SciPost Submission Page
Orbital Edelstein effect from the gradient of a scalar potential
by Ivan A. Ado, Mikhail Titov, Rembert A. Duine, Arne Brataas
Submission summary
| Authors (as registered SciPost users): | Ivan Ado |
| Submission information | |
|---|---|
| Preprint Link: | https://arxiv.org/abs/2407.00516v2 (pdf) |
| Date submitted: | 2024-10-03 00:32 |
| Submitted by: | Ado, Ivan |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Phenomenological |
Abstract
We study the orbital Edelstein effect (OEE) that originates from a particular inversion symmetry breaking mechanism: an asymmetric scalar potential. We compute OEE of this kind with the help of the Kubo formula in the diffusive regime for a parabolic band Hamiltonian. We also present a qualitative derivation of the effect. Both approaches give the same result. This result does not rely on spin-orbit coupling (SOC) and scales as a cube of the momentum relaxation time. In sufficiently clean large systems with weak SOC, OEE of this nature should exceed the spin Edelstein effect by orders of magnitude. It may also provide an alternative interpretation for some experiments concerning the spin Hall effect.
Author indications on fulfilling journal expectations
- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
Current status:
Reports on this Submission
Strengths
1- The submitted paper addresses a topic of much current interest, the orbital Edelstein effect.
2- A new finding is that the orbital effect scales as the cube of the momentum relaxation time.
Weaknesses
1- although a part of the theory is on a high level, there can be technical questions around certain model assumptions.
2- the derived expression does not explicitly depend on the materials' specific electronic structure.
Report
The manuscript of Ado and collaborators addresses the origin of the orbital Edelstein effect. In the manuscript, an induced orbital momentum density is derived for a scalar potential gradient. Two derivations are in fact made, an elementary one and a microscopic derivation. These give both a scaling of the effect as tau^3.
1- In ref. 8 it was shown that in order to have the OEE in a crystal the local point group of the atom should not have inversion symmetry. It would be appropriate to specify in how far the here proposed gradient of the potential is different from the mechanism of ref. 8. When there is no inversion symmetry in z direction, there is a difference of the potential in +z and -z direction. The here considered gradient seems to be a special and less general form of this condition.
2- In section 2.2 there is a subtle change performed from operators in the first equations macroscopic quantities such as the drift velocity. It might be correct, but the expectational value of zv_x is then the product of two quantities, which is dangerous. The authors should specify why their rewriting of <zv_x> is possible.
3- The final equation (12) or (13) is written to depend on tau^3. This might be so when one rewrites the mean free path l, but then a further E also appears. In the end, the equation has then M proportional to E^3, but this is a higher order correction to the OEE. Eq. (25) seems to be different, however.
4- The form of how the electric field is included might also warrant further explanation. It is done through the mentioned substitution of the drift velocity, whereas the applied electric field doesn't appear in the Hamiltonian. There is instead the magnetic field that is derived from the vector potential in the Hamiltonian. An explanation is appropriate here, since E would be the time derivative of the vector potential, but this is zero for the chosen form, i.e., no E field.
Requested changes
The authors should consider points 1 to 4 in the above section and address these.
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