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. 2022 Sep 14;22(17):7049-7056.
doi: 10.1021/acs.nanolett.2c01943. Epub 2022 Aug 23.

Small Charging Energies and g-Factor Anisotropy in PbTe Quantum Dots

Affiliations

Small Charging Energies and g-Factor Anisotropy in PbTe Quantum Dots

Sofieke C Ten Kate et al. Nano Lett. .

Abstract

PbTe is a semiconductor with promising properties for topological quantum computing applications. Here, we characterize electron quantum dots in PbTe nanowires selectively grown on InP. Charge stability diagrams at zero magnetic field reveal large even-odd spacing between Coulomb blockade peaks, charging energies below 140 μeV and Kondo peaks in odd Coulomb diamonds. We attribute the large even-odd spacing to the large dielectric constant and small effective electron mass of PbTe. By studying the Zeeman-induced level and Kondo splitting in finite magnetic fields, we extract the electron g-factor as a function of magnetic field direction. We find the g-factor tensor to be highly anisotropic with principal g-factors ranging from 0.9 to 22.4 and to depend on the electronic configuration of the devices. These results indicate strong Rashba spin-orbit interaction in our PbTe quantum dots.

Keywords: PbTe; charging energy; g-factor; quantum dot; selective-area growth; spin−orbit interaction.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Two quantum dot devices in SAG PbTe nanowires on (111)A InP. (a,b) False-colored SEM micrographs of devices with crystal and magnetic field directions indicated. The nanowires are red, the Ti/Au contacts are yellow, and the Ti/Au gates are orange. For Device 2, VR was grounded. (c,d) Schematic cross sections as indicated in (a,b) by blue dashed lines. The terminating facets of the nanowires differ due to their different crystal directions.
Figure 2
Figure 2
Electrical characterization of quantum dot Device 1 at zero and finite magnetic fields. (a–d) Evolution of even–odd spacing between Coulomb blockade peaks as a function of magnetic field. VPG = −1.4 V is applied to the lower plunger gate in Figure 1a. Note that the rapid changes in slope at VR = −1.9 V are due to fast gate resetting after each horizontal scan. (e,f) Charge stability diagrams showing Kondo peaks, which split in a finite magnetic field. VPG = −1.25 V and VL = −2.4 V. The onset of inelastic cotunneling, which coincides with an excited state, is marked in (e) with an orange arrow and the level splitting is marked in (f) with a yellow double-arrow.
Figure 3
Figure 3
Electrical characterization of quantum dot Device 2 at zero and finite magnetic field. (a) Charge stability diagram at zero magnetic field and VL = −3.825 V, showing Kondo peaks in odd Coulomb diamonds and inelastic cotunneling in even diamonds. (b,c) Zoom-ins of the Coulomb diamond indicated with an arrow in (a), depicting the (split) Kondo peak at zero and finite magnetic field. (d) Evolution of the Kondo peak splitting as a function of magnetic field. The dashed line is a guide for the eye, which shows that the splitting is linear. For (a–c), VL = −3.825 V. For (d), VL = −3.825 V and VPG = −2.344 V.
Figure 4
Figure 4
g-factor anisotropy of all investigated quantum dot gate configurations. (a–c) In-plane g-factors extracted from energy level and Kondo peak splittings (red) and fits of the effective g-factor tensors (blue). The magnetic field was rotated in steps of 15°. The nanowires are displayed in each polar plot. (d–f) 3D plots of the g-factors extracted from three magnetic field rotations (red, purple, green lines) and the fits of the effective g-factor tensors (surface plots and black lines). The nanowire devices (orange), substrate planes (gray), and the magnetic field coordinate system are depicted.

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