arXiv subjects

Felix Eder

Publications and source records attributed to Felix Eder.

7 recordsLinked to original sources

arXiv2026

Quasi-one-dimensional topological band structure and van Hove singularities in monolayer TaIrTe$_4$ from laser $\mu$-ARPES

Recent transport experiments reported a quantum spin Hall insulator phase in monolayer 1T-TaIrTe$_4$ gated away from charge neutrality. This phase is not predicted by band structure calculations and has been attributed to an electronic instability induced by strong correlations at a putative van Hove singularity. Here, we investigate the electronic structure of exfoliated monolayer 1T-TaIrTe$_4$ using micro-focus laser angle resolved photoemission. We find a strongly anisotropic band structure susceptible to density wave instabilities. Our data further reveal a saddle point singularity in the density of states. However, we find that the saddle point lies at a density for which transport experiments found no anomalies. Moreover, the quasiparticle line widths suggest weak electron correlations only. This points to a secondary role of van Hove singularities and electron correlations in the transport phase diagram of monolayer 1T-TaIrTe$_4$.

cond-mat.mtrl-sci↗

arXiv2026

In-Plane Ferromagnetism and Critical Dynamics in Alkali-Deficient K$_{1-x}$CrTe$_2$ (with $x \approx$ 0.3) Single Crystals

Layered chromium tellurides are model systems for studying low-dimensional magnetism in van der Waals materials. We report the synthesis and characterization of K$_{1-x}$CrTe$_2$ single crystals ($x \approx 0.3$), which crystallize in the $Cm$ space group with trigonal prismatic K$^+$ coordination, unlike the octahedral environments of more stoichiometric ACrX$_2$ compounds. Magnetization measurements show a sharp ferromagnetic transition at $T_{\rm C}=117$ K and in-plane magnetic anisotropy, supported by density functional theory. Neutron diffraction reveals ferromagnetic alignment of Cr spins within and between layers. This contrasts with the out-of-plane A-type antiferromagnetism in LiCrTe$_2$ and NaCrTe$_2$, but resembles CrTe$_2$. These differences likely arise from changes in interlayer spacing, Cr oxidation state, or stacking. AC susceptibility and $\mu$SR indicate short-range order above $T_{\rm C}$ and dynamic behavior below. Overall, K$_{1-x}$CrTe$_2$ provides a tunable platform for studying spin orientation and dimensionality in two-dimensional magnets.

cond-mat.mtrl-sci↗

arXiv2026

Metastable Cu$_{1-x}$CrTe$_2$ -- Completing the copper chromium delafossite series through soft chemistry

In the layered copper chromium dichalcogenide series CuCr$X_2$, the oxide, the sulfide, and the selenide analogues have been reported, but the telluride CuCrTe$_2$ has remained unsynthesized so far. Here, we report the synthesis of Cu$_{1-x}$CrTe$_2$ ($x \approx 0.3$), which forms only within a narrow temperature window near 90 {\deg}C by solvothermal cation exchange of K$_{1-x}$CrTe$_2$ ($x \approx 0.3$) and CuBr. Cu$_{1-x}$CrTe$_2$ undergoes a magnetostructural transition to an antiferromagnetic state at $T_\mathrm{N}=239$ K, a N\'eel temperature that is high relative to other $A$CrTe$_2$ phases and comparable to that of ferromagnetic, fully-deintercalated CrTe$_2$. Cu$_{1-x}$CrTe$_2$ is metastable and decomposes at temperatures as low as 250 {\deg}C to form spinel CuCr$_2$Te$_4$. These results highlight the importance of low-temperature topochemical routes for accessing metastable Cu(I)-containing tellurides that are inaccessible by conventional solid-state synthesis.

cond-mat.mtrl-sci↗

arXiv2026

Resolving growth-induced off-stoichiometry in AgCrSe$_2$ single crystals

The layered delafossite-like antiferromagnet AgCrSe$_2$ is a superionic conductor at high temperatures and has been reported to exhibit anomalous Hall behavior and Kondo physics at low temperatures. These extraordinary transport properties have been established almost exclusively on single crystals grown by chemical vapor transport, raising questions about the role of growth-induced off-stoichiometry. Using elemental analysis, single-crystal X-ray diffraction, and magnetization measurements, we show that such crystals are indeed systematically off-stoichiometric, with a general composition of Ag$_{1-x}$Cr(Se$_{2-y}$Cl$_y$) ($x \approx y \approx 0.08$) arising from the use of CrCl$_3$ as a transport agent. This off-stoichiometry manifests in altered magnetic properties, most notably a suppressed N\'{e}el temperature of 46\,K compared to 58\,K in stoichiometric polycrystalline samples prepared by solid-state synthesis. By optimizing an Ag/Se self-flux growth method, we obtained large single crystals of AgCrSe$_2$ that recover the magnetic transition temperature and saturation field of stoichiometric powder samples. These results establish self-flux growth as a route to high-quality stoichiometric AgCrSe$_2$ single crystals and provide a reliable platform for reassessing whether the reported anomalous transport phenomena are intrinsic or arise from off-stoichiometry.

