arXiv subjects

Eteri Svanidze

Publications and source records attributed to Eteri Svanidze.

11 recordsLinked to original sources

arXiv2026

Crystallographic imperfections and exotic superconductivity of UBe$_{13}$

The symmetry of the superconducting gap is related to the symmetry of the crystal structure. In unconventional superconductors, big changes of the critical temperature, critical field or even the gap structure can happen even for small perturbations of the lattice. In this letter, we use microstructuring to study aluminium-free crystals of UBe$_{13}$ which are expected to be closer to "perfect" material than previously studied aluminium-grown single crystals. We compare the effect of minuscule imperfections on the value of the critical temperature and critical field, which, in the case of UBe$_{13}$, has drastic effects, supporting its unconventional nature. We conjecture that this likely arises from the oxidation state of uranium, which is sensitive to its crystal environment. Our findings suggests that uranium-based materials provide not only an excellent reservoir of new unconventional phenomena, but also a way to identify the gap symmetry of unconventional superconductors.

cond-mat.supr-con↗

arXiv2026

Emergent Surface Kondo Flat Band Driven by Competing Interactions in a Topological Ferromagnet

A central goal of modern condensed matter physics is to uncover new quantum states of matter arising from the intertwined effects of strong electron correlations, magnetism, and band topology. Heavy-fermion phases, generated by Kondo interactions, represent one of the most remarkable manifestations of electronic correlations, and topological heavy-fermion states have been identified in several non-magnetic materials. Yet, the consequences of their competition with magnetic order have remained largely unexplored. Here, we reveal a new phenomenon: the spontaneous spatial separation of correlated quantum phases. By showing that magnetism can drive distinct strongly correlated electronic states to coexist in different regions of a single material, our work establishes a previously unknown mechanism for organizing quantum matter and opens a new direction in the study of correlated topological systems. Using \emph{bulk-sensitive} probes, we show that UAsS crystals are, in the bulk, metallic ferromagnets with only moderate correlation-driven band renormalizations. First-principles calculations reveal a topological electronic structure hosting both nodal lines and Weyl points, pointing to a rich underlying topology. Angle-resolved photoemission spectroscopy (ARPES) measurements are consistent with these predictions, resolving the nodal lines and Weyl crossings. In striking contrast, \emph{surface-sensitive} ARPES and scanning tunneling microscopy/spectroscopy (STM/STS) measurements reveal a pronounced flat band pinned at the Fermi level, accompanied by a sharp resonance -- hallmarks of an emergent, strongly correlated Kondo state not captured by first-principles calculations.

cond-mat.str-el↗

arXiv2026

Soft and chiral phonons in chiral phase of K3NiO2

Raman scattering measurements confirmed the theoretical prediction that the structural phase transition from the achiral tetragonal to the chiral tetragonal phase, which occurs near 400 K, is induced by a doubly degenerate soft phonon at the Z point of the Brillouin zone. In the low-temperature chiral phase, the soft mode activates in Raman spectra, splits into two components with A1 and B1 symmetries and harden with cooling according to Cochran law. Circularly polarized Raman scattering did not reveal the angular momentum of these singly degenerate phonons at the Gamma point, which is consistent with theory. We also calculated the phonon branches in the whole Brillouin zone for both crystalline phases and compared the results with the phonons observable in the Raman spectra. The calculations revealed that some phonons with nonzero k have angular momentum in the chiral phase. A pronounced circular motion of atoms can be observed, for example, in a Dirac-type topological phonon at the M-point of the Brillouin zone with a frequency of 168 cm-1.

cond-mat.mtrl-sci↗

arXiv2025

Anisotropy of the chiral, semiconducting phase LaRhC$_{2}$: a handedness resolved study

Chirality in quantum materials is a topic of significant importance due to its profound effects on the electronic, magnetic, and optical properties of these systems. However, it is non-trivial to decouple the behavior of two enantiomorphs within the same material -- perhaps explaining why the influence of chirality on electrical properties has remained largely unexplored. In this work, we examine the electrical conductivity, magnetoresistance, and thermal expansion coefficient of LaRhC$_{2}$ -- a compound with a chiral crystal structure (tetragonal symmetry, space groups $\textit{P}$4$_{1}$ or $\textit{P}$4$_{3}$). The identification of a suitable monochiral domain was achieved via electron backscatter diffraction, which simultaneously determines crystallographic orientation and handedness. Both enantiomorphs are confirmed by single-crystal X-ray diffraction on monochiral specimens. The analysis of electrical resistivity was made possible through the single-domain extraction of enantiopure specimens from a polycrystalline sample using focused ion beam techniques. We establish that LaRhC$_{2}$ is a semiconductor with band gaps of approximately 20 meV and 33 meV parallel and perpendicular to the fourfold screw axis of the crystal structure, respectively -- consistent with band structure calculations. A significant anisotropy is also observed in the thermal expansion, electrical resistivity as well as angular-dependent magnetoresistance parallel and perpendicular o [001] crystallographic directions.

