Pure electron-electron dephasing in percolative aluminum ultrathin film grown by molecular beam epitaxy

Nanoscale Research Letters, Feb 2015

We have successfully grown ultrathin continuous aluminum film by molecular beam epitaxy. This percolative aluminum film is single crystalline and strain free as characterized by transmission electron microscopy and atomic force microscopy. The weak anti-localization effect is observed in the temperature range of 1.4 to 10 K with this sample, and it reveals that, for the first time, the dephasing is purely caused by electron-electron inelastic scattering in aluminum.

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Pure electron-electron dephasing in percolative aluminum ultrathin film grown by molecular beam epitaxy

Lin et al. Nanoscale Research Letters Pure electron-electron dephasing in percolative aluminum ultrathin film grown by molecular beam epitaxy Shih-Wei Lin 0 3 Yue-Han Wu 1 3 Li Chang 1 3 Chi-Te Liang 2 3 4 Sheng-Di Lin 0 3 0 Department of Electronics Engineering, National Chiao Tung University , 1001 University Road, Hsinchu 30010 , Taiwan 1 Department of Materials 2 Department of Physics, National Taiwan University , Taipei 10617 , Taiwan 3 Science and Engineering, National Chiao Tung University , Hsinchu 30010 , Taiwan 4 Geballe Laboratory for Advanced Materials (GLAM), Stanford University , Stanford, CA 94305 , USA We have successfully grown ultrathin continuous aluminum film by molecular beam epitaxy. This percolative aluminum film is single crystalline and strain free as characterized by transmission electron microscopy and atomic force microscopy. The weak anti-localization effect is observed in the temperature range of 1.4 to 10 K with this sample, and it reveals that, for the first time, the dephasing is purely caused by electron-electron inelastic scattering in aluminum. Weak anti-localization; Ultrathin metal films; Pure electron-electron dephasing - Background Weak localization (WL) is the quantum correction to the conductance which occurs in weakly disordered systems due to coherent backscattering of electrons (or holes). As a results of spin-orbit coupling, weak antilocalization (WAL) may be observed in a weakly disordered electron (or hole) system [1]. The theoretic derivation and experimental proof of WAL were extensively developed since 1980s, and the investigation on various materials in all dimensions has been a central topic in condensed matter physics for decades. In particular, a wide variety of experimental results of WAL were obtained in two-dimensional (2D) systems. 2D system is suitable for experimental study of WAL because of its stronger WAL contribution than three-dimensional (3D) ones and its easier sample fabrication than onedimensional (1D) ones. Recently, due to its sensitivity to the electron dephasing and spin dephasing, WAL has been widely applied to studying the spin-orbit interaction in new materials, such as graphene, topological insulator, magnetic-doped semiconductor, and narrowgap semiconductor, to evaluate the potential for spintronics devices [2-7]. In addition, the interplay between superconducting effect and WAL also attracts much attention and has been investigated extensively. Ebisawa et al. derived the relationship between the superconducting pair-breaking parameter and the inelastic scattering rate i1 by = (/ 8kBT)i1 [8]. Their results have been used to study experiments of WAL in aluminum thin films [9-11]. However, it is a chanting challenge to grow an ideal 2D superconducting metallic sample. As the thickness of evaporated metal goes thinner, the discontinuity of the metal film un-avoidably appears due to large lattice mismatch between the template and metallic material as well as the surface non-uniformity of the bottom template. Previously, the reported metallic films were in the thickness of ten to a few tens of nanometers [9-14]. Although plenty of the theoretic works of WAL in twodimensional systems have been published in the past few decades, the experimental proof toward WAL in an ideal two-dimensional metallic system is still lacking. In this work, we have used molecular beam epitaxy (MBE) system as the deposition technique to prepare ultrathin Al films. By using gallium-rich GaAs as the epi-template, we are able to successfully deposit ultrathin percolated Al film for studying WAL toward the 2D limit. Interestingly, we have observed a pure electron-electron dephasing in this sample over the whole temperature range that WAL effect exists. Note that all of our characterizations including structural and electrical assessments were fulfilled ex situ, and the continuity of the Al film remains even after the post-processing for the Hall device fabrication. Even though our sample is not thin enough to reach the ultimate two-dimensional limit such as monolayer graphene, our results still provide an experimental proof that Nyquist scattering becomes the dominant inelastic scattering mechanism at all temperatures when the system approaches an ideal twodimensional one. Theory Magneto-resistance measurements are commonly used to study WAL. The theoretical calculation of 2D WAL in a perpendicular magnetic field was derived by Hikami, Larkin, and Nagaoka [1]. The difference of conductance induced by applied magnetic field can be expressed as: where B is the applied magnetic field. Y(x) represents (1/2 + x) ln(x), B2 = Bi + 3/4Bso, (x) is the digamma function. Here, Bi and Bso represent the strength of electron dephasing and spin-orbit interaction, respectively. For a superconducting material near its critical temperature Tc, superconducting fluctuations must be considered. Maki has calculated the effect of superconducting fluctuations in a 2D system ( (...truncated)


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Shih-Wei Lin, Yue-Han Wu, Li Chang, Chi-Te Liang, Sheng-Di Lin. Pure electron-electron dephasing in percolative aluminum ultrathin film grown by molecular beam epitaxy, Nanoscale Research Letters, 2015, pp. 71, Volume 10, Issue 1, DOI: 10.1186/s11671-015-0782-x