Giant thermopower in carbon nanotubes: A one-dimensional Kondo system

Grigorian, L.; Суманасекера, Гамини; Loper, A. L.; Fang, Siyuan; Allen, J. S.; Eklund, P. C.

doi:10.1103/physrevb.60.r11309

Cited by 88 publications

(71 citation statements)

References 17 publications

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“…We believe that this observation is consistent with the predicted value of T K , although the disappearance occurs at a temperature ~10 K lower than that obtained from the fit. Interestingly, the Kondo temperature determined from our local spectroscopic measurement falls within the Kondo temperature range suggested on the basis of thermopower measurements on mats of SWNTs containing transition metal catalysts (14). In addition, we find that spectra taken above Co clusters of different sizes exhibit slightly different peak widths.…”

mentioning

confidence: 50%

“…A magnetic nanostructure composed of a magnetic impurity and a carbon nanotube host is an interesting system because the impurity spins would interact with conduction electrons confined to 1D, and, in addition, might potentially spincouple to a strongly (versus weakly) interacting electron system. The possibility of a Kondo state in SWNTs was recently suggested on the basis of thermopower measurements made on SWNT mats (14), although the complexity of such samples makes detailed analysis difficult.…”

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confidence: 99%

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Magnetic Clusters on Single-Walled Carbon Nanotubes: The Kondo Effect in a One-Dimensional Host

Odom¹,

Huang²,

Cheung³

et al. 2000

Science

119

116

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Single-walled carbon nanotubes are ideal systems for investigating fundamental properties and applications of one-dimensional electronic systems. The interaction of magnetic impurities with electrons confined in one dimension has been studied by spatially resolving the local electronic density of states of small cobalt clusters on metallic single-walled nanotubes with a low-temperature scanning tunneling microscope. Spectroscopic measurements performed on and near these clusters exhibit a narrow peak near the Fermi level that has been identified as a Kondo resonance. Using the scanning tunneling microscope to fabricate ultrasmall magnetic nanostructures consisting of small cobalt clusters on short nanotube pieces, spectroscopic studies of this quantum box structure exhibited features characteristic of the bulk Kondo resonance, but also new features due to finite size.

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confidence: 50%

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confidence: 99%

Magnetic Clusters on Single-Walled Carbon Nanotubes: The Kondo Effect in a One-Dimensional Host

Odom¹,

Huang²,

Cheung³

et al. 2000

Science

119

116

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“…In all other cases, the tiny values of T K make our results difficult to verify experimentally, which is a bit disappointing. There is however a positive implication, namely that, according to these results, the increase in the resistivity observed in nanotubes below 100 K 44-46 as well as the associated peak in the thermopower 44,45 could indeed be caused by magnetic impurities trapped inside the tube. A remarkable magnetic impurity is the single carbon atom vacancy.…”

Section: Discussionmentioning

confidence: 82%

Magnetic impurities in nanotubes: From density functional theory to Kondo many-body effects

et al. 2013

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Low temperature electronic conductance in nanocontacts, scanning tunneling microscopy (STM), and metal break junctions involving magnetic atoms or molecules is a growing area with important unsolved theoretical problems. While the detailed relationship between contact geometry and electronic structure requires a quantitative ab initio approach such as density functional theory (DFT), the Kondo many body effects ensuing from the coupling of the impurity spin with metal electrons are most properly addressed by formulating a generalized Anderson impurity model to be solved with, for example, the numerical renormalization group (NRG) method. Since there is at present no seamless scheme that can accurately carry out that program, we have in recent years designed a systematic method for semiquantitatively joining DFT and NRG. We apply this DFT-NRG scheme to the ideal conductance of single wall (4,4) and (8,8) nanotubes with magnetic adatoms (Co and Fe), both inside and outside the nanotube, and with a single carbon atom vacancy. A rich scenario emerges, with Kondo temperatures generally in the Kelvin range, and conductance anomalies ranging from a single channel maximum to destructive Fano interference with cancellation of two channels out of the total four. The configuration yielding the highest Kondo temperature (tens of Kelvins) and a measurable zero bias anomaly is that of a Co or Fe impurity inside the narrowest nanotube. The single atom vacancy has a spin, but a very low Kondo temperature is predicted. The geometric, electronic, and symmetry factors influencing this variability are all accessible, which makes this approach methodologically instructive and highlights many delicate and difficult points in the first principles modeling of the Kondo effect in nanocontacts.

