Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 24: Quantum dots and wires: Transport properties II

HL 24.2: Talk

Tuesday, March 27, 2007, 14:15–14:30, H15

Sound-wave-like collective electronic excitations in atomic-scale conductive chains — •Tadaaki NAGAO — National Institue for Materials Science (NIMS), Tsukuba

In his pioneering work in 1950, Tomonaga has theoretically proven the existence of a sound-wave like excitation in one-dimensional array of Fermi particles that follows Bose statistics [1]. We have been searching for such one-dimensional (1D) collective excitation in high electron density-limit in atomic-scale conductive chains supported on semiconductor substrates. Electron energy loss spectroscopy using highly collimated slow electron beam has detected a characteristic sound wave-like excitations that propagate along the chains showing strong anisotropy [2]. These excitations are strongly dipole active and their lifetime rapidly drops as a function of momentum. From these features, the observed losses are identified as one-dimensional collective excitation (plasmon) that Tomonaga has mentioned. These plasmons shows highly metallic feature such as high intensity near the elastic peak, but at low temperatures (<70K), some of these plasmons show reduced density of states which indicates gap opening at the Fermi level, due to Peierls-type metal to insulator transition. [1] S. Tomonaga, Progress of Theoretical Physics Vol. 5, No.4, 544 (1950). [2] T. Nagao, S. Yaginuma, T. Inaoka, S. Sakurai, Phys. Rev. Lett. 97, 116802 (2006).