# RN, R0 and temperature give unexpected junction resistance

Check the selected junction model and RTYPE. Noise temperature and temperature-dependent junction behaviour are separate settings.

## Compatibility

2.9.0 release target; review-build/source evidence

Published guidance with release-applicability limits. Confirm package applicability before following this guide.

## Identify the intended branch

RN is the normal resistance; R0 is the subgap resistance. RTYPE selects the subgap treatment. The maintained reference documents RTYPE=0 with conductance 1/RN and RTYPE=1 with a subgap branch based on R0 under its stated gap conditions.

For a fitted constant-resistance RSJ-style model, check whether RTYPE=0 and the intended RN express the chosen approximation. This is a modelling choice, not a universal replacement for an RCSJ model.

## Check temperature and scaling

Model T and TC enable temperature-dependent RCSJ behaviour. Instance area also changes scaled parameters. Check these settings when a nominal RN/R0 comparison seems inconsistent.

Use .TEMP and device noise attributes for the documented thermal-noise excitation. Do not assume a noise-temperature command and model-temperature parameters have identical effects.

## Limits of a fitted parameter

A constant or bias-stepped resistance fit is not automatically a runtime current-dependent RN model. Re-evaluate the selected model against the intended physics rather than inferring an unsupported expression from a fitted sweep.

## Sources and verification details

Recorded inputs/builds only. Complete walkthrough and final-package acceptance remain separate.



- support:SUP-015: Generalised editorial finding; outcome qualification retained
- josim-pro:docs/manual_source/sections/syntax.tex: Josephson junction model parameters; small-signal quasiparticle branch
- owner:technical-review-20261102: JoSIM-Pro 2.9 chosen as the public starting path; release availability must be checked before publication

- The owner accepted the modelling explanation on 2 November 2026. Applicable release/platform and unrecorded walkthrough checks remain pending.

## Related guides

- [Characterise a junction model with an IV curve](/knowledge-base/josim-iv-characterisation)
- [An IV curve or run record does not match the expected model](/knowledge-base/josim-iv-result-checks)
- [A junction model is missing or behaves like the wrong model](/knowledge-base/josim-model-syntax)
- [Check temperature, noise bandwidth and sample time in JoSIM®-Pro](/knowledge-base/josim-noise-settings)