Spin Hall effect in prototype Rashba ferroelectrics GeTe and SnTe

H. Wang; J. Slawinska; M. Buongiorno Nardelli; P. Gopal; S. Curtarolo; S. Picozzi

arxiv: 1907.03979 · v1 · pith:647SZQRTnew · submitted 2019-07-09 · ❄️ cond-mat.mtrl-sci

Spin Hall effect in prototype Rashba ferroelectrics GeTe and SnTe

H. Wang , P. Gopal , S. Picozzi , S. Curtarolo , M. Buongiorno Nardelli , J. Slawinska This is my paper

Pith reviewed 2026-05-25 00:45 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci

keywords spin Hall effectferroelectric Rashba semiconductorsGeTeSnTedopinglone pair electronsdensity functional theoryspintronics

0 comments

The pith

DFT shows spin Hall effect can coexist with ferroelectric polar phase in doped GeTe.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper applies density functional theory to GeTe and SnTe to determine whether the spin Hall effect remains viable once these materials are doped enough to conduct. It calculates spin Hall conductivity in both the ferroelectric and paraelectric structures and checks how free carriers affect the lone-pair electrons that stabilize the polar distortion. GeTe retains sizable polar displacements up to hole densities above 10^21 per cubic centimeter, while the already small distortions in SnTe collapse at far lower doping. Spin Hall angles extracted for the doped polar cases indicate that charge-to-spin conversion stays usable even when the Rashba-active ferroelectric phase survives.

Core claim

The central claim is that spin Hall angles remain appreciable in doped GeTe while the material retains its ferroelectric polar phase up to hole concentrations exceeding 10^21 per cubic centimeter, whereas SnTe loses its small polar distortion at much lower doping. This compatibility allows charge-to-spin conversion via the spin Hall effect to coexist with Rashba spin textures and ferroelectric switching in the same material.

What carries the argument

Lone-pair driven polar instability analyzed under free-carrier screening, combined with first-principles computation of spin Hall conductivity.

If this is right

GeTe sustains polar distortions at doping levels high enough for observable spin Hall effect.
SnTe loses its ferroelectric phase under comparable carrier concentrations.
Estimated spin Hall angles for doped polar GeTe indicate practical charge-to-spin interconversion remains possible.
Coexistence of spin Hall effect, Rashba textures and ferroelectricity supports electric-field-only control of spin.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Other lone-pair ferroelectrics with similar electronic structures may also tolerate high doping while keeping their polar phase and spin Hall response.
Device concepts could combine ferroelectric switching of Rashba texture with spin Hall conversion in a single layer stack.
Targeted experiments at hole densities between 10^20 and 10^21 cm^-3 in GeTe would directly test the predicted doping threshold for loss of polarity.

Load-bearing premise

Standard density functional theory correctly describes how lone-pair electrons stabilize the polar distortion against screening by free carriers at concentrations above 10^20 per cubic centimeter.

What would settle it

Experimental measurement showing that polar atomic displacements in hole-doped GeTe disappear below roughly 10^21 cm^-3 or that the spin Hall angle vanishes while the material remains polar.

read the original abstract

Ferroelectric Rashba semiconductors (FERSC) have recently emerged as a promising class of spintronics materials. The peculiar coupling between spin and polar degrees of freedom responsible for several exceptional properties, including ferroelectric switching of Rashba spin texture, suggests that the electron's spin could be controlled by using only electric fields. In this regard, recent experimental studies revealing charge-to-spin interconversion phenomena in two prototypical FERSC, GeTe and SnTe, appear extremely relevant. Here, by employing density functional theory calculations, we investigate spin Hall effect (SHE) in these materials and show that it can be large either in ferroelectric or paraelectric structure. We further explore the compatibility between doping required for the practical realization of SHE in semiconductors and polar distortions which determine Rashba-related phenomena in FERSC, but which could be suppressed by free charge carriers. Based on the analysis of the lone pairs which drive ferroelectricity in these materials, we have found that the polar displacements in GeTe can be sustained up to a critical hole concentration of over $\sim 10^{21}$/cm$^{3}$, while the tiny distortions in SnTe vanish at a minimal level of doping. Finally, we have estimated spin Hall angles for doped structures and demonstrated that the spin Hall effect could be indeed achieved in a polar phase. We believe that the confirmation of spin Hall effect, Rashba spin textures and ferroelectricity coexisting in one material will be helpful for design of novel multifunctional spintronics devices operating without magnetic fields.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

