arXiv subjects

Eli Zoghlin

Publications and source records attributed to Eli Zoghlin.

13 recordsLinked to original sources

arXiv2026

Frustration induced dimensional reduction and coexistence of long and short-range magnetic order in NdCl$_{3}$

The phenomenon of frustration greatly enriches the accessible physics of quantum magnets. With this in mind we study the magnetism of NdCl$_{3}$ using a combination of bulk properties measurements and neutron scattering techniques. The low-temperature heat capacity reveals two magnetic transitions at $T_{N1}$ = 270 mK and $T_{N2}$ = 180 mK. However, much of the magnetic entropy is released above $T_{N1}$, manifesting as a broad peak centered at $T^{*} \approx$ 450 mK. Single crystal elastic neutron scattering reveals highly anisotropic magnetic diffuse scattering above $T_{N2}$, confirming that quasi-one-dimensional, short-range, antiferromagnetic order is the origin of the broad peak in the heat capacity. Magnetic Bragg peaks characterized by a $\vec{k}$ = ($0$ $0$ $\frac{1}{2}$) propagation vector emerge below $T_{N1}$. Interestingly, the magnetic diffuse scattering persists for $T_{N2} < T < T_{N1}$, indicating a regime of coexisting short and long-range order. The magnetic Bragg peaks exhibit an additional increase in intensity below $T_{N2}$ with no change in $\vec{k}$. Concomitantly, the diffuse scattering disappears indicating the attainment of full long-range order. While the precise nature of the ordered magnetic ground state remains unresolved, the observed magnetic scattering indicates predominate $c$-axis moments with a small $ab$-plane component. We propose that the quasi-one-dimensional behavior and the coexistence of short and long-range order are driven by frustration of anisotropic exchange interactions.

cond-mat.str-el↗

arXiv2025

Probing scattering of Raman phonons on magnetic and electronic excitations in pyrochlores Nd$_2$Zr$_2$O$_7$ and Nd$_2$Ir$_2$O$_7$

Magnetic rare earth atoms on pyrochlore lattice can produce such exotic magnetic states as spin ice and quantum spin ice. These states are a result of the frustration in the pyrochlore lattice, as well as crystal field degrees of freedom of rare earth atoms, and their interactions with the lattice. Raman scattering spectroscopy, which possess high spectral resolution and can easily access broad energy and temperature ranges, is an optimum tool to study these excitations and their interactions. In this work we follow Raman scattering of zone center phonons and crystal field excitations of Nd$^{3+}$ in Nd$_2$Zr$_2$O$_7$ and Nd$_2$Ir$_2$O$_7$ in the temperature range where these materials are paramagnetic. A comparison between an insulating Nd$_2$Zr$_2$O$_7$ and semimetallic Nd$_2$Ir$_2$O$_7$ materials allow us to distinguish between scattering of phonons on other phonons, crystal field excitations, and electrons, highlighting interactions between these degrees of freedom.

cond-mat.str-el↗

arXiv2025

Real-space orbital tiling approach for the design of novel superconductors

Despite substantial advances in the field, we still lack a predictive framework capable of guiding the discovery of new families of superconductors. While momentum-space approaches have advanced the microscopic understanding of superconductivity, they offer limited guidance for materials design based on atomic building blocks. Here, we propose a real-space framework which conceptualizes Cooper pairs as confined standing waves resulting from coherent tilings of atomic orbitals. We call this model the Real-space Orbital Superconducting Pathway (ROSP). Using a tight-binding toy model, we show that the energetics of electron pairing depend on the configuration and overlap of real-space orbitals, which motivates \textit{a priori} design of superconducting families from orbital tiling. We connect the ROSP model to Roald Hoffmann's isolobal analogy to classify families of superconductors based on shared orbital tilings, rather than structure or electron count. As an example, we suggest that superconductivity in La$_{3}$Ni$_{2}$O$_{7}$ and LaNiO$_{2}$, despite differing structures and electron counts, may arise from a common ROSP. We introduce a new notation to classify two-dimensional square-net ROSPs and further propose several new families of superconductors on the anti-cuprate lattice. This framework provides a new model for predicting and designing families of high-T$_c$ superconductors from real-space orbital architecture, even without microscopic knowledge of the attractive pairing interaction.

