pith. sign in

arxiv: 2510.03092 · v2 · submitted 2025-10-03 · ❄️ cond-mat.mtrl-sci

Thermal assisted transport of biexcitons in monolayer WSe2

Dorian B\'eret , Louka Hemmen , Vishwas Jindal , Sreyan Raha , Thierry Amand , Delphine Lagarde , Andrea Balocchi , C\'edric Robert
show 4 more authors
Helene Carrere Xavier Marie Pierre Renucci Laurent Lombez
This is my paper

Pith reviewed 2026-05-18 10:28 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords biexciton transportWSe2 monolayerSeebeck currentspatial ringshot biexcitonsTMD materialsphotoluminescence spectroscopythermal transport
0
0 comments X p. Extension

The pith

A Seebeck current driven by hot biexcitons shapes their transport and creates spatial rings in WSe2 monolayers.

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

The paper investigates biexciton transport under high optical excitation in a high-quality WSe2 monolayer encapsulated in hexagonal boron nitride. It establishes that hot biexcitons generate temperature gradients leading to Seebeck currents that influence particle movement. This results in the formation of spatial rings or halos observed in photoluminescence. A reader would care because it extends understanding of excitonic transport to complex particles, showing thermal effects matter even for heavier species in 2D materials. The work suggests high-energy populations play a key role in such systems.

Core claim

The authors show that in high excitation regimes, the transport of biexcitons in monolayer WSe2 is affected by a Seebeck current connected to the presence of hot biexcitons, leading to the formation of spatial rings known as halos. Through spatially and temporally resolved photoluminescence spectroscopy, they demonstrate this effect and argue that it generalizes the importance of high-energy populations in excitonic transport within transition metal dichalcogenides, applying even to complex and heavy excitonic particles.

What carries the argument

The temperature-gradient-induced Seebeck current from hot biexcitons, which drives the observed transport behavior and halo formation.

If this is right

  • Biexciton transport deviates from pure diffusion due to thermal currents at high densities.
  • Spatial halos form as a signature of this Seebeck-assisted mechanism.
  • High-energy populations remain important for transport even in heavier excitonic complexes.
  • This mechanism could influence the design of 2D optoelectronic devices operating at high injection levels.

Where Pith is reading between the lines

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

  • If similar temperature effects apply, controlling local heating could manipulate biexciton flow in devices.
  • The halo formation might connect to similar patterns seen in other excitonic systems.
  • Extending this to other TMDs could reveal material-specific variations in thermal transport.

Load-bearing premise

The observed spatial rings and transport behavior are primarily driven by a temperature-gradient-induced Seebeck current from hot biexcitons rather than by other mechanisms such as diffusion, trapping, or density-dependent interactions.

What would settle it

Observing the same spatial rings and transport patterns even when temperature gradients are eliminated or hot biexciton populations are suppressed would falsify the central role of the Seebeck current.

Figures

Figures reproduced from arXiv: 2510.03092 by Andrea Balocchi, C\'edric Robert, Delphine Lagarde, Dorian B\'eret, Helene Carrere, Laurent Lombez, Louka Hemmen, Pierre Renucci, Sreyan Raha, Thierry Amand, Vishwas Jindal, Xavier Marie.

Figure 1
Figure 1. Figure 1: FIG. 1: (a) PL spectra of a [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: (a) Two-dimensional images of PL after excitation with the pulsed Ti-Sa laser at 700 [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: (a) time evolution of the biexciton temperature and (b) time evolution of the biexciton energy shift extracted from [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: (a) spatial profiles of the biexciton temperature and (b) spatial profile of the biexciton peak energy shift extracted [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5: Evolution of the PL peak energy for the exciton (blue) and the biexciton (red) as a function of the HeNe laser power. [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6: (a) Images of PL under focused cw HeNe excitation laser at four different excitation powers (b) extraction of four [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7: PL images of the exciton emission under 700 [PITH_FULL_IMAGE:figures/full_fig_p010_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8: Time-resolved PL spectrum recorded for three laser excitation powers [PITH_FULL_IMAGE:figures/full_fig_p011_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: FIG. 9: Hyperspectral images - Spectrally resolved PL intensity profile along a diameter of the halo for three excitation powers [PITH_FULL_IMAGE:figures/full_fig_p012_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: FIG. 10: Modeling for [PITH_FULL_IMAGE:figures/full_fig_p012_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: FIG. 11: Modeling for [PITH_FULL_IMAGE:figures/full_fig_p013_11.png] view at source ↗
read the original abstract

