Tunable few-electron double quantum dots and Klein tunnelling in ultraclean carbon nanotubes

Steele, Gary A.; Götz, G.; Kouwenhoven, Leo P.

doi:10.1038/nnano.2009.71

Cited by 137 publications

(166 citation statements)

References 31 publications

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“…18 and 20. At the ͑11͒ side, the magnetic field splits the ͉⌽ 14, 15 11 ͘ Kramers doublet ͑that was only slightly above the ground state in Fig. 9͒ and shifts its ͉⌽ 14 ͘ component to the spectrum bottom; it is spin and isospin polarized with s = ↓ , = +.…”

Section: ↑ϯmentioning

confidence: 95%

“…[10][11][12][13][14] This band gap allows for electrostatic confinement of electrons and creation of few-electron QDs, otherwise not possible due to the Klein paradox. 15 Recent experiments have shown that it is indeed possible to confine electrons in single [16][17][18][19] and double QDs ͑DQDs͒ in a CNT by means of electrostatic gates in cleanly grown small band-gap nanotubes. 5,15,20 The present study is motivated by these experimental results.…”

Section: Introductionmentioning

confidence: 99%

“…15 Recent experiments have shown that it is indeed possible to confine electrons in single [16][17][18][19] and double QDs ͑DQDs͒ in a CNT by means of electrostatic gates in cleanly grown small band-gap nanotubes. 5,15,20 The present study is motivated by these experimental results.…”

Section: Introductionmentioning

confidence: 99%

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Spin-orbit effects in carbon-nanotube double quantum dots

Weiss¹,

Rashba²,

Kuemmeth³

et al. 2010

Phys. Rev. B

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We study the energy spectrum of symmetric double quantum dots in narrow-gap carbon nanotubes with one and two electrostatically confined electrons in the presence of spin-orbit and Coulomb interactions. Compared to GaAs quantum dots, the spectrum exhibits a much richer structure because of the spin-orbit interaction that couples the electron's isospin to its real spin through two independent coupling constants. In a single dot, both constants combine to split the spectrum into two Kramers doublets while the antisymmetric constant solely controls the difference in the tunneling rates of the Kramers doublets between the dots. For the two-electron regime, the detailed structure of the spin-orbit split energy spectrum is investigated as a function of detuning between the quantum dots in a 22-dimensional Hilbert space within the framework of a single-longitudinalmode model. We find a competing effect of the tunneling and Coulomb interaction. The former favors a left-right symmetric two-particle ground state while in the regime where the Coulomb interaction dominates over tunneling, a left-right antisymmetric ground state is found. As a result, ground states on both sides of the ͑11͒-͑02͒ degeneracy point may possess opposite left-right symmetry, and the electron dynamics when tuning the system from one side of the ͑11͒-͑02͒ degeneracy point to the other is controlled by three selection rules ͑in spin, isospin, and left-right symmetry͒. We discuss implications for the spin-dephasing and Pauli blockade experiments.

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Section: ↑ϯmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Spin-orbit effects in carbon-nanotube double quantum dots

Weiss¹,

Rashba²,

Kuemmeth³

et al. 2010

Phys. Rev. B

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“…A 1000 nm deep trench was dry etched, leaving a thin oxide layer on top of the gates. A 5/25 nm W/Pt layer was then deposited to serve as source and drain contacts, and a single-walled carbon nanotube was grown at the last fabrication step at a temperature of 900 • C from patterned Mo/Fe catalysts [31,28]. I PC (pA)…”

Section: Methodsmentioning

confidence: 99%

Identifying signatures of photothermal current in a double-gated semiconducting nanotube

2014

Self Cite

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).The remarkable electrical and optical properties of single-walled carbon nanotubes (SWNT) have allowed for engineering device prototypes showing great potential for applications such as photodectors and solar cells. However, any path towards industrial maturity requires a detailed understanding of the fundamental mechanisms governing the process of photocurrent generation. Here, we present scanning photocurrent microscopy measurements on a double-gated suspended semiconducting SWNT and show that both photovoltaic and photothermal mechanisms are relevant for the interpretation of the photocurrent. We find that the dominant or non-dominant character of one or the other processes depends on the doping profile, and that the magnitude of each contribution is strongly influenced by the series resistance from the band alignment with the metal contacts. These results provide new insight into the interpretation of features in scanning photocurrent microscopy and lay the foundation for the understanding of optoelectronic devices made from SWNTs. [6,7,8,9,10,11,12,13, 15] as well as 2D materials like graphene [16,17,18,19,20,21,22,23] and MoS 2 [24,25]. In such nanoscale systems, two mechanisms have been identified for the generation of photocurrent: i) photovoltaic processes where photo-excited carriers are separated by built-in electrical fields and ii) photothermal processes where thermoelectric forces drive carriers through light-induced thermal gradients.Single-walled carbon nanotubes (SWNT) are long, one dimensional conductors with a band structure ranging from quasimetallic (bandgap E g ∼ 30 meV) to semiconducting character (E g typically in the range of 0.1 to 1 eV) depending on chirality and diameter. These properties make SWNTs an ideal platform for exploring photocurrent generation with SPCM. In early single-walled nanotubes SPCM work the interpretation of photocurrent was mostly based on photovoltaic mechanisms [6,7,8,9,11].The importance of photothermal effects has been suggested in the context of measurements of bulk SWNT films [12,13,14] and very recently, SPCM work on graphene and individual metallic SWNTs has emphasized the importance of photothermal mechanisms in materials with no or small bandgaps [22,26].The question of the role of photothermal mechanisms in larger bandgap semiconducting nanotubes has been studied very recently in double-gated [26] and single-gated [27] suspended carbon nanotube devices.These two studies report contradictory results, leaving the understanding of fundamental mechanisms underlying photocurrent generation in semiconducting nanotubes unclear.Here we report on the study of a suspended semiconducting nanotube device where we show that both photovoltaic and photothermal mechanisms compete in the generation of photocurrent. In particular, we find that the dominant or non-dominant character of one or the other processes is a function of the doping profile and that the magnitude of each contribution is strongly influenced by the band alignment with the metal contacts throu...

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“…Quantum dots allow a range of fundamental phenomena to be explored, such as the coupling of both the electron and the hole confined within a double dot, which can be controlled by applying suitable gate voltages 8 . Image reproduced from Gary Steele, Georg Gotz and Leo Kouwenhoven (cover image) 8 , © 2009 NPG.…”

Section: Join the Dotsmentioning

confidence: 99%