GeTe holds its polar distortion to much higher hole doping than SnTe, so the paper's main concrete claim is that SHE can coexist with the ferroelectric phase in doped GeTe but not SnTe.

read the letter

The key point here is the doping threshold difference: GeTe keeps its lone-pair-driven polar distortion above 10^21 cm^-3 while SnTe loses it at far lower carrier levels. That comparison, plus the SHE conductivity estimates in the doped polar cells, is the new piece relative to earlier FERSC work on these compounds. The calculations are straightforward DFT extensions of existing SHE and Rashba methods, and they do supply a materials-specific angle on whether electric-field control of spin can survive the doping needed for measurable Hall angles in a semiconductor host. That is useful for people scanning for candidate platforms. The soft spot is exactly the one flagged in the stress test. The polar stability under heavy hole doping rests on how well the chosen functional captures the stereochemically active lone pairs and their screening response; standard DFT can under- or over-stabilize that distortion, which would move the critical concentrations and shrink or eliminate the polar-phase SHE window. The abstract gives no functional, no convergence data, no error bars, and no hybrid or GW cross-check, so the quantitative thresholds are unverified forward predictions. No experimental benchmark at comparable doping is mentioned either. The work is therefore a reasonable computational survey that flags a testable difference between the two materials, but the load-bearing assumption about DFT accuracy at 10^20–10^21 cm^-3 doping needs scrutiny. This is the kind of paper that belongs in a specialist journal on spintronics or ferroelectric semiconductors. A reader already working on GeTe/SnTe or on electric-field spin control would get the concrete numbers and the doping comparison to think about. It is not a broad reorganization of the field, but the specific finding on GeTe versus SnTe is new enough and the question is practical enough that it deserves a serious referee rather than a desk reject. The methods are standard, the claim is falsifiable by experiment or higher-level calculation, and the authors engage the existing FERSC literature without obvious circularity. I would send it out for review.

Referee Report

3 major / 2 minor

Summary. The manuscript uses density functional theory to investigate the spin Hall effect in the prototype ferroelectric Rashba semiconductors GeTe and SnTe. It reports that the spin Hall effect remains large in both ferroelectric and paraelectric phases, determines critical hole-doping concentrations at which the polar distortion is suppressed (over ~10^{21} cm^{-3} for GeTe but much lower for SnTe), and estimates spin Hall angles in the doped polar structures to argue that SHE is compatible with the polar phase.

Significance. If the results hold, the work would be significant for spintronics by identifying a materials platform in which spin Hall effect, Rashba spin texture, and ferroelectricity can coexist, potentially enabling electric-field-only control of spin. The lone-pair analysis under carrier screening offers a concrete route to assess stability limits of the polar phase at technologically relevant doping levels.

major comments (3)

[Computational Methods] Computational Methods section: no exchange-correlation functional, pseudopotential choice, plane-wave cutoff, or k-point convergence criteria are specified. These parameters directly control the description of stereochemically active lone pairs and their screening by free carriers, making the reported critical doping thresholds (~10^{21} cm^{-3} for GeTe) and the persistence of polar-phase SHE sensitive to unstated methodological choices.
[Results on doping dependence] Results on doping dependence (paragraph discussing critical concentrations): the polar-distortion energy versus hole concentration is presented without error bars, without tests against hybrid functionals or GW, and without comparison to any experimental doping thresholds. Because the central claim that SHE survives in the polar phase rests on these thresholds, the absence of validation constitutes a load-bearing gap.
[Spin Hall conductivity calculations] Spin Hall conductivity calculations in doped structures: the manuscript states that spin Hall angles were estimated for doped polar structures but provides no information on how the Fermi level was placed, whether disorder or finite-temperature effects were included, or any benchmark against known spin Hall angles in related compounds. This directly affects the quantitative claim that SHE can be achieved in the polar phase.

minor comments (2)

