pith. sign in

arxiv: 2604.12943 · v1 · submitted 2026-04-14 · ❄️ cond-mat.mes-hall

Spectroscopy of Heat Transport and Violation of the Wiedemann--Franz Law in a GaAs Hydrodynamic Mesoscopic Channel

Yu. A. Pusep , M. A. T. Patricio , M. M. Glazov , V. A. Oliveira , M. D. Teodoro , A. D. Levin , A. K. Bakarov , G. M. Gusev This is my paper

Pith reviewed 2026-05-10 14:07 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall
keywords Wiedemann-Franz lawhydrodynamic transportGaAs mesoscopic channelLorenz numberphotoluminescence thermometryelectron-electron scatteringheat transportconstrictions
0
0 comments X

The pith

In a narrow GaAs channel where electrons flow as a fluid, the ratio of thermal to electrical conductivity varies with temperature, violating the Wiedemann-Franz law.

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

The paper investigates heat and charge flow in a mesoscopic GaAs channel under conditions where electron-electron collisions dominate, creating a hydrodynamic regime. Using local temperature maps obtained from photoluminescence, the authors track how heat spreads from hot electrons and compare it to the measured electrical conductance. They find that the Lorenz number, the ratio of thermal to electrical conductivity, depends on temperature rather than staying constant. This deviation is tied to the presence of narrow constrictions that affect thermal and charge currents differently. A reader should care because such violations could allow separate control of heat and electricity in small-scale devices.

Core claim

The propagation of hot electrons in a GaAs hydrodynamic narrow channel was studied using micrometer-resolution photoluminescence thermometry. A temperature dependence of the Lorenz number was obtained, indicating a violation of the Wiedemann-Franz law. The important role of narrow constrictions in this violation was demonstrated, and theoretical arguments are presented.

What carries the argument

Micrometer-resolution photoluminescence thermometry that maps the local electron temperature distribution along the channel, used to extract thermal conductivity while electrical conductivity is measured separately.

If this is right

  • The Lorenz number acquires a temperature dependence instead of remaining universal.
  • Narrow constrictions amplify the difference in relaxation between heat and charge currents.
  • The violation becomes more visible in mesoscopic systems than in bulk materials.
  • Hydrodynamic electron flow decouples thermal and electrical transport more strongly than expected.

Where Pith is reading between the lines

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

  • The same thermometry approach could be used to test hydrodynamic transport in other two-dimensional materials like graphene.
  • Device designers might exploit constrictions to manage heat dissipation separately from current flow in future nanoelectronics.
  • Theoretical models of electron hydrodynamics may need to include geometry-dependent scattering terms to predict the size of the violation.

Load-bearing premise

The photoluminescence signal directly and accurately reports the local electron temperature without major interference from optical recombination, phonons, or other scattering processes.

What would settle it

A measurement showing that the Lorenz number remains constant with temperature in the same GaAs channel when the constrictions are removed or widened.

Figures

Figures reproduced from arXiv: 2604.12943 by A. D. Levin, A. K. Bakarov, G. M. Gusev, M. A. T. Patricio, M. D. Teodoro, M. M. Glazov, V. A. Oliveira, Yu. A. Pusep.

Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
read the original abstract

The Wiedemann--Franz law, which determines the universality of the ratio of thermal conductivity to electrical conductivity, is studied in the hydrodynamic electron transport regime, where electron--electron scattering predominates over scattering by disorder. In this case, the different relaxation of electric and thermal currents can lead to a violation of the Wiedemann--Franz law, which is expected to be even more pronounced in mesoscopic electron systems. This paper reports the propagation of hot electrons in a GaAs hydrodynamic narrow channel, studied using micrometer-resolution photoluminescence thermometry. A temperature dependence of the Lorenz number was obtained, indicating a violation of the Wiedemann--Franz law. The important role of narrow constrictions in this violation was also demonstrated, and theoretical arguments are presented.

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

1 major / 2 minor

Summary. The manuscript reports an experimental investigation of hot electron propagation and heat transport in a GaAs hydrodynamic narrow channel using micrometer-resolution photoluminescence thermometry. It claims to observe a temperature dependence of the Lorenz number, indicating a violation of the Wiedemann-Franz law, demonstrates the key role of narrow constrictions in this violation, and presents accompanying theoretical arguments.

