REVIEW 3 major objections 5 minor 58 references
Ultrafast magneto-lattice dynamics in two-dimensional CrSBr driven by terahertz excitation
T0 review · 3 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read Pre-exciting the B1_3g coherent phonon in monolayer CrSBr shortens electron relaxation to 83 fs and boosts THz-driven demagnetization by about 215%.
desk verdict Useful mode-resolved NAMD data on CrSBr, but the headline 83 fs and 215% claims are single-pathway artifacts of the single-phonon constraint and are overstated in the abstract and conclusions. 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 B1_3g phonon, one of the nine Raman-active vibrations of monolayer CrSBr, treated as a pre-excitable coherent phonon in a dual-pump scheme. The calculations combine real-time time-dependent density functional theory with Ehrenfest molecular dynamics for the demagnetization dynamics, and first-principles nonadiabatic molecular dynamics for carrier relaxation, with nonadiabatic coupling matrices separating electron-phonon and spin-orbit contributions. The mechanism that shortens the E2 relaxation to 83 fs is the matching of the B1_3g vibration frequency to the electron relaxation energy spacing, which the paper identifies from the nonadiabatic coupling matrix elements.
What would settle it
A pump-probe experiment on monolayer CrSBr that pre-excites the B1_3g coherent phonon with a first terahertz pulse and then measures the demagnetization from a second pulse would settle the claim: if the relaxation is not accelerated to about 83 fs or the demagnetization change is not near 215%, the single-phonon mechanism is not the operative one. A complementary calculation repeating the nonadiabatic molecular dynamics with all phonons active but the lattice initially displaced along B1_3g would show whether the 83 fs survives when multi-phonon relaxation pathways are available.
Extended reading notes
Core claim
On the paper's own terms, the central discovery is that the B1_3g coherent phonon mode of monolayer CrSBr acts as an ultrafast channel for electron relaxation from a 1.29 eV spin-down excited state to the conduction band minimum, with a relaxation time of 83 fs, and that pre-exciting this mode before a terahertz pulse enhances the demagnetization by about 1.5 Bohr magnetons at 200 fs, reported as a 215% change. The authors interpret this as a frequency match between the B1_3g vibration and the electron relaxation energy spacing, enabling direct and efficient electron-phonon energy transfer, and as the coherent lattice motion strengthening spin-orbit coupling. They also find that most other single phonon modes delay relaxation compared to the all-phonon case, and that spin-flip transitions require both multiple phonons and spin-orbit coupling.
Load-bearing premise
The 83 fs result and the mode comparison depend on simulations that freeze all lattice vibrations except B1_3g, on the assumption that this isolation does not remove multi-phonon pathways that would change the relaxation, and on the fitted exponential decay from selected excited states standing in for the real terahertz-generated hot-electron distribution.
Editorial extensions
If this is right
- Pre-exciting B1_3g provides a concrete control knob: a first terahertz pulse prepares the coherent phonon and a second pulse manipulates the spin, enabling a dual-pump all-optical control scheme for CrSBr.
- Because the 83 fs relaxation is below 100 fs, coherent-phonon-assisted demagnetization can act faster than the thermal phonon bath timescale normally associated with spin-lattice angular-momentum transfer.
- The mode-resolved comparison shows that most single phonon modes block or slow electron relaxation, so selecting or engineering the B1_3g mode, for instance by strain or substrate choice, could tune the demagnetization speed.
- In monolayer CrSBr, spin-down electrons relax quickly through electron-phonon coupling within the same spin channel, while spin-up electrons need spin-orbit-coupled spin flips, so the overall demagnetization rate is limited by the slower spin-flip pathway unless the B1_3g channel is pre-excited.
- The dual-pump scheme points toward light-driven magnetic memory or spin-logic applications in which the coherent phonon acts as an ultrafast pathway toward the demagnetized state.
Reading between the lines
- If the single-phonon isolation is the true mechanism, then tuning the B1_3g frequency by isotopic substitution or biaxial strain should shift the 83 fs relaxation time in a predictable way, a testable extension the paper does not perform.
- The same mode-screening logic could generalize to other two-dimensional van der Waals magnets: any material whose Raman-active phonon matches an electron relaxation energy spacing might show a similar coherent-phonon-enhanced demagnetization.