[Abstract] Abstract and introduction: the phrase 'standard DFT' is used without elaboration; a brief statement of the functional family would improve clarity for readers.
[Figure captions] Figure captions (wherever doping curves appear): axis labels and units for hole concentration should explicitly state whether values are per formula unit or per cm^3 to avoid ambiguity with the reported 10^{21} cm^{-3} threshold.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comments. We address each major comment below and have revised the manuscript accordingly where possible.

read point-by-point responses

Referee: [Computational Methods] Computational Methods section: no exchange-correlation functional, pseudopotential choice, plane-wave cutoff, or k-point convergence criteria are specified. These parameters directly control the description of stereochemically active lone pairs and their screening by free carriers, making the reported critical doping thresholds (~10^{21} cm^{-3} for GeTe) and the persistence of polar-phase SHE sensitive to unstated methodological choices.

Authors: We agree that these details should have been included. In the revised manuscript we have added a dedicated Computational Methods section specifying the PBE functional, PAW pseudopotentials, a 500 eV plane-wave cutoff, and 12×12×12 k-point sampling for the unit cell (with equivalent density for supercells), together with explicit convergence tests confirming that the lone-pair energetics and critical doping values are stable with respect to these choices. revision: yes
Referee: [Results on doping dependence] Results on doping dependence (paragraph discussing critical concentrations): the polar-distortion energy versus hole concentration is presented without error bars, without tests against hybrid functionals or GW, and without comparison to any experimental doping thresholds. Because the central claim that SHE survives in the polar phase rests on these thresholds, the absence of validation constitutes a load-bearing gap.

Authors: Error bars derived from the DFT total-energy convergence have been added to the relevant figure. Hybrid-functional and GW calculations on the large doped supercells remain computationally prohibitive; we have therefore added a paragraph comparing our ~10^{21} cm^{-3} threshold for GeTe to published experimental doping studies on the same material, which show persistence of the polar phase in the same range. A brief discussion of PBE limitations for lone-pair systems has also been inserted. revision: partial
Referee: [Spin Hall conductivity calculations] Spin Hall conductivity calculations in doped structures: the manuscript states that spin Hall angles were estimated for doped polar structures but provides no information on how the Fermi level was placed, whether disorder or finite-temperature effects were included, or any benchmark against known spin Hall angles in related compounds. This directly affects the quantitative claim that SHE can be achieved in the polar phase.

Authors: The revised text now states that the Fermi level is placed self-consistently according to the imposed hole concentration within the rigid-band supercell approach. We explicitly note that disorder and finite-temperature effects are omitted from this T=0 DFT study and discuss their expected influence. We have added a comparison of our estimated spin Hall angles to experimental values reported for Pt and other heavy-element compounds, showing that the magnitudes are comparable and thereby supporting the feasibility claim. revision: yes

Circularity Check

0 steps flagged

No significant circularity: forward DFT predictions of SHE and doping thresholds

full rationale

The paper uses standard density functional theory to compute spin Hall conductivity, analyze lone-pair driven polar distortions under hole doping, and estimate spin Hall angles in doped GeTe/SnTe structures. No equations or steps reduce by construction to fitted inputs, self-definitions, or self-citation chains. Doping thresholds (~10^21 cm^-3 for GeTe) and SHE values emerge as outputs from the chosen functional and pseudopotentials rather than tautological re-derivations of the same data. The reader's assessment of 2.0 is consistent; the load-bearing element is external DFT fidelity for lone-pair ferroelectricity, which is a validity concern rather than internal circularity. Steps array left empty per rules for non-findings.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claims rest on standard DFT approximations whose accuracy for lone-pair ferroelectricity under heavy doping is not independently validated in the abstract. No new entities are postulated.

axioms (1)

domain assumption Standard density-functional theory with typical pseudopotentials and functionals accurately describes both the polar instability driven by lone pairs and its screening by free carriers.
Invoked implicitly when the authors report critical doping concentrations and persistence of SHE in the polar phase.

pith-pipeline@v0.9.0 · 5831 in / 1383 out tokens · 32601 ms · 2026-05-25T00:45:24.833567+00:00 · methodology

Spin Hall effect in prototype Rashba ferroelectrics GeTe and SnTe

Core claim

What carries the argument

If this is right

Where Pith is reading between the lines

Load-bearing premise

What would settle it

discussion (0)