We investigated the optical properties of rhenium-doped MoS2 nanoparticles and compared our findings with the pristine and bulk analogues. Our measurements reveal that confinement softens the exciton ...positions and reduces spin–orbit coupling, whereas doping has the opposite effect. We model the carrier-induced exciton blue shift in terms of the Burstein–Moss effect. These findings are important for understanding doping and finite length scale effects in low-dimensional nanoscale materials.
We combined synchrotron-based infrared absorbance and Raman scattering spectroscopies with diamond anvil cell techniques and a symmetry analysis to explore the properties of multiferroic ...(NH4)2FeCl5·H2O under extreme pressure–temperature conditions. Compression-induced splitting of the Fe–Cl stretching, Cl–Fe–Cl and Cl–Fe–O bending, and NH4 + librational modes defines two structural phase transitions, and a group–subgroup analysis reveals space group sequences that vary depending upon proximity to the unexpectedly wide order–disorder transition. We bring these findings together with prior high-field work to develop the pressure–temperature–magnetic field phase diagram uncovering competing polar, chiral, and magnetic phases in this system.
We combined synchrotron-based infrared absorbance and Raman scattering spectroscopies with diamond anvil cell techniques and a symmetry analysis to explore the properties of multiferroic (NH
)
FeCl
...·H
O under extreme pressure-temperature conditions. Compression-induced splitting of the Fe-Cl stretching, Cl-Fe-Cl and Cl-Fe-O bending, and NH
librational modes defines two structural phase transitions, and a group-subgroup analysis reveals space group sequences that vary depending upon proximity to the unexpectedly wide order-disorder transition. We bring these findings together with prior high-field work to develop the pressure-temperature-magnetic field phase diagram uncovering competing polar, chiral, and magnetic phases in this system.
One emergent property of ferroelectric nanoparticles is the sized-induced structural distortion to a high-symmetry paraelectric phase at small particle sizes. Finite length scale effects can thus be ...advantageously employed to elucidate ferroelectric transition mechanisms. In this work, we combine infrared spectroscopy with group theory and lattice dynamics calculations to reveal the displacive nature of the ferroelectric transition in BiFeO3, a room temperature multiferroic. Systematic intensity and frequency trends in selected vibrational modes show that the paraelectric phase is Pm3̅m and the lowest frequency A1 feature is the soft mode that drives the first order transition. Finite length scale effects are also evident in the electronic structure with a red-shifted band gap in nanoscale BiFeO3 compared with that of the rhombohedral film, a result that can impact the development of ferroelectric photovoltaics and oxide-based electronics. Taken together, these findings demonstrate the foundational importance of size effects for enhancing the rich functionality and broad utility of transition metal oxides.
We combine Raman scattering spectroscopy and lattice dynamics calculations to reveal the fundamental excitations of the intercalated metal monolayers in the Fe
TaS
(
= 1/4, 1/3) family of materials. ...Both in- and out-of-plane modes are identified, each of which has trends that depend upon the metal-metal distance, the size of the van der Waals gap, and the metal-to-chalcogenide slab mass ratio. We test these trends against the response of similar systems, including Cr-intercalated NbS
and RbFe(SO
)
, and demonstrate that the metal monolayer excitations are both coherent and tunable. We discuss the consequences of intercalated metal monolayer excitations for material properties and developing applications.
Interface materials offer a means to achieve electrical control of ferrimagnetism at room temperature as was recently demonstrated in (LuFeO
)
/(LuFe
O
)
superlattices. A challenge to understanding ...the inner workings of these complex magnetoelectric multiferroics is the multitude of distinct Fe centres and their associated environments. This is because macroscopic techniques characterize average responses rather than the role of individual iron centres. Here, we combine optical absorption, magnetic circular dichroism and first-principles calculations to uncover the origin of high-temperature magnetism in these superlattices and the charge-ordering pattern in the m = 3 member. In a significant conceptual advance, interface spectra establish how Lu-layer distortion selectively enhances the Fe
→ Fe
charge-transfer contribution in the spin-up channel, strengthens the exchange interactions and increases the Curie temperature. Comparison of predicted and measured spectra also identifies a non-polar charge ordering arrangement in the LuFe
O
layer. This site-specific spectroscopic approach opens the door to understanding engineered materials with multiple metal centres and strong entanglement.
Vibrations play a prominent role in magnetic relaxation processes of molecular spin qubits as they couple to spin states, leading to the loss of quantum information. Direct experimental determination ...of vibronic coupling is crucial to understand and control the spin dynamics of these nano-objects, which represent the limit of miniaturization for quantum devices. Herein, we measure the magneto-infrared properties of the molecular spin qubit system Na9Ho(W5O18)2·35H2O. Our results place significant constraints on the pattern of crystal field levels and the vibrational excitations allowing us to unravel vibronic decoherence pathways in this system. We observe field-induced spectral changes near 63 and 370 cm–1 that are modeled in terms of odd-symmetry vibrations mixed with f-manifold crystal field excitations. The overall extent of vibronic coupling in Na9Ho(W5O18)2·35H2O is limited by a modest coupling constant (on the order of 0.25) and a transparency window in the phonon density of states that acts to keep the intramolecular vibrations and M J levels apart. These findings advance the understanding of vibronic coupling in a molecular magnet with atomic clock transitions and suggest strategies for designing molecular spin qubits with improved coherence lifetimes.
We investigated the infrared vibrational properties of pristine and Re-substituted MoS2 nanoparticles and analyzed the extracted phonon lifetimes in terms of multiple scattering events. Our ...measurements reveal both size- and doping-dependent changes that we attribute to grain boundary scattering and charge and mass effects, respectively. By contrast, Born charge is affected only by size. These findings illustrate the utility of reaching beyond traditional bulk semiconductors and quantum dots to explore how doping and confinement impact carrier-phonon interactions in low-dimensional semiconducting nanomaterials.
High 'n low: The novel {Fe(tmphen)23Os(CN)62} complex (see structure) is the first example of a cluster in which a high‐spin FeIII ion is in a coordination environment of four imine nitrogen atoms ...and two N‐coordinated cyanides. Magnetic studies reveal an unprecedented type of reversible charge transfer induced spin transition (CTIST) between the low‐spin FeIINCOsIII and high‐spin FeIIINCOsII systems.
In order to explore how spectral sparsity and vibronic decoherence pathways can be controlled in a model qubit system with atomic clock transitions, we combined diamond anvil cell techniques with ...synchrotron-based far infrared spectroscopy and first-principles calculations to reveal the vibrational response of Na9Ho(W5O18)2·35H2O under compression. Because the hole in the phonon density of states acts to reduce the overlap between the phonons and f manifold excitations in this system, we postulated that pressure might move the HoO4 rocking, bending, and asymmetric stretching modes that couple with the MJ = ±5, ±2, and ±7 levels out of resonance, reducing their interactions and minimizing decoherence processes, while a potentially beneficial strategy for some molecular qubits, pressure slightly hardens the phonons in Na9Ho(W5O18)2·35H2O and systematically fills in the transparency window in the phonon response. The net result is that the vibrational spectrum becomes less sparse and the overlap with the various MJ levels of the Ho3+ ion actually increases. These findings suggest that negative pressure, achieved using chemical means or elongational strain, could further open the transparency window in this rare earth-containing spin qubit system, thus paving the way for the use of device surfaces and interface elongational/compressive strains to better manage decoherence pathways.
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