arXiv subjects

J. Noky

Publications and source records attributed to J. Noky.

3 recordsLinked to original sources

arXiv2025

Emergent Spin-Singlet Pairing in the Frustrated Kagome Metal Sc$_3$Mn$_3$Al$_7$Si$_5$

The metallic kagome compound Sc$_3$Mn$_3$Al$_7$Si$_5$ has attracted attention as a candidate platform where geometric frustration and itinerant electrons may cooperate to stabilize a quantum-disordered magnetic ground state. Here, we combine bulk thermodynamic probes, low-noise FIB-device transport, and comprehensive $^{55}$Mn Nuclear Magnetic Resonance (NMR) measurements to elucidate the low-temperature spin dynamics of this system. The bulk data reveal strongly reduced magnetic entropy, a negative magnetoresistance arising from spin scattering, and field-dependent transport indicates the spin fluctuations, while showing no signatures of long-range magnetic order. NMR provides a direct local view of the correlated Mn moments: the nuclear spin-spin relaxation $T_2$ exhibits a pronounced low-temperature enhancement driven by an indirect internuclear coupling through electronic spin fluctuations, whose temperature and distance dependence point to partially gapped low-energy spin excitations. The spin-lattice relaxation rate $T_1^{-1}$ displays a Hebel-Slichter-like coherence peak near \SI{10}{K}, coincident with the resistivity crossover and a subtle heat-capacity anomaly, indicating the formation of short-range spin-singlet correlations. Together, our results demonstrate that Sc$_3$Mn$_3$Al$_7$Si$_5$ hosts an unconventional correlated state dominated by frustrated, gapped spin dynamics, placing it among the rare metallic kagome systems proximate to a quantum spin liquid.

cond-mat.str-el↗

arXiv2021

Observation of pressure-induced Weyl state and superconductivity in a chirality-neutral Weyl semimetal candidate SrSi2

Quasi-particle excitations in solids described by the Weyl equation have attracted significant attention in recent years. Thus far, a wide range of solids that have been experimentally realized as Weyl semimetals (WSMs) lack either mirror or inversion symmetry. For the first time, in the absence of both mirror and inversion symmetry, SrSi2 has been predicted as a robust WSM by recent theoretical works. Herein, supported by first-principles calculations, we present systematic angle-resolved photoemission studies of undoped SrSi2 and Ca-doped SrSi2 single crystals. Our results show no evidence of the predicted Weyl fermions at the kz = 0 plane or the Fermi arcs on the (001) surface. With external pressure, the electronic band structure evolved and induced Weyl fermions in this compound, as revealed by first-principle calculations combined with electrical transport property measurements. Moreover, a superconducting transition was observed at pressures above 20 GPa. Our investigations indicate that the SrSi2 system is a good platform for studying topological transitions and correlations with superconductivity.

cond-mat.mtrl-sci↗

arXiv2020

Pressure tuning of the anomalous Hall effect in the chiral antiferromagnet Mn3Ge

We report on the pressure evolution of the giant anomalous Hall effect (AHE) in the chiral antiferromagnet Mn$_3$Ge. The AHE originating from the non-vanishing Berry curvature in Mn$_3$Ge can be continuously tuned by application of hydrostatic pressure. At room temperature, the Hall signal changes sign as a function of pressure and vanishes completely at $p=1.53$ GPa. Even though the Hall conductivity changes sign upon increasing pressure, the room-temperature saturation value of 23 ${\rm Ω^{-1}cm^{-1}}$ at 2.85 GPa is remarkably high and comparable to the saturation value at ambient pressure of about 40 ${\rm Ω^{-1}cm^{-1}}$. The change in the Hall conductivity can be directly linked to a gradual change of the size of the in-plane components of the Mn moments in the non-collinear triangular magnetic structure. Our findings, therefore, provide a route for tuning of the AHE in the chiral antiferromagnetic Mn$_3$Ge.

cond-mat.mtrl-sci↗