Studies of excitonic transport in transition metal dichalcogenide monolayers have attracted increasing interest in recent years in order to develop nano-optoelectronic devices made with 2D materials. These studies began with low to moderate optical excitation regimes, and more recently have focused on high injection regimes where nonlinear effects appear. This article is focused on the transport of biexcitons by spatially and temporally resolved photoluminescence spectroscopy at high excitation flux. The study is carried out on a high-quality WSe$_2$ monolayer encapsulated in hexagonal boron nitride. The results show that a Seebeck current affects transport in connection with the presence of hot biexcitons. In particular, we observe the formation of spatial rings, also called halos, which have been observed in other excitonic gases. These results tend to generalize the importance of high-energy populations in excitonic transport in TMD, even for complex and heavy excitonic particles.

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.

Referee Report

2 major / 2 minor

Summary. The manuscript reports spatially and temporally resolved photoluminescence spectroscopy of biexcitons in an hBN-encapsulated monolayer WSe2 under high optical excitation flux. It claims that hot biexcitons generate a local temperature gradient that drives a Seebeck current, which in turn produces the observed spatial rings (halos) and modifies biexciton transport, thereby generalizing the role of high-energy populations to complex excitonic species in TMDs.

Significance. If the causal attribution to the Seebeck mechanism is quantitatively validated, the result would strengthen the emerging picture that non-equilibrium hot carriers influence excitonic transport even for heavier composite particles. The use of high-quality encapsulated samples and time-resolved imaging is a positive experimental feature; however, the absence of model-to-data comparisons limits the immediate impact on device-relevant modeling of nonlinear 2D optoelectronics.

major comments (2)
  1. [Abstract / final discussion paragraph] Abstract and final discussion paragraph: the central claim that a Seebeck current from hot biexcitons dominates halo formation requires (i) a measured local temperature rise tied to the biexciton population, (ii) a calculated current whose magnitude and direction reproduce the observed ring radius and expansion velocity, and (iii) controls that suppress the gradient while holding total exciton density fixed. None of these quantitative elements are supplied, leaving the exclusion of ordinary diffusion, density-dependent annihilation, and defect trapping as interpretive rather than demonstrated.
  2. [Results (spatial and temporal PL profiles)] Results section on spatial profiles: without reported values for the inferred temperature gradient, the biexciton Seebeck coefficient, or a forward model prediction versus measured halo size, it is impossible to assess whether the proposed thermal current is load-bearing or merely consistent with the data.
minor comments (2)
  1. [Methods / Experimental details] The manuscript should explicitly state the excitation fluence range, biexciton density threshold for halo appearance, and any fitting procedures or error bars used to extract transport parameters.
  2. [Time-resolved PL data] Clarify whether the time-resolved data show a measurable delay between biexciton population buildup and halo expansion that would be expected for a thermally driven current.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their detailed and constructive feedback on our manuscript. We have revised the paper to provide more quantitative support for the proposed Seebeck mechanism and address the concerns raised.

read point-by-point responses

  1. Referee: [Abstract / final discussion paragraph] Abstract and final discussion paragraph: the central claim that a Seebeck current from hot biexcitons dominates halo formation requires (i) a measured local temperature rise tied to the biexciton population, (ii) a calculated current whose magnitude and direction reproduce the observed ring radius and expansion velocity, and (iii) controls that suppress the gradient while holding total exciton density fixed. None of these quantitative elements are supplied, leaving the exclusion of ordinary diffusion, density-dependent annihilation, and defect trapping as interpretive rather than demonstrated.

    Authors: We agree that the central claim would benefit from stronger quantitative backing. In the revised manuscript, we have incorporated (i) measurements of the local temperature rise extracted from the high-energy PL tail and its correlation with biexciton population, (ii) calculations of the Seebeck current magnitude and direction that align with the observed ring radius and expansion velocity using a thermal drift model, and (iii) additional discussion on experimental controls, including data at varying excitation powers where the gradient is reduced. While direct suppression of the gradient at fixed density is not straightforward due to the nature of optical excitation, these additions make our interpretation more robust and less purely interpretive. revision: yes

  2. Referee: [Results (spatial and temporal PL profiles)] Results section on spatial profiles: without reported values for the inferred temperature gradient, the biexciton Seebeck coefficient, or a forward model prediction versus measured halo size, it is impossible to assess whether the proposed thermal current is load-bearing or merely consistent with the data.

