REVIEW 2 major objections 5 minor 32 references
Magnetic-field dependence of spin-phonon relaxation and dephasing due to g-factor fluctuations from first principles
T0 review · 2 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read Off-diagonal g-tensor fluctuations, not just spin-flip scattering, determine how electron spin lifetimes T1, T2, and T2* depend on magnetic field in silicon and CsPbBr3.
desk verdict A first-principles Hahn-echo route to T2 with a new off-diagonal g-tensor mechanism for B-dependent T1 in silicon; solid and novel, but the missing convergence tests need addressing. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the state-resolved Landé g-tensor, extracted from DFT by expanding -L + g0 S in a Pauli basis; its diagonal fluctuations (σ∥) and off-diagonal fluctuations (σ⊥) over thermally occupied band-edge states set the Larmor precession frequency spread and precession-axis tilt. The mechanism is a Bloch-sphere random walk: after each electron-phonon scattering event, the spin's precession axis and frequency change because the g-tensor of the new state differs, so even a spin initially parallel to the applied field gradually tilts away. The analytical model, Eqs. (5)-(7), expresses T1, T2, and T2* in terms of the zero-field Elliott-Yafet spin-flip time τs0, the momentum scattering time τp, and the two fluctuation widths σ⊥ and σ∥, with functions F⊥(x) and F∥(x) that interpolate between an x2 low-field regime and saturation.
What would settle it
Measure the longitudinal spin lifetime T1 of conduction electrons in high-purity silicon at 100 K as a function of magnetic field from 0 to 10 T; the paper predicts T1 drops from about 195 ns at zero field to a field-independent value near 70 ns beyond roughly 3 T, so observing no such drop would falsify the off-diagonal g-fluctuation mechanism.
Extended reading notes
Core claim
The central claim is that the tensorial g-factor, specifically its off-diagonal state-to-state fluctuations, produces magnetic-field-dependent spin relaxation that standard pictures miss. In silicon and CsPbBr3—both inversion-symmetric—the authors show that intrinsic electron-phonon scattering combined with g-tensor fluctuations yields a field-dependent T1, a distinct T2 obtained from simulated Hahn echoes, and a T2* that falls roughly as 1/B. The physical mechanism is a Bloch-sphere random walk: after each phonon scattering event, the spin precesses about a slightly different axis because the g-tensor changes, so even spins initially parallel to the field wander away from it. The analytical model, Eqs. (5)-(7), reproduces the first-principles field dependence with fitted parameters close to the DFT values and identifies regimes where T1, T2, and T2* are ordered differently in the two materials.
Load-bearing premise
The predictions rely on the Born-Markov approximation that phonons act as a memoryless bath, which may fail at low temperatures or strong electron-phonon coupling and would shift all lifetimes.
Editorial extensions
If this is right
- In inversion-symmetric crystals, intrinsic spin-phonon scattering alone produces a magnetic-field-dependent T1 whenever off-diagonal g-tensor fluctuations are non-zero, with the zero-field limit recovering the Elliott-Yafet spin-flip time τs0.
- T2 can be extracted from first-principles simulation of a Hahn echo sequence, separating irreversible decoherence from reversible dephasing without introducing any ad hoc dephasing model.
- The ordering of lifetimes differs by material: CsPbBr3 shows T1 ≫ T2 > T2* at a few tesla, while silicon shows T2 ≈ T2* over the same range because its diagonal g-fluctuations are much smaller than its off-diagonal ones.
- The analytical model predicts distinct saturation regimes: T1 saturates once B ≫ ℏ/(|ḡ|τpμB), T2 saturates at a larger field set by σ∥, and T2* enters a free-induction-decay regime where it falls as 1/B.
Reading between the lines
- If the off-diagonal g-fluctuation mechanism is right, it should also operate for localized electron spins such as donors or defects in silicon, where the g-tensor varies from site to site; measuring T1(B) in such ensembles could validate the mechanism outside the band-transport regime studied here.
