Electron-phonon coupling in the copper intercalated Bi2Se3 hybrid devices

We investigated charge and heat transport in copper intercalated Bi2Se3 topological insulator in temperatures ranging from 15 mK up to 250 K. Both superconducting aluminium leads and normal, golden leads were employed for contacting the samples. Measurements of magnetoconductivity of the Al-contacted sample were performed at temperature T = 100 mK using magnetic fields ranging from 0 T up to 5 T. Fitting results of the experiment with the HLN model1 were consistent with weak localization, and it yielded the materials parameters: the coherence length (33 nm), mean-free path (12 nm), spin-orbit scattering length (19 nm) and mobility (593 cm2/Vs). Weak localisation and electron-electron intercatios2 were major processes contributing to the conductivity in the Au-contacted sample. Disorder-related small unit cell deformation of the topological insulator enhanced separation of the in-plane and cross-plane processes. Such separation resulted in charge and phonon confinement in quintuple layers of the topological insulator. Shot noise measurements revealed that heat transport in the layered material is more sensitive to such an anisotropy than charge transport. The anisotropy was reflected in the heat flux investigated in three temperature ranges. The heat flux showed T2 temperature dependence at T < 7 K, which changed to T3 at 7 K < T < 12 K and to T4 at T > 12K. A model of electron scattering on transverse acoustic phonons taking into account dynamic and static disorder as well as the Kapitza3 resistance originating from the mismatch between acoustic phonons impedances of an investigated material and a substrate is found to be in accordance with the data. References: [1] Assaf, B. A. et al. Linear magnetoresistance in topological insulator thin films: Quantum phase coherence effects at high temperatures. Appl. Phys. Lett. 102, 012102 (2013). [2] Wang, J. et al. Evidence for electron-electron interaction in topological insulator thin films. Phys. Rev. B Condens. Matter Mater. Phys. 83, 245438 (2011). [3] Elo, T. et al. Thermal Relaxation in Titanium Nanowires: Signatures of Inelastic ElectronBoundary Scattering in Heat Transfer. J. Low Temp. Phys. 189, 204–216 (2017).