33 research outputs found
Resonant x-ray scattering reveals possible disappearance of magnetic order under hydrostatic pressure in the Kitaev candidate -LiIrO
Honeycomb iridates such as -LiIrO are argued to realize
Kitaev spin-anisotropic magnetic exchange, along with Heisenberg and possibly
other couplings. While systems with pure Kitaev interactions are candidates to
realize a quantum spin liquid ground state, in -LiIrO it has
been shown that the balance of magnetic interactions leads to the
incommensurate spiral spin order at ambient pressure below 38 K. We study the
fragility of this state in single crystals of -LiIrO using
resonant x-ray scattering (RXS) under applied hydrostatic pressures of up to
3.0 GPa. RXS is a direct probe of the underlying electronic order, and we
observe the abrupt disappearance of the =(0.57, 0, 0) spiral order at a
critical pressure GPa with no accompanying change in the symmetry
of the lattice. This dramatic disappearance is in stark contrast with recent
studies of -LiIrO that show continuous suppression of the spiral
order in magnetic field; under pressure, a new and possibly nonmagnetic ground
state emerges
Local orthorhombicity in the magnetic phase of the hole-doped iron-arsenide superconductor SrNaFeAs
We report temperature-dependent pair distribution function measurements of
SrNaFeAs, an iron-based superconductor system that
contains a magnetic phase with reentrant tetragonal symmetry, known as the
magnetic phase. Quantitative refinements indicate that the instantaneous
local structure in the phase is comprised of fluctuating orthorhombic
regions with a length scale of 2 nm, despite the tetragonal symmetry of
the average static structure. Additionally, local orthorhombic fluctuations
exist on a similar length scale at temperatures well into the paramagnetic
tetragonal phase. These results highlight the exceptionally large nematic
susceptibility of iron-based superconductors and have significant implications
for the magnetic phase and the neighboring and superconducting
phases
Short-range nematic fluctuations in Sr1-xNaxFe2As2 superconductors
Interactions between nematic fluctuations, magnetic order and
superconductivity are central to the physics of iron-based superconductors.
Here we report on in-plane transverse acoustic phonons in hole-doped
SrNaFeAs measured via inelastic X-ray scattering, and
extract both the nematic susceptibility and the nematic correlation length. By
a self-contained method of analysis, for the underdoped () sample,
which harbors a magnetically-ordered tetragonal phase, we find it hosts a short
nematic correlation length ~ 10 and a large nematic susceptibility
. The optimal-doped () sample exhibits weaker phonon
softening effects, indicative of both reduced and . Our
results suggest short-range nematic fluctuations may favor superconductivity,
placing emphasis on the nematic correlation length for understanding the
iron-based superconductors
Discovery of Charge Order in the Transition Metal Dichalcogenide FeNbS
The Fe intercalated transition metal dichalcogenide (TMD), FeNbS,
exhibits remarkable resistance switching properties and highly tunable spin
ordering phases due to magnetic defects. We conduct synchrotron X-ray
scattering measurements on both under-intercalated ( = 0.32) and
over-intercalated ( = 0.35) samples. We discover a new charge order phase in
the over-intercalated sample, where the excess Fe atoms lead to a zigzag
antiferromagnetic order. The agreement between the charge and magnetic ordering
temperatures, as well as their intensity relationship, suggests a strong
magnetoelastic coupling as the mechanism for the charge ordering. Our results
reveal the first example of a charge order phase among the intercalated TMD
family and demonstrate the ability to stabilize charge modulation by
introducing electronic correlations, where the charge order is absent in bulk
2H-NbS compared to other pristine TMDs
Spin-carrier coupling induced ferromagnetism and giant resistivity peak in EuCdP
EuCdP is notable for its unconventional transport: upon cooling the
metallic resistivity changes slope and begins to increase, ultimately 100-fold,
before returning to its metallic value. Surprisingly, this giant peak occurs at
18K, well above the N\'{e}el temperature () of 11.5K. Using a suite of
sensitive probes of magnetism, including resonant x-ray scattering and
magneto-optical polarimetry, we have discovered that ferromagnetic order onsets
above in the temperature range of the resistivity peak. The observation
of inverted hysteresis in this regime shows that ferromagnetism is promoted by
coupling of localized spins and itinerant carriers. The resulting carrier
localization is confirmed by optical conductivity measurements
Detection of a two-phonon mode in a cuprate superconductor via polarimetric RIXS
Recent improvements in the energy resolution of resonant inelastic x-ray
scattering experiments (RIXS) at the Cu-L edge have enabled the study of
lattice, spin, and charge excitations. Here, we report on the detection of a
low intensity signal at 140meV, twice the energy of the bond-stretching (BS)
phonon mode, in the cuprate superconductor
(Bi-2212).
Ultra-high resolution polarimetric RIXS measurements allow us to resolve the
outgoing polarization of the signal and identify this feature as a two-phonon
excitation. Further, we study the connection between the two-phonon mode and
the BS one-phonon mode by constructing a joint density of states toy model that
reproduces the key features of the data