cond-mat.mtrl-sci↗

arXiv2026

Ladder-like Structural Architecture of Layered Magnetic $A_{2.4}$Cr$_8$Te$_{14}$ ($A$ = Rb, Cs) Compounds by Self-flux Synthesis

The discovery and control of intergrowth structures represent an important avenue for the targeted synthesis of new, more complex structure types. When including magnetic framework metal atoms, this enhanced complexity can transfer to rich magnetic ground states. Here, we show that the subtle adjustment of the composition of alkali-tellurium fluxes enables the synthesis of a new family of alkali chromium tellurides, $A_{2.4}$Cr$_8$Te$_{14}$ ($A$ = Rb, Cs). Their ladder-like crystal structures integrate the two-dimensional character of delafossite-like $A$CrTe$_2$ with the tunnel motifs of hollandite-like $A_{x}$Cr$_5$Te$_8$ phases. This results in a previously unobserved unique hybrid framework. Direction-dependent magnetization measurements on oriented single crystals reveal distinct magnetic ground states: Rb$_{2.4}$Cr$_8$Te$_{14}$ is antiferromagnetic with $T_{\rm N}$ = 114.5 K, while Cs$_{2.4}$Cr$_8$Te$_{14}$ is ferrimagnetic with $T_{\rm C}$ = 125.0 K. This work underscores the simplicity and effectiveness of flux growth as a design strategy for discovering low-dimensional materials.

cond-mat.mtrl-sci↗

arXiv2025

Stoichiometry and Phase Control in K$_{1-x}$CrSe$_2$ via Self-Flux Synthesis

Layered delafossite-type magnetic materials, such as KCrSe$_2$, are promising platforms for studying magnetic systems and potential frustration on triangular lattices. Synthesis, structure-type control, and off-stoichiometries remain major challenges in the investigation of these delafossite-type magnets. Starting from the same self-flux composition (K:Cr:Se = 8:1:8), we isolated three distinct K$_{1-x}$CrSe$_2$ phases with $x$ = 0, 0.13--0.17, and 0.32--0.35, each adopting a different structure type depending on the quenching temperature applied. The phase evolution indicates a sequence of transformations during synthesis between compounds with varying degrees of potassium deficiency. Building on these insights into phase stability and crystal growth, we successfully grew single crystals of full-stoichiometric KCrSe$_2$ -- enabling direction-dependent magnetization measurements. These measurements reveal a pronounced field dependence of the N\'{e}el temperature at low external fields, as well as a weak metamagnetic transition. Our findings demonstrate that even a simple parameter -- such as quenching temperature -- can be used to control stoichiometry, direct phase formation, and ultimately tune the magnetic properties of delafossite-type materials.

cond-mat.mtrl-sci↗

arXiv2025

Structural Modulation and Enhanced Magnetic Ordering in Incommensurate K$_{1-{x}}$CrSe$_2$ Crystals

Layered delafossite-type compounds and related transition metal dichalcogenides, characterized by their triangular net structures, serve as prototypical systems for exploring the intricate interplay between crystal structure and magnetic behavior. Herein, we report on the discovery of the compound K$_{1-x}$CrSe$_2$ ($x \approx$ 0.13), an incommensurately modulated phase. Single crystals of this compound were grown for the first time using a K/Se self-flux. We find a monoclinic crystal structure with incommensurate modulation, that can be rationalized by a 3+1 dimensional model. This modulation compensates for the under-stoichiometry of K cations, creating pronounced undulations in the CrSe$_2$ layers. Our anisotropic magnetization measurements reveal that K$_{1-x}$CrSe$_2$ undergoes a transition to a long-range magnetically ordered state below $T_{\mathrm N}$ = 133 K, a temperature 1.6 to 3.3 times higher than in earlier reported KCrSe$_2$ compounds. Our findings open new avenues for tuning the magnetic properties of these layered materials through structural modulation.

cond-mat.mtrl-sci↗