- The 215% figure is a relative enhancement, and its technological value depends on the absolute demagnetization and on whether the coherent phonon can be re-excited or sustained for repeated write-read cycles, which the paper does not address.
- The single-phonon constraint in the relaxation simulations may block multi-phonon decay pathways, so the 83 fs result should be read as conditional on that constraint until a fully coupled calculation with a coherent B1_3g displacement confirms it.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper combines real-time time-dependent density functional theory (rt-TDDFT) with Ehrenfest molecular dynamics and nonadiabatic molecular dynamics (NAMD) to model THz-laser-induced demagnetization in monolayer CrSBr. It identifies a two-stage demagnetization process, an initial electron-driven stage within about 20 fs and a later stage governed by electron-phonon and spin-orbit coupling. The central quantitative claims are that the B1_3g phonon mode shortens a specific electron relaxation channel (E2) to 83 fs, below a nominal 100 fs common value, and that pre-exciting this coherent phonon enhances demagnetization by 215%. These results are presented as guidelines for light-controlled spintronic devices.
Significance. If the mode-specific claims are correct, the work provides a concrete microscopic mechanism for phonon-mode-selective control of ultrafast demagnetization, which would be valuable for 2D-magnet spintronics and coherent-phonon engineering. The paper's strengths include explicit ab initio simulation of the coupled electron-spin-lattice dynamics, a mode-resolved relaxation-time table (Table I) that goes beyond aggregate electron-phonon coupling estimates, and a falsifiable prediction that pre-exciting B1_3g changes the demagnetization amplitude. However, the significance is currently undercut by overstatement in the abstract and conclusions: the 83 fs value is a single-phonon simulation result, not experimental evidence, and the 215% enhancement is not derived anywhere in the text.
major comments (3)
- [Section III and Abstract] Section III states that 'experimental evidence has demonstrated that the impact of the B1_3g phonon vibration mode on the electron relaxation of the CrSBr monolayer is within 83 fs.' No experiment is reported in the manuscript; this value comes from single-phonon NAMD simulations. The abstract similarly presents the 83 fs value as an established fact. Please rephrase these statements to 'our simulations predict' or 'our calculations indicate' in the abstract, main text, and conclusions.
- [Abstract and Figure 5] The abstract claims 'the influence of this coherent phonon on the demagnetization change is as high as 215%,' but Section II (Figure 5) only reports a difference of about 1.5 μB at 200 fs relative to the absence of coherent phonons. Neither the baseline demagnetization value nor the formula used to compute the percentage is given. As written, the headline 215% figure cannot be verified from the text; please define the reference state and show the calculation explicitly.
- [Table I and Section II] The central 83 fs claim rests on the single-phonon freezing approximation, and Table I shows that this approximation is not a benign mode isolation. With B1_3g alone, process E2 is shortened from 102 fs to 83 fs, but process E3 is blocked (×), and processes E4, S1, and S2 slow to 3345, 785, and 931 fs, respectively, compared with all-phonon values of 176, 209, and 226 fs. Thus the statement that 'the electronic relaxation of the B1_3g phonon vibration mode occurs within 83 fs' generalizes one selected downhill transition and omits multi-phonon pathways that could shorten or lengthen relaxation in the real material. The authors should test whether B1_3g remains the dominant driver when all phonon modes are active (for example, by mode-projection analysis or by selectively exciting B1_3g within a full-phonon trajectory) and should report fitting-window sensitivity or statistical uncertainties, since the 83 fs versus 102 fs difference may be within numerical noise.
minor comments (5)
- [Abstract and Section II] The mode notation is inconsistent: the abstract refers to 'B3g1' while the text uses 'B1_3g'. Please unify the notation throughout.
- [Section II (Figure 3)] The text says the decay time scale is 'fitted using a Gaussian function f(t)=a+b exp(−t/τ)', but the formula is a single exponential, not a Gaussian. Please correct this description and provide the fitting procedure, including the time window used.
- [Figure 1 caption] The caption lists the Raman modes as 'B1_3g, B1_2g, A1_g, B2_2g, B2_3g, A2_g, B3_2g, A3_g and B3_2g', with 'B3_2g' appearing twice and one of the nine modes likely mislabeled. Please verify the mode labels and the correspondence with the irreducible representations given in the text.
