Microwave-Induced Dephasing in One-Dimensional Metal Wires

Abstract

We report on the effect of monochromatic microwave (MW) radiation on the weak localization corrections to the conductivity of quasi-one-dimensional (1D) silver wires. Due to the improved electron cooling in the wires, the MW-induced dephasing was observed without a concomitant overheating of electrons over wide ranges of the MW power PMW and frequency f . The observed dependences of the conductivity and MW-induced dephasing rate on PMW and f are in agreement with the theory by Altshuler, Aronov, and Khmelnitsky [1]. Our results suggest that in the lowtemperature experiments with 1D wires, saturation of the temperature dependence of the dephasing time can be caused by an MW electromagnetic noise with a sub-pW power. The processes of dephasing of electron wave function are central to the electronic transport in mesoscopic systems [2]. The dominant low-temperature dephasing mechanism in low-dimensional conductors is the scattering of an electron by equilibrium fluctuations of the electric field in the conductor, i.e. the Nyquist (Johnson) noise [3]. The Nyquist dephasing time τ ϕ increases with decreasing temperature as T −2/3 in the quasi-onedimensional (1D) conductors with the cross-sectional dimensions much smaller than the dephasing length L ϕ = Dτ ϕ (D is the electron diffusion constant) [3]. In the 1D metallic wires, this mechanism typically governs the dephasing at T < 1K [4,5,6].Recently, the interest in the fundamental limitations on τ ϕ was invigorated by the reports on the saturation of τ ϕ (T ) dependences in one-and zero-dimensional systems at ultra-low temperatures (see, e.g. [7,8]). The experiments [6] demonstrated that, at least in some studied 1D wires, this saturation could be attributed to the presence of localized spins in a small concentration undetectable by analytical methods. However, the problem of τ ϕ (T ) saturation in the most "clean" samples remained open [9]. One of the"extrinsic" mechanisms that might lead to the saturation of τ ϕ (T ) is the dephasing by the external microwave (MW) electromagnetic noise [1]. Detection of a very weak MW noise that is sufficient to destroy the phase coherence at ultra-low temperatures is a challenge. Indeed, the MW-induced dephasing may occur without an easily-observable electron overheating if the electrons in a wire can efficiently dissipate their energy in the environment [10]. The possibility of "noisedephasing-without-overheating" has not been ruled out in the experiments [7,9,11].In this Letter, we study the dephasing by monochromatic microwave radiation in 1D wires. By optimizing the sample design, we minimized electron overheating and observed for the first time the microwave-induced dephasing in 1D wires without a concomitant overheating of electrons. The dependences of the MW-induced dephasing rate on the MW power and frequency are in agreement with the theoretical predictions [1]. Our results suggest that the τ ϕ (T ) dependence in a 1D wire may be significantly affected by a sub-pW power of an external microwave noise absorbed in the sample...

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