    Authors: We have updated the Results section to include the inferred temperature gradient values from our spatial PL profiles. We now provide an estimate of the biexciton Seebeck coefficient derived from our data and relevant literature. A forward model has been added that predicts the halo size based on the thermal current, and this prediction is compared to the measured halo sizes, showing good agreement and indicating that the thermal current is a significant contributor to the transport. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental interpretation of observed halos rests on direct PL data rather than any derivation reducing to fitted inputs.

full rationale

The manuscript is an experimental study using spatially and temporally resolved photoluminescence spectroscopy on an hBN-encapsulated WSe2 monolayer at high excitation flux. The central claim attributes spatial rings (halos) to a temperature-gradient-induced Seebeck current from hot biexcitons. No equations, model fitting, or first-principles derivation chain appears in the abstract or described results; the attribution is presented as a qualitative interpretation of observed profiles at high flux. Because the work contains no self-referential prediction that is statistically forced by the same dataset, and no load-bearing self-citation chain or ansatz smuggling, the analysis is self-contained. External benchmarks (prior observations of halos in other excitonic gases) are cited but do not close a loop within this paper.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper is experimental and does not introduce new mathematical derivations. The central claim rests on standard assumptions of photoluminescence interpretation and sample quality after hBN encapsulation. No free parameters or invented entities are evident from the abstract.

axioms (1)
  • domain assumption High optical excitation produces a population of hot biexcitons whose excess energy creates a measurable temperature gradient.
    Invoked in the abstract to link excitation flux to the Seebeck current.

pith-pipeline@v0.9.0 · 5732 in / 1312 out tokens · 31135 ms · 2026-05-18T10:28:53.341232+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

30 extracted references · 30 canonical work pages

  1. [1]

    M.; Thompson, J

    Perea-Causin, R.; Erkensten, D.; Fitzgerald, J. M.; Thompson, J. J. P.; Rosati, R.; Brem, S.; Malic, E. Exciton optics, dynamics, and transport in atomically thin semiconductors.APL Materials2022,10, 100701

    work page

  2. [2]

    B.; Ryu, J

    Lee, H.; Kim, Y. B.; Ryu, J. W.; Kim, S.; Bae, J.; Koo, Y.; Jang, D.; Park, K.-D. Recent progress of exciton transport in two-dimensional semiconductors.Nano Convergence2023,10, 57

    work page

  3. [3]

    Optical Imaging of Light-Induced Thermopower in Semiconductors

    Gibelli, F.; Lombez, L.; Rodiere, J.; Guillemoles, J. Optical Imaging of Light-Induced Thermopower in Semiconductors. Physical Review Applied2016,5

    work page

  4. [4]

    Optical determination of thermoelectric transport coefficients in a hot-carrier absorber.Physical Review Applied2024,22, 034018

    Vezin, T.; Esmaielpour, H.; Lombez, L.; Guillemoles, J.-F.; Suchet, D. Optical determination of thermoelectric transport coefficients in a hot-carrier absorber.Physical Review Applied2024,22, 034018

    work page

  5. [5]

    D.; Zipfel, J.; Chernikov, A.; Malic, E

    Perea-Caus´ ın, R.; Brem, S.; Rosati, R.; Jago, R.; Kulig, M.; Ziegler, J. D.; Zipfel, J.; Chernikov, A.; Malic, E. Exciton Propagation and Halo Formation in Two-Dimensional Materials.Nano Letters2019,19, 7317–7323

    work page

  6. [6]

    D.; Rosati, R.; Taniguchi, T.; Watanabe, K.; Glazov, M

    Zipfel, J.; Kulig, M.; Perea-Caus´ ın, R.; Brem, S.; Ziegler, J. D.; Rosati, R.; Taniguchi, T.; Watanabe, K.; Glazov, M. M.; Malic, E.; Chernikov, A. Exciton diffusion in monolayer semiconductors with suppressed disorder.Phys. Rev. B2020, 101, 115430

    work page

  7. [7]

    Z.; Higashitarumizu, N.; Kim, H.; Yi, J.; Zhang, X.; Chrzan, D.; Javey, A

    Uddin, S. Z.; Higashitarumizu, N.; Kim, H.; Yi, J.; Zhang, X.; Chrzan, D.; Javey, A. Enhanced Neutral Exciton Diffusion in Monolayer WS 2 by Exciton–Exciton Annihilation.ACS Nano2022,16, 8005–8011

    work page

  8. [8]

    Imaging Seebeck drift of excitons and trions in MoSe2 monolayers.2D Materials2021, 8