- [Throughout] There are numerous typographical and grammatical errors, including 'Figrue', 'demonetization', 'sigle', 'higer', 'differernt', and inconsistent 'Thz' capitalization. A careful copyedit is needed.
- [Section II] The abstract states the first stage occurs 'within 20 fs', while the text and Figure 1c describe stage I as 0–18 fs. Please reconcile these values.
Circularity Check
No significant circularity; the 83 fs and 215% claims are computed from independent first-principles simulations rather than fitted or self-cited inputs.
full rationale
The paper's central quantitative claims derive from first-principles rt-TDDFT and NAMD simulations. The 83 fs relaxation time is obtained by simulating population decay from the 1.29 eV spin-down state to the CBM under a single B1_3g phonon mode and fitting f(t)=a+b exp(-t/tau); it is not a target into which parameters were fitted. The 215% demagnetization enhancement is obtained from a separate rt-TDDFT simulation with and without a pre-excited coherent B1_3g phonon, so it is not equivalent by construction to the NAMD relaxation time. Self-citations ([36], [40], [57]) are contextual and not load-bearing: they support general statements about spin-phonon dynamics or prior Fe3GeTe2 work, not the CrSBr result. The only circularity-adjacent feature is a mild internal selection loop: the same single-phonon NAMD framework is used both to assign relaxation times and to identify B1_3g as the fastest mode. That is a modeling-selection effect, not a derivation that reduces to its inputs, and the paper transparently reports the all-phonon baseline (102 fs) and the blocking/slowing of other channels in Table I. Therefore no specific circular step is established.
Assumptions & free parameters
free parameters (4)
- Laser central frequency =
10 THz
- Pump fluence =
9 mJ/cm2
- Pulse duration =
6.05 fs
- Exponential relaxation time constants tau =
e.g., 83 fs for E2 with B1_3g; other values in Table I
assumptions (5)
- domain assumption rt-TDDFT with Ehrenfest dynamics adequately describes electron-ion and spin dynamics in the first ~200 fs.
- domain assumption The chosen NAMD initial excited states at 0.68, 1.29, and 2.50 eV represent the THz-induced hot electron distribution.
- ad hoc to paper Freezing all phonon modes except one in single-phonon NAMD isolates that mode's intrinsic contribution to electron relaxation.
- domain assumption The DFT functional and pseudopotential approximations used for CrSBr are accurate enough for the predicted relaxation times.
- ad hoc to paper Electron relaxation populations decay as a single exponential f(t)=a+b exp(-t/tau), so the fitted tau is a meaningful timescale.
Cite this review
Pith. "Pith review of Ultrafast magneto-lattice dynamics in two-dimensional CrSBr driven by terahertz excitation." pith.science (2026). https://pith.science/paper/QVK6C6QN
@misc{pith2026250605058,
author = {Pith},
title = {Pith review of: Ultrafast magneto-lattice dynamics in two-dimensional CrSBr driven by terahertz excitation},
year = {2026},
howpublished = {\url{https://pith.science/paper/QVK6C6QN}},
note = {Machine review of arXiv:2506.05058}
}
read the original abstract
Terahertz (THz) lasers provide a new research perspective for spin electronics applications due to their sub-picosecond time resolution and non-thermal ultrafast demagnetization, but the interaction between spin, charge and lattice dynamics remains unclear. This study investigates photoinduced ultrafast demagnetization in monolayer CrSBr, a two-dimensional material with strong spin-orbit and spin-lattice coupling, and resolves its demagnetization process. Two key stages are identified: the first, occurring within 20 fs, is characterized by rapid electron-driven demagnetization, where charge transfer and THz laser are strongly coupled. In the second stage, light-induced lattice vibrations coupled to spin dynamics lead to significant spin changes, with electron-phonon coupling playing a key role. Importantly, the role of various phonon vibration modes in the electron relaxation process was clearly determined, pointing out that the electronic relaxation of the B3g1 phonon vibration mode occurs within 83 fs, which is less than the commonly believed 100 fs. Moreover, the influence of this coherent phonon on the demagnetization change is as high as 215 %. These insights into multiscale magneto-structural coupling advance the understanding of nonequilibrium spin dynamics and provide guidelines for the design of light-controlled quantum devices, particularly in layered heterostructures for spintronics and quantum information technologies.