cond-mat.mtrl-sci↗

arXiv2025

Unusual magnetic order in Eu$_{10}$Hg$_{55}$

In solid-state compounds, the valence of europium can sometimes be mixed -- which is especially favored in structures with several positions for the europium atoms. In this work, we study the Eu-based intermetallic noncentrosymmetric system Eu$_{10}$Hg$_{55}$ which has 65 atoms per unit cell and 4 distinct crystallographic positions for europium and 17 positions for mercury. Our detailed analysis of magnetism of large single crystals suggests that europium in Eu$_{10}$Hg$_{55}$ might be present in two valence states, resulting in a fragile magnetic ground state. Due to the cage-like structure with a large distance between the Eu atoms, those atoms are weakly ferromagnetically coupled and Eu$_{10}$Hg$_{55}$ orders at low temperatures, below $T_{1} = 5.5$ K, with a subsequent spin re-orientation at $T_{2} = 4.3$ K. There is no sign of magnetic frustration. Interestingly, the magnetic ordering of europium sub-lattices results in a magnetization pole reversal with a weak ferrimagnetic ground state. Additional magnetic phases can be induced by application of a modest external magnetic field.

cond-mat.mtrl-sci↗

arXiv2025

Emergent heavy-fermion physics in a new family of topological insulators RAsS (R = Y, La, and Sm)

Realizing topological phases in strongly correlated materials has become a major impetus in condensed matter physics. Although many compounds are now classified as topological insulators, $f$-electron systems (with their strong electron correlations) provide an especially fertile platform for emergent heavy-fermion phenomena driven by the interplay of topology and many-body effects. In this study, we examine the crystalline topology of a new RAsS series (R = Y, La, Sm), revealing a structural variant from previous reports. We demonstrate that YAsS and SmAsS host hourglass fermions protected by glide symmetry. SmAsS notably exhibits a strong effective-mass enhancement, placing it alongside SmB${}_6$ and YbB${}_{12}$ as a material that couples topological surface states with emergent Kondo physics, yet distinguished by its crystalline symmetry constraints and $f$-$p$ orbital hybridization. To capture these features, we construct a minimal model incorporating $f$-electron degrees of freedom, which reproduces the observed topological properties and predicts that the surface states survive in the correlated regime, albeit shifted in energy. Our work thus introduces a new family of correlated topological materials and forecasts the robustness of their surface states under Kondo correlations.

cond-mat.mtrl-sci↗

arXiv2025

Influence of pressure on properties of multi-gap type-I superconductor BeAu

We report on studies of the superconducting and normal state properties of the noncentrosymmetric superconductor BeAu under hydrostatic pressure conditions. The room-temperature equation of state (EOS) reveals the values of the bulk modulus ($B_0$) and its first derivative ($B^\prime_0$) at ambient pressure to be $B_0 \simeq 132$~GPa and $B^\prime_0 \simeq 30$, respectively. Up to the highest pressures studied ($p \simeq 2.2$~GPa), BeAu remains a multi-gap type-I superconductor. The analysis of $B_{\rm c}(T, p)$ data within the self-consistent two-gap approach suggests the presence of two superconducting energy gaps, with the gap-to-$T_{\rm c}$ ratios $Δ_1/k_{\rm B}T_{\rm c} \sim 2.3$ and $Δ_2/k_{\rm B}T_{\rm c} \sim 1.1$ for the larger and smaller gaps, respectively [$Δ= Δ(0)$ is the zero-temperature value of the gap and $k_{\rm B}$ is the Boltzmann constant]. With increasing pressure, $Δ_1/k_{\rm B}T_{\rm c}$ increases while $Δ_2/k_{\rm B}T_{\rm c}$ decreases, suggesting that pressure enhances (weakens) the coupling strength between the superconducting carriers within the bands where the larger (smaller) superconducting energy gap has opened. The superconducting transition temperature $T_{\rm c}$, \textcolor{black}{the zero-temperature values of the superconducting gaps $Δ_1$ and $Δ_2$} and the zero-temperature value of the thermodynamic critical field $B_{\rm c}(0)$ decrease with increasing pressure, with the rates of ${\rm d}T_{\rm c}/{\rm d}p \simeq -0.195$~K/GPa, \textcolor{black}{${\rm d}Δ_1/{\rm d}p \simeq -0.034$~meV/GPa, ${\rm d}Δ_2/{\rm d}p \simeq -0.029$~meV/GPa,} and ${\rm d}B_{\rm c}(0)/{\rm d}p = -2.65(1)$~mT/GPa, respectively. The measured $B_{\rm c}(0)$ values plotted as a function of $T_{\rm c}$ follow an empirical scaling relation established for conventional type-I superconductors.

