Supporting Information: Enlightening the Ultrahigh Electrical Conductivities of Doped Double-Wall Carbon Nanotube Fibers by Raman Spectroscopy and First-Principles Calculations Damien Tristant, ab Ahmed Zubair, c Pascal Puech, ∗ a Fr´ ed´ eric Neumayer, a S´ ebastien Moyano, a Robert J. Headrick, def Dmitri E. Tsentalovich, def Colin C. Young, def Iann C. Gerber, b Matteo Pasquali, def Junichiro Kono, cfg and Jean Leotin h This Supporting Information document presents additional DFT calculations, Raman spectroscopy experiments and analyses performed on high-conductivity double-wall carbon nanotube fibers as a function of temperature and current. In the first section, we study using ab initio calculations, the electronic properties between SO 3 Cl molecules and metallic/semiconducting CNT, allowing us to use the equation (1) from the paper for our system. In the second section we describe the lattice temperature (T L ) dependence of the G-peak frequency, ω G . A linear relationship between ω G and T L was found with a slope dω G / dT L = −0.020 ± 0.002 cm −1 ·K −1 , which agrees with previous reports. 1 The third section deals with the temperature of a phonon system when the lattice is heated. The ratio between the anti-Stokes intensity, I AS , and the Stokes intensity, I S , allowed us to determine the thermal populations of phonons, which in turn yielded a photon temperature. The obtained phonon temperature agreed with the lattice temperature, confirming that phonons are in thermal equilibrium with the lattice (i.e., there are no hot phonons). Finally, in the third section, we present and analyze Raman spectra for the double-wall carbon nanotube fiber at different currents from 0 to 80 mA. As the current increases, the G-band frequency, ω G , decreases. The value of ω G at each current can be associated with a lattice temperature through the linear ω G − T L relationship established in the first section. Specifically, we found that ∆T is equal to 135 K as the current increases form 0 to 80 mA. a CEMES-CNRS, UPR-8011, Universit´ e F´ ed´ erale de Toulouse-Midi-Pyr´ en´ ees, 29 rue Jeanne Marvig, BP 94347 Toulouse, Cedex 4, France. Fax: +33 05 62 25 79 99; Tel: +33 05 67 52 43 57; E-mail: pascal.puech@cemes.fr b LPCNO, UMR-5215 CNRS, INSA, Universit´ e F´ ed´ erale de Toulouse-Midi-Pyr´ en´ ees, Universit´ e de Toulouse, 135 Avenue de Rangueil, 31077 Toulouse, France. c Department of Electrical and Computer Engineering, Rice University, 6100 Main St., Houston, Texas 77005, USA. d Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main St., Houston, Texas 77005, USA. e Department of Chemistry, Rice University, 6100 Main St., Houston, Texas 77005, USA. f Department of Materials Science and NanoEngineering, Rice University, 6100 Main St., Houston, Texas 77005, USA. g Department of Physics and Astronomy, Rice University, 6100 Main St., Houston, Texas 77005, USA. h LNCMI-CNRS, UPR 3228, Universit´ e F´ ed´ erale de Toulouse-Midi-Pyr´ en´ ees, 143 avenue de Rangueil, 31400 Toulouse, France. 1 Electronic Supplementary Material (ESI) for Nanoscale. This journal is © The Royal Society of Chemistry 2016