Abstract
Polar metals are commonly defined as metals with polar structural distortions. Strict symmetry restrictions make them an extremely rare breed as the structural constraints favor insulating over metallic phase. Moreover, no polar metals are known to be magnetic. Here we report on the realization of a magnetic polar metal phase in a BaTiO3/SrRuO3/BaTiO3 heterostructure. Electron microscopy reveals polar lattice distortions in three-unit-cells thick SrRuO3 between BaTiO3 layers. Electrical transport and magnetization measurements reveal that this heterostructure possesses a metallic phase with high conductivity and ferromagnetic ordering with high saturation moment. The high conductivity in the SrRuO3 layer can be attributed to the effect of electrostatic carrier accumulation induced by the BaTiO3 layers. Density-functional-theory calculations provide insights into the origin of the observed properties of the thin SrRuO3 film. The present results pave a way to design materials with desired functionalities at oxide interfaces.
Highlights
Polar metals are commonly defined as metals with polar structural distortions
In transition-metal oxides (TMOs), polar distortions exist in ferroelectric materials, which are typically insulating with empty d orbitals (e.g., d0 configuration)[7]
Due to the strong interplay among spin, lattice, and charge degrees of freedom at the heterointerface[14,15,16,17,18], in BaTiO3/SrRuO3/BaTiO3 (BTO/SRO/BTO) heterostructures, we demonstrate that polar distortions can be induced in 3-u.c. of SRO by interfacial effects as revealed by aberration corrected electron microscopy and spectroscopy
Summary
Polar metals are commonly defined as metals with polar structural distortions. Strict symmetry restrictions make them an extremely rare breed as the structural constraints favor insulating over metallic phase. In NdNiO3(111) thin films, Nd off-centering and partially filled Ni orbitals are responsible for polar distortions and conductivity, respectively[12] In both cases, the coupling strength between polar distortions and itinerant electrons is intrinsically weak as the two features originate from different ion sublattices[12]. Due to the strong interplay among spin, lattice, and charge degrees of freedom at the heterointerface[14,15,16,17,18], in BaTiO3/SrRuO3/BaTiO3 (BTO/SRO/BTO) heterostructures, we demonstrate that polar distortions can be induced in 3-u.c. of SRO by interfacial effects as revealed by aberration corrected electron microscopy and spectroscopy This 3-u.c. SRO exhibits high conductivity and ferromagnetism with high magnetic moment, forming a unique magnetic polar metal phase. The polar distortions, metallicity, and magnetism in our system all originate from the Ru–O atomic layers so that intrinsic coupling among these features is expected
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