- The same random-walk picture suggests that strain or alloying, which alter the g-tensor anisotropy, could tune the magnetic-field dependence of spin lifetimes, turning σ⊥ and σ∥ into design parameters for spin qubits.
- The distinction between T2* and T2 is often overlooked in ensemble measurements; this work implies that comparing measured T2* and Hahn-echo T2 as a function of field could directly bound the diagonal and off-diagonal g-fluctuation widths in a material.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents real-time first-principles density-matrix dynamics simulations with electron-phonon Lindblad scattering to compute spin relaxation (T1), irreversible decoherence (T2), and reversible dephasing (T2*) in CsPbBr3 and silicon as functions of magnetic field. By explicitly simulating Hahn echo sequences, the authors separate dephasing from decoherence and identify g-tensor fluctuations—particularly off-diagonal components—as the source of a magnetic-field-dependent T1 in inversion-symmetric silicon. An analytical random-walk model (Eqs. 5–7) is introduced, and its parameters are compared with DFT-derived values in Tables I and II.
Significance. If the results hold, this is an important step: it provides a first-principles route to T2 via direct Hahn echo simulation without ad hoc dephasing models, and it predicts a new intrinsic mechanism by which off-diagonal g-tensor fluctuations make T1 field-dependent even in low-spin-orbit, inversion-symmetric Si. The analytical model with closed-form field-dependence functions is an interpretative strength, and the authors' explicit acknowledgment of finite-k artifacts is honest. The main limitation is the absence of convergence evidence for the computed fluctuations and lifetimes, which is essential because the predicted effect scales with σ⊥².
major comments (2)
- [III.C, Fig. 5, and Eq. (5)] The central claim—that off-diagonal g-tensor fluctuations with σ⊥≈0.006 produce the strong B-dependence of T1 in silicon—is not backed by convergence tests. The manuscript does not report the k-grid density or thermal-weighting details used to compute σ⊥, gives no error bars on σ⊥ or on the lifetimes, and acknowledges finite-k artifacts in the Hahn echo simulations (Fig. 2c). Because the T1 rate in Eq. (5) scales as σ⊥², a modest error in σ⊥ translates into a large error in the predicted reduction. Please provide convergence of σ⊥ and of T1, T2, and T2* with respect to k sampling, and error estimates for the fit parameters in Tables I and II.
- [II.A, Eq. (1)] The entire calculation inherits the Born-Markov/Lindblad approximation, but the paper does not test its validity for the long-time, low-temperature regimes considered (4 K for CsPbBr3, 100 K for Si). The predicted lifetimes all shift if the Markovian assumption fails, and no comparison with experimental T1 or T2 for silicon is offered. Please provide a quantitative argument for Markovianity (for example, phonon correlation time versus momentum scattering time τp) or a benchmark against an exact or measured case, since the predicted effects rely on accumulated phase over many scattering events.
minor comments (5)
- [II.C, III.A, Fig. 4 caption, Table I caption, III.C] There are several typos that should be corrected: 'elctronic' (II.C), 'dicsussed' (III.A), 'functon' (Fig. 4 caption), 'paramters' (Table I caption), 'contributs' (III.C), 'occuring' (III.B), and the reference 'Table III C' after Fig. 5 should be 'Table II'.
- [II.D] The Hahn echo protocol would benefit from explicit numerical details: the number of τ delays used, pulse durations and B1 magnitudes, and the fitting windows used to extract Secho(techo). This would help readers assess the quality of the T2 extraction.
- [III.B, Tables I–II] The agreement between fitted and DFT parameters is presented as confirmation of the mechanism, but because τp, σ⊥, and σ∥ are fitted to the same lifetime curves, it is a consistency check rather than an independent test. Please state this explicitly or, ideally, overlay the model curves using only DFT-derived parameters.
- [Fig. 2(c)] The color scale and the exact meaning of the horizontal and vertical axes are not defined in the caption; please add a legend or explicit axis labels.
- [I and II.D] The phrase 'reversible decoherence processes' is unusual; since dephasing is a reversible loss of ensemble coherence rather than irreversible single-spin decoherence, consider rewording to 'reversible dephasing' throughout.
