Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures

Ryan F Need,Patrick B Marshall,Michael J Graf,Eric Kenney,Brian J Kirby,Thomas Prokscha,Susanne Stemmer,Stephen D Wilson,Andreas Suter,Zaher Salman

doi:10.1038/s41535-018-0081-8

Abstract

High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required. Here we address this challenge by exploring the magnetic properties of high-density SrTiO3 quantum wells embedded within the antiferromagnetic Mott insulator SmTiO3 via muon spin relaxation and polarized neutron reflectometry measurements. The one electron per planar unit cell acquired by the nominal d0 band insulator SrTiO3 when embedded within a d1 Mott SmTiO3 matrix exhibits slow magnetic fluctuations that begin to freeze into a quasistatic spin state below a critical temperature T*. The appearance of this quasistatic well magnetism coincides with the previously reported opening of a pseudogap in the tunneling spectra of high carrier density wells inside this film architecture. Our data suggest a common origin of the pseudogap phase behavior in this quantum critical oxide heterostructure with those observed in bulk Mott materials close to an antiferromagnetic instability.

Highlights

Correlation effects can be activated as the electron density in the well diverges,[18] and heterostructures built from R3+TiO3/SrTiO3 (R = rare earth) interfaces have demonstrated that metal-insulator transitions can be driven near the thin well limit of a single SrO layer.[19]
We report the results of a combined muon spin relaxation and polarized neutron reflectometry (PNR) study exploring the origins of the pseudogap state in high carrier density SmTiO3/SrTiO3 quantum well heterostructures
Low energy μSR data were collected from three thin film samples in both a weak transverse field and under zero applied field (ZF)

Summary

Introduction

The origin of pseudogaps near electronic instabilities and their relationship to emergent phase behaviors in numerous transition metal oxides remains an enduring topic of research.[1,2] Though the underlying mechanisms of pseudogap formation remain debated in many compounds, canonical examples of pseudogaps in strongly correlated oxide systems often appear coincident with the partial suppression of the Mott state and the disappearance of long-range antiferromagnetism.[3,4] Pseudogaps in these systems develop below a characteristic temperature T*, leading to the conjecture that they are the consequence of an unresolved order parameter or crossover;[5,6] the myriad of competing states (e.g., superconductivity,[7] charge density wave order,[8,9] spin stripe order10) that arise in close proximity to the Mott phase render this connection difficult.

Results

Conclusion