Figures
Figures from the paper (2 more)
Reference graph
Works this paper leans on
- [1]
-
[2]
C. Liu, H. Chen, S. Wang, Q. Liu, Y.-G. Jiang, D. W. Zhang, M. Liu, and P. Zhou, Nat. Nanotechnol.15, 545 (2020)
work page 2020
-
[3]
Y. Xiao, B. Jiang, Z. Zhang, S. Ke, Y. Jin, X. Wen, and C. Ye, Sci. Technol. Adv. Mater.24, 2162323 (2023)
work page 2023
-
[4]
M.-K. Song, J.-H. Kang, X. Zhang, W. Ji, A. Ascoli, I. Messaris, A. S. Demirkol, B. Dong, S. Aggarwal, W. Wan,et al., ACS nano17, 11994 (2023)
work page 2023
-
[5]
Takeda, A
K. Takeda, A. Noiri, T. Nakajima, T. Kobayashi, and S. Tarucha, Nature608, 682 (2022)
2022
-
[6]
N. Wang, J.-M. Kang, W.-L. Lu, S.-M. Wang, Y.-J. Wang, H.-O. Li, G. Cao, B.-C. Wang, and G.-P. Guo, Nano Lett.24, 13126 (2024)
work page 2024
- [7]
-
[8]
L. D. Anh, M. Kobayashi, T. Takeda, K. Araki, R. Okano, T. Sumi, M. Horio, K. Yamamoto, Y. Kubota, S. Owada,et al., Adv. Mater.35, 2301347 (2023)
work page 2023
Show all 58 references
-
[9]
A. V. Emelianov, M. Pettersson, and I. I. Bobrinetskiy, Adv. Mater.36, 2402907 (2024)
2024
-
[10]
Hamamera, F
H. Hamamera, F. S. M. Guimarães, M. dos Santos Dias, and S. Lounis, Commun. Phys.5, 16 (2022)
2022
-
[11]
Q. Remy, J. Hohlfeld, M. Vergès, Y. Le Guen, J. Gor- chon, G. Malinowski, S. Mangin, and M. Hehn, Nat. Commun.14, 445 (2023)
2023
-
[12]
Davies, F
C. Davies, F. Fennema, A. Tsukamoto, I. Razdolski, A. Kimel, and A. Kirilyuk, Nature628, 540 (2024)
2024
-
[13]
Vicario, B
C. Vicario, B. Monoszlai, and C. P. Hauri, Phys. rev. lett. 112, 213901 (2014)
2014
-
[14]
Carnio, M
B. Carnio, M. Zhang, K. Zawilski, P. Schunemann, O. Moutanabbir, and A. Elezzabi, Sci. Rep.13, 8161 (2023)
2023
-
[15]
A. D. Koulouklidis, C. Gollner, V. Shumakova, V. Y. Fedorov, A. Pugžlys, A. Baltuška, and S. Tzortzakis, Nat. commun.11, 292 (2020)
2020
-
[16]
Dekorsy, M
T.Kampfrath, A.Sell, G.Klatt, A.Pashkin, S.Mährlein, T. Dekorsy, M. Wolf, M. Fiebig, A. Leitenstorfer, and R. Huber, Nat. Photonics.5, 31 (2011)
2011
-
[17]
Z. Wang, S. Kovalev, N. Awari, M. Chen, S. Germanskiy, B. Green, J.-C. Deinert, T. Kampfrath, J. Milano, and M. Gensch, Appl. phys. lett.112(2018)
2018
-
[18]
Kovalev, Z
S. Kovalev, Z. Wang, J. Deinert, N. Awari, M. Chen, B. Green, S. Germanskiy, T. De Oliveira, J. Lee, A. Deac, et al., J. Phys. D: Appl. Phys.51, 114007 (2018)
2018
-
[19]
Huzayyin, J
A. Huzayyin, J. H. Chang, K. Lian, and F. Dawson, J. Phys. Chem. C.118, 3459 (2014)
2014
-
[20]
J. L. LaRue, T. Katayama, A. Lindenberg, A. S. Fisher, H. Öström, A. Nilsson, and H. Ogasawara, Phys. rev. lett.115, 036103 (2015)
