Browsing by Author "Kim, Yong"

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    Charge density wave paraconductivity in K0.3MoO3
    (1994) Gorshunov, Boris P.; Volkov, Alexander; Kozlov, Gennadij V.; Degiorgi, Leonardo; Blank, A.; Csiba, T.; Dressel, Martin; Kim, Yong; Schwartz, A.; Grüner, George
    The dynamic conductivity has been measured in K0.3MnO3 single crystals in the conducting phase (above 180 K), for the first time over a broad frequency range 1-105 cm-1, using a combination of different spectroscopic techniques. Together with a pseudogap, clearly pronounced excitations are observed below 50 cm-1 for E||b, the direction along which the charge density wave develops. We associate these excitations with charge-density-wave fluctuations which exist even at room temperature and give a collective contribution to the conductivity. For the transverse polarization, E|b, a usual single-particle Drude behavior of the conductivity is observed.
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    The electrodynamics of the spin density wave ground state : optical experiments on (TMTSF)2PF6
    (1994) Donavan, Steve; Kim, Yong; Degiorgi, Leonardo; Dressel, Martin; Grüner, George; Wonneberger, Wolfgang
    Conductivity measurements are reported in the organic linear-chain compound (TMTSF)2PF6 , in both the metallic and spin-density-wave states. The components of the complex conductivity were established by measurements in the radio-frequency, micro- and millimeter wave, and infrared spectral ranges. At temperatures above the spin-density-wave transition, a Drude-like metallic behavior was found together with a temperature-independent feature at higher frequencies. An observed Drude scattering rate of 3 cm-1 was found, placing the material well into the clean limit. In the spin-density-wave state, the low field dc resistivity shows an activated behavior similar to a standard semiconductor with a gap value 2Δ/kB≈45 K. The ac response shows a strong frequency dependence, and most importantly, we observe two subgap modes: a very broad one in the radio frequency range, due to internal deformations of the spin density wave, and a narrow mode near 0.1 cm-1, which we interpret as the response of the q=O phason. Furthermore, as expected for a material in the clean limit, we do not see evidence for a single particle gap in the infrared spectral ange. In this paper, we will compare our experimental results with the various models of spindensity-wave dynamics and comment on the current status of the understanding of the dynamical response of spin density waves.