Kohn anomalies and non-adiabaticity in doped carbon nanotubes
| dc.creator | Caudal, Nicolas | |
| dc.creator | Saitta, A. Marco | |
| dc.creator | Lazzeri, Michele | |
| dc.creator | Mauri, Francesco | |
| dc.date | 2007-02-21 | |
| dc.date.accessioned | 2026-07-07T07:47:56Z | |
| dc.date.available | 2026-07-07T07:47:56Z | |
| dc.description | The high-frequency Raman-active phonon modes of metallic single-walled carbon nanotubes (SWNTs) are thought to be characterized by Kohn anomalies (KAs), which are expected to be modified by the doping-induced tuning of the Fermi energy level $ε_F$, obtained through the intercalation of SWNTs with alkali atoms or by the application of a gate potential. We present a Density-Functional Theory (DFT) study of the phonon properties of a (9,9) metallic SWNT as a function of electronic doping. For such study, we use, as in standard DFT calculations of vibrational properties, the Born-Oppenheimer (BO) approximation. We also develop an analytical model capable of reproducing and interpreting our DFT results. Both DFT calculations and this model predict, for increasing doping levels, a series of EPC-induced KAs in the vibrational mode parallel to the tube axis at the $\mathbfΓ$ point of the Brillouin zone, usually indicated in Raman spectroscopy as the $G^-$ peak. Such KAs would arise each time a new conduction band is populated. However, we show that they are an artifact of the BO approximation. The inclusion of non-adiabatic (NA) effects dramatically affects the results, predicting KAs at $\mathbfΓ$ only when $ε_F$ is close to a band crossing $E_{X}$. For each band crossing a double KA occurs for $ε_F=E_{X}\pm \hbarω/2$, where $\hbarω$ is the phonon energy. In particular, for a 1.2 $nm$ metallic nanotube, we predict a KA to occur in the so-called $G^-$ peak at a doping level of about $N_{el}/C=\pm 0.0015$ atom ($ε_F\approx \pm 0.1 ~eV$). Furthermore, we predict that the Raman linewidth of the $G^-$ peak significantly decreases for $|ε_F| \geq \hbarω/2$. | |
| dc.description | 11 pages, 6 figures | |
| dc.identifier | https://arxiv.org/abs/cond-mat/0702493 | |
| dc.identifier | http://arxiv.org/abs/cond-mat/0702493 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/124333 | |
| dc.subject | Soft Condensed Matter | |
| dc.subject | Materials Science | |
| dc.title | Kohn anomalies and non-adiabaticity in doped carbon nanotubes | |
| dc.type | text |