We report evidence for a structural phase transition in individual suspended metallic carbon nanotubes by examining their Raman spectra and electron trans- port under electrostatic gate potentials. The current-gate vo...We report evidence for a structural phase transition in individual suspended metallic carbon nanotubes by examining their Raman spectra and electron trans- port under electrostatic gate potentials. The current-gate voltage characteristics reveal anomalously large quasi-metallic band gaps as high as 240 meV, the largest reported to date. For nanotubes with band gaps larger than 200 meV, we observe a pronounced M-shape profile in the gate dependence of the 2D band （or G＇ band） Raman frequency. The pronounced dip （or softening） of the phonon mode near zero gate voltage can be attributed to a structural phase transition （SPT） that occurs at the charge neutrality point （CNP）. The 2D band Raman intensity also changes abruptly near the CNP, providing further evidence for a change in the lattice symmetry and a possible SPT. Pronounced non-adiabatic effects are observed in the gate dependence of the G band Raman mode, however, this behavior deviates from non-adiabatic theory near the CNP. For nanotubes with band gaps larger than 200 meV, non-adiabatic effects should be largely suppressed, which is not observed experimentally. This data suggests that these large effective band gaps are primarily caused by a SPT to an insulating state, which causes the large modulation observed in the conductance around the CNP. Possible mechanisms for this SPT are discussed, including electron-electron （e.g., Mott） and electron-phonon （e.g., Peierls） driven transitions.展开更多
基金Acknowledgements This work was supported in part by Department of Energy （Award No. DE-FG02-07ER46376 （SWC）） and Office of Naval Research （Award No. N000141010511） （RD） of the United States. A portion of this work was carried out in the University of California Santa Barbara （UCSB） nanofabrication fadlity, part of the National Science Foundation （NSF） funded National Nanotechnology Infrastructure Network （NNIN） net- work. This work was also supported in part by JSPS KAKENHI （Grant Nos. 20241023 and 23710118）.
文摘We report evidence for a structural phase transition in individual suspended metallic carbon nanotubes by examining their Raman spectra and electron trans- port under electrostatic gate potentials. The current-gate voltage characteristics reveal anomalously large quasi-metallic band gaps as high as 240 meV, the largest reported to date. For nanotubes with band gaps larger than 200 meV, we observe a pronounced M-shape profile in the gate dependence of the 2D band （or G＇ band） Raman frequency. The pronounced dip （or softening） of the phonon mode near zero gate voltage can be attributed to a structural phase transition （SPT） that occurs at the charge neutrality point （CNP）. The 2D band Raman intensity also changes abruptly near the CNP, providing further evidence for a change in the lattice symmetry and a possible SPT. Pronounced non-adiabatic effects are observed in the gate dependence of the G band Raman mode, however, this behavior deviates from non-adiabatic theory near the CNP. For nanotubes with band gaps larger than 200 meV, non-adiabatic effects should be largely suppressed, which is not observed experimentally. This data suggests that these large effective band gaps are primarily caused by a SPT to an insulating state, which causes the large modulation observed in the conductance around the CNP. Possible mechanisms for this SPT are discussed, including electron-electron （e.g., Mott） and electron-phonon （e.g., Peierls） driven transitions.