cond-mat.supr-con↗

arXiv2024

Probing the superconducting pairing of the La$_{4}$Be$_{33}$Pt$_{16}$ alloy via muon-spin spectroscopy

We report a study of the superconducting pairing of the noncentrosymmetric La$_{4}$Be$_{33}$Pt$_{16}$ alloy using muon-spin rotation and relaxation ($μ$SR) technique. Below $T_c = 2.4$ K, La$_{4}$Be$_{33}$Pt$_{16}$ exhibits bulk superconductivity (SC), here characterized by heat-capacity and magnetic-susceptibility measurements. The temperature dependence of the superfluid density $ρ_\mathrm{sc}(T)$, extracted from the transverse-field {\textmu}SR measurements, reveals a nodeless SC in La$_{4}$Be$_{33}$Pt$_{16}$. The best fit of $ρ_\mathrm{sc}(T)$ using an $s$-wave model yields a magnetic penetration depth $λ_0 = 542$ nm and a superconducting gap $Δ_0 = 0.37$ meV at zero Kelvin. The single-gapped superconducting state is further evidenced by the temperature-dependent electronic specific heat $C_\mathrm{e}(T)/T$ and the linear field-dependent electronic specific-heat coefficient $γ_\mathrm{H}(H)$. The zero-field $μ$SR spectra collected in the normal- and superconducting states of La$_{4}$Be$_{33}$Pt$_{16}$ are almost identical, confirming the absence of an additional field-related relaxation and, thus, of spontaneous magnetic fields below $T_c$. The nodeless SC combined with a preserved time-reversal symmetry in the superconducting state prove that the spin-singlet pairing is dominant in La$_{4}$Be$_{33}$Pt$_{16}$. This material represents yet another example of a complex system showing only a conventional behavior, in spite of a noncentrosymmetric structure and a sizeable spin-orbit coupling.

cond-mat.supr-con↗

arXiv2020

The single- vs. two-gap scenario: the specific heat and the thermodynamic critical field of BeAu superconductor

The puzzling situation where some thermodynamic quantities require a single-gap description, while others need a more complex gap scenario, is discussed. Our approach reveals that in some cases, the conclusions based on measurements of only one thermodynamic quantity may lead to conflicting results. As an example, temperature evolutions of the electronic specific heat [$C_{\rm e}(T)$] and the thermodynamic critical field [$B_{\rm c}(T)$] of BeAu superconductor were reconsidered within the framework of the single-gap and the two-gap scenarios. The analysis shows that the single-gap approach describes the temperature dependencies of $C_{\rm e}(T)$ and the superfluid density $ρ_{\rm s}(T)$ satisfactorily. However it fails in the case of $B_{\rm c}(T)$. The self-consistent two-gap model, in contrast, is able to describe all of the mentioned thermodynamic quantities by using a similar set of parameters. Our results reveal that a proper description of the thermodynamic quantities, related to the superconducting pairing mechanism, requires the use of similar model containing the same set of parameters.

cond-mat.supr-con↗

arXiv2020

Multiple-gap response of type-I noncentrosymmetric BeAu superconductor

Precise measurements of the thermodynamic critical field ($B_{\rm c}$) in type-I noncentrosymmetric superconductor BeAu were performed by means of the muon-spin rotation/relaxation technique. The temperature evolution of $B_{\rm c}$ can not be described within the single gap scenario and it requires the presence of at least two different types of the superconducting order parameters. The self-consistent two-gap approach, adapted for analysis of $B_{\rm c}(T)$ behavior, suggests the presence of two superconducing energy gaps with the gap to $T_{\rm c}$ ratios $2Δ/k_{\rm B}T_{\rm c}\simeq4.52$ and $\simeq2.37$ for the big and the small gap, respectively. This implies that the superconductivity in BeAu is unconventional and that the supercarrier pairing occurs at various energy bands.

cond-mat.supr-con↗

arXiv2019

muSR and Magnetometry Study of the Type-I Superconductor BeAu

We present muon spin rotation and relaxation (muSR) measurements as well as demagnetising field corrected magnetisation measurements on polycrystalline samples of the noncentrosymmetric superconductor BeAu. From muSR measurements in a transverse field, we determine that BeAu is a type-I superconductor with Hc = 256 Oe, amending the previous understanding of the compound as a type-II superconductor. To account for demagnetising effects in magnetisation measurements, we produce an ellipsoidal sample, for which a demagnetisation factor can be calculated. After correcting for demagnetising effects, our magnetisation results are in agreement with our muSR measurements. Using both types of measurements we construct a phase diagram from T = 30 mK to Tc = 3.25 K. We then study the effect of hydrostatic pressure and find that 450 MPa decreases Tc by 34 mK, comparable to the change seen in type-I elemental superconductors Sn, In and Ta, suggesting BeAu is far from a quantum critical point accessible by the application of pressure.

cond-mat.supr-con↗