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UTe₂ has been thrust into the spotlight since the discovery of two magnetic field induced re-entrant superconducting phases a few years ago. [1,2] However, the relationship between these phases to the zero-magnetic field superconducting phase is not that well known. Recent work has discovered that tellurium deficiency, already known to suppress superconductivity at zero magnetic field [3], does not suppress the field polarized and ‘Lazarus’ superconducting high magnetic field phases. [4] Here we substitute thorium for uranium and investigate the phase diagram as a function of magnetic field (up to 60 T) at low temperatures by proximity diode oscillator measurements.  While we still detect a zero-magnetic field superconducting phase for thorium substituted samples with up to 5% nominal thorium content, we observe a disappearance of all the high magnetic field phases above 2% nominal thorium content.

[1] Ran, S., Liu, IL., Eo, Y.S. et al. Extreme magnetic field-boosted superconductivity. Nat. Phys. 15, 1250–1254 (2019).

[2] G. Knebel, W. Knafo, A. Pourret, et al Field-Reentrant Superconductivity Close to a Metamagnetic Transition in the Heavy-Fermion Superconductor UTe2 J. Phys. Soc. Jpn. 88, 063707 (2019)

[3] C. Yang, J. Guo, S. Cai, et al. Quasi-uniaxial pressure induced superconductivity in the stoichiometric compound UTe₂ Phys. Rev. B 106, 024503 (2022)

[4] C. E. Frank, S. K. Lewin, G. S. Salas, et al.Orphan High Field Superconductivity in Non-Superconducting Uranium Ditelluride 

arXiv:2304.12392 [cond-mat.supr-con] (2023)