arXiv subjects

Elena I. Zhilyaeva

Publications and source records attributed to Elena I. Zhilyaeva.

8 recordsLinked to original sources

arXiv2022

Charge and spin interplay in a molecular-dimer-based organic Mott insulator

Triangular lattice quasi-two-dimensional Mott insulators based on BEDT-TTF molecule and its analogies present a possibility to produce exotic phases by coupling charge and spin degrees of freedom. In this work we discuss magnetic properties of one of such materials, $κ$-(BEDT-TTF)$_2$Hg(SCN)$_2$Cl, which is found at the border of the phase transition between a Mott insulator into a charge ordered state. Our magnetic susceptibility and cantilever magnetisation measurements demonstrate how the charge degree of freedom defines magnetic properties for few different charge phases observed in this material as a function of temperature. Between $T_{CO}=30~K$ and $T_S=24~K$ we observe charge and spin separation due to one-dimensional charge stripes formed in this material below $T_{CO}=30~K$. Below $T_S=24~K$ charge and spin degrees of freedom demonstrate coupling. Spin singlet correlations develop below 24~K, however melting of charge order below 15~K prevents the spin singlet state formation, leaving the system in the inhomogeneous state with charge ordered spin singlet domains and charge and spin fluctuating ones.

cond-mat.str-el↗

arXiv2022

Anomalously field-susceptible spin soft-matter emerging in an electric-dipole liquid candidate

Mutual interactions in many-body systems bring about a variety of exotic phases, among which liquid-like states failing to order due to frustration are of keen interest. Recently, an organic system with an anisotropic triangular lattice of molecular dimers has been suggested to host a dipole liquid arising from intradimer charge-imbalance instability, possibly offering an unprecedented stage for the spin degrees of freedom. Here we show that an extraordinary unordered(unfrozen) spin state having soft-matter-like spatiotemporal characteristics is substantiated in this system. $^1$H NMR spectra and magnetization measurements indicate that gigantic, staggered moments are non-linearly and inhomogeneously induced by magnetic field whereas the moments vanish in the zero-field limit. The analysis of the NMR relaxation rate signifies that the moments fluctuate at a characteristic frequency slowing down to below MHz at low temperatures. The inhomogeneity, local correlation, and slow dynamics indicative of middle-scale dynamical correlation length suggest a novel frustration-driven spin clusterization.

cond-mat.str-el↗

arXiv2021

Ferromagnetism out of charge fluctuation of strongly correlated electrons in $κ$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br

We perform magnetic susceptibility and magnetic torque measurements on the organic $κ$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br, which is recently suggested to host an exotic quantum dipole-liquid in its low-temperature insulating phase. Below the metal-insulator transition temperature, the magnetic susceptibility follows a Curie-Weiss law with a positive Curie-Weiss temperature, and a particular $M\propto \sqrt{H}$ curve is observed. The emergent ferromagnetically interacting spins amount to about 1/6 of the full spin moment of localized charges. Taking account of the possible inhomogeneous quasi-charge-order that forms a dipole-liquid, we construct a model of antiferromagnetically interacting spin chains in two adjacent charge-ordered domains, which are coupled via fluctuating charges on a Mott-dimer at the boundary. We find that the charge fluctuations can draw a weak ferromagnetic moment out of the spin singlet domains.

cond-mat.str-el↗

arXiv2019

Melting of charge order in the low-temperature state of an electronic ferroelectric

Strong electronic interactions can drive a system into a state with a symmetry breaking. Lattice frustration or competing interactions tend to prevent a symmetry breaking, leading to quantum disordered phases. In spin systems frustration can produce a spin liquid state. Frustration of a charge degree of freedom also can result in various exotic states, however, experimental data on these effects is scarce. In this work we demonstrate how a charge ordered ferroelectric looses the order on cooling to low temperatures using an example of a Mott insulator on a weakly anisotropic triangular lattice $κ$-(BEDT-TTF)$_2$Hg(SCN)$_2$Cl. Typically, a low temperature ordered state is a ground state of a system, and the demonstrated re-entrant behavior is unique. Raman scattering spectroscopy finds that this material enters an insulating ferroelectric `dipole solid' state at $T=30~K$, but below $T=15~K$ the order melts, while preserving the insulating energy gap. The resulting phase diagram is relevant to other quantum paraelectric materials.

cond-mat.str-el↗

arXiv2019

Evidence for a quantum dipole liquid state in an organic quasi-two-dimensional material

Mott insulators are commonly pictured with electrons localized on lattice sites. Their low-energy degrees of freedom involve spins only. Here we observe emerging charge degrees of freedom in a molecule-based Mott insulator $κ$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br, resulting in a quantum dipole liquid state. Electrons localized on molecular dimer lattice sites form electric dipoles that do not order at low temperatures and fluctuate with frequency detected experimentally in our Raman spectroscopy experiments. The heat capacity and Raman scattering response are consistent with a scenario where the composite spin and electric dipole degrees of freedom remain fluctuating down to the lowest measured temperatures.

cond-mat.str-el↗

arXiv2017

Metal-Insulator Transition in the Dimerized Organic Conductor $κ$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br

The organic charge-transfer salt $κ$-(BEDT-TTF)$_{2}$Hg(SCN)$_{2}$Br is a quasi two-dimensional metal with a half-filled conduction band at ambient conditions. When cooled below $T=80$ K it undergoes a pronounced transition to an insulating phase where the resistivity increases many orders of magnitude. In order to elucidate the nature of this metal-insulator transition we have performed comprehensive transport, dielectric and optical investigations. The findings are compared with other dimerized $κ$-(BEDT-TTF) salts, in particular the Cl-analogue, where a charge-order transition takes place at $T_{\rm CO}=30$ K.

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arXiv2017

The metal-insulator transition in the organic conductor $β^{\prime\prime}$-(BEDT-TTF)$_{2}$Hg(SCN)$_{2}$Cl

We explore the nature of the metal-insulator transition in $β^{\prime\prime}$-(BEDT-TTF)$_{2}$Hg(SCN)$_{2}$Cl by x-ray, electrical transport, ESR, Raman and infrared investigations. Magnetic and vibrational spectroscopy concurrently reveal a gradual dimerization along the stacking direction $a$, setting in already at the crossover temperature of 150K from the metallic to the insulating state. A spin gap $Δ_σ= 47$meV is extracted. From the activated resistivity behavior below 55K a charge gap $Δ_ρ=60$meV is derived. At $T_{\rm CO} = 72$K the C=C vibrational modes reveal the development of a charge-ordered state with a charge disproportionation of $2δ_ρ=0.34e$

cond-mat.str-el↗

arXiv2013

Onsager phase factor of quantum oscillations in the organic metal theta-(BEDT-TTF)4CoBr4(C6H4Cl2)

De Haas-van Alphen oscillations are studied for Fermi surfaces illustrating the Pippard's model, commonly observed in multiband organic metals. Field- and temperature-dependent amplitude of the various Fourier components, linked to frequency combinations arising from magnetic breakdown between different bands, are considered. Emphasis is put on the Onsager phase factor of these components. It is demonstrated that, in addition to the usual Maslov index, field-dependent phase factors must be considered to precisely account for the data at high magnetic field. We present compelling evidence of the existence of such contributions for the organic metal theta-(BEDT-TTF)4CoBr4(C6H4Cl2).

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