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Transport through a strongly coupled graphene quantum dot in perpendicular magnetic field.

Güttinger J, Stampfer C, Frey T, Ihn T, Ensslin K - Nanoscale Res Lett (2011)

Bottom Line: Lateral graphene gates are used to electrostatically tune the device.We show the evolution of Coulomb resonances as a function of perpendicular magnetic field, which provides indications of the formation of the graphene specific 0th Landau level.Finally, we demonstrate that the complex pattern superimposing the quantum dot energy spectra is due to the formation of additional localized states with increasing magnetic field.

View Article: PubMed Central - HTML - PubMed

Affiliation: Solid State Physics Laboratory, ETH Zurich, 8093 Zurich, Switzerland. guettinj@phys.ethz.ch.

ABSTRACT
We present transport measurements on a strongly coupled graphene quantum dot in a perpendicular magnetic field. The device consists of an etched single-layer graphene flake with two narrow constrictions separating a 140 nm diameter island from source and drain graphene contacts. Lateral graphene gates are used to electrostatically tune the device. Measurements of Coulomb resonances, including constriction resonances and Coulomb diamonds prove the functionality of the graphene quantum dot with a charging energy of approximately 4.5 meV. We show the evolution of Coulomb resonances as a function of perpendicular magnetic field, which provides indications of the formation of the graphene specific 0th Landau level. Finally, we demonstrate that the complex pattern superimposing the quantum dot energy spectra is due to the formation of additional localized states with increasing magnetic field.

No MeSH data available.


Related in: MedlinePlus

Device characterization. (a) Scanning force microscopy of the graphene quantum dot device. The overall chemical potential of the device is tuned by a global back gate, where as the right side gate (RG) is used for local asymmetric tuning. The extension of the dot is around 140 nm with 75 nm wide and 25 nm long constrictions. The white dashed lines delineating the quantum dot perimeter are added for clarity. (b) Measurement of the source (S)-drain (D) conductance for varying back gate voltage showing a transport gap from around -5 to 3 V (Vb = 200 μV). (c) Coulomb diamond measurements in the gap showing a charging energy of around 4.5 meV. This energy is lower than what has been measured in an other dot of similar size (Ref. [26]), most likely because of the increased coupling to the leads. The arrows point to faint lines outside the diamonds. The extracted energy difference of around 1 meV is a reasonable addition energy for excited states. Note that for the measurement in (c), in addition to the BG the right side gate was changed according to Vrg = -0.57·Vbg -1.59 V.
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Figure 1: Device characterization. (a) Scanning force microscopy of the graphene quantum dot device. The overall chemical potential of the device is tuned by a global back gate, where as the right side gate (RG) is used for local asymmetric tuning. The extension of the dot is around 140 nm with 75 nm wide and 25 nm long constrictions. The white dashed lines delineating the quantum dot perimeter are added for clarity. (b) Measurement of the source (S)-drain (D) conductance for varying back gate voltage showing a transport gap from around -5 to 3 V (Vb = 200 μV). (c) Coulomb diamond measurements in the gap showing a charging energy of around 4.5 meV. This energy is lower than what has been measured in an other dot of similar size (Ref. [26]), most likely because of the increased coupling to the leads. The arrows point to faint lines outside the diamonds. The extracted energy difference of around 1 meV is a reasonable addition energy for excited states. Note that for the measurement in (c), in addition to the BG the right side gate was changed according to Vrg = -0.57·Vbg -1.59 V.

Mentions: A scanning force microscope image of the final device studied here is shown in Figure 1a. The approximately 140 nm diameter graphene quantum dot is connected to source (S) and drain (D) via two graphene constrictions with a width of ≈75 nm and a length of ≈25 nm, both acting as tunneling barriers. The dot and the leads can be further tuned by the highly doped silicon substrate used as a back gate (BG) and three in-plane graphene gates: the left side gate (LG), the plunger gate (PG) and the right side gate (RG). Apart from the geometry, the main difference of this sample compared to the device presented in Ref. [27] is the higher root mean square variation of the height (rh) on the island. While there are no visible resist residues on the island of the sample in Ref. [27] with rh ≈ 0.35 nm, there are many dot-like residues on the sample presented here giving rh ≈ 1.1 nm.