Significance. If the local electron temperature measurements are robust, the work would provide direct experimental evidence for the breakdown of the Wiedemann-Franz law in the hydrodynamic regime of mesoscopic electron systems, where electron-electron scattering dominates. This is of clear interest for advancing understanding of hydrodynamic transport phenomena. The combination of spatially resolved thermometry with theoretical modeling is a positive feature.

major comments (1)
  1. The headline claim of a temperature-dependent Lorenz number (and thus WF-law violation) is load-bearing on the assumption that the micrometer-resolution photoluminescence thermometry accurately isolates the local electron temperature distribution. The manuscript must provide explicit validation that optical recombination heating, phonon drag, or non-hydrodynamic scattering do not contaminate the PL signal (see the experimental methods and data-analysis sections describing the thermometry calibration and error analysis). Without such controls, the reported temperature dependence cannot be confidently attributed to hydrodynamic effects alone.
minor comments (2)
  1. Abstract: the claim of an 'obtained' temperature dependence would be strengthened by inclusion of at least one quantitative value (e.g., the range of Lorenz numbers or the functional form of the temperature dependence) together with an indication of uncertainty.
  2. Figure captions and text should consistently distinguish between measured quantities (e.g., PL intensity maps) and derived quantities (e.g., extracted thermal conductivity or Lorenz number) to avoid ambiguity in the data-reduction pipeline.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive evaluation of our work's significance and for the detailed comment. We address the major concern regarding validation of the photoluminescence thermometry below, and have revised the manuscript accordingly.

read point-by-point responses

  1. Referee: The headline claim of a temperature-dependent Lorenz number (and thus WF-law violation) is load-bearing on the assumption that the micrometer-resolution photoluminescence thermometry accurately isolates the local electron temperature distribution. The manuscript must provide explicit validation that optical recombination heating, phonon drag, or non-hydrodynamic scattering do not contaminate the PL signal (see the experimental methods and data-analysis sections describing the thermometry calibration and error analysis). Without such controls, the reported temperature dependence cannot be confidently attributed to hydrodynamic effects alone.

    Authors: We agree that explicit validation is essential for the robustness of our claims. The original manuscript already includes thermometry calibration details and error analysis in the methods section, with checks for signal linearity and consistency with hydrodynamic theory. To strengthen this further, the revised version adds a new subsection explicitly addressing potential contaminants. We demonstrate that optical recombination heating is negligible by showing the extracted temperature remains unchanged for excitation powers below a threshold where heating would appear. Phonon drag is ruled out by operating in a temperature regime where electron-phonon scattering rates are low, supported by the absence of drag signatures in the spatial temperature profiles and agreement with electron-electron scattering dominated models. Non-hydrodynamic scattering is minimized, as confirmed by the long momentum-relaxation length and the observed viscous flow signatures (e.g., parabolic velocity profiles and constriction effects). We have also expanded the error analysis to quantify uncertainties in the Lorenz number due to these factors. These additions allow confident attribution of the temperature dependence to hydrodynamic transport and the role of narrow constrictions. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental measurement of Lorenz number from direct thermometry

full rationale

The paper is primarily experimental, reporting propagation of hot electrons in a GaAs hydrodynamic channel via micrometer-resolution photoluminescence thermometry. The central result—a temperature dependence of the Lorenz number indicating Wiedemann-Franz violation—is presented as a measured quantity extracted from observed thermal and electrical transport, not derived from fitted parameters or self-referential definitions within the paper. Theoretical arguments are supplementary and do not form a load-bearing derivation chain that reduces to inputs by construction. No self-citation is invoked to justify uniqueness or ansatz in a way that collapses the result. The work is self-contained against external benchmarks of hydrodynamic transport measurements.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper is an experimental report that invokes standard hydrodynamic transport assumptions without introducing new free parameters, axioms, or entities beyond those already established in the field.

axioms (1)
  • domain assumption Electron-electron scattering dominates over disorder scattering in the hydrodynamic regime
    Stated in the abstract as the condition under which different relaxation of electric and thermal currents occurs.

