Electronic behavior in mats of single-walled carbon nanotubes under pressure

Abstract

Single-walled carbon nanotubes (SWNTs) have many interesting properties; they may be metallic or semiconducting depending on their diameter and helicity of the graphene sheet. Hydrostatic or quasi-hydrostatic high pressures can probe many electronic features. Resistance -temperature measurements in SWNTs from normal condition and under 0.4 GPa of quasi-hydrostatic pressures reveal a semiconducting-like behavior. From 0.5 to about 2.0 GPa the resistance changes to a Kondo-like feature due to magnetic impurities used to catalyse the nanotube formation. Above 2.0 GPa, they become metallic and at about 2.4 GPa the resistance decreases dramatically around 3 K suggesting a superconducting transition. 71.30.+h, 74.10.+v, 75.20.Hr, 74.62.Fj Two unique characteristics of carbon nanotubes are their different electronic behavior depending on diameter and helicity [1,2]. Electronic and transport properties of singlewalled carbon nanotubes (SWNTs) also differ depending on chirality [3][4][5]. Many theoretical studies indicate that the local density of electronic states changes if the graphene sheet is wrapped in a zigzag or an armchair configuration. Armchair

Raman spectroscopy of open‐ended Single Wall Carbon Nanotubes under pressure: effect of the pressure transmitting medium

“…Several theoretical works have predicted that phase transitions should occur under pressure [1][2][3][4][5][6] implying a change of the tube cross section. Many experiments under pressure have also been performed: X-ray diffraction [7][8][9][10], neutron diffraction [11], resistivity [12][13][14][15] and Raman spectroscopy [16][17][18][19][20][21][22][23][24]. In some cases, signs of phase transitions are observed around 3 GPa, in others [8,20] no phase transition is observed up to 10 GPa and in our previous work [16] we have not observed phase transformations up to 40 GPa.…”

Pressure Stimulated Electronic Transitions in Mats of Single-Walled Carbon Nanotubes

“…The main panel of this figure shows the overall behavior of selected R(T) curves at different quasi-hydrostatic pressures for SWNTs cleaned with hydrochloric acid only. The presented data was normalized to the resistance value at 50 K. An analysis of the curves for this sample can be found in our previous work [9]. Measurements performed in various samples show that R(T) at atmospheric pressure, does not follow a Fermi liquid behavior, but a law, R ∼ T −β and β with values from 0.65 to 0.7.…”

“…However, theoretical studies suggest that the superconductivity observed in ropes of nanotubes by Kociak et al [7] may be an intertube coupling effect between nanotubes [8], rather than an intrinsic electronic mechanism as was proposed by Tang et al [6] for narrow nanotubes. More recently Falconi et al, [9] have reported signs of superconducting behavior in mats of SWNTs under high pressure conditions. The commercial samples studied by Falconi et al have magnetic impurities.…”

“…Those materials were cleaned with diluted solutions of acids in order to decrease the metallic impurities founded inside and outside of the nanotubes. These metallic impurities, mainly Co, Fe or Ni, are used as a normal procedure to catalyze the formation of the nanotubes [9]. From the experimentalist point of view should be clear, that defects, metallic impurities, and also diameter and chirality, as was mentioned before in this introductory part, will change the electronic behavior [10].…”

Superconductivity in an ultra‐small radius SWCNT

“…In this manner, increasing N(E F ) could also be carried out by rather doping of tube or applied pressure. Recently, Falconi et al [17] have reported superconductivity in SWCNTs with average diameter of 0.7-3 nm under 2.4 GPa quasi-hydrostatic pressure around 3 K, which could be due to increasing the N(E F ) [18]. Figure 3 shows the band structure of (4,0) SWCNT before and after ionic relaxation, which both are metallic.…”