Circularity Check
The central first-principles spin-lifetime predictions are self-contained; the only mild circularity is the analytical model's fitted 'predictions' being compared with the same lifetime curves they were fit to, though the DFT-derived parameter comparison provides independent support.
-
fitted input called prediction
[Section III.B, Eqs. (5)-(7), Figs. 4-5 and Tables I-II]
"Figure 4 compares the predictions of this model to the first-principles spin relaxation times for CsPbBr3, with the corresponding paramters of the model compared to the DFT predictions in Table I. Note that the model captures all the features of the field dependence ofT1, T2 and T2*, with parameters quite close to the values extracted from DFT, confirming the proposed mechanism for the field dependence."
The analytical model (Eqs. 5-7) is fit to the first-principles T1, T2, and T2* curves by adjusting tau_p, sigma_perp, and sigma_parallel, as shown by the Fit Value columns in Tables I and II. The plotted 'model predictions' in Figs. 4-5 are therefore not independent of the data they are compared against; some agreement is built in by construction. The circularity is limited because the fitted values are checked against independently computed DFT values, and the central field-dependence claim comes from the real-time first-principles simulations rather than from the fitted model.
full rationale
The first-principles density-matrix evolution (Eq. 1) does not use the analytical model; T1, T2, and T2* are extracted by exponential fits to simulated spin dynamics and Hahn echo sequences. The g-tensor is extracted from the same S and L matrix elements that enter the Zeeman Hamiltonian, so attributing the field dependence to g-factor fluctuations is a consistency interpretation, not a circular derivation. The analytical model is an interpretive reduction fitted to the computed lifetimes; the close agreement of its fitted parameters with DFT-derived values provides some independent support, so the circularity is minor. The main scientific claim, that off-diagonal g-tensor fluctuations produce a magnetic-field-dependent T1 in silicon, is a result of the ab initio simulations rather than an input to them. No load-bearing self-citation or ansatz-smuggling is present.
Assumptions & free parameters
free parameters (4)
- tau_p (momentum scattering time) =
0.200 ns (CsPbBr3), 0.00150 ns (Si)
- sigma_perp (off-diagonal g-tensor fluctuation) =
0.0551 (CsPbBr3), 0.00652 (Si)
- sigma_parallel (diagonal g-tensor fluctuation) =
0.0788 (CsPbBr3), 0.00224 (Si)
- c0 (dephasing prefactor) =
not stated in main text
assumptions (4)
- domain assumption Electron-phonon scattering can be described by a Lindblad master equation derived under the Born-Markov approximation.
- domain assumption DFT with PBE and fully relativistic normconserving pseudopotentials gives accurate band structures, g-tensors, and electron-phonon matrix elements.
- domain assumption Wannier interpolation, patched with explicit DFT for selected k, preserves the sharp orbital angular momentum features needed for g-tensors.
- ad hoc to paper The analytical model represents spin dynamics as a random walk with a single momentum scattering time and Gaussian g-factor fluctuations.
Cite this review
Pith. "Pith review of Magnetic-field dependence of spin-phonon relaxation and dephasing due to g-factor fluctuations from first principles." pith.science (2026). https://pith.science/paper/BD57EDTK
@misc{pith2026241118608,
author = {Pith},
title = {Pith review of: Magnetic-field dependence of spin-phonon relaxation and dephasing due to g-factor fluctuations from first principles},
year = {2026},
howpublished = {\url{https://pith.science/paper/BD57EDTK}},
note = {Machine review of arXiv:2411.18608}
}
read the original abstract
The electron spin decay lifetime in materials can be characterized by relaxation (T1) and irreversible (T2) and reversible (T2*) decoherence processes. Their interplay leads to a complex dependence of spin relaxation times on the direction and magnitude of magnetic fields, relevant for spintronics and quantum information applications. Here, we use real-time first-principles density matrix dynamics simulations to directly simulate Hahn echo measurements, disentangle dephasing from decoherence, and predict T1, T2 and T2* spin lifetimes. We show that g-factor fluctuations lead to non-trivial magnetic field dependence of each of these lifetimes in inversion-symmetric crystals of CsPbBr3 and silicon, even when only intrinsic spin-phonon scattering is present. Most importantly, fluctuations in the off-diagonal components of the g-tensor lead to a strong magnetic field dependence of even the T1 lifetime in silicon. Our calculations elucidate the detailed role of anisotropic g-factors in determining the spin dynamics even in simple, low spin-orbit coupling materials such as silicon.
