Electronic and magnetic order protected by entanglement

Electrons in materials interact with their environment, and one another, through a hierarchy of energy scales. In functional oxides, such as high-temperature superconductors and colossal magneto-resistance materials, the hierarchy is such that the coupling of the electronic orbital motion to the crystal environment is greater than it is to the intrinsic electronic spin. This regime of weak spin-orbit coupling (SOC) typifies the first-row, 3d series, of transition metal elements, e.g. copper, manganese, etc., and it is an important ingredient in explaining the magnetic and electronic properties of materials of which they are composed.

Recently, considerable theoretical attention has been focussed on the opposite limit, i.e. strong spin-orbit coupling, as exhibited by the 5d transition metal elements. The inherent entanglement of spin and orbital magnetic moments in this limit has been predicted to support a range of novel electronic states of matter, from topological insulators to unconventional metals, and even high-temperature superconductivity (see Figure).

In an article recently published in Physical Review Letters, a team led by researchers from the LCN, in collaboration with colleagues from other laboratories in the UK, Germany and Switzerland, have reported the results of a comparative study of the magnetic and electronic properties of a new family of iridium based transition metal oxides. They have discovered that both the magnetic and electronic structures in the layered perovskites are remarkably robust to structural distortions, a fact that can be linked directly to the unique three-dimensional character of the electronic state produced by the strong SOC which renders them less sensitive to perturbations in local symmetry.

Journal Link: Robustness of basal-plane antiferromagnetic order and the Jeff=1/2 state in single-layer iridate spin-orbit Mott insulators. DOI: 10.1103/PhysRevLett.110.117207

Figure caption: The proposed Jeff=1/2 electronic ground state wavefunction (in the strong spin-orbit coupling limit) of the 5d transition metal oxides such as Sr2IrO4 and Ba2IrO4 studied by Boseggia et al. The Jeff=1/2 state is itself formed from a coherent superposition of two entangled orbital-spin wavefunctions: |xy,↑> and |yz+i xz, ↓>. The extended, three-dimensional nature of the Jeff=1/2 state is believed to make it more robust to local structural distortions.

LCN Author(s): 
Other contributors: 
R. Springell, H. C. Walker, H. M. Rønnow, Ch. Rüegg, H. Okabe, M. Isobe, R. S. Perry, and S. P. Collins