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Abstract Ferro-rotational magnet RbFe(SO₄)₂has attracted attention for its stable ferro-rotational phase and electric-field-controlled magnetic chirality. This work presents the multiferroic properties andH–Tphase diagram of RbFe(SO₄)₂, which have been underexplored. Our measurements of magnetic susceptibility, ferroelectric polarization, and dielectric constant under various magnetic fields reveal four distinct phases: (I) a ferroelectric and helical magnetic phase below 4 K and 6 T, (II) a paraelectric and collinear magnetic phase below 4 K and above 6 T, (III) a paraelectric and non-collinear magnetic phase below 4 K and above 9 T, and (IV) a paraelectric and paramagnetic above 4 K. This study clarifies the multiferroic behavior andH–Tphase diagram of RbFe(SO₄)₂, providing valuable insights into ferro-rotational magnets. 

We combined synchrotron-based near field infrared spectroscopy and atomic force microscopy to image the properties of ferroelastic domain walls in Sr3Sn2O7. Although frequency shifts at the walls are near the limit of our sensitivity, we can confirm semiconducting rather than metallic character and widths between 20 and 60 nm. The latter is significantly narrower than in other hybrid improper ferroelectrics like Ca3Ti2O7. We attribute this trend to the softer lattice in Sr3Sn2O7, which may enable the octahedral tilt and rotation order parameters to evolve more quickly across the wall without significantly increased strain. These findings are crucial for the understanding of phononic properties at interfaces and the development of domain wall-based devices. 

The nodal-line semiconductor Mn3Si2Te6 is generating enormous excitment due to the recent discovery of a field-driven insulator-to-metal transition and associated colossal magnetoresistance as well as evidence for a new type of quantum state involving chiral orbital currents. Strikingly, these qualities persist even in the absence of traditional Jahn-Teller distortions and double-exchange mechanisms, raising questions about exactly how and why magnetoresistance occurs along with conjecture as to the likely signatures of loop currents. Here, we measured the infrared response of Mn3Si2Te6 across the magnetic ordering and field-induced insulator-to-metal transitions in order to explore colossal magnetoresistance in the absence of Jahn-Teller and double-exchange interactions. Rather than a traditional metal with screened phonons, the field-driven insulator-to-metal transition leads to a weakly metallic state with localized carriers. Our spectral data are fit by a percolation model, providing evidence for electronic inhomogeneity and phase separation. Modeling also reveals a frequency-dependent threshold field for carriers contributing to colossal magnetoresistance which we discuss in terms of polaron formation, chiral orbital currents, and short-range spin fluctuations. These findings enhance the understanding of insulator-to-metal transitions in new settings and open the door to the design of unconventional colossal magnetoresistant materials. 

Abstract Kagomé metals are widely recognized, versatile platforms for exploring topological properties, unconventional electronic correlations, magnetic frustration, and superconductivity. In theRV₆Sn₆family of materials (R= Sc, Y, Lu), ScV₆Sn₆hosts an unusual charge density wave ground state as well as structural similarities with theAV₃Sb₅system (A= K, Cs, Rb). In this work, we combine Raman scattering spectroscopy with first-principles lattice dynamics calculations to reveal phonon mixing processes in the charge density wave state of ScV₆Sn₆. In the low temperature phase, we find at least four new peaks in the vicinity of the V-containing totally symmetric mode near 240 cm⁻¹suggesting that the density wave acts to mix modes ofP6/mmmand$$R\bar{3}m$$ $R\overline{3}m$symmetry - a result that we quantify by projecting phonons of the high symmetry state onto those of the lower symmetry structure. We also test the stability of the short-range ordered density wave state under compression and propose that both physical and chemical pressure quench the effect. We discuss these findings in terms of symmetry and the structure-property trends that can be unraveled in this system. 

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 Na9[Ho(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 Na9[Ho(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.