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# Atomic-scale observation of structural and electronic orders in the layered compound α-RuCl 3

Nature Communications

Nature Publishing Group

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### Abstract

A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, α-RuCl 3. Our local crystallography analysis reveals considerable variations in the geometry of the ligand sublattice in thin films of α-RuCl 3 that opens a way to realization of a spatially inhomogeneous magnetic ground state at the nanometre length scale. Using scanning tunnelling techniques, we observe the electronic energy gap of ≈0.25 eV and intra-unit cell symmetry breaking of charge distribution in individual α-RuCl 3 surface layer. The corresponding charge-ordered pattern has a fine structure associated with two different types of charge disproportionation at Cl-terminated surface.

### Abstract

The two-dimensional Kitaev model is a quantum spin liquid state that theory predicts should appear in some materials with a honeycomb lattice. Here, the authors use atom-resolution scanning transmission electron and scanning tunnelling microscopies to characterize one such candidate material, α-RuCl 3.

### Most cited references21

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### Mott Insulators in the Strong Spin-Orbit Coupling Limit: From Heisenberg to a Quantum Compass and Kitaev Models

(2008)
We study the magnetic interactions in Mott-Hubbard systems with partially filled $$t_{2g}$$-levels and with strong spin-orbit coupling. The latter entangles the spin and orbital spaces, and leads to a rich variety of the low energy Hamiltonians that extrapolate from the Heisenberg to a quantum compass model depending on the lattice geometry. This gives way to "engineer" in such Mott insulators an exactly solvable spin model by Kitaev relevant for quantum computation. We, finally, explain "weak" ferromagnetism, with an anomalously large ferromagnetic moment, in Sr$$_2$$IrO$$_4$$.
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### Quantum spin Hall effect in a transition metal oxide Na2IrO3

(2008)
We study theoretically the electronic states in a $$5d$$ transition metal oxide Na$$_2$$IrO$$_3$$, in which both the spin-orbit interaction and the electron correlation play crucial roles. Tight-binding model analysis together with the fisrt-principles band structure calculation predicts that this material is a layered quantum spin Hall system. Due to the electron correlation, an antiferromagnetic order first develops at the edge, and later inside the bulk at low temperatures.
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### Author and article information

###### Journal
Nat Commun
Nat Commun
Nature Communications
Nature Publishing Group
2041-1723
12 December 2016
2016
: 7
###### Affiliations
[1 ]Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, USA
[2 ]Institute for Functional Imaging of Materials, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, USA
[3 ]Quantum Condensed Matter Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, USA
[4 ]Bredesen Center for Interdisciplinary Research, University of Tennessee , Knoxville, Tennessee 37996, USA
[5 ]Computer Science and Mathematics Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, USA
[6 ]Material Science & Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, USA
[7 ]Department of Material Science and Engineering, University of Tennessee , Knoxville, Tennessee 37996, USA
[8 ]Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, USA
###### Article
ncomms13774
10.1038/ncomms13774
5159869
27941761