43 research outputs found
Unconventional magnetic order on the hyperhoneycomb Kitaev lattice in -Li2IrO3: full solution via magnetic resonant x-ray diffraction
The recently-synthesized iridate -LiIrO has been proposed as a
candidate to display novel magnetic behavior stabilized by frustration effects
from bond-dependent, anisotropic interactions (Kitaev model) on a
three-dimensional "hyperhoneycomb" lattice. Here we report a combined study
using neutron powder diffraction and magnetic resonant x-ray diffraction to
solve the complete magnetic structure. We find a complex, incommensurate
magnetic order with non-coplanar and counter-rotating Ir moments, which
surprisingly shares many of its features with the related structural polytype
"stripyhoneycomb" -LiIrO, where dominant Kitaev interactions
have been invoked to explain the stability of the observed magnetic structure.
The similarities of behavior between those two structural polytypes, which have
different global lattice topologies but the same local connectivity, is
strongly suggestive that the same magnetic interactions and the same underlying
mechanism governs the stability of the magnetic order in both materials,
indicating that both - and -LiIrO are strong candidates
to realize dominant Kitaev interactions in a solid state material.Comment: 14 pages, 9 figure
Effect of isoelectronic doping on honeycomb lattice iridate A_2IrO_3
We have investigated experimentally and theoretically the series
(NaLi)IrO. Contrary to what has been believed so far,
only for the system forms uniform solid solutions. For larger Li
content, as evidenced by powder X-ray diffraction, scanning electron microscopy
and density functional theory calculations, the system shows a miscibility gap
and a phase separation into an ordered NaLiIrO phase with
alternating Na and LiIrO planes, and a Li-rich phase close to pure
LiIrO. For we observe (1) an increase of with Li
doping up to , despite the fact that in pure LiIrO is
smaller than in NaIrO, and (2) a gradual reduction of the
antiferromagnetic ordering temperature and ordered moment. The
previously proposed magnetic quantum phase transition at may
occur in a multiphase region and its nature needs to be re-evaluated.Comment: 8 pages, 9 figures including supplemental informatio
Kitaev interactions between j=1/2 moments in honeycomb Na2IrO3 are large and ferromagnetic: insights from ab initio quantum chemistry calculations
NaIrO, a honeycomb 5 oxide, has been recently identified as a
potential realization of the Kitaev spin lattice. The basic feature of this
spin model is that for each of the three metal-metal links emerging out of a
metal site, the Kitaev interaction connects only spin components perpendicular
to the plaquette defined by the magnetic ions and two bridging ligands. The
fact that reciprocally orthogonal spin components are coupled along the three
different links leads to strong frustration effects and nontrivial physics.
While the experiments indicate zigzag antiferromagnetic order in NaIrO,
the signs and relative strengths of the Kitaev and Heisenberg interactions are
still under debate. Herein we report results of ab initio many-body electronic
structure calculations and establish that the nearest-neighbor exchange is
strongly anisotropic with a dominant ferromagnetic Kitaev part, whereas the
Heisenberg contribution is significantly weaker and antiferromagnetic. The
calculations further reveal a strong sensitivity to tiny structural details
such as the bond angles. In addition to the large spin-orbit interactions, this
strong dependence on distortions of the IrO plaquettes singles out the
honeycomb 5 oxides as a new playground for the realization of
unconventional magnetic ground states and excitations in extended systems.Comment: 13 pages, 2 tables, 3 figures, accepted in NJ
Spectral signatures of a unique charge density wave in TaNiSe
Charge Density Waves (CDW) are commonly associated with the presence of
near-Fermi level states which are separated from others, or "nested", by a
wavector of . Here we use Angle-Resolved Photo Emission
Spectroscopy (ARPES) on the CDW material TaNiSe and identify a total
absence of any plausible nesting of states at the primary CDW wavevector
. Nevertheless we observe spectral intensity on replicas of the
hole-like valence bands, shifted by a wavevector of , which appears
with the CDW transition. In contrast, we find that there is a possible nesting
at , and associate the characters of these bands with the reported
atomic modulations at . Our comprehensive electronic structure
perspective shows that the CDW-like transition of TaNiSe is unique,
with the primary wavevector being unrelated to any low-energy
states, but suggests that the reported modulation at , which would
plausibly connect low-energy states, might be more important for the overall
energetics of the problem
One-ninth magnetization plateau stabilized by spin entanglement in a kagome antiferromagnet
The spin-1/2 antiferromagnetic Heisenberg model on a Kagome lattice is
geometrically frustrated, which is expected to promote the formation of
many-body quantum entangled states. The most sought-after among these is the
quantum spin liquid phase, but magnetic analogs of liquid, solid, and
supersolid phases may also occur, producing fractional plateaus in the
magnetization. Here, we investigate the experimental realization of these
predicted phases in the Kagome material YCu3(OD)6+xBr3-x (x=0.5). By combining
thermodynamic and Raman spectroscopic techniques, we provide evidence for
fractionalized spinon excitations and observe the emergence of a 1/9
magnetization plateau. These observations establish YCu3(OD)6+xBr3-x as a model
material for exploring the 1/9 plateau phase.Comment: to appear in Nature Physics, 33 pagses, 15 figure