Tuning magnetic confinement of spin-triplet superconductivity

Abstract

Electrical magnetoresistance and tunnel diode oscillator measurements were performed under external magnetic fields up to 41 T applied along the crystallographic b axis (hard axis) of UTe2 as a function of temperature and applied pressures up to 18.8 kbar. In this work, we track the field-induced first-order transition between superconducting and magnetic field-polarized phases as a function of applied pressure, showing suppression of the transition with increasing pressure until the demise of superconductivity near 16 kbar and the appearance of a pressure-induced ferromagnetic-like ground state that is distinct from the field-polarized phase and stable at zero field. Together with evidence for the evolution of a second superconducting phase and its upper critical field with pressure, we examine the confinement of superconductivity by two orthogonal magnetic phases and the implications for understanding the boundaries of triplet superconductivity.

Comparison of two superconducting phases induced by a magnetic field in UTe2

“…Rich-phase diagrams were obtained for UTe 2 under different field directions and pressures. Although the measurements presented here and in other works 33,[37][38][39]41,61,71 start to bring a clear picture of the complex phase diagram of UTe 2 , which includes multiple superconducting and magnetic phases, we are still far from a deep understanding of its electronic properties. A target is now to perform microscopic studies to identify the nature of the magnetic fluctuations and their change through H m .…”

“…Calorimetric studies showed the appearance of a second superconducting phase, labeled by SC2, under pressure in zero magnetic field 38 . A boundary between SC2 and the ambient-pressure and low-field superconducting phase SC1 was observed from tunnel-diodeoscillator measurements under pressure and magnetic field H || b 39 . The extrapolation of this boundary for p → 0 suggests that the superconducting phase SC2 induced under pressure and the superconducting region induced by a magnetic field H || b could be the same phase.…”

Anapole superconductivity from $${{{{{{{\mathcal{PT}}}}}}}}$$-symmetric mixed-parity interband pairing

“…However, multiple superconducting phases similar to Fig. 1a have been observed under pressure [26][27][28][29][30][31][32][33] , and the antiferromagnetic quantum criticality implies the spin-singlet superconductivity there 31 . A theoretical study based on the periodic Anderson model verified this naive expectation and predicted the parity-mixed superconducting state in the intermediate pressure region 25 .…”

“…The PT -symmetric mixed-parity pairing has also been theoretically proposed in Sr 2 RuO 4 24 . Furthermore, a mixed-parity superconducting state in UTe 2 25 has been predicted to explain experimentally-observed multiple superconducting phases [26][27][28][29][30][31][32][33] .…”

“…Based on the obtained results, we predict the possible asymmetric BS and anapole superconductivity in UTe 2 , a recentlydiscovered candidate of a spin-triplet superconductor 54 . The multiple pairing instabilities [26][27][28][29][30][31][32][33] and T -symmetry breaking [55][56][57][58] were recently observed there.…”