Using gate-modulated Raman scattering and electron-phonon interactions to probe single layer graphene: A new technique to assign phonon combination modes Mildred S. Dresselhaus, Massachusetts Institute of Technology, DMR Gate modulated and excitation laser dependent Raman spectroscopy (figure) have been widely used to study zone center q = 0 phonon modes, their self-energy, and their coupling to electrons in graphene systems. In this work we use gate-modulated Raman with q ≠ 0 phonons as a new technique to understand the nature of five combination modes in the second order Raman spectra observed in the frequency range of cm -1 of single layer graphene. Anomalous phonon self-energy renormalization phenomena are observed in all five of these intermediate-frequency combination modes which can clearly be distinguished from one another. By combining double resonance Raman theory with the anomalous phonon renormalization effect, we show a new technique for using Raman spectroscopy to identify the proper phonon mode assignment for each combination mode. This is done by using this new approach and comparing the experimentally obtained phonon dispersion, measured by using different laser excitation energies, with the help of both theoretical phonon dispersion relations and the angular dependence of the electron-phonon scattering matrix elements. This new approach will shed light on the understanding of more complex structures, such as occur in few-layer graphene with different stacking orders and in other 2D-like materials. An exfoliated graphene sample is back-gated and probed by the laser in a back scattering geometry so that the five Raman modes, related to vibrations of carbon atoms composing the graphene, are observed through the spectrometer. For each different laser line (E L ) and back- gate voltage (V G ), a Raman spectrum is acquired and its features, such as frequencies of vibrations and their linewidths, are analyzed as regards their E L and V G - dependence.

This year the P.I. received the Fermi Prize for fifty years of contributions to carbon research, starting with high magnetic field studies in the 1960s, graphite intercalation compounds in the 1970s and 1980s, fullerene studies in the 1980s and 1990s, carbon nanotubes in the 1990s and beyond, and finally graphene in the past decade, all supported by the present NSF/DMR grant and its predecessors going back to my appointment to the MIT faculty in The Fermi award emphasized research, as well as contributions to education, mentoring, and outreach to women. In my acceptance of the Fermi award I spoke to the importance of Fermi to all forefront subfields of physics, but also of his unique contributions to public welfare through the Man- hattan Project, to the education of a generation of physics students to gain an in-depth understanding of physics, and as a role model for all of his students. From him I also learned the importance of science education, mentorship, outreach, and role model activities. This was my take-home message on this occasion, celebrated in the Obama Oval Office. Professor Dresselhaus accepting congratulations from President Obama on receiving the Fermi award. (Left-to-right: Gene Dresselhaus, Mildred Dresselhaus, Laurose Richter, co-recipient Burton Richter) Using gate-modulated Raman scattering and electron-phonon interactions to probe single layer graphene: A new technique to assign phonon combination modes Mildred S. Dresselhaus, Massachusetts Institute of Technology, DMR