AQP Seminar: Probing dynamical structural defects in nanodevices

Aalto Quantum Physics Seminar (Nanotalo). Speaker: Dr. Sheng-Shiuan Yeh (Institute of Physics, National Chiao Tung University, Taiwan)
 

Dynamical structural defects exist naturally in a wide spectrum of materials. These defects are modeled as two-level systems (TLSs) [1, 2]. The dynamical objects, which can be individual atoms (atomic TLSs) [3] or nanocrystalline grains (granular TLSs) [4], switch forth and back, causing mobility fluctuations due to the variation of scattering cross section. Such defect dynamics impacts on the current development of nanodevices with ultralow electrical noise, qubits with long quantum coherence time, and nanoelectromechanical system sensors with ultrahigh resolution. In materials, the TLSs usually possess a wide distribution of relaxation time, owing to the distribution of the barrier height between the two levels. This leads to a 1/f dependence of the noise power spectrum density (PSD) [5]. By measuring 1/f noise as a function of temperature, the distribution of the barrier height of TLSs, g(E), where E is the potential energy, can be quantitatively inferred [6]. Accordingly, the TLS density nTLS can also be obtained. This approach can be applied to quantitatively obtain g(E) and nTLS in a wide variety of materials where the 1/f noise is dominated by the mobility fluctuations. In this talk, I will present our recent noise study in metallic thin films and nanowires: (1) Activation energy distribution of dynamical structural defects in small conductors [6], and (2) Probing nanocrystalline grain dynamics in nanodevices [4].

[1] P. W. Anderson, B. I. Halperin, C. M. Varma, Anomalous low-temperature thermal properties of glasses and spin glasses. Philos. Mag. 25, 1 (1972).
[2] W. A. Phillips, Tunneling states in amorphous solids. J. Low Temp. Phys. 7, 351 (1972).
[3] G. J. Grabovskij, T. Peichl, J. Lisenfeld, G. Weiss, A. V. Ustinov, Strain tuning of individual atomic tunneling systems detected by a superconducting qubit. Science 338, 232 (2012).
[4] S.-S. Yeh, W.-Y. Chang, and J.-J. Lin, Probing nanocrystalline grain dynamics in nanodevices, Sci. Adv. 3, e1700135 (2017).
[5] P. Dutta and P. M. Horn, Low-frequency fluctuations in solids: 1/f noise, Rev. Mod. Phys. 53, 497 (1981).
[6] S.-S. Yeh, K. H. Gao, T.-L. Wu, T.-K. Su, and J.-J. Lin, Activation energy distribution of dynamical structural defects in RuO2 Films, Phys. Rev. Appl. 10, 034004 (2018).