16 research outputs found
High order magnon bound states in the quasi-one-dimensional antiferromagnet -NaMnO
Here we report on the formation of two and three magnon bound states in the
quasi-one-dimensional antiferromagnet -NaMnO, where the single-ion,
uniaxial anisotropy inherent to the Mn ions in this material provides a
binding mechanism capable of stabilizing higher order magnon bound states.
While such states have long remained elusive in studies of antiferromagnetic
chains, neutron scattering data presented here demonstrate that higher order
composite magnons exist, and, specifically, that a weak three-magnon
bound state is detected below the antiferromagnetic ordering transition of
NaMnO. We corroborate our findings with exact numerical simulations of a
one-dimensional Heisenberg chain with easy-axis anisotropy using matrix-product
state techniques, finding a good quantitative agreement with the experiment.
These results establish -NaMnO as a unique platform for exploring
the dynamics of composite magnon states inherent to a classical
antiferromagnetic spin chain with Ising-like single ion anisotropy.Comment: 5 pages, 4 figure
Quantitative investigation of the short-range magnetic correlations in candidate quantum spin liquid NaYbO
We present a neutron diffraction study of NaYbO, a candidate quantum spin
liquid compound hosting a geometrically frustrated triangular lattice of
magnetic Yb ions. We observe diffuse magnetic scattering that persists
to at least 20 K, demonstrating the presence of short-range magnetic
correlations in this system up to a relatively high energy scale. Using reverse
Monte Carlo and magnetic pair distribution function analysis, we confirm the
predominant antiferromagnetic nature of these correlations and show that the
diffuse scattering data can be well described by noninteracting layers of XY
spins on the triangular lattice. We rule out Ising spins and
short-range-ordered stripe or 120 phases as candidate ground states
of NaYbO. These results are consistent with a possible QSL ground state in
NaYbO and showcase the benefit of combined reciprocal- and real-space
analysis of materials with short-range magnetic correlations
Defect Tolerance to Intolerance in the Vacancy-Ordered Double Perovskite Semiconductors Cs<sub>2</sub>SnI<sub>6</sub> and Cs<sub>2</sub>TeI<sub>6</sub>
Vacancy-ordered double
perovskites of the general formula <i>A</i><sub>2</sub><i>BX</i><sub>6</sub> are a family
of perovskite derivatives composed of a face-centered lattice of nearly
isolated [<i>BX</i><sub>6</sub>] units with <i>A</i>-site cations occupying the cuboctahedral voids. Despite the presence
of isolated octahedral units, the close-packed iodide lattice provides
significant electronic dispersion, such that Cs<sub>2</sub>SnI<sub>6</sub> has recently been explored for applications in photovoltaic
devices. To elucidate the structure–property relationships
of these materials, we have synthesized solid-solution Cs<sub>2</sub>Sn<sub>1–<i>x</i></sub>Te<sub><i>x</i></sub>I<sub>6</sub>. However, even though tellurium substitution
increases electronic dispersion via closer I–I contact distances,
the substitution experimentally yields insulating behavior from a
significant decrease in carrier concentration and mobility. Density
functional calculations of native defects in Cs<sub>2</sub>SnI<sub>6</sub> reveal that iodine vacancies exhibit a low enthalpy of formation,
and that the defect energy level is a shallow donor to the conduction
band rendering the material tolerant to these defect states. The increased
covalency of Te–I bonding renders the formation of iodine vacancy
states unfavorable and is responsible for the reduction in conductivity
upon Te substitution. Additionally, Cs<sub>2</sub>TeI<sub>6</sub> is
intolerant to the formation of these defects, because the defect level
occurs deep within the band gap and thus localizes potential mobile
charge carriers. In these vacancy-ordered double perovskites, the
close-packed lattice of iodine provides significant electronic dispersion,
while the interaction of the <i>B</i>- and <i>X</i>-site ions dictates the properties as they pertain to electronic
structure and defect tolerance. This simplified perspective based
on extensive experimental and theoretical analysis provides a platform
from which to understand structure–property relationships in
functional perovskite halide
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Magnetic properties and signatures of ordering in triangular lattice antiferromagnet KCeO2.
The magnetic ground state and the crystalline electric field level scheme of the triangular lattice antiferromagnet KCeO2 are investigated. Below TN=300 mK, KCeO2 develops signatures of magnetic order in specific heat measurements and low energy inelastic neutron scattering data. Trivalent Ce3+ ions in the D3d local environment of this compound exhibit large splittings among the lowest three 4f1 Kramers doublets defining for the free ion the J=5/2 sextet and a ground state doublet with dipole character, consistent with recent theoretical predictions in M. S. Eldeeb et al. Phys. Rev. Materials 4, 124001 (2020). An unexplained, additional local mode appears, and potential origins of this anomalous mode are discussed
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Field-tunable quantum disordered ground state in the triangular-lattice antiferromagnet NaYbO2
Antiferromagnetically coupled S=1/2 spins on an isotropic triangular lattice
is the paradigm of frustrated quantum magnetism, but structurally ideal
realizations are rare. Here we investigate NaYbO, which hosts an ideal
triangular lattice of moments with no inherent site disorder. No
signatures of conventional magnetic order appear down to 50 mK, strongly
suggesting a quantum spin liquid ground state. We observe a two-peak specific
heat and a nearly quadratic temperature dependence in accord with expectations
for a two-dimensional Dirac spin liquid. Application of a magnetic field
strongly perturbs the quantum disordered ground state and induces a clear
transition into a collinear ordered state consistent with a long-predicted
up-up-down structure for a triangular lattice XXZ Hamiltonian driven by quantum
fluctuations. The observation of spin liquid signatures in zero field and
quantum-induced ordering in intermediate fields in the same compound
demonstrate an intrinsically quantum disordered ground state. We conclude that
NaYbO is a model, versatile platform for exploring spin liquid physics with
full tunability of field and temperature