# Parallel conduction and Planckian scattering in FeTeSe

Connect optical parallel-channel fits with Planckian rate conventions and nonlinear resistance, while keeping the pairing mechanism unresolved.

## Review scope

Selected author-version passages; final-version comparison and independent review pending.

- Author self-review; no independent scientific review or raw-data reproduction.
- Selected preprint passages, not a complete final published-version comparison.
- The missing-area normalization and precise condensate fractions remain unresolved.

## What was measured

Romero and colleagues analyzed complex terahertz conductivity alongside DC resistance in two FeTe1−xSex films. Their model separates a narrow Drude response from a much broader background. Within the measured frequency window, the narrow-channel width is approximately linear in temperature, while the total resistance need not be. The inferred condensate weight is mainly associated with that channel. This is an author-version interpretation, not a unique determination of the pairing interaction.

Evidence: experiment. Source relationship: direct-support. Sources: romero-v1.

## Keep the frequency convention explicit

For a Drude denominator $\Gamma-i\nu$, both variables use ordinary frequency. The corresponding pole decay rate is $\gamma=2\pi\Gamma$. Thus $\Gamma=\alpha k_BT/h$ and $\gamma=\alpha k_BT/\hbar$ express the same coefficient after conversion. The inherited reading note mixed these conventions. Its numerical expressions must not be copied unchanged.

Evidence: theory. Source relationship: context-for-local-derivation. Sources: romero-v1.

## Why parallel channels matter

As a separate local illustration, take fixed $S>0$, $\sigma_0\geq0$, $c>0$, $\Gamma_0\geq0$ and $T>0$:

$$\sigma_{\rm DC}=\sigma_0+\frac{S}{\Gamma_0+cT},\qquad \rho_{\rm DC}=\frac{\Gamma_0+cT}{S+\sigma_0(\Gamma_0+cT)}.$$

Differentiation gives $d\rho_{\rm DC}/dT=cS/[S+\sigma_0(\Gamma_0+cT)]^2$. A linear narrow-channel rate therefore need not give linear total resistivity. When $\sigma_0=0$, this model does recover a linear resistivity. The approximation $\sigma_{\rm DC}=a+b/T$ additionally neglects $\Gamma_0$ and assumes sufficiently constant amplitudes. This algebra is not a fit to the experimental data.

Evidence: theory. Source relationship: context-for-local-derivation. Sources: romero-v1.

## What remains unresolved

The broad contribution is not resolved as an independent complete Drude peak. Its microscopic origin and a unique relaxation coefficient are therefore not established by this fit. The manuscript discusses nematic pairing qualitatively and leaves the mechanism open. Its printed missing-area prefactor requires comparison with the final paper and normalization before precise condensate fractions are imported. No third-party figures or full text are reproduced here.

Evidence: theory. Source relationship: direct-support. Sources: romero-v1.

## Sources

romero-v1: Ralph Romero III, Hee Taek Yi, Seongshik Oh and N. P. Armitage. [Planckian scattering and parallel conduction channels in the iron chalcogenide superconductors FeTe1−xSex](https://arxiv.org/abs/2505.00623v1). preprint; Submitted 2025-05-01; v1; manuscript dated 2 May 2025. Selected PDF pages 1–5; page 4 figure and equations inspected visually. Final-version comparison pending.

## Editorial corrections

- Frequency convention: Use Gamma=Gamma0+alpha*kBT/h; gamma=2*pi*Gamma is the angular pole decay rate. Manuscript p3 and p4 Fig3.
- Composition label: x is Se fraction in FeTe(1-x)Se(x); the Se/Te ratio would be x/(1-x).
- Residual-rate omission: Retain Gamma0; a+b/T is approximate when Gamma0 is negligible and S/background are sufficiently constant.
- Condensate attribution: Author claims mainly slow-channel origin; pairing mechanism remains open on p4. Treat nematic comparison as qualitative.
- Sum-rule normalization: Author p2 numerator implies integral pi*S/2, whereas p4 printed SU=pi/2*integral creates inconsistent normalization. Final-version/calibration comparison unresolved. Do not import fractions as validated measurements.

## Provenance

papers/CROSS_H2_H8_RomeroPlanckian.md; commit 0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf; SHA-256 aef4a2f9efe186b0fc094ab424bba412128be75bae28d4c15fe6ad1797ba478e; merge-into. Coverage: Whole source-note disposition; the primary scientific review remains limited to the stated scope.

papers/library/Romero_Planckian-FeTeSe_READING_NOTES.md; commit 0a7c9d6696804ec26aa12f8eed68b55c9b3c0fcf; SHA-256 c26198323fa69f7603870d26b455aca4ee4ae4edbbf7aa9a94ce6bb8f7f4acd5; merge-into. Coverage: Whole source-note disposition; the primary scientific review remains limited to the stated scope.

Original editorial summary and local explanatory calculations. Linked papers retain their own rights; no third-party figures or full text are reproduced.

Note ID: romero-parallel-conduction. Revision: ee1e0016dba349182c88.