Quantum critical behaviour in confined SrTiO3 quantum wells embedded in antiferromagnetic SmTiO3.

Quantum phase transitions are driven by quantum fluctuations that alter the nature of the electronic quasiparticles, resulting in phenomena such as non-Fermi liquid behaviour. Oxide heterostructures offer fundamentally new ways of manipulating quantum criticality. Here, we report on non-Fermi liquid behaviour in thin SrTiO3 quantum wells that are embedded in insulating, antiferromagnetic SmTiO3, as a function of temperature, quantum well thickness and SmTiO3 layer thickness in superlattices. Such quantum wells contain very high sheet carrier densities on the order of one electron per pseudocubic planar unit cell. We show that the quantum well thickness is a tuning parameter for non-Fermi liquid behaviour. Increasing the thickness by a single atomic layer and coupling in superlattices recover the Fermi liquid behaviour. The critical exponents, the symmetry of the order parameter, the role of carrier densities and symmetry-lowering distortions are discussed, and the results are compared with those of quantum wells embedded in ferrimagnetic GdTiO3.