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Enhanced superconductivity and ferroelectric quantum criticality in plastically deformed strontium titanate

Abstract

The properties of quantum materials are commonly tuned using experimental variables such as pressure, magnetic field and doping. Here we explore a different approach using irreversible, plastic deformation of single crystals. We show that compressive plastic deformation induces low-dimensional superconductivity well above the superconducting transition temperature (Tc) of undeformed SrTiO3, with evidence of possible superconducting correlations at temperatures two orders of magnitude above the bulk Tc. The enhanced superconductivity is correlated with the appearance of self-organized dislocation structures, as revealed by diffuse neutron and X-ray scattering. We also observe deformation-induced signatures of quantum-critical ferroelectric fluctuations and inhomogeneous ferroelectric order using Raman scattering. Our results suggest that strain surrounding the self-organized dislocation structures induces local ferroelectricity and quantum-critical dynamics that strongly influence Tc, consistent with a theory of superconductivity enhanced by soft polar fluctuations. Our results demonstrate the potential of plastic deformation and dislocation engineering for the manipulation of electronic properties of quantum materials.

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Fig. 1: Structure of plastically deformed SrTiO3.
Fig. 2: Local structure of deformed SrTiO3 from diffuse neutron scattering.
Fig. 3: Inversion-symmetry breaking and ferroelectric fluctuations in deformed SrTiO3.
Fig. 4: Low-temperature superconducting properties of plastically deformed SrTiO3.
Fig. 5: Evidence for high-temperature superconducting correlations in plastically deformed SrTiO3.
Fig. 6: Local Tc enhancement due to ferroelectric fluctuations enhanced by dislocation-induced strain.

Data availability

All data and materials are available from the corresponding authors upon request.

Code availability

All computer codes used to generate the results presented in the paper are available from the corresponding authors upon request.

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Acknowledgements

We thank L.J. Thompson and Z. Jiang for help with sample preparation, S.L. Griffitt and A. Najev for assistance with the design and manufacturing of polishing rigs, C.N. Irfan Habeeb for help with figures, D. Robinson and S. Rosenkranz for assistance with X-ray scattering experiments, and B.I. Shklovskii, Y. Ayino, V. Pribiag, B. Kalisky and J. Ruhman for discussions and comments. The work at the University of Minnesota was funded by the US Department of Energy through the University of Minnesota Center for Quantum Materials, under grant number DE-SC-0016371. The work at Argonne was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. This research used resources of the Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract number DE-AC02-06CH11357. D.P. acknowledges support from the Croatian Science Foundation through grant number UIP-2020-02-9494. The work at Peking University was funded by the National Natural Science Foundation of China, under grant number 11874069. Sputtering and contacting of samples was conducted in the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nano Coordinated Infrastructure Network, award number NNCI-1542202.

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D.P. and M.G. conceived the research. S.H., R.J.S., D.P., B.D. and J.R. performed transport and susceptibility measurements. S.H., Z.W.A., D.P. and Y. Liu. performed neutron scattering experiments and analysed data. Z.W.A., R.J.S., D.P., M.J.K. and R.O. performed X-ray scattering experiments and analysed data. L.Y. and Y. Li. performed Raman scattering experiments. S.H., L.Y., D.P. and Y. Li. analysed Raman data. A.K. and R.M.F. performed calculations. C.L. provided and characterized samples. C.L. and D.P oversaw transport measurements by S.H., B.D. and J.R. M.L. and D.P. designed and manufactured the pressure cells. D.P., A.K. and M.G. wrote the paper, with input from all authors.

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Correspondence to D. Pelc or M. Greven.

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Hameed, S., Pelc, D., Anderson, Z.W. et al. Enhanced superconductivity and ferroelectric quantum criticality in plastically deformed strontium titanate. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-01102-3

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