Effect of carrier mobility on magnetothermoelectric transport properties of graphene

Xinfei Liu, Deqi Wang, Peng Wei, Lijun Zhu, and Jing Shi

Phys. Rev. B 86, 155414 – Published 10 October 2012

Abstract

With a method to systematically tune the mobility of the same graphene devices, we have investigated the dependence of magnetothermoelectric transport properties of graphene on the carrier mobility. In a zero magnetic field, we find that, as the mobility increases, the Seebeck coefficient $S_{x x}$ exhibits a more pronounced diverging trend near the Dirac point. In an external magnetic field, regular oscillations in $S_{x x}$ are identified corresponding to quantized Landau levels. Only in high-mobility states does an extra pair of peaks and dips in $S_{x x}$ emerge near the Dirac point that persists, at least, to 150 K, and the sign of the peak/dip is reversed as the mobility increases. Based on the signatures in the electrical conductivity and the Hall conductance near the Dirac point, we argue that the extra peak/dip in $S_{x x}$ is associated with an insulating behavior. Furthermore, the main Nernst coefficient peak increases linearly as the mobility increases. Our magnetothermoelectric transport results reflect the contrast in the electronic properties of graphene between low and high carrier mobility states.

Received 7 February 2012

DOI:https://doi.org/10.1103/PhysRevB.86.155414

Authors & Affiliations

Xinfei Liu¹, Deqi Wang¹, Peng Wei¹, Lijun Zhu², and Jing Shi¹

¹Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
²Theoretical Division, Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

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Issue

Vol. 86, Iss. 15 — 15 October 2012

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Images

Figure 1
(a) Zero-field electrical conductivity σ and (b) Seebeck coefficient $S_{x x}$ vs Δ $V_{g}$ of device A measured at 150 K with three mobility values. Δ $V_{g}$ is the gate voltage relative to the Dirac point. The inset of (b) is a false-colored scanning electron microscopy image of a graphene device. The graphene flake is connected to multiple leads for different purposes: 1 and 6 are for both thermovoltages and local thermometry via four-terminal resistivity; 2 and 4 and 3 and 5 are for Hall and Nernst voltages. A heater is located on the left end.Reuse & Permissions
Figure 2
Seebeck coefficient $S_{x x}$ vs $V_{g}$ for different magnetic fields in (a) low-mobility and (b) high-mobility states of device A measured at 150 K. Open arrows in both (a) and (b) indicate the position of the main peak at different magnetic fields. The solid arrow in (b) indicates the new peak near the Dirac point at high magnetic fields.Reuse & Permissions
Figure 3
(a) Nernst signal $S_{x y}$ at 8 T vs Δ $V_{g}$ for different mobility states of sample A at 150 K. The inset shows the linear dependence of the central Nernst peak height on carrier mobility. (b) Magnetic-field dependence of $S_{x y}$ of the same device in the highest-mobility state.Reuse & Permissions
Figure 4
(a) Seebeck coefficient $S_{x x}$ of device B at its highest-mobility state measured at 150 K up to 14 T. The open arrow shows the major peak shift as a function of the magnetic field, and the solid arrow shows the shift in the new peak near the Dirac point. The inset shows the contrast between two magnetic fields (4 and 14 T). (b) The magnetic-field dependence of the peak positions associated with E0, H0, E1, and H1 as labeled in the inset of (a). The inset of (b) shows the double-peak feature in $σ_{x x}$ measured at 150 K that corresponds to the subfeatures in $S_{x x}$ measured at the same temperature. In both $σ_{x x}$ and $S_{x x}$ , the corresponding first-LL features are also shown at higher gate voltages.Reuse & Permissions
Figure 5
(a) Quantum oscillations in $S_{x x}$ vs $V_{g}$ for different quantizing magnetic fields for device A at 20 K (curves are offset for clarity). Open and solid arrows indicate the first- and zeroth-LL features as well as their position shifts as the magnetic field is varied. (b) Both $σ_{x x}$ and $S_{x x}$ taken at 20 K are plotted together to show the correspondence of the subfeatures near the Dirac point. (c) Positions of E0, H0, E1, and H1 identified from $σ_{x x}$ and $S_{x x}$ (labeled by E0σ, E0S, etc.) measured at 20 K vs the magnetic field.Reuse & Permissions
Figure 6
(a) Quantum oscillations in $S_{x y}$ for different quantizing magnetic fields for device A at 20 K. (b) $S_{x y}$ for device B measured at 8 T and 20 K for four different mobility states. The inset shows the linear dependence of the central $S_{x y}$ peak height on carrier mobility.Reuse & Permissions

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