Possible chiral superconductivity in Sr2RuO4: combined evidence from the µSR study under uniaxial and hydrostatic pressure, and with disorder

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• Dr. Vadim Grinenko, Technical University of Dresden
• Friday 12 March 2021, 14:00-15:00
• https://bham-ac-uk.zoom.us/j/88096472694?pwd=UXIyMVdCUkJFUjVTNlFCZVBWWWlWQT09 .

If you have a question about this talk, please contact Dr Clifford W. Hicks.

There is considerable evidence that the superconducting state of Sr2RuO4 breaks time reversal symmetry [1,2]. In the experiments showing time reversal symmetry breaking its onset temperature, TTRSB , is generally found to match the critical temperature, Tc, within the resolution. In combination with evidence for even parity [3], this result has led to consideration of a chiral dxz ± idyz order parameter. The degeneracy of the two components of this order parameter is protected by symmetry, yielding TTRSB = Tc, but it has a hard-to-explain horizontal line node at kz = 0. Therefore, s ± id and d ± ig order parameters with accidentally degenerated components are also under consideration [4-7]. These avoid the horizontal line node, but require fine-tuning to obtain TTRSB ≈ Tc. To distinguish between chiral and accidentally degenerated order parameters, we studied the system under uniaxial strain [8], hydrostatic pressure and chemical disorder. Based on general theoretical arguments and simulations, the uniaxial pressure applied along [100] or [110] splits TTRSB and Tc for all possible types of the TRSB order parameters. However, hydrostatic pressure and chemical disorder lead to Tc = TBTRS for the chiral phase but would separate them for other types of two-component order parameters. Our systematic experimental study demonstrates that the transition splits under uniaxial pressure. In contrast, no splitting results from hydrostatic pressure and disorder with a nearly 50% reduced superconducting critical temperature than an impurity-free compound. These results, combined with theoretical analysis, strongly suggest a chiral dxz+idyz -wave superconductivity in Sr2RuO4. This superconductivity implies interlayer pairing, which is highly unusual in such a strongly anisotropic layered system as Sr2RuO4 and, therefore, may require a new type of pairing mechanism. In this talk, I will also discuss what we can learn from µSR experiments regarding the nature of spontaneous currents in the TRSB state of two systems Sr2RuO4 and Ba1-xKxFe2As2 [9].

1. G. Luke et al., Nature 394, 558-561 (1998). 2. J. Xia, et al., Phys. Rev. Lett. 97, 167002 (2006). 3. A. Pustogow et al., Nature 574, 72-75 (2019). 4. A. T. Rømer et al., Phys. Rev. Lett. 123, 247001 (2019). 5. A. T. Rømer et al., Phys. Rev. B 102 , 054506 (2020). 6. S. A. Kivelson et al., npj Quantum Mat. 5, 43 (2020). 7. R. Willa, Phys. Rev. B 102 , 180503® (2020). 8. V. Grinenko et al., Nat. Phys. (2021) https://doi.org/10.1038/s41567-021-01182-7 9. V. Grinenko et al., Nat. Phys. 16, 789 – 794 (2020).

This talk is part of the Condensed Matter Physics Seminars series.

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