Magnetotransport in an aluminum thin film on a GaAs substrate grown by molecular beam epitaxy.
Bottom Line:
A crossover from electron- to hole-dominant transport can be inferred from both longitudinal resistivity and Hall resistivity with increasing the perpendicular magnetic field B.Also, phenomena of localization effects can be seen at low B.By analyzing the zero-field resistivity as a function of temperature T, we show the importance of surface scattering in such a nanoscale film.
Affiliation: Department of Physics, National Taiwan University, No, 1, Sec, 4, Roosevelt Rd, Taipei 106, Taiwan. sdlin@mail.nctu.edu.tw.
ABSTRACT
Magnetotransport measurements are performed on an aluminum thin film grown on a GaAs substrate. A crossover from electron- to hole-dominant transport can be inferred from both longitudinal resistivity and Hall resistivity with increasing the perpendicular magnetic field B. Also, phenomena of localization effects can be seen at low B. By analyzing the zero-field resistivity as a function of temperature T, we show the importance of surface scattering in such a nanoscale film. No MeSH data available. Related in: MedlinePlus |
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Mentions: where A and B are system-dependent constants. The first term represents the residual resistivity. The second and the third terms are due to electron-electron scattering and Bloch-Gruneisen electron-phonon scattering, respectively. The fittings of Eq. (1) to the resistivity over the whole temperature range and above T = 30 K are shown in Figure 4a and its inset, respectively. It can be seen that the good fitting is limited to the temperature above 30 K. The obtained coefficient of T2 dependence is approximately equal to 600 fΩmK-2. However, Soffer's theory cannot produce such a large T2 term over such a wide temperature range 30 K <T < 78 K. Also, electron-electron scattering would not exist at such high T. It is believed that the violation of Soffer's theory in aluminum is due to its complex Fermi surface. As suggested by Sambles et al. [30], T2 dependence can exist alone without a T5 term, which is derived by considering the Umklapp scattering process occurring at the surface for materials with a disconnected Fermi surface [31]. Figure 4b shows that ρxx follows the T2 dependence as T > 30 K, indeed consistent with the model of surface Umklapp scattering. On the other hand, it shows a trend toward a T3 dependence with decreasing T below 30 K, as shown in Figure 4c, which can be ascribed to the electron-phonon scattering introducing the Umklapp process, usually observed in the bulk material [13]. Even though we know that the Umklapp process is likely to be important in our system, the crossover from T2 to T3 dependence with decreasing T can still be explained by Olsen's argument for low-angle scattering qualitatively. At relatively low T, the magnitude of the momentum of phonons is too small to induce the size effect such that the Umklapp scattering process occurring in the interior may possibly be dominant over that occurring at the interface. Thus, the crossover from the T2 dependence to T3 dependence of resistivity with decreasing T below 30 K can be predicted. A similar T2 term can be observed for 46 K <T < 90 K performed in a subsequent cooldown in a closed cycle system, as shown in Figure 5. A deviation from this dependence at T > 90 K is ascribed to the mean free path shortening with decreasing T. Thus, the size effect becomes less important, also consistent with Olsen's argument. At T > 105 K, ρxx shows a tendency toward a linear dependence on T, as shown in the inset of Figure 5. A classical model has predicted such a linear term at high T (much larger than the Debye temperature, about 394 K for aluminum). However, our result is not in this case. The onset of this linear dependence with increasing T and how the size effects modulate the magnetoresistance requires further investigations. |
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Affiliation: Department of Physics, National Taiwan University, No, 1, Sec, 4, Roosevelt Rd, Taipei 106, Taiwan. sdlin@mail.nctu.edu.tw.
No MeSH data available.