cond-mat.supr-con↗

arXiv2025

Growth of hexagonal BN crystals by traveling-solvent floating zone

Large, high-purity single-crystals of hexagonal BN (h-BN) are essential for exploiting its many desirable and interesting properties. Here, we demonstrate via X-ray tomography, X-ray diffraction and scanning electron microscopy that h-BN crystals can be grown by traveling-solvent floating-zone (TSFZ). The diameters of grown boules range from 3 - 5 mm with lengths from 2 - 10 mm. Tomography indicates variable grain sizes within the boules, with the largest having areas of $\approx$ 1 mm $\times$ 2 mm and thickness $\approx$ 0.5 mm. Although the boules contain macroscale flux inclusions, the h-BN lattice itself is of high quality for samples grown under optimized conditions. The currently optimized growth procedure employs an Fe flux, moderate N$_2$ pressure ($P_{N2} \approx$ 6 bar), and a growth rate of 0.1 mm/h. Raman spectroscopy for an optimized sample gives an average linewidth of 7.7(2) cm$^{-1}$ for the E$_{\mathrm{2g}}$ intralayer mode at 1365.46(4) cm$^{-1}$ and 1.0(1) cm$^{-1}$ for the E$_{\mathrm{2g}}$ interlayer shear mode at 51.78(9) cm$^{-1}$. The corresponding photoluminescence spectrum shows sharp phonon-assisted free exciton peaks and minimal signal in the energy range corresponding to carbon-related defects ($E$ = 3.9 4.1 eV). Our work demonstrates the viability of growing h-BN by the TSFZ technique, thereby opening a new route towards larger, high-quality crystals and advancing the state of h-BN related research.

cond-mat.mtrl-sci↗

arXiv2024

Quasi-one-dimensional exchange interactions and short-range magnetic correlations in CuTeO4

CuTeO4 has been proposed as a crystallographically distinct, yet electronic structure analog, of the superconducting cuprates. Here, we present detailed characterization of the of the physical properties of CuTeO4 to address this proposal. Fitting of magnetic susceptibility data indicates unexpected quasi-one-dimensional, antiferromagnetic correlations at high temperature, with a nearest neighbour Heisenberg exchange of J1=165(4) K. Low temperature heat capacity measurements reveal a sizable T-linear contribution of $γ= 9.58(8) mJ mol^{-1} K^{-2}$, qualitatively consistent with expectations for a S=1/2, uniform, Heisenberg spin chain. Below T ~ 40 K, the susceptibility shows an upturn inconsistent with quasi-one-dimensional behaviour. While heat capacity measurements show no signs of magnetic order down to low temperature, the upturn in the magnetic susceptibility coincides with the emergence of a diffuse peak (centered at |Q| ~ 0.7 Angstrom) in the neutron diffraction data, indicative of persistent, short-range, antiferromagnetic order with a correlation length of $ξ$ = 10.1(9) Angstrom at T = 10 K. The onset of nonlinearity and hysteresis in the isothermal magnetization curves suggest the presence of a small ferromagnetic component. This persistent, short-range order is understood in the context of structural modeling of the x-ray and neutron diffraction data that show the presence of a significant density of stacking faults. No evidence for substantive dopability is observed and CuTeO4 appears qualitatively, to have a larger band gap than predicted by density functional theory. We ascribe this finding to the inductive withdrawal effect from high-valence Te and suggest that superconductivity in the copper tellurates is more likely to be found in compounds with a decreased reductive withdrawal effect from Te.

cond-mat.str-el↗

arXiv2024

Hydroflux-Controlled Growth of Magnetic K-Cu-Te-O(H) Phases

Innovative synthetic approaches can yield new phases containing novel structural and magnetic motifs. In this work, we show the synthesis and magnetic characterization of three new and one previously reported layered phase in the K-Cu-Te-O(H) phase space using a tunable hydroflux technique. The hydroflux, with a roughly equal molar ratio of water and alkali hydroxide, is a highly oxidizing, low melting solvent which can be used to isolate metastable phases unattainable through traditional solid state or flux techniques. The newly synthesized phases, K$_{2}$Cu$_{2}$TeO$_{6}$, K$_{2}$Cu$_{2}$TeO$_{6}$ $\cdot$ H$_{2}$O, and K$_{6}$Cu$_{9}$Te$_{4}$O$_{24}$ $\cdot$ 2 H$_{2}$O, contain Cu$^{2+}$ within CuO$_{4}$ square planar plaquettes and TeO$_{6}$ octahedra ordering to form structural honeycomb layers isolated by interlayer K$^{+}$ ions and H$_{2}$O molecules. We find the synthesized structures display varying tilt sequences of the CuO$_{4}$ plaquettes, leading to distinct Cu$^{2+}$ magnetic motifs on the structural honeycomb lattice and a range of effective magnetic dimensionalities. We find that K$_{2}$Cu$_{2}$TeO$_{6}$ $\cdot$ H$_{2}$O does not order and displays alternating chain Heisenberg antiferromagnetic (AFM) behavior, while K$_{2}$Cu$_{2}$TeO$_{6}$ and K$_{6}$Cu$_{9}$Te$_{4}$O$_{24}$ $\cdot$ 2 H$_{2}$O order antiferromagnetically (T$_{N}$ = 100 K and T$_{N}$ = 6.5 K respectively). The previously known phase, K$_{2}$CuTeO$_{4}$(OH)$_{2}$ $\cdot$ H$_{2}$O, we find contains structurally and magnetically one-dimensional CuO$_{4}$ plaquettes leading to uniform chain Heisenberg AFM behavior and shows no magnetic order down to T = 0.4 K. We discuss and highlight the usefulness of the hydroflux technique in novel syntheses and the interesting magnetic motifs that arise in these particular phases.

