arXiv subjects

Jesse Liebman

Publications and source records attributed to Jesse Liebman.

6 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 $\nu_{27}(b_{1u})$ and 98 cm$^{-1}$$e$ for $\nu_2$($a_g$) 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 $\Delta\rho~\approx~(~\pm~0.045)e$, 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

Raman scattering spectroscopic observation of a ferroelastic crossover in bond-frustrated PrCd$_3$P$_3$

2D magnetism in triangular lattices has already shown potential for hosting exotic magnetic states. Control of these magnetic states, both in terms of magnetic properties and in terms of charge doping would be the next step. This makes materials which combine triangular lattice magnetic layers with layers hosting interesting structural or electronic properties particularly useful. PrCd$_3$P$_3$, studied in this work, is one of a family of materials where triangular lattice layers of magnetic rare earth ions alternate with semiconducting hexagonal CdP layers. Using Raman scattering spectroscopy we uncover a structural instability in the CdP layers, associated with a soft mode behavior of a phonon in these layers. Raman scattering detects crystal electric field excitations, and confirms a singlet ground state for Pr$^{3+}$ and splitting of the doublet levels as a result of the structural instability in CdP layers. While Pr$^{3+}$ is non-magnetic in PrCd$_3$P$_3$ we speculate that this family of materials can realize control of the magnetic layer through the CdP layer which can become ferroelectric under strain that would relieve frustration.

cond-mat.mtrl-sci↗

arXiv2025

Tuning Charge Order in $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$X (X=Br, Cl) via Uniaxial Strain

In condensed matter physics, experimental control over material properties reflects a deep understanding of the underlying physics. In recent years, meaningful progress has been made towards a description of the physics of correlated electron systems, but examples of control of these systems remain rare. In this work, we confirm a phase diagram theoretically proposed for organic Mott insulators. We use $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$X (X=Br,Cl) (BEDT-TTF = bis(ethylenedithio)tetrathiafuvalene) materials as experimental realization of the proposed model and demonstrate the ability to tune them both ways across a phase border between a Mott insulator with a uniformly distributed charge and a charge ordered state through the application of uniaxial strain. We induce charge order at 33 K in the quantum dipole liquid material $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br through the application of tensile strain of 0.4% along the c-axis. We suppress charge order down to 10 K in $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Cl by applying a tensile strain of 1.6% along the b-axis. We use Raman scattering spectroscopy to probe the charge state through analysis of charge sensitive molecular vibrations and a low frequency mode of collective dipole fluctuations close to the phase border.

cond-mat.str-el↗

arXiv2024

Novel Dipole-Lattice coupling in the Quantum-Spin-Liquid Material $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$

A family of molecular Mott insulators on triangular lattice provided a few S=1/2 triangular quantum spin liquid candidates, with $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ being the most studied material of this group. The large number experimental works present a conflicting set of evidence, with some suggesting spin liquid behavior, while others point towards a valence bond solid with orphan spins. In this work we use Raman scattering spectroscopy to probe both local charge on molecular sites and lattice phonons as a function of temperature down to 6~K. Based on the analysis of the line shape of the BEDT-TTF charge sensitive vibration $\nu_2$ on cooling below 40 K, we suggest a development of disordered fluctuating charge disproportionation on (BEDT-TTF)$_2$ dimers of amplitude as small as 0.06$e$. The lattice phonons show strong anomalous broadening on cooling only in the (c,c) scattering channel, associated with the developing charge disproportionation. We suggest an interpretation, where the coupling of disordered charge dipoles on dimers to the lattice results in anisotropic modulation of charge transfer integrals between dimer lattice sites. Such fluctuations would result in modulation of magnetic coupling between spins which can produce fluctuating charge ordered spin-singlet pairs.

cond-mat.str-el↗

arXiv2023

Disorder-induced excitation continuum in a spin-1/2 cobaltate on a triangular lattice

A spin-1/2 triangular-lattice antiferromagnet is a prototypical frustrated quantum magnet, which exhibits remarkable quantum many-body effects that arise from the synergy between geometric spin frustration and quantum fluctuations. It can host quantum frustrated magnetic topological phenomena like quantum spin liquid (QSL) states, highlighted by the presence of fractionalized quasiparticles within a continuum of magnetic excitations. In this work, we use neutron scattering to study CoZnMo$_3$O$_8$, which has a triangular lattice of Jeff = 1/2 Co2+ ions with octahedral coordination. We found a wave-vector-dependent excitation continuum at low energy that disappears with increasing temperature. Although these excitations are reminiscent of a spin excitation continuum in a QSL state, their presence in CoZnMo$_3$O$_8$ originates from magnetic intersite disorder-induced dynamic spin states with peculiar excitations. Our results, therefore, give direct experimental evidence for the presence of a disorder-induced spin excitation continuum.

cond-mat.str-el↗

arXiv2023

Diffusive Excitonic Bands from Frustrated Triangular Sublattice in a Singlet-Ground-State System

Magnetic order in most materials occurs when magnetic ions with finite moments in a crystalline lattice arrange in a particular pattern below the ordering temperature determined by exchange interactions between the ions. However, when the crystal electric field (CEF) effect results in a spin-singlet ground state on individual magnetic sites, the collective ground state of the system can either remain non-magnetic, or more intriguingly, the exchange interactions between neighboring ions, provided they are sufficiently strong, can admix the excited CEF levels, resulting in a magnetically ordered ground state. The collective magnetic excitations in such a state are so-called spin excitons that describe the CEF transitions propagating through the lattice. In most cases, spin excitons originating from CEF levels of a localized single ion are dispersion-less in momentum (reciprocal) space and well-defined in both the magnetically ordered and paramagnetic states. Here we use thermodynamic and neutron scattering experiments to study stoichiometric Ni2Mo3O8 without site disorder, where Ni2+ ions form a bipartite honeycomb lattice comprised of two triangular lattices, with ions subject to the tetrahedral and octahedral crystalline environment, respectively. We find that in both types of ions, the CEF excitations have nonmagnetic singlet ground states, yet the material has long-range magnetic order. Furthermore, CEF spin excitons from the triangular-lattice arrangement of tetrahedral sites form, in both the antiferromagnetic and paramagnetic states, a dispersive diffusive pattern around the Brillouin zone boundary in reciprocal space. The present work thus demonstrates that spin excitons in an ideal triangular lattice magnet can have dispersive excitations, irrespective of the existence of static magnetic order, and this phenomenon is most likely due to spin entanglement and geometric frustrations.

cond-mat.str-el↗