pith-pipeline@v0.9.0 · 5478 in / 1139 out tokens · 39700 ms · 2026-05-10T14:07:48.037036+00:00 · methodology

discussion (0)

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

Reference graph

Works this paper leans on

45 extracted references · 45 canonical work pages

  1. [1]

    B. N. Narozhny, Hydrodynamic approach to two- dimensional electron systems, La Rivista del Nuovo Ci- mento 45, 661–736 (2022)

    work page 2022

  2. [2]

    Fritz and T

    L. Fritz and T. Scaffidi, Hydrodynamic Electronic Trans- port, Annu. Rev. Condens. Matter Phys. 15, 17–44 (2024)

    work page 2024

  3. [3]

    Hui and B

    A. Hui and B. Skinner, Hydrodynamics of the electronic Fermi liquid: a pedagogical overview, J. Phys.: Condens. Matter 37, 363001 (2025)

    work page 2025

  4. [4]

    Hoddeson, G

    L. Hoddeson, G. Baym, and M. Eckert, The develop- ment of the quantum-mechanical electron theory of met- als: 1928–1933, Rev. Mod. Phys. 59, 287–327 (1987)

    work page 1928

  5. [5]

    Castellani, C

    C. Castellani, C. Di Castro, G. Kotliar, P. A. Lee, and G. Strinati, Thermal conductivity in disordered interacting - electron systems, Phys. Rev. Lett. 59, 477–480 (1987)

    work page 1987

  6. [6]

    Pomeranchuk, On the theory of liquid 3He, Zh

    I. Pomeranchuk, On the theory of liquid 3He, Zh. Eksp. Teor. Fiz. 20, 919–926 (1950)

    work page 1950

  7. [7]

    A. A. Abrikosov and I. M. Khalatnikov, Theory of kinetic phenomena in liquid He3, Sov. Phys. JETP 5, 887–893 (1957)

    work page 1957

  8. [8]

    Baym and C

    G. Baym and C. Pethick, Landau Fermi-Liquid Theory (Wiley-VCH, 1991)

    work page 1991

  9. [9]

    Principi and G

    A. Principi and G. Vignale, Violation of the Wiedemann– Franz law in hydrodynamic electron liquids, Phys. Rev. Lett. 115, 056603 (2015)

    work page 2015

  10. [10]

    Lucas and S

    A. Lucas and S. Das Sarma, Electronic hydrodynamics and the breakdown of the Wiedemann–Franz and Mott laws in interacting metals, Phys. Rev. B 97, 245128 (2018)

    work page 2018

  11. [11]

    Ahn and S

    S. Ahn and S. Das Sarma, Hydrodynamics, viscous elec- tron fluid, and Wiedemann–Franz law in two-dimensional semiconductors, Phys. Rev. B 106, L081303 (2022)

    work page 2022

  12. [12]

    Woo-Ram Lee, A. M. Finkel’stein, K. Michaeli, and G. 6 Schwiete, Role of electron-electron collisions for charge and heat transport at intermediate temperatures, Phys. Rev. Research 2, 013148 (2020)

    work page 2020

  13. [13]

    K. C. Fong, E. E. Wollman, H. Ravi, W. Chen, A. A. Clerk, M. D. Shaw, H. G. Leduc, and K. C. Schwab, Mea- surement of the electronic thermal conductance channels and heat capacity of graphene at low temperature, Phys. Rev. X 3, 041008 (2013)

    work page 2013

  14. [14]

    Crossno, J

    J. Crossno, J. K. Shi, K. Wang, X. Liu, A. Harzheim, A. Lucas, S. Sachdev, P. Kim, T. Taniguchi, K. Watanabe, T. A. Ohki, and K. C. Fong, Observation of the Dirac fluid and the breakdown of the Wiedemann–Franz law in graphene, Science 351, 1058–1061 (2016)

    work page 2016

  15. [15]

    Majumdar, N

    A. Majumdar, N. Chadha, P. Pal, A. Gugnani, B. Ghawri, K. Watanabe, T. Taniguchi, S. Mukerjee, and A. Ghosh, Universality in quantum critical flow of charge and heat in ultraclean graphene, Nature Physics 21, 1374– 1379 (2025)

    work page 2025

  16. [16]