cond-mat.str-el↗

arXiv2024

Advances in high-pressure laser floating zone growth: the Laser Optical Kristallmacher II

The optical floating zone crystal growth technique is a well-established method for obtaining large, high-purity single crystals. While the floating zone method has been constantly evolving for over six decades, the development of high-pressure (up to 1000 bar) growth systems has only recently been realized via the combination of laser-based heating sources with an all-metal chamber. While our inaugural high-pressure laser floating zone furnace design demonstrated the successful growth of new volatile and metastable phases, the furnace design faces several limitations with imaging quality, heating profile control, and chamber cooling power. Here, we present a second-generation design of the high-pressure laser floating zone furnace, "Laser Optical Kristallmacher II" (LOKII), and demonstrate that this redesign facilitates new advances in crystal growth by highlighting several exemplar materials: $α$-Fe$_2$O$_3$, $β$-Ga$_2$O$_3$, and La$_2$CuO$_{4+δ}$. Notably, for La$_2$CuO$_{4+δ}$, we demonstrate the feasibility and long-term stability of traveling solvent floating zone growth under a record pressure of 700 bar.

physics.app-ph↗

arXiv2023

Refined Spin Wave Model and Multi-magnon Bound States in $Li_{2}CuO_{2}$

Here we report a study of the spin dynamics in the ferromagnetic chain compound $Li_{2}CuO_{2}$. Inelastic neutron scattering measurements allow for the spin Hamiltonian to be determined using a $J_{1}-J_{2}$ $XXZ$-Heisenberg spin chain model with weak interchain interactions. The primary exchange parameters determined from our data are qualitatively consistent with those of Lorenz $et$ $al.$ [Europhys. Lett. 88, 37002 (2009)], and our data allow for the resolution of additional interchain exchange interactions. We also observe the formation of two- and, potentially, three-magnon bound states. The two-magnon bound state exists only in the magnetically ordered phase of this material, consistent with stabilization by the weak, Ising-like exchange anisotropy of the nearest-neighbor intrachain interaction. In contrast, the potential three-magnon state persists in a finite temperature regime above $T_{N}$, indicating an unconventional character. Our results establish $Li_{2}CuO_{2}$ as an experimental platform for the study of exchange anisotropy-stabilized bound states in a ferromagnetic chain.

cond-mat.str-el↗

arXiv2021

Band Splitting and Long-lived Carrier Recombination in Ferromagnetic CrSiTe3 Nanosheets

Magnetic layered ternary chalcogenides hold great promise for future spin-optoelectronic devices in the two dimensional limit. Understanding how the properties of the materials are impacted by magnetic ordering and the spin-orbit interactions is critically needed information for the development of applications. Ultrafast transient reflectance (TR) and photocurrent (PC) spectroscopies are combined with ab initio density functional theory (DFT) calculations to investigate the band structure and photoresponse of a layered magnetic semiconductor CrSiTe3 (CST) nanosheet in the paramagnetic (PM, 300K) and ferromagnetic (FM, 10 K) phases. We observe both a decrease of the direct bandgap and emergence of a 120 meV splitting of the optical transition when the FM phase is present. DFT band structure calculations suggest that the band modifications are driven by a FM ordering-induced band splitting between the Te p and the Cr d states at the valence and conduction band edges. We find that the majority of carriers photoexcited at the direct gap recombine within picoseconds through defect-mediated recombination, but that 2-3 % of the electrons scatter into indirect conduction band valleys resulting in very long-lived electrons and holes. Those long-lived carriers contribute to the broadband PC response of CST devices that also features indirect absorption. These results provide critical insights into the dynamics and energy landscape of photoexcited electrons and holes, and how they are impacted by spin-ordering effects in layered ferromagnets.

cond-mat.mtrl-sci↗

arXiv2021

Evaluating the Effects of Structural Disorder on the Magnetic Properties of Nd$_{2}$Zr$_{2}$O$_{7}$

