arXiv subjects

Savita Priya

Publications and source records attributed to Savita Priya.

4 recordsLinked to original sources

arXiv2026

Charge-sensitive vibrational modes in BEDT-TTF salts: Signatures of charge ordering and site charge

BEDT-TTF-based organic conductors host a number of ground states, tuned by electron repulsion from Mott and charge ordered insulators to superconductors. Knowing charge distribution on the molecular sites in the insulating state of these materials is a key to understanding the origin of these ground states. We survey and discuss the C=C stretching modes in BEDT-TTF based molecular conductors. These molecular vibrations are extremely crucial in characterization of charge-ordered insulators, and are recently linked to superconductivity in some compounds. Focusing on the known examples of BEDT-TTF$^{+0.5}$ salts, we analyse the reliability of the C=C stretching modes for the determination of charge ordering and absolute site charge. Considering the charge-ordered states, a prominent shift in frequency of 141 cm$^{-1}$ per elementary charge $e$ for $ν_{27}(b_{1u})$ and 98 cm$^{-1}$$e$ for $ν_2$($a_g$) can be clearly realised, however, the distribution resulting from different compounds span over 20 cm$^{-1}$. For nominal BEDT-TTF$^{+0.5}$ compounds, the distribution of the resonance also extends around 20 cm$^{-1}$, yielding an unexpected large uncertainty of $Δρ~\approx~(~\pm~0.045)e$, which is presumably due to the influence of small differences in the structure. This highlights the limitations of charge-frequency relations to detect small deviations in absolute charge values on molecular lattice sites, and emphasises on the use of the relations to estimate charge-ordering, rather than absolute site charge.

cond-mat.str-el↗

arXiv2026

ESR Investigations of the Magnetic Anisotropy in $κ$-(BETS)$_2$Mn[N(CN)$_{2}$]$_3$

The two-dimensional molecular conductor $κ$-(BETS)$_2$Mn[N(CN)$_2$]$_3$ has been studied because of the intriguing magnetic coupling of the molecular $π$-electrons to the Mn$^{2+}$ ions. Utilizing X-band electron spin resonance spectroscopy we have performed comprehensive investigations of the magnetic properties, in particular on the temperature and angular dependences of the spin susceptibility, the $g$-factor and the linewidth. Due to the $π$-$d$-coupling, a rearrangement of the $π$-spins occurs: At low temperatures the $g$-factor shifts enormously with a pronounced in-plane anisotropy that flips as the temperature decreases; the lines broaden significantly; and the spin susceptibility increases upon cooling with a kink at the phase transition. By carefully analyzing the angular dependence of $g(θ)$ and $ΔH(θ)$ we reveal the influence of anisotropic Zeeman interaction in addition to spin-phonon coupling. We conclude the presence of two magnetically distinct BETS chains and discuss the possibility of altermagnetic order.

cond-mat.str-el↗

arXiv2025

Charge-localization-driven metal-insulator phase transition in layered molecular conductors

The organic conductor $α$-(BEDT-TTF)$_2$I$_3$ provides the prime example of a charge-order-driven metal-insulator transition. Restricted chemical substitution of S atoms by Se in the constituent molecules allows us to modify the electronic properties. This not only decreases the transition temperature but, in addition, alters the phase transition mechanism, resulting in the ground state deviating from the charge-ordered insulator state of the parent compound. Employing infrared optical spectroscopy, we investigate changes in the charge dynamics. Furthermore, we demonstrate the absence of charge ordering in the Se-substituted materials and suggest that the phase transition is instead driven by the localization of the itinerant charge carriers due to strong electron-phonon interactions.

cond-mat.str-el↗

arXiv2024

Electronic properties of the dimerized organic conductor $κ$-(BETS)$_2$Mn[N(CN)$_2$]$_3$

The two-dimensional molecular conductor $κ$-(BETS)$_2$Mn[N(CN)$_2$]$_3$ undergoes a sharp metal-to-insulator phase transition at $T_{\rm MI}\approx$ 21 K, which has been under scrutiny for many years. We have performed comprehensive infrared investigations along the three crystallographic directions as a function of temperature down to 10 K, complemented by electron spin resonance and dc-transport studies. The in-plane anisotropy of the optical conductivity is more pronounced than in any other $κ$-type BEDT-TTF or related compounds. The metal-insulator transitions affects the molecular vibrations due to the coupling to the electronic system; in addition we observe a clear splitting of the charge-sensitive vibrational modes below $T_{\rm MI}$ that evidences the presence of two distinct BETS dimers in this compound. The Mn[N(CN)$_2$]$_3^-$ layers are determined by the chain structure of the anions resulting in a rather anisotropic behavior and remarkable temperature dependence of the vibronic features. At low temperatures the ESR properties are affected by the Mn$^{2+}$ ions via $π$-$d$-coupling and antiferromagnetic ordering within the $π$-spins: The $g$-factor shifts enormously with a pronounced in-plane anisotropy that flips as the temperature decreases; the lines broaden significantly; and the spin susceptibility increases upon cooling with a kink at the phase transition.

cond-mat.str-el↗