1,699 research outputs found
Room temperature Peierls distortion in small radius nanotubes
By means of {\it ab initio} simulations, we investigate the phonon band
structure and electron-phonon coupling in small 4-\AA diameter nanotubes. We
show that both the C(5,0) and C(3,3) tubes undergo above room temperature a
Peierls transition mediated by an acoustical long-wavelength and an optical
phonons respectively. In the armchair geometry, we verify that the
electron-phonon coupling parameter originates mainly from phonons at
and is strongly enhanced when the diameter decreases. These results
question the origin of superconductivity in small diameter nanotubes.Comment: submitted 21oct2004 accepted 6jan2005 (Phys.Rev.Lett.
Gap Structure of the Overdoped Iron-Pnictide Superconductor Ba(FeNi)As: A Low-Temperature Specific-Heat Study
Low-temperature specific heat (SH) is measured on the postannealed
Ba(Fe_{1-x}Ni_x)_2As_2 single crystal with x = 0.058 under different magnetic
fields. The sample locates on the overdoped sides and the critical transition
temperature is determined to be 14.8 K by both the magnetization and SH
measurements. A simple and reliable analysis shows that, besides the phonon and
normal electronic contributions, a clear T2 termemerges in the low temperature
SH data.Our observation is similar to that observed in the Co-doped system in
our previous work and is consistent with the theoretical prediction for a
superconductor with line nodes in the energy gap.Comment: 5 pages, 4 figure
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