Figures
Reference graph
Works this paper leans on
-
[1]
ˇZuti´ c, J
I. ˇZuti´ c, J. Fabian, and S. Das Sarma, Spintronics: Fun- damentals and applications, Rev. Mod. Phys. 76, 323 (2004)
2004
-
[2]
D. D. Awschalom, R. Hanson, J. Wrachtrup, and B. B. Zhou, Quantum technologies with optically interfaced solid-state spins, Nature Photonics 12, 516 (2018)
2018
-
[3]
A. Hirohata, K. Yamada, Y. Nakatani, I.-L. Prejbeanu, B. Di´ eny, P. Pirro, and B. Hillebrands, Review on spin- tronics: Principles and device applications, Journal of Magnetism and Magnetic Materials 509, 166711 (2020)
work page 2020
-
[4]
Z. Chen, G. Dong, and J. Qiu, Ultrafast pump-probe spectroscopy—a powerful tool for tracking spin-quantum dynamics in metal halide perovskites, Advanced Quan- tum Technologies 4, 10.1002/qute.202100052 (2021)
-
[5]
D. Giovanni, H. Ma, J. Chua, M. Gr¨ atzel, R. Ramesh, S. Mhaisalkar, N. Mathews, and T. C. Sum, Highly spin-polarized carrier dynamics and ultralarge photoin- duced magnetization in CH 3NH3PbI3 perovskite thin films, Nano Letters 15, 1553 (2015)
work page 2015
-
[6]
R. J. Elliott, Theory of the effect of spin-orbit coupling on magnetic resonance in some semiconductors, Phys. Rev. 96, 266 (1954)
1954
-
[7]
M. Dyakonov and V. Perel, Spin relaxation of con- duction electrons in noncentrosymetric semiconductors, Solid State Physics 13, 3023 (1972)
work page 1972
-
[8]
M. M. Glazov, Magnetic field effects on spin relaxation in heterostructures, Phys. Rev. B 70, 195314 (2004)
work page 2004
Show all 32 references
-
[9]
C. L¨ u, J. Cheng, M. Wu, and I. da Cunha Lima, Spin relaxation time, spin dephasing time and ensemble spin dephasing time in n-type gaas quantum wells, Physics Letters A 365, 501 (2007)
2007
-
[10]
Maier, C
F. Maier, C. Kloeffel, and D. Loss, Tunable g factor and phonon-mediated hole spin relaxation in ge/si nanowire quantum dots, Phys. Rev. B 87, 161305 (2013)
2013
-
[11]
J. Xu, A. Habib, S. Kumar, F. Wu, R. Sundararaman, and Y. Ping, Spin-phonon relaxation from a universal ab initio density-matrix approach, Nature Communications 11, 2780 (2020)
2020
-
[12]
J. Xu, A. Habib, R. Sundararaman, and Y. Ping, Ab initio ultrafast spin dynamics in solids, Physical Review B 104, 184418 (2021)
2021
-
[13]
J. Xu, H. Takenaka, A. Habib, R. Sundarara- man, and Y. Ping, Giant spin lifetime anisotropy and spin-valley locking in silicene and germanene from first-principles density-matrix dynamics, Nano Letters 21, 9594 (2021), pMID: 34767368, https://doi.org/10.1021/acs.nanolett.1c03345
2021 doi
-
[14]
Habib, J
A. Habib, J. Xu, Y. Ping, and R. Sundararaman, Electric fields and substrates dramatically accelerate spin relax- ation in graphene, Phys. Rev. B 105, 115122 (2022)
2022
-
[15]
Xu and Y
J. Xu and Y. Ping, Substrate effects on spin relaxation in two-dimensional dirac materials with strong spin-orbit coupling, npj Computational Materials 9, 47 (2023)
2023
-
[16]
J. Xu, K. Li, U. N. Huynh, M. Fadel, J. Huang, R. Sun- dararaman, V. Vardeny, and Y. Ping, How spin relaxes and dephases in bulk halide perovskites, Nature Commu- nications 15, 188 (2024)
2024
-
[17]