Motivated by the variation in reported lattice parameters of floating-zone-grown Nd$_{2}$Zr$_{2}$O$_{7}$ crystals, we have performed a detailed study of the relationship between synthesis environment, structural disorder, and magnetic properties. Using a combination of polycrystalline standards, electron-probe microanalysis and scattering techniques, we show that crystals grown under atmospheric conditions have a reduced lattice parameter - relative to pristine polycrystalline powders - due to occupation of the Nd-site by excess Zr (i.e. "negative" stuffing). In contrast, crystals grown under high-pressure Ar are nearly stoichiometric with an average lattice parameter approaching the polycrystalline value. While minimal disorder of the oxygen sublattices is observed on the scale of the average structure, neutron pair-distribution function analysis indicates a highly local disorder of the oxygen coordination, which is only weakly dependent on growth environment. Most importantly, our magnetization, heat capacity and single-crystal neutron scattering data show that the magnetic properties of crystals grown under high-pressure Ar match closely with those of stoichiometric powders. Neutron scattering measurements reveal that the signature of magnetic moment fragmentation - the coexistence of all-in-all-out (AIAO) magnetic Bragg peaks and diffuse pinch-point scattering due to spin-ice correlations - persists in these nearly stoichiometric crystals. However, in addition to an increased AIAO transition temperature, the diffuse signal is seemingly stabilized and remains nearly unchanged upon warming to 800 mK. This behavior indicates that both the AIAO magnetic order and spin-ice correlations are sensitive to deviations of the Nd stoichiometry.

cond-mat.mtrl-sci↗

arXiv2019

Evolution of structure and magnetism across the metal-insulator transition in the pyrochlore iridate $($Nd$_{1-x}$Ca$_x)_2$Ir$_2$O$_7$

We report on the evolution of the thermal metal-insulator transition in polycrystalline samples of Nd$_2$Ir$_2$O$_7$ upon hole-doping via substitution of Ca$^{2+}$ for Nd$^{3+}$. Ca substitution mediates a filling-controlled Mott-like transition with minimal resolvable structural changes and without altering site symmetry. Local structure confirms that Ca substitution does not result in local chemical phase separation, and absorption spectroscopy establishes that Ir cations maintain a spin-orbit entangled electronic configuration. The metal-insulator transition coincides with antiferromagnetic ordering on the Ir sublattice for all measured samples, and both decrease in onset temperature with Ca content. Weak low-temperature upturns in susceptibility and resistivity for samples with high Ca content suggest that Nd sublattice antiferromagnetism continues to couple to carriers in the metallic regime.

cond-mat.mtrl-sci↗

arXiv2019

High-Pressure Laser Floating Zone Furnace

The floating zone technique is a well-established single crystal growth method in materials research, able to produce volumetrically large specimens with extremely high purities. However, traditional furnace designs have relied on heating from high-powered bulb sources in combination with parabolic mirrors, and hence are constrained to transparent growth chambers with large solid angles of optical access. This results in a stark limitation on achievable processing gas pressures, and in turn renders a range of compounds unsuitable for crystal growth by the floating zone technique, either due to excessive volatility or due to metastability. Here, we demonstrate a novel high-pressure laser-based floating zone system (HP-LFZ). The use of lasers for heating allows implementation of a high-strength metal growth chamber, permitting greatly enhanced processing pressures over conventional mirror-based designs, with the current design allowing for pressures up to 1000 bar. We demonstrate a series of example single crystal growths using this design in pressures up to 675 bar, a significant increase over processing pressures attainable in commercially available floating zone systems. The general utility of the HP-LFZ is also illustrated via growths of a range of complex oxides.

cond-mat.mtrl-sci↗

arXiv2018

Unidirectional spin density wave state in metallic (Sr1-xLax)2IrO4

Materials that exhibit both strong spin orbit coupling and electron correlation effects are predicted to host numerous new electronic states. One prominent example is the Jeff =1/2 Mott state in Sr2IrO4, where introducing carriers is predicted to manifest high temperature superconductivity analogous to the S=1/2 Mott state of La2CuO4. While bulk superconductivity currently remains elusive, anomalous quasi-particle behaviors paralleling those in the cuprates such as pseudogap formation and the formation of a d-wave gap are observed upon electron-doping Sr2IrO4. Here we establish a magnetic parallel between electron-doped Sr2IrO4 and hole-doped La2CuO4 by unveiling a spin density wave state in electron-doped Sr2IrO4. Our magnetic resonant x-ray scattering data reveal the presence of an incommensurate magnetic state reminiscent of the diagonal spin density wave state observed in the monolayer cuprate (La1-xSrx)2CuO4. This link supports the conjecture that the quenched Mott phases in electron-doped Sr2IrO4 and hole-doped La2CuO4 support common competing electronic phases.

cond-mat.mtrl-sci↗