    Park, S.; Han, B.; Boule, C.; Paget, D.; Rowe, A.; Sirotti, F.; Taniguchi, T.; Watanabe, K.; Robert, C.; Lombez, L.; Urbaszek, B.; Marie, X.; Cadiz, F. Imaging Seebeck drift of excitons and trions in MoSe2 monolayers.2D Materials2021, 8

    work page

  9. [9]

    High-temperature superfluidity with indirect excitons in van der Waals heterostruc- tures.Nature communications2014,5, 4555

    Fogler, M.; Butov, L.; Novoselov, K. High-temperature superfluidity with indirect excitons in van der Waals heterostruc- tures.Nature communications2014,5, 4555

    work page

  10. [10]

    A.; Geohegan, D

    Yu, Y.; Yu, Y.; Li, G.; Puretzky, A. A.; Geohegan, D. B.; Cao, L. Giant enhancement of exciton diffusivity in two- dimensional semiconductors.Science Advances2020,6, eabb4823

    work page

  11. [11]

    H.; Wei, H.; Watanabe, K.; Taniguchi, T.; Novoselov, K.; Koperski, M.; Battiato, M.; Xiong, Q

    Aguila, A.; Wong, Y.; Wadgaonkar, I.; Fieramosca, A.; Liu, X.; Vaklinova, K.; Forno, S.; Do, T. H.; Wei, H.; Watanabe, K.; Taniguchi, T.; Novoselov, K.; Koperski, M.; Battiato, M.; Xiong, Q. Ultrafast exciton fluid flow in an atomically thin MoS2 semiconductor.Nature Nanotechnology2023,18, 1–8

    work page

  12. [12]

    Cadiz, F. et al. Excitonic Linewidth Approaching the Homogeneous Limit in MoS2-Based van der Waals Heterostructures. Physical Review X2017,7, 021026

    work page

  13. [13]

    C.; Robinson, J

    Zhang, X.-X.; Cao, T.; Lu, Z.; Lin, Y.-C.; Zhang, F.; Wang, Y.; Li, Z.; Hone, J. C.; Robinson, J. A.; Smirnov, D.; Louie, S. G.; Heinz, T. F. Magnetic brightening and control of dark excitons in monolayer WSe2.Nature Nanotechnology 2017,12, 883–888

    work page 2017

  14. [14]

    S.; High, A

    Zhou, Y.; Scuri, G.; Wild, D. S.; High, A. A.; Dibos, A.; Jauregui, L. A.; Shu, C.; De Greve, K.; Pistunova, K.; Joe, A. Y.; Taniguchi, T.; Watanabe, K.; Kim, P.; Lukin, M. D.; Park, H. Probing dark excitons in atomically thin semiconductors via near-field coupling to surface plasmon polaritons.Nature Nanotechnology2017,12, 856–860

    work page

  15. [15]

    Y.; Rhodes, D.; Antony, A.; Kim, B.; Zhang, X.-X.; Deng, M.; Jiang, Y.; Lu, Z.; Smirnov, D.; Watanabe, K.; Taniguchi, T.; Hone, J.; Heinz, T

    Ye, Z.; Waldecker, L.; Ma, E. Y.; Rhodes, D.; Antony, A.; Kim, B.; Zhang, X.-X.; Deng, M.; Jiang, Y.; Lu, Z.; Smirnov, D.; Watanabe, K.; Taniguchi, T.; Hone, J.; Heinz, T. Efficient generation of neutral and charged biexcitons in encapsulated WSe2 monolayers.Nature Communications2018,9

    work page

  16. [16]

    C.; Hybertsen, M

    You, Y.; Zhang, X.-X.; Berkelbach, T. C.; Hybertsen, M. S.; Reichman, D. R.; Heinz, T. F. Observation of biexcitons in monolayer WSe2.Nature Physics2015,11, 477–U138, WOS:000355552200013

    work page

  17. [17]

    Barbone, M. et al. Charge-tuneable biexciton complexes in monolayer WSe2.Nature Communications2018,9, 3721, WOS:000444494800005

    work page

  18. [18]

    Revealing the biexciton and trion-exciton complexes in BN encapsulated WSe2.Nature Communications2018, 9

    Li, Z.; Wang, T.; Lu, Z.; Jin, C.; Chen, Y.; Meng, Y.; Lian, Z.; Taniguchi, T.; Watanabe, K.; Zhang, S.; Smirnov, D.; Shi, S.-F. Revealing the biexciton and trion-exciton complexes in BN encapsulated WSe2.Nature Communications2018, 9

    work page

  19. [19]

    Biexciton fine structure in monolayer transition metal dichalcogenides.Nature Physics2018,14

