Reviewer Comments: Reviewer #1 Evaluations: RECOMMENDATION: Reconsider for APL after mandatory revision (major) Paper Interesting: No Original Paper: No Sufficient Physics: No Well Organized: Yes Clear and Error Free: No Conclusions Supported: No Appropriate Title: Yes Good Abstract: Yes Satisfactory English: Yes Adequate References: Yes Clear Figures: No OVERALL RATING: Poor
Reviewer #1 (Comments to the Author): The work reports on the B-field dependence of the spacing between Coulomb oscillations peaks in a GaAs/AlGaAs quantum point contact device with inter-digital transducers intended for surface acoustic wave operation. The authors interpret their work in terms of an impurity-induced quantum dot. In its current form I do not recommend this paper for publication in APL.
I have the distinct impression the authors are attempting to make a publication out of what seems to be a defective device. If the device in Fig 1 had actually worked as intended the physics (of moving quantum dots) would potentially be interesting. Instead fairly ordinary looking Coulomb diamonds and Coulomb oscillations are measured and interpreted in terms of an unintentional impurity-induced (static) quantum dot. Since the basic measurements and analysis have already been performed and well documented for intentional GaAs/AlGaAs quantum dots [see in particular Ref. 8 from 2002] does the work described really warrant publication in APL? At least I learnt nothing new nor did I gain any new insight (in to for instance g-factors, spin filling sequences, or impurity physics). What is important, interesting, timely or original in the work presented? The authors seem inspired by the work of Makarovsky et al in Refs 13,14 but I see little in common. Refs 13,14 describe dots formed by intentionally adding Mn. These dots have deep and strong confinement (strength ~20meV which is a thousand times bigger than the mean level spacing indirectly determined by the authors for their large dot), and the measurements are solely single-particle, i.e., in the one-electron limit so Coulomb blockade is not relevant. Most of the discussion is focused on the data shown in Figs 3 and 4. Aspects of Fig 4 are potentially interesting, but it is practically impossible to see (and be confident about) the origin of the peak spacing dependences presented looking at Fig 3. Why is such a large source drain bias (0.5mV) applied? Coulomb oscillation peaks numbered 1-3 are consequently very broad and arguably peaks numbered 4-7 are not really Coulomb oscillations at all (the source drain bias voltage applied is bigger then the half-width of the Coulomb diamonds so there is large current between the peaks). This is an important point since only the spacings between peaks 6-5 and 7-6 seem to have any significant non-zero slope in Fig. 4. The measurements should really be done at much smaller source drain bias [see Ref. 8]. At the very least, why not extract the position of the peaks and plot just these points instead in Fig. 3? Also, it would help significantly to show the current versus gate voltage traces for 0T and 8T. Concerning Fig 4, no explanation is given why the extracted g-factors are different from the expected/established value for a GaAs 2DEG. The authors argue that below 2T the Zeeman splitting is less than the thermal energy. Surely this means that below 2T no valid information about any of the peaking spacings can be determined and the data should probably be excluded (see also Ref. 8). The authors seem to think the fluctuations (also seen in Ref. 8) in the peak spacing curves have some deep significance. Could this not just be experimental error in determining the peak position (and the change in peak spacing is clearly small compared to the peak spacing) or due to the increment step in gate voltage? There could be other reasons but I certainly would not be convinced of the very speculative "single-particle dynamics that are most chaotic" explanation taken directly from Ref. 18 without better explanation and more compelling evidence. Some sentences or arguments have non-physical descriptions or are inconsistent: Page 3/ "These electrons may screen the external magnetic field...", I have no idea what the authors are talking about (and there is no mention of screening in Refs. 3,6-9). Pages 3-4/ On the one hand the authors tell us that orbital motion of the electrons and the level spacing should not be affected by the in-plane magnetic field. On the other hand the authors tell us the scattering effect is strong leading to large random peak spacing fluctuations ("singleparticle dynamics that are most chaotic"). The magnitude of the peak spacing fluctuations is clearly very small compared the spacing of the peaks evident in Fig. 3 so whatever effect is at play is small.
If the authors intend to resubmit, then the following must be addressed: 1. What is important, interesting, timely or original? These are critical criteria for publication in Appl. Phys. Lett. 2. Data in Figure 3 needs to be presented more clearly and the use (validity) of such a high value for the source drain bias needs to be justified. If data is available for smaller source drain bias then this should be considered. 3. The discussion of the physics needs correcting and improving. Lastly, although the English is adequate it could still be improved.