arXiv subjects

Victoria A. Ginga

Publications and source records attributed to Victoria A. Ginga.

6 recordsLinked to original sources

arXiv2026

Quantum spin ladder with ferromagnetic rungs in Bi$_2$CuO$_3$(SO$_4$)

We introduce Bi$_2$CuO$_3$(SO$_4$) as a rare example of a spin-ladder magnet with ferromagnetic interactions on the rungs. Its magnetic response is studied through measurements of heat capacity, temperature-dependent magnetic susceptibility, and field-dependent magnetization, as well as electron spin resonance spectroscopy. These experiments are complemented by density-functional-theory calculations combined with the construction of maximally localized Wannier functions and an analysis of the relevant superexchange pathways. Quantum Monte Carlo simulations are employed to model thermodynamic properties and to quantitatively determine the magnetic exchange parameters. Our combined approach identifies Bi$_2$CuO$_3$(SO$_4$) as a two-leg spin-ladder system with ferromagnetic rungs ($J'$ $\approx -208$ K) and antiferromagnetic legs ($J$ $\approx 258$ K). These interactions of similar magnitude arise from remarkably different superexchange pathways, with the Cu--Cu distance along the leg being almost twice as long than the respective distance along the rung. The antiferromagnetic leg coupling represents the strongest oxygen-mediated long-range superexchange in a Cu$^{2+}$ compound reported to date and sets the benchmark for the role of complex superexchange pathways in quantum magnets.

cond-mat.str-el↗

arXiv2026

Revisiting the symmetry and optical phonons of altermagnetic $α$-MnTe

Using infrared (IR) and Raman spectroscopies combined with high-resolution x-ray diffraction, we address several controversial aspects of altermagnetic $α$-MnTe. We show that mechanical stress applied to crystals of this material causes a drastic broadening of Bragg peaks that conceals signatures of additional phases present in the sample. Indeed, spatially resolved Raman spectroscopy reveals that the modes around 175 cm$^{-1}$ often reported in $α$-MnTe are not reproducible across different positions and samples and originate from the secondary phase of MnTe$_2$. By combining spectroscopic probes with ab initio calculations, we establish the IR-active optical phonon of $α$-MnTe around 155 cm$^{-1}$ ($E_{1u}$) and the Raman-active optical phonon around 100 cm$^{-1}$ ($E_{2g}$) at room temperature. Two intense Raman modes around 120 and 140 cm$^{-1}$ are shown to be intrinsic, even though they can not be assigned to $Γ$-point optical phonons. These modes couple to magnetic order in $α$-MnTe and also to the transient reflectivity resulting in coherent oscillations. Both 6-fold rotation symmetry and inversion symmetry are preserved in $α$-MnTe within our experimental resolution.

cond-mat.mtrl-sci↗

arXiv2025

Pressure-tuned spin chains in brochantite, Cu$_4$SO$_4$(OH)$_6$

Using high-pressure single-crystal x-ray diffraction combined with thermodynamic measurements and density-functional calculations, we uncover the microscopic magnetic model of the mineral brochantite, Cu$_4$SO$_4$(OH)$_6$, and its evolution upon compression. The formation of antiferromagnetic spin chains with the effective intrachain coupling of $J\simeq 100$\,K is attributed to the occurrence of longer Cu--Cu distances and larger Cu--O--Cu bond angles between the structural chains within the layers of the brochantite structure. These zigzag spin chains are additionally stabilized by ferromagnetic couplings $J_2$ between second neighbors and moderately frustrated by several antiferromagnetic couplings that manifest themselves in the reduced Néel temperature of the material. Pressure tuning of the brochantite structure keeps its monoclinic symmetry unchanged and leads to the growth of antiferromagnetic $J$ with the rate of 3.2\,K/GPa, although this trend is primarily caused by the enhanced ferromagnetic couplings $J_2$. Our results show that the nature of magnetic couplings in brochantite and in other layered Cu$^{2+}$ minerals is controlled by the size of the lattice translation along their structural chains and by the extent of the layer buckling.

cond-mat.str-el↗

arXiv2025

Pressure-induced strange metal phase in a metallic kagome ferromagnet

Strange metallicity with $T$-linear electrical resistance preceding high-$T_c$ superconductivity remains an enigmatic, yet crucial, signature of correlation physics. Using electrical transport and magnetization measurements up to 50 GPa, we show that such a strange-metal phase is formed in pressurized kagome ferromagnet CrNiAs. In contrast to other kagome materials, a linear suppression of the Curie temperature is found, with the ferromagnetic quantum critical point at $p_{\rm{c}} \approx 12.5$ GPa. Remarkably, from $p_{\rm{c}}$ up to the highest measured pressure, characteristic strange-metal behavior is observed, whereas magnetic field reinstates the Fermi liquid. Electronic structure calculations reveal robust weakly dispersive bands persisting unchanged beyond $p_{\rm{c}}$, possibly at the origin of the $T$-linear electrical resistance. This establishes pressurized kagome ferromagnets as an intriguing platform for strange-metal behavior.

cond-mat.str-el↗

arXiv2024

Tunable Dirac nodal line in orthorhombic RuO$_2$

Pressure evolution of RuO2 is studied using single-crystal x-ray diffraction in a diamond anvil cell, combined with \textit{ab initio} band-structure calculations. The tetragonal rutile structure transforms into the orthorhombic CaCl$_2$-type structure above 13 GPa under quasi-hydrostatic pressure conditions. This second-order transition is ferroelastic in nature and accompanied by tilts of the RuO$_6$ octahedra. Orthorhombic RuO$_2$ is expected to be paramagnetic metal, similar to ambient-pressure RuO$_2$. It shows the increased $t_{2g}-e_g$ crystal-field splitting that is responsible for the pressure-induced color change. It further features the Dirac nodal line that shifts across the Fermi level upon compression.

cond-mat.mtrl-sci↗

arXiv2024

Magnetic versus nonmagnetic polymorphs of RuBr$_3$ under pressure

Pressure evolution of the crystal structure and magnetism of the honeycomb $α$-RuBr$_3$ is studied using high-pressure x-ray diffraction, magnetometry, and density-functional band-structure calculations. Hydrostatic compression transforms antiferromagnetic $α$-RuBr$_3$ ($R\bar 3$) into paramagnetic $α'$-RuBr$_3$ ($P\bar 1$) where short Ru-Ru bonds cause magnetism collapse above 1.3 GPa at 0 K and 2.5 GPa at 295 K. Below this critical pressure, the Néel temperature of $α$-RuBr$_3$ increases with the slope of 1.8 K/GPa. Pressure tunes $α$-RuBr$_3$ away from the Kitaev limit, whereas increased third-neighbor in-plane coupling and interlayer coupling lead to a further stabilization of the collinear zigzag state. Both $α$- and $α'$-RuBr$_3$ are metastable at ambient pressure, but their transformation into the thermodynamically stable $β$-polymorph is kinetically hindered at room temperature.

cond-mat.str-el↗