Abstract
Layered Li-rich transition metal oxides undergo O-redox, involving the oxidation of the O
2−
ions charge compensated by extraction of Li
+
ions. Recent results have shown that for 3d ...transition metal oxides the oxidized O
2−
forms molecular O
2
trapped in the bulk particles. Other forms of oxidised O
2−
such as O
2
2−
or (O–O)
n−
with long bonds have been proposed, based especially on work on 4 and 5d transition metal oxides, where TM–O bonding is more covalent. Here, we show, using high resolution RIXS that molecular O
2
is formed in the bulk particles on O
2‒
oxidation in the archetypal Li-rich ruthenates and iridate compounds, Li
2
RuO
3
, Li
2
Ru
0.5
Sn
0.5
O
3
and Li
2
Ir
0.5
Sn
0.5
O
3
. The results indicate that O-redox occurs across 3, 4, and 5d transition metal oxides, forming O
2
, i.e. the greater covalency of the 4d and 5d compounds still favours O
2
. RIXS and XAS data for Li
2
IrO
3
are consistent with a charge compensation mechanism associated primarily with Ir redox up to and beyond the 5+ oxidation state, with no evidence of O–O dimerization.
Abstract
In ultrathin films of FeSe grown on SrTiO
3
(FeSe/STO), the superconducting transition temperature
T
c
is increased by almost an order of magnitude, raising questions on the pairing ...mechanism. As in other superconductors, antiferromagnetic spin fluctuations have been proposed to mediate SC making it essential to study the evolution of the spin dynamics of FeSe from the bulk to the ultrathin limit. Here, we investigate the spin excitations in bulk and monolayer FeSe/STO using resonant inelastic x-ray scattering (RIXS) and quantum Monte Carlo (QMC) calculations. Despite the absence of long-range magnetic order, bulk FeSe displays dispersive magnetic excitations reminiscent of other Fe-pnictides. Conversely, the spin excitations in FeSe/STO are gapped, dispersionless, and significantly hardened relative to its bulk counterpart. By comparing our RIXS results with simulations of a bilayer Hubbard model, we connect the evolution of the spin excitations to the Fermiology of the two systems revealing a remarkable reconfiguration of spin excitations in FeSe/STO, essential to understand the role of spin fluctuations in the pairing mechanism.
Absence of a single smoking-gun experiment to identify a quantum spin liquid, has kept their characterisation difficult till date. Featureless dc magnetic susceptibility and large antiferromagnetic ...frustration are always considered as the essential pointers to these systems. However, we show that the amount of frustration estimated by using generalised Curie-Weiss law on these susceptibility data are prone to errors and thus should be dealt with caution. We measure and analyse susceptibility data of Ba3ZnIr2O9, a spin orbital liquid candidate and Gd2O3, a 1.5K antiferromagnet and show the distinguishing features between them. A continuous and significant change in Curie and Weiss constants is seen to take place in Ba3ZnIr2O9 and other reported spin liquids with the change in the range of fitting temperatures showing the need of a temperature ‘range-of-fit’ analysis before commenting on the Weiss constants of spin liquids. The variation observed is similar to fluctuations among topological sectors persisting over a range of temperature in spin-ice candidates. On the other hand, even though we find correlations to exist at even 100 times the ordering temperature in Gd2O3, no such fluctuation is observed which may be used as an additional distinguishing signature of spin liquids over similarly featureless correlated paramagnets.
Display omitted
•Curie-Weiss fitting may give erroneous frustration parameters in spin-liquids.•The results depend upon choice of fitting method and temperature range used.•More appropriate method is to use a ʽrange of fit’ analysis.•Can distinguish between spin-liquids and correlated paramagnets.
Cuprate superconductors have the highest critical temperatures (T
) at ambient pressure, yet a consensus on the superconducting mechanism remains to be established. Finding an empirical parameter ...that limits the highest reachable T
can provide crucial insight into this outstanding problem. Here, in the first two Ruddlesden-Popper members of the model Hg-family of cuprates, which are chemically nearly identical and have the highest T
among all cuprate families, we use inelastic photon scattering to reveal that the energy of magnetic fluctuations may play such a role. In particular, we observe the single-paramagnon spectra to be nearly identical between the two compounds, apart from an energy scale difference of ~30% which matches their difference in T
. The empirical correlation between paramagnon energy and maximal T
is further found to extend to other cuprate families with relatively high T
's, hinting at a fundamental connection between them.
Along with the advancement of technology, Negative bias temperature instability (NBTI) has now been considered a severe reliability threat in modern processors causing the device to deteriorate over ...time. SRAM-based architectures within the memory array are very much prone to the NBTI effect. Since SRAM cells are composed of cross-coupled inverters, one of the PMOS transistors will always be under constant stress and heavily degraded by NBTI, resulting in an increase in threshold voltage and degradation of SNM and performance of SRAM. Similarly, as one the PMOS transistor is always ON, so there will be a leakage power from
V
DD
to the ground. In this paper, we have proposed a power gated SRAM architecture to reduce the NBTI effect and standby leakage power of a
4
×
4
SRAM array. The proposed gated logic is introduced during the hold state of the SRAM operation. So both the PMOS of the SRAM cell will be OFF during this period and will get sufficient time to relax from NBTI stress. The simulation result shows using our proposed approach overall, 30.41% NBTI-related
V
th
degradation can be saved and considering only the standby mode, 96.24% NBTI-related degradation can be minimized compared to the conventional SRAM design. Moreover, 79.10% leakage power can be reduced over the conventional design using the proposed approach.
The I21 beamline at Diamond Light Source is dedicated to advanced resonant inelastic X‐ray scattering (RIXS) for probing charge, orbital, spin and lattice excitations in materials across condensed ...matter physics, applied sciences and chemistry. Both the beamline and the RIXS spectrometer employ divergent variable‐line‐spacing gratings covering a broad energy range of 280–3000 eV. A combined energy resolution of ∼35 meV (16 meV) is readily achieved at 930 eV (530 eV) owing to the optimized optics and the mechanics. Considerable efforts have been paid to the design of the entire beamline, particularly the implementation of the collection mirrors, to maximize the X‐ray photon throughput. The continuous rotation of the spectrometer over 150° under ultra high vacuum and a cryogenic manipulator with six degrees of freedom allow accurate mappings of low‐energy excitations from solid state materials in momentum space. Most importantly, the facility features a unique combination of the high energy resolution and the high photon throughput vital for advanced RIXS applications. Together with its stability and user friendliness, I21 has become one of the most sought after RIXS beamlines in the world.
The design of the resonant inelastic X‐ray scattering beamline at Diamond Light Source, I21, is presented. X‐ray commissioning results are shown and compared with the optical simulations.
A photon carrying one unit of angular momentum can change the spin angular momentum of a magnetic system with one unit (ΔM
= ±1) at most. This implies that a two-photon scattering process can ...manipulate the spin angular momentum of the magnetic system with a maximum of two units. Herein we describe a triple-magnon excitation in α-Fe
O
, which contradicts this conventional wisdom that only 1- and 2-magnon excitations are possible in a resonant inelastic X-ray scattering experiment. We observe an excitation at exactly three times the magnon energy, along with additional excitations at four and five times the magnon energy, suggesting quadruple and quintuple-magnons as well. Guided by theoretical calculations, we reveal how a two-photon scattering process can create exotic higher-rank magnons and the relevance of these quasiparticles for magnon-based applications.
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