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“…Since Kondo physics is historically interpreted as the interplay between the d-orbitals of magnetic impurities and the conduction continuum, we have to eliminate the possibility that the observed Fano resonance comes from residual traces of the Fe/Si catalyst in the MWNT samples. It has been shown that magnetic impurities in MWNTs cause an enhancement of thermoelectric power [17], which is absent in our careful TEP measurements [18]. Furthermore, no Fe signature can be detected in the body of the MWNT bundles within the instrumental resolution in the energy dispersion X-ray and TEM studies.…”

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confidence: 70%

Tunneling into Multiwalled Carbon Nanotubes: Coulomb Blockade and the Fano Resonance

Lü

et al. 2003

Phys. Rev. Lett.

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Tunneling spectroscopy measurements of single tunnel junctions formed between multiwalled carbon nanotubes (MWNTs) and a normal metal are reported. Intrinsic Coulomb interactions in the MWNTs give rise to a strong zero-bias suppression of a tunneling density of states (TDOS) that can be fitted numerically to the environmental quantum-fluctuation (EQF) theory. An asymmetric conductance anomaly near zero bias is found at low temperatures and interpreted as Fano resonance in the strong tunneling regime. PACS numbers: 73.63.Fg, 73.23.Hk, 85.35.Kt Coulomb blockade (CB) has been studied intensely in a multi-junction configuration, in which electron tunnel rates from the environment to a capacitively isolated "island" are blocked by the e-e interaction if the thermal fluctuation is below the charging energy E c = e 2 /2C and the quantum fluctuation is suppressed with sufficiently large tunnel resistance R t ≫ R Q = h 2 /2e. In the case of a single-junction circuit, the understanding of CB is less straightforward. The Coulomb gap, supposedly less significant for the case of low-impedance environments, should be established only if the environmental impendence exceeds R Q .In single-walled carbon nanotubes (SWNTs), the reduced geometry gives rise to strong e-e interaction. Indeed, CB oscillations and evidence of Luttinger liquid (LL) have been observed [1]. In contrast to SWNTs, in which only two conductance channels are available for current transport, MWNTs with diameter in the range of d=20-40 nm have several tens of conductance channels. The energy separation of the quantized subbands, given by ∆E = υ f /d, is about 13-26 meV taking the Fermi velocity υ f = 8 × 10 5 m/s. This value is about an order of magnitude smaller than that of SWNTs. Experiments indicate that MWNTs are considerably holedoped, thus a large number of subbands, on the order of ten, are occupied. Observations of weak localization [3], electron phase interference effect [2] and universal conductance fluctuations [3] support the view that low frequency conductance in MWNTs is contributed mostly by the outmost graphene shell and is characterized by 2D diffusive transport. In addition to the phase interference effects, a strong e-e interaction has also been observed in MWNTs. Pronounced zero-bias suppression of the TDOS has been observed several times in the tunneling measurements [4,5,6]. Moreover, the TDOS shows a power-law, i.e., ν(E) ∼ E α , which resembles the case of a LL. It is noteworthy that in the EQF theory, for a * Present address: Gordon McKay Laboratory of Applied Science, Harvard University, MA 02138, USA single tunnel junction coupled to high-impedance transmission lines, such a scaling behavior is also predicted at the limit of many parallel transmission modes [7]. The physical origin of these power laws is the linear dispersion of bosonic excitations that are characteristic both for LL, which is a strictly 1D ballistic conductor, and a single tunnel junction connected to a 3D disordered conductor. In the latter case, the quasiparti...

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Giant thermopower in carbon nanotubes: A one-dimensional Kondo system

Cited by 88 publications

References 17 publications

Magnetic Clusters on Single-Walled Carbon Nanotubes: The Kondo Effect in a One-Dimensional Host

Magnetic Clusters on Single-Walled Carbon Nanotubes: The Kondo Effect in a One-Dimensional Host

Magnetic impurities in nanotubes: From density functional theory to Kondo many-body effects

Tunneling into Multiwalled Carbon Nanotubes: Coulomb Blockade and the Fano Resonance

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