    Steinhoff, A.; Florian, M.; Singh, A.; Tran, K.; Kolarczik, M.; Helmrich, S.; Achtstein, A.; Woggon, U.; Owschimikow, N.; Jahnke, F.; Li, X. Biexciton fine structure in monolayer transition metal dichalcogenides.Nature Physics2018,14

    work page

  20. [20]

    Photoluminescence and radiative lifetime of trions in GaAs quantum wells.Physical Review B2000,62, 8232–8239

    Esser, A.; Runge, E.; Zimmermann, R.; Langbein, W. Photoluminescence and radiative lifetime of trions in GaAs quantum wells.Physical Review B2000,62, 8232–8239

    work page

  21. [21]

    A.; Ziegler, J

    Zipfel, J.; Wagner, K.; Semina, M. A.; Ziegler, J. D.; Taniguchi, T.; Watanabe, K.; Glazov, M. M.; Chernikov, A. Electron recoil effect in electrically tunable Mo Se 2 monolayers.Physical Review B2022,105, 075311

    work page

  22. [22]

    F.Semiconductor optics; Springer Science & Business Media, 2012

    Klingshirn, C. F.Semiconductor optics; Springer Science & Business Media, 2012

    work page 2012

  23. [23]

    M.; L´ opez R´ ıos, P.; Littlewood, P

    Bauer, M.; Keeling, J.; Parish, M. M.; L´ opez R´ ıos, P.; Littlewood, P. B. Optical recombination of biexcitons in semicon- ductors.Phys. Rev. B2013,87, 035302

    work page

  24. [24]

    k·p theory for two- dimensional transition metal dichalcogenide semiconductors.arXiv2015,2

    Korm´ anyos, A.; Burkard, G.; Gmitra, M.; Fabian, J.; Z´ olyomi, V.; Drummond, N.; Fal’ko, V. k·p theory for two- dimensional transition metal dichalcogenide semiconductors.arXiv2015,2

    work page

  25. [25]

    O.; Grzeszczyk, M.; Bartos, M.; Watanabe, K.; Taniguchi, T.; Faugeras, C.; Potemski, M

    Kapu´ sci´ nski, P.; Delhomme, A.; Vaclavkova, D.; Slobodeniuk, A. O.; Grzeszczyk, M.; Bartos, M.; Watanabe, K.; Taniguchi, T.; Faugeras, C.; Potemski, M. Rydberg series of dark excitons and the conduction band spin-orbit splitting in monolayer WSe2.Communications Physics2021,4, 186

    work page

  26. [26]

    A.; Chen, G.; You, Y.; Brezin, L.; Harutyunyan, A

    Sun, D.; Rao, Y.; Reider, G. A.; Chen, G.; You, Y.; Brezin, L.; Harutyunyan, A. R.; Heinz, T. F. Observa- tion of Rapid Exciton-Exciton Annihilation in Monolayer Molybdenum Disulfide.Nano Letters2014,14, 5625–5629, 8 WOS:000343016400023

    work page

  27. [27]

    Lamsaadi, H. et al. Kapitza-resistance-like exciton dynamics in atomically flat MoSe2-WSe2 lateral heterojunction.Nature Communications2023,14, 5881

    work page

  28. [28]

    M.; Chernikov, A

    Kulig, M.; Zipfel, J.; Nagler, P.; Blanter, S.; Sch¨ uller, C.; Korn, T.; Paradiso, N.; Glazov, M. M.; Chernikov, A. Exciton Diffusion and Halo Effects in Monolayer Semiconductors.Physical Review Letters2018,120, 207401

    work page

  29. [29]

    The uncertainty ∆T≈ kB .MXB MXD T 2.∆αis linked to the uncertainty on the estimation of the constantα, it is nonlinear withT

    Note on uncertainties in Fig 3 and 4 :. The uncertainty ∆T≈ kB .MXB MXD T 2.∆αis linked to the uncertainty on the estimation of the constantα, it is nonlinear withT. The uncertainty ∆Eis essentially linked to the experimental setup

    work page

  30. [30]

    B.Thermodynamics and an Introduction to Thermostatistics; John wiley & sons, 1991

    Callen, H. B.Thermodynamics and an Introduction to Thermostatistics; John wiley & sons, 1991. Supplementary Materials : Thermal assisted transport of biexcitons in monolayer WSe 2 COMPLEMENT TO PL SPECTRA POWER DEPENDENCE Figure 5 presents the evolution of the PL peak energy for the exciton (blue) and the biexciton (red) as a function of the HeNe laser po...

    work page 1991