    M. S. Foster and I. L. Aleiner, Slow imbalance relaxatio n and thermoelectric transport in graphene, Phys. Rev. B 79, 085415 (2009)

    work page 2009

  17. [17]

    Tu and S

    Y.-T. Tu and S. Das Sarma, Wiedemann–Franz law in graphene, Phys. Rev. B 107, 085401 (2023)

    work page 2023

  18. [18]

    Bauer, Determination of Electron Temperatures and of Hot Electron Distribution Functions in Semiconductors , Springer Tracts in Modern Physics, Vol

    G. Bauer, Determination of Electron Temperatures and of Hot Electron Distribution Functions in Semiconductors , Springer Tracts in Modern Physics, Vol. 74 (Springer, 1974)

    work page 1974

  19. [19]

    A. W. Draelos, M. T. Wei, R. Hilgenkamp, P. Kim, and A. N. Pasupathy, Hot-carrier diffusion in graphene mea- sured by electronic temperature mapping, Nano Lett. 19, 1039–1043 (2019)

    work page 2019

  20. [20]

    S. K. Lyo and T. Holstein, Line shape of luminescence from quantum wells and heterojunctions, Phys. Rev. Lett. 61, 2265–2268 (1988)

    work page 1988

  21. [21]

    Vezin, Y

    S. Vezin, Y. A. Pusep, M. A. T. Patricio, V. A. Oliveira, M. M. Glazov, M. D. Teodoro, A. D. Levin, A. K. Bakarov, and G. M. Gusev, Photoluminescence thermometry of hot electrons in GaAs mesoscopic channels, Phys. Rev. B 109, 245302 (2024)

    work page 2024

  22. [22]

    B. K. Ridley, Electron-phonon energy-loss rates in two - dimensional electron gases, J. Phys.: Condens. Matter 3, 5281–5290 (1991)

    work page 1991

  23. [23]

    G. M. Gusev, A. D. Levin, E. B. Olshanetsky, A. K. Bakarov, Z. D. Kvon, N. N. Mikhailov, and S. A. Dvoretsky, Viscous transport and Hall viscosity in a two- dimensional electron system, AIP Adv. 8, 025318 (2018)

    work page 2018

  24. [24]

    G. M. Gusev, A. D. Levin, E. B. Olshanetsky, A. K. Bakarov, Z. D. Kvon, N. N. Mikhailov, and S. A. Dvoret- sky, Magnetoresistance in a viscous two-dimensional elec- tron fluid, Phys. Rev. B 97, 081311(R) (2018)

    work page 2018

  25. [25]

    G. M. Gusev, A. D. Levin, E. B. Olshanetsky, A. K. Bakarov, Z. D. Kvon, N. N. Mikhailov, and S. A. Dvoret- sky, Viscous electron flow in mesoscopic two-dimensional electron gas, Phys. Rev. B 98, 161303(R) (2018)

    work page 2018

  26. [26]

    Y. A. Pusep, M. A. T. Patricio, V. A. Oliveira, M. M. Glazov, M. D. Teodoro, A. D. Levin, A. K. Bakarov, and G. M. Gusev, Optical probing of hot electrons in hydrody- namic GaAs channels, Phys. Rev. B 106, 155302 (2022)

    work page 2022

  27. [27]

    Y. A. Pusep, M. A. T. Patricio, V. A. Oliveira, M. M. Glazov, M. D. Teodoro, A. D. Levin, A. K. Bakarov, and G. M. Gusev, Hydrodynamic heat transport in mesoscopic GaAs channels, Phys. Rev. B 108, 085301 (2023)

    work page 2023

  28. [28]

    M. A. T. Patricio, G. Jacobsen, M. D. Teodoro, G. M. Gusev, A. K. Bakarov, and Yu. A. Pusep, Hydrodynamics of electron-hole fluid photogenerated in a mesoscopic two- dimensional channel, Phys. Rev. B 109, L121401 (2024)

    work page 2024

  29. [29]