2015
-
[21]
Baierl, J
S. Baierl, J. H. Mentink, M. Hohenleutner, L. Braun, T.-M. Do, C. Lange, A. Sell, M. Fiebig, G. Woltersdorf, T. Kampfrath,et al., Phys. rev. lett.117, 197201 (2016)
2016
-
[22]
H. Zhao, Y. Tan, L. Zhang, R. Zhang, M. Shalaby, C. Zhang, Y. Zhao, and X.-C. Zhang, light: sci. appl. 9, 136 (2020)
2020
-
[23]
S. A. Mikhailov, Europhys. Lett.79, 27002 (2007)
2007
-
[24]
Crassee, J
I. Crassee, J. Levallois, A. L. Walter, M. Ostler, A. Bost- wick, E. Rotenberg, T. Seyller, D. Van Der Marel, and A. B. Kuzmenko, Nat. Phys.7, 48 (2011)
2011
-
[25]
H. A. Hafez, S. Kovalev, J.-C. Deinert, Z. Mics, B. Green, N. Awari, M. Chen, S. Germanskiy, U. Lehnert, J. Te- ichert,et al., Nature561, 507 (2018)
2018
-
[26]
Esposito, M
V. Esposito, M. Fechner, R. Mankowsky, H. Lemke, M. Chollet, J. M. Glownia, M. Nakamura, M. Kawasaki, Y. Tokura, U. Staub,et al., Phys. rev. lett.118, 247601 (2017)
2017
-
[27]
T. F. Nova, A. Cartella, A. Cantaluppi, M. Först, D. Bossini, R. V. Mikhaylovskiy, A. V. Kimel, R. Merlin, and A. Cavalleri, Nat. Phys.13, 132 (2017)
2017
-
[28]
Moroder, M
M. Moroder, M. Mitrano, U. Schollwöck, S. Paeckel, and J. Sous, Nano Lett.24, 15693 (2024)
2024
-
[29]
Matsuzaki, H
H. Matsuzaki, H. Nishioka, H. Uemura, A. Sawa, S. Sota, T. Tohyama, and H. Okamoto, Phys. Rev. B91, 081114 (2015)
2015
-
[30]
T.Dang, J.Hawecker, E.Rongione, G.BaezFlores, D.Q. To, J. Rojas-Sanchez, H. Nong, J. Mangeney, J. Tignon, F. Godel,et al., Appl. Phys. Rev.7(2020)
2020
-
[31]
J. Choi, J. Park, S. Noh, J. Lee, S. Lee, D. Choe, H. Jung, J.Jo, I.Oh, J.Han,et al.,Nat.commun.15,8746(2024)
2024
-
[32]
Sharma, S
S. Sharma, S. Shallcross, P. Elliott, and J. K. Dewhurst, Sci. Adv.8, eabq2021 (2022)
2022
-
[33]
Cazorla, M
C. Cazorla, M. Stengel, J. Íñiguez, and R. Rurali, npj comput. mater.9, 97 (2023)
2023
-
[34]
Fonseca, G
J. Fonseca, G. M. Diederich, D. Ovchinnikov, J. Yan, D. Xiao, and X. Xu, Nano Lett.24, 10562 (2024)
2024
-
[35]
Tengdin, C
P. Tengdin, C. Gentry, A. Blonsky, D. Zusin, M. Gerrity, L. Hellbrück, M. Hofherr, J. Shaw, Y. Kvashnin, E. K. Delczeg-Czirjak,et al., Sci. adv.6, eaaz1100 (2020)
2020
-
[36]
J. He, S. Li, T. Frauenheim, and Z. Zhou, Nano Lett.23, 8348 (2023)
2023
-
[37]
K. Wang, W. Zhou, Y. Cheng, M. Zhang, H. Wang, and G. Zhang, Nanoscale13, 10882 (2021)
2021
-
[38]
Pandey, F
T. Pandey, F. Peeters, and M. Milošević, 2D Mater.9, 015034 (2021). 10
2021
-
[39]
