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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

Conductance of the quantum dot with varying right gate and back gate voltage measured at bias voltage Vb = 200 μV. Coulomb resonances and modulations of their amplitude with different slopes are observed (dashed white lines). The extracted relative side gate back gate lever arms are ,  and . Lever arm (III) is attributed to resonances in the right constriction which are strongly tuned by the right side gate. In contrast resonances with lever arm (II) are only weakly affected by the right side gate and therefore attributed to states in the left constriction. The periodic resonances marked with (I) are attributed to resonances in the dot in agreement with the intermediate slope.
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Figure 2: Conductance of the quantum dot with varying right gate and back gate voltage measured at bias voltage Vb = 200 μV. Coulomb resonances and modulations of their amplitude with different slopes are observed (dashed white lines). The extracted relative side gate back gate lever arms are , and . Lever arm (III) is attributed to resonances in the right constriction which are strongly tuned by the right side gate. In contrast resonances with lever arm (II) are only weakly affected by the right side gate and therefore attributed to states in the left constriction. The periodic resonances marked with (I) are attributed to resonances in the dot in agreement with the intermediate slope.

Mentions: By focusing on a smaller back gate voltage range within the transport gap (indicated by the dashed lines in Figure 1b) and measuring the conductance as a function of Vbg and the right side gate Vrg much more fine-structure appears, as shown in Figure 2. A large number of resonances is observed with sequences of diagonal lines (see white lines in Figure 2) with different slopes, corresponding to different lever arms (α's). By sweeping the right side gate (Vrg) we break the left-right symmetry of the transport response (see also Figure 1a). This allows us to distinguish between resonances located either near the quantum dot or the left and right constriction. The steeper the slope in Figure 2 the less this resonance can be electrostatically tuned by the right side gate and, consequently, the larger the distance between the corresponding localized state and the right side gate. Subsequently, the steepest slope (II, corresponding to ) can be attributed to resonances in the left constriction and the least steepest slope (III, ) belongs to resonances in the right constriction. Both are highlighted as white dashed lines in Figure 2. The Coulomb resonances of the quantum dot appear with an intermediate slope (I, ) and exhibit clearly the smallest spacing in back gate voltage, ΔVbg ≈ 0.1 V. This is a good indication that they belong to the largest charged island in the system, which obviously is the 140 nm large graphene quantum dot, which is much larger than the localized states inside the graphene constrictions acting as tunneling barriers.


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)

Conductance of the quantum dot with varying right gate and back gate voltage measured at bias voltage Vb = 200 μV. Coulomb resonances and modulations of their amplitude with different slopes are observed (dashed white lines). The extracted relative side gate back gate lever arms are ,  and . Lever arm (III) is attributed to resonances in the right constriction which are strongly tuned by the right side gate. In contrast resonances with lever arm (II) are only weakly affected by the right side gate and therefore attributed to states in the left constriction. The periodic resonances marked with (I) are attributed to resonances in the dot in agreement with the intermediate slope.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Conductance of the quantum dot with varying right gate and back gate voltage measured at bias voltage Vb = 200 μV. Coulomb resonances and modulations of their amplitude with different slopes are observed (dashed white lines). The extracted relative side gate back gate lever arms are , and . Lever arm (III) is attributed to resonances in the right constriction which are strongly tuned by the right side gate. In contrast resonances with lever arm (II) are only weakly affected by the right side gate and therefore attributed to states in the left constriction. The periodic resonances marked with (I) are attributed to resonances in the dot in agreement with the intermediate slope.
Mentions: By focusing on a smaller back gate voltage range within the transport gap (indicated by the dashed lines in Figure 1b) and measuring the conductance as a function of Vbg and the right side gate Vrg much more fine-structure appears, as shown in Figure 2. A large number of resonances is observed with sequences of diagonal lines (see white lines in Figure 2) with different slopes, corresponding to different lever arms (α's). By sweeping the right side gate (Vrg) we break the left-right symmetry of the transport response (see also Figure 1a). This allows us to distinguish between resonances located either near the quantum dot or the left and right constriction. The steeper the slope in Figure 2 the less this resonance can be electrostatically tuned by the right side gate and, consequently, the larger the distance between the corresponding localized state and the right side gate. Subsequently, the steepest slope (II, corresponding to ) can be attributed to resonances in the left constriction and the least steepest slope (III, ) belongs to resonances in the right constriction. Both are highlighted as white dashed lines in Figure 2. The Coulomb resonances of the quantum dot appear with an intermediate slope (I, ) and exhibit clearly the smallest spacing in back gate voltage, ΔVbg ≈ 0.1 V. This is a good indication that they belong to the largest charged island in the system, which obviously is the 140 nm large graphene quantum dot, which is much larger than the localized states inside the graphene constrictions acting as tunneling barriers.

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