Transport through a strongly coupled graphene quantum dot in perpendicular magnetic field.

Güttinger J, Stampfer C, Frey T, Ihn T, Ensslin K - Nanoscale Res Lett (2011)

Device characterization. (a) Scanning force microscopy of the graphene quantum dot device. The overall chemical potential of the device is tuned by a global back gate, where as the right side gate (RG) is used for local asymmetric tuning. The extension of the dot is around 140 nm with 75 nm wide and 25 nm long constrictions. The white dashed lines delineating the quantum dot perimeter are added for clarity. (b) Measurement of the source (S)-drain (D) conductance for varying back gate voltage showing a transport gap from around -5 to 3 V (Vb = 200 μV). (c) Coulomb diamond measurements in the gap showing a charging energy of around 4.5 meV. This energy is lower than what has been measured in an other dot of similar size (Ref. [26]), most likely because of the increased coupling to the leads. The arrows point to faint lines outside the diamonds. The extracted energy difference of around 1 meV is a reasonable addition energy for excited states. Note that for the measurement in (c), in addition to the BG the right side gate was changed according to Vrg = -0.57·Vbg -1.59 V.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3211315&req=5

Figure 1: Device characterization. (a) Scanning force microscopy of the graphene quantum dot device. The overall chemical potential of the device is tuned by a global back gate, where as the right side gate (RG) is used for local asymmetric tuning. The extension of the dot is around 140 nm with 75 nm wide and 25 nm long constrictions. The white dashed lines delineating the quantum dot perimeter are added for clarity. (b) Measurement of the source (S)-drain (D) conductance for varying back gate voltage showing a transport gap from around -5 to 3 V (Vb = 200 μV). (c) Coulomb diamond measurements in the gap showing a charging energy of around 4.5 meV. This energy is lower than what has been measured in an other dot of similar size (Ref. [26]), most likely because of the increased coupling to the leads. The arrows point to faint lines outside the diamonds. The extracted energy difference of around 1 meV is a reasonable addition energy for excited states. Note that for the measurement in (c), in addition to the BG the right side gate was changed according to Vrg = -0.57·Vbg -1.59 V.
Mentions: A scanning force microscope image of the final device studied here is shown in Figure 1a. The approximately 140 nm diameter graphene quantum dot is connected to source (S) and drain (D) via two graphene constrictions with a width of ≈75 nm and a length of ≈25 nm, both acting as tunneling barriers. The dot and the leads can be further tuned by the highly doped silicon substrate used as a back gate (BG) and three in-plane graphene gates: the left side gate (LG), the plunger gate (PG) and the right side gate (RG). Apart from the geometry, the main difference of this sample compared to the device presented in Ref. [27] is the higher root mean square variation of the height (rh) on the island. While there are no visible resist residues on the island of the sample in Ref. [27] with rh ≈ 0.35 nm, there are many dot-like residues on the sample presented here giving rh ≈ 1.1 nm.

Bottom Line: Lateral graphene gates are used to electrostatically tune the device.We show the evolution of Coulomb resonances as a function of perpendicular magnetic field, which provides indications of the formation of the graphene specific 0th Landau level.Finally, we demonstrate that the complex pattern superimposing the quantum dot energy spectra is due to the formation of additional localized states with increasing magnetic field.

View Article: PubMed Central - HTML - PubMed

Affiliation: Solid State Physics Laboratory, ETH Zurich, 8093 Zurich, Switzerland. guettinj@phys.ethz.ch.

ABSTRACT
We present transport measurements on a strongly coupled graphene quantum dot in a perpendicular magnetic field. The device consists of an etched single-layer graphene flake with two narrow constrictions separating a 140 nm diameter island from source and drain graphene contacts. Lateral graphene gates are used to electrostatically tune the device. Measurements of Coulomb resonances, including constriction resonances and Coulomb diamonds prove the functionality of the graphene quantum dot with a charging energy of approximately 4.5 meV. We show the evolution of Coulomb resonances as a function of perpendicular magnetic field, which provides indications of the formation of the graphene specific 0th Landau level. Finally, we demonstrate that the complex pattern superimposing the quantum dot energy spectra is due to the formation of additional localized states with increasing magnetic field.

No MeSH data available.


Related in: MedlinePlus