Enhanced superconductivity and ferroelectric quantum criticality in plastically deformed strontium titanate

The properties of quantum materials are typically tuned via application of pressure, magnetic field or chemical substitution. In this talk, I will describe a novel approach using irreversible, plastic deformation of single crystals, which we apply to the well-known dilute superconductor SrTiO₃ (STO). We find that plastically deformed electron-doped STO exhibits low-dimensional superconductivity with a significant enhancement of the superconducting transition temperature, T_c. Furthermore, we find evidence of possible superconducting correlations already at temperatures two orders of magnitude higher than the bulk T_c. Using neutron and x-ray scattering, we demonstrate that the primary effect of compressive plastic deformation is the creation and self-organization of dislocations into wall-like structures. The strong strain fields near such walls induce local ferroelectricity and enhanced quantum critical ferroelectric fluctuations, evidenced by Raman scattering measurements. The T_c enhancement is consistent with a theoretical proposal in which superconductivity in STO is mediated by soft polar fluctuations. I will also briefly describe more recent results on the structural, electronic, and magnetic properties of deformed STO as well as our efforts to extend this novel approach to other systems. These emerging results demonstrate the promise of plastic deformation and dislocation engineering as tools for the manipulation of electronic properties of quantum materials [1-4].

[1] S. Hameed, D. Pelc et al., Nature Materials 21, 54 (2022)

[2] M. Li and Y. Wang, Nature Materials 21, 3 (2022)

[3] X. Wang, A. Kundu, B. Xu et al., arXiv:2308.14801v1 (2023)

[4] I. Khayr et al., in preparation