dibenzopentacene

We have prepared potassium intercalated 1,2;8,9-dibenzopentacene films under vacuum conditions. The evolution of the electronic excitation spectra upon potassium addition as measured using electron energy-loss spectroscopy clearly indicate the formation of particular doped phases with compositions K$_x$dibenzopentacene ($x$ = 1,2,3). Moreover, the stability of these phases as a function of temperature has been explored. Finally, the electronic excitation spectra also give insight into the electronic ground state of the potassium doped 1,2;8,9-dibenzopentacene films.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with arXiv:1201.200

Crystal Growth, Dynamic and Charge Transfer Properties of New Coronene Charge Transfer Complexes

© 2015 American Chemical Society. Two new coronene charge transfer complexes with F4-TCNQ of 2:1 and 1:1:1 (solvate with acetonitrile, MeCN) stoichiometry were obtained using crystal growth procedures from the solution and vapor phase. It was shown that mobility of coronene molecules in crystals is more affected by the asymmetry of its surrounding than by the composition and degree of charge transfer and interstack interactions. The combination of X-ray diffraction and electrochemistry in the solid state and a time-resolved one in solution allowed us to clarify the nucleation in solution showing that the formation of 2:1 coronene/F4-TCNQ complexes is thermodynamically preferable. The X-ray single crystal data for pristine coronene showed the crystal structure to be the same as at ambient temperature, raising doubt about the previously reported phase transitions at 140-180 K

Crystal growth, structure, and transport properties of the charge-transfer salt picene/2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane

Single crystals of the charge-transfer salt picene/2,3,5,6-tetrafluoro-7,7, 8,8-tetracyanoquinodimethane have been grown using physical vapor transport. The crystal structure was determined using single-crystal X-ray diffraction. It was found that the crystals grow in a 1:1 molecular ratio and adopt a monoclinic structure with alternate stacking. Both X-ray data and Raman measurements show that the grown crystals are of good quality. From structure and infrared data, the charge transfer between acceptor and donor molecules was estimated to be approximately 0.14-0.19 electron. Transport measurements indicate a nonmetallic ground state with an activation energy of 0.6 eV. The supporting density functional theory calculations on molecular model systems as well as on crystalline structures confirm the amount of charge transfer and provide first insights into the electronic structure of the new material. © 2014 American Chemical Society