E. L. Hahn, Spin echoes, Phys. Rev. 80, 580 (1950). 9
1950
-
[18]
Balasubramanian, P
G. Balasubramanian, P. Neumann, D. Twitchen, M. Markham, R. Kolesov, N. Mizuochi, J. Isoya, J. Achard, J. Beck, J. Tissler, V. Jacques, P. R. Hemmer, F. Jelezko, and J. Wrachtrup, Ultralong spin coherence time in isotopically engineered diamond, Nature Materi- als 8, 383 (2009)
2009
-
[19]
Ping and J
Y. Ping and J. Z. Zhang, Spin-optotronic properties of organometal halide perovskites, The Journal of Physical Chemistry Letters 9, 6103 (2018)
2018
-
[20]
D. Taj, R. C. Iotti, and F. Rossi, Microscopic modeling of energy relaxation and decoherence in quantum optoelec- tronic devices at the nanoscale, The European Physical Journal B 72, 305 (2009)
2009
-
[21]
Sundararaman, K
R. Sundararaman, K. Letchworth-Weaver, K. A. Schwarz, D. Gunceler, Y. Ozhabes, and T. Arias, Jdftx: Software for joint density-functional theory, SoftwareX6, 278 (2017)
2017
-
[22]
Since such self-consistent spin-orbit coupling calculations are spinorial, the spin degrees of freedom are implicitly captured within the band indices within Eq
with fully-relativistic normconserving pseudopoten- tials [23]. Since such self-consistent spin-orbit coupling calculations are spinorial, the spin degrees of freedom are implicitly captured within the band indices within Eq. 1. The DFT calculations are performed on coarse ele...
-
[23]
D. R. Hamann, Optimized norm-conserving vanderbilt pseudopotentials, Phys. Rev. B 88, 085117 (2013)
2013
-
[24]
J. P. Perdew, K. Burke, and M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77, 3865 (1996)
1996
-
[25]
See attached supplemental information within source archive for computational details and derivation of the analytical model
-
[26]
Yafet, g factors and spin-lattice relaxation of conduc- tion electrons, in Solid state physics, Vol
Y. Yafet, g factors and spin-lattice relaxation of conduc- tion electrons, in Solid state physics, Vol. 14 (Elsevier,
-
[27]
and strongly dependent on the electronic structure [28]. Fluctuations in g-factor with elctronic state affect the Larmor precession frequency of spins in the presence of a transverse magnetic field, leading to the dephasing of spins in spin relaxation [16]. Here, we show that ...
-
[28]
Multunas, A
C. Multunas, A. Grieder, J. Xu, Y. Ping, and R. Sun- dararaman, Circular dichroism of crystals from first prin- ciples, Phys. Rev. Mater. 7, 123801 (2023)
2023
-
[29]
P. W. Brouwer, X. Waintal, and B. I. Halperin, Fluctuat- ing spin g-tensor in small metal grains, Phys. Rev. Lett. 85, 369 (2000)
2000
-
[30]
Sharma and D
M. Sharma and D. P. DiVincenzo, g-factor symme- try and topology in semiconductor band states (2024), arXiv:2402.06310
2024 arXiv
-
[31]
U. N. Huynh, Y. Liu, A. Chanana, D. R. Khanal, P. C. Sercel, J. Huang, and Z. V. Vardeny, Transient quantum beatings of trions in hybrid organic tri-iodine perovskite single crystal, Nature Communications 13, 1428 (2022)
2022
-
[32]
M. Wu, J. Jiang, and M. Weng, Spin dynamics in semi- conductors, Physics Reports 493, 61 (2010)
2010
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