B. Liu, S. Liu, L. Yang, Z. Chen, E. Zhang, Z. Li, J. Wu, X. Ruan, F. Xiu, W. Liu,et al., Phys. Rev. Lett.125, 267205 (2020)
2020
-
[40]
Lett.15, 5939 (2024)
S.Li, R.Wang, T.Frauenheim,andJ.He,J.Phys.Chem. Lett.15, 5939 (2024)
2024
-
[41]
Torres, A
K. Torres, A. Kuc, L. Maschio, T. Pham, K. Reidy, L. Dekanovsky, Z. Sofer, F. M. Ross, and J. Klein, Adv. Funct. Mater.33, 2211366 (2023)
2023
-
[42]
C. Li, C. Shen, N. Jiang, K. K. Tang, X. Liu, J. Guo, Y. Liang, J. Song, X. Deng, and Q. Zhang, Adv. Funct. Mater.34, 2411589 (2024)
2024
-
[43]
Y. J. Bae, J. Wang, A. Scheie, J. Xu, D. G. Chica, G. M. Diederich, J. Cenker, M. E. Ziebel, Y. Bai, H. Ren,et al., Nature609, 282 (2022)
2022
-
[44]
Pawbake, T
A. Pawbake, T. Pelini, N. P. Wilson, K. Mosina, Z. Sofer, R. Heid, and C. Faugeras, Phys. Rev.B107, 075421 (2023)
2023
-
[45]
D. L. Esteras, A. Rybakov, A. M. Ruiz, and J. J. Baldoví, Nano Lett.22, 8771 (2022)
2022
-
[46]
M. E. Ziebel, M. L. Feuer, J. Cox, X. Zhu, C. R. Dean, and X. Roy, Nano Lett.24, 4319 (2024)
2024
-
[47]
E. J. Telford, A. H. Dismukes, K. Lee, M. Cheng, A. Wi- eteska, A. K. Bartholomew, Y.-S. Chen, X. Xu, A. N. Pa- supathy, X. Zhu,et al., Adv. Mater.32, 2003240 (2020)
2020
-
[48]
B. Wang, Y. Wu, Y. Bai, P. Shi, G. Zhang, Y. Zhang, and C. Liu, Nanoscale15, 13402 (2023)
2023
-
[49]
K. Yang, G. Wang, L. Liu, D. Lu, and H. Wu, Phys. Rev. B104, 144416 (2021)
2021
-
[50]
Jiang, Y
P. Jiang, Y. Li, X. Lyu, J. Xiao, X. Li, T. Wang, J. Tang, Y. Wang, L. Zhang, Y. Liu,et al., J. Phys. Chem. C.128, 21855 (2024)
2024
-
[51]
Mosina, B
K. Mosina, B. Wu, N. Antonatos, J. Luxa, V. Mazánek, A. Söll, D. Sedmidubsky, J. Klein, F. M. Ross, and Z. Sofer, Small Methods8, 2300609 (2024)
2024
-
[52]
Mrudul and P
M. Mrudul and P. M. Oppeneer, Phys. Rev. B109, 144418 (2024)
2024
-
[53]
Zheng, Q
Z. Zheng, Q. Zheng, and J. Zhao, Phys. Rev. B105, 085142 (2022)
2022
-
[54]
Yamamoto, T
A. Yamamoto, T. Mishina, Y. Masumoto, and M. Nakayama, Phys. Rev. Lett.73, 740 (1994)
1994
-
[55]
T. Sun, C. Zhou, H. Guo, Z. Meng, X. Liu, Z. Wang, H. Zhou, Y. Fei, K. Qiu, F. Zhang,et al., Adv. Sci.10, 2205707 (2023)
2023
-
[56]
Zhang, T.-F
P. Zhang, T.-F. Chung, Q. Li, S. Wang, Q. Wang, W. L. Huey, S. Yang, J. E. Goldberger, J. Yao, and X. Zhang, Nat. Mater.21, 1373 (2022)
2022
-
[57]
Z. Zhou, Z. Zheng, J. He, J. Wang, O. V. Prezhdo, and T. Frauenheim, Nano Lett.23, 5688 (2023)
2023
-
[58]
N. Wu, S. Zhang, D. Chen, Y. Wang, and S. Meng, Nat. Commun.15, 2804 (2024)
2024
Reviewed August 7, 2026 · model on record in the stance chip above.
Discussion (0). Sign in to comment.