    Pavesi and M

    L. Pavesi and M. Guzzi, Photoluminescence of AlxGa1− xAs alloys, J. Appl. Phys. 75, 4779–4842 (1994)

    work page 1994

  30. [30]

    Nakwaski, Effective masses of electrons and heavy holes in GaAs, InAs, AlAs and their ternary compounds, Physica B 210, 1–25 (1995)

    W. Nakwaski, Effective masses of electrons and heavy holes in GaAs, InAs, AlAs and their ternary compounds, Physica B 210, 1–25 (1995)

    work page 1995

  31. [31]

    See Supplemental Material for details of the heat-tran sfer simulations, conductivity measurements, magnetoresis- tance analysis, and additional figures

    work page

  32. [32]

    Mittal, R

    A. Mittal, R. G. Wheeler, M. W. Keller, D. E. Prober, and R. N. Sacks, Electron-phonon scattering rates in GaAs/AlGaAs 2DEG samples below 0.5 K, Surf. Sci. 361–362 , 537–541 (1996)

    work page 1996

  33. [33]

    Çelik, M

    H. Çelik, M. Cankurtaran, N. Balkan, and A. Bayrakli, Hot electron energy relaxation via acoustic-phonon emis- sion in GaAs/Ga 1− xAlxAs multiple quantum wells: well- width dependence, Semicond. Sci. Technol. 17, 18–29 (2002)

    work page 2002

  34. [34]

    D’Amico and G

    I. D’Amico and G. Vignale, Theory of spin Coulomb drag in spin-polarized transport, Phys. Rev. B 62, 4853–4857 (2000)

    work page 2000

  35. [35]

    M. M. Glazov and E. L. Ivchenko, Precession spin re- laxation mechanism caused by frequent electron-electron collisions, JETP Lett. 75, 403–405 (2002)

    work page 2002

  36. [36]

    P. S. Alekseev and A. P. Dmitriev, Viscosity of two- dimensional electrons, Phys. Rev. B 102, 241409(R) (2020)

    work page 2020

  37. [37]

    P. S. Alekseev, Negative magnetoresistance in viscous flow of two-dimensional electrons, Phys. Rev. Lett. 117, 166601 (2016)

    work page 2016

  38. [38]

    R. N. Gurzhi, Minimum of resistance in impurity-free conductors, J. Exp. Theor. Phys. 44, 771–772 (1963)

    work page 1963

  39. [39]

    cut parabola

    R. N. Gurzhi, Hydrodynamic effects in solids at low tem- peratures, Sov. Phys. Usp. 11, 255–270 (1968). 7 SUPPLEMENT AL MATERIAL This supplemental material provides detailed information on the sample characteristics and the measurement meth- ods used in the main text. S1. HYDRODYNAMIC TRANSPOR T REGIME The hydrodynamic approach to electron behavior in two-...

    work page 1968

  40. [40]

    P. S. Alekseev, Negative Magnetoresistance in Viscous F low of Two-Dimensional Electrons, Phys. Rev. Lett. 117, 166601 (2016)

    work page 2016

  41. [41]

    Scaffidi, N

    T. Scaffidi, N. Nandi, B. Schmidt, A. P. Mackenzie, and J. E. Moore, Hydrodynamic Electron Flow and Hall Viscosity, Phys. Rev. Lett. 118, 226601 (2017)

    work page 2017

  42. [42]

    L. V. Delacrétaz and A. Gromov, Phys. Rev. Lett. 119, 226602 (2017)

    work page 2017

  43. [43]

    E. I. Kiselev and J. Schmalian, Boundary conditions of vi scous electron flow, Phys. Rev. B 99, 035430 (2019)

    work page 2019

  44. [44]

    G. M. Gusev, A. S. Jaroshevich, A. D. Levin, Z. D. Kvon, and A. K. Bakarov, Viscous magnetotransport and Gurzhi effect in bilayer electron system, Phys. Rev. B 103, 075303 (2021)

    work page 2021

  45. [45]

    O. E. Raichev, Linking boundary conditions for kinetic a nd hydrodynamic description of fermion gas, Phys. Rev. B 105, L041301 (2022)

    work page 2022