An arXiv preprint reports that nominally 10% V-substituted RuO2 single crystals had a room-temperature resistivity of 14.7 µΩ cm, 60% lower than pristine RuO2. The crystals behaved as metals from 2 to 400 K and remained paramagnetic from 1.8 to 300 K. On altermagnetism, the authors reported no such behavior in the studied crystals.
The experimental work focused on Ru0.9V0.1O2, with pristine RuO2 used for comparison. Among candidate elements, only vanadium formed a single-phase compound and was selected for crystal growth.
Researchers grew the crystals by sublimation transport. The material was held at 1000 °C for 20 hours, then at 1200 °C for 100 hours under flowing oxygen at 40 cc/min. The team characterized it with XRD, EPMA with EDS/WDS, XPS, four-probe AC resistivity and SQUID magnetometry.
Room-temperature transport stood out
The resistivity measurements showed metallic behavior across 2 to 400 K. The study reported a residual resistivity of 8.6 µΩ cm, a residual-resistivity ratio of 1.8 and an estimated mean free path of 1.5 nm. At room temperature, the 14.7 µΩ cm value was essentially unchanged when the magnetic field reached 4 T.
The researchers also fitted the temperature dependence using several scattering terms. At room temperature, the fit assigned 36% of the contribution to acoustic phonons, 5% to an Einstein-phonon term and 1% to an AT2 term. The fitted Debye temperature increased by 11%. The authors associated the lower resistivity with weaker electron-phonon scattering.
The crystals showed a clean chemical picture
Powder XRD showed only the RuO2 phase, with no detectable impurity phases. Relative to pristine RuO2, the a-axis expanded by 0.12% to 4.496 Å, while the c-axis contracted by 0.58% to 3.092 Å. Unit-cell volume decreased by 0.38%. WDS reported a Ru:V:O ratio of 0.89:0.10:2.37, and elemental maps were uniform without V clustering.
XPS found mixed Ru4+ and Ru3+ components, with relative areas of 80% and 20%. Average Ru valence was +3.83 in pristine RuO2 and +3.80 in the V-substituted material. Vanadium was predominantly V4+, with an average oxidation state of +3.97.
Charge-neutrality analysis estimated oxygen off-stoichiometry of -0.08 for RuO2+y and -0.09 for Ru0.9V0.1O2+y. The reported effect of V substitution on oxygen stoichiometry was negligible.
Magnetism remained quiet
Magnetic susceptibility measurements found that the V-substituted crystals remained paramagnetic, with no transition between 1.8 and 300 K. Their low-temperature upturn ratio was 1.01, compared with 1.02 for pristine RuO2, and their room-temperature susceptibility was lower.
A susceptibility fit estimated a localized paramagnetic impurity concentration of about 4 ppm in the V-substituted material, compared with about 19 ppm in RuO2. These were fitted estimates rather than direct counts of impurities.
For the paper’s altermagnetism question, the authors reported that the studied 10% V-substituted crystals did not show altermagnetism. The paper did not report a direct probe specifically establishing or excluding altermagnetic order, so the finding is tied to these crystals and measurements.
Higher substitution was tested on a computer
Alongside the laboratory measurements, the researchers calculated electronic structure with DFT-based PAW and TB-LMTO approaches. They used GGA/PBE without a Hubbard correction, corresponding to U = 0. The calculations extended the analysis beyond the experimentally studied nominal 10% material to additional V concentrations.
In PAW calculations of the electronic density of states, or DOS, the lower modeled concentration, x = 0.0625, left the Ru-d DOS almost unchanged, with V-d peaks slightly above the Fermi level. At x = 0.125, a V-d shoulder appeared at the Fermi level and the DOS increased considerably.
A separate TB-LMTO calculation placed the V-d peak within 0.34 eV above the Fermi level at 10% substitution and within 0.3 eV at 20%. The authors said the DOS at the Fermi level changed little through 10% substitution but might change at higher levels. The 20% result is a computational prediction, not an experimental test of 20% crystals.
A result limited to the studied composition
Taken together, the preprint reports single-phase, spatially uniform crystals at the nominal 10% composition that remained metallic and paramagnetic, alongside a 60% lower room-temperature resistivity than pristine RuO2 and no reported altermagnetism. Its indications of larger electronic changes at higher substitution come from calculations, not higher-concentration crystal measurements. The manuscript is identified as an arXiv preprint.
Paper data and sources
Original title: Substitution effects in RuO$_2$ single crystals
Authors: Shubhankar Paul, Kunihiko Yamauchi, Shogo Yamashita et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-26
DOI: Not available
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