arXiv subjects

Keenan E. Avers

Publications and source records attributed to Keenan E. Avers.

5 recordsLinked to original sources

arXiv2026

Non-Fermi liquid behavior in La$_3$Ni$_2$O$_7$ thin films under hydrostatic pressure

The discovery of superconductivity in bilayer nickel-oxides has revived an intense effort to understand the potential of high-temperature superconductivity in these materials and their relation to cuprate superconductors. In this work, we investigate the growth and properties of bilayer La$_3$Ni$_2$O$_7$ thin films as a function of substrate, oxygen treatment and applied pressure in order to study the evolution of transport properties. We report epitaxial growth of La$_3$Ni$_2$O$_7$ thin films on LaAlO$_3$ (LAO) (001) and SrLaAlO$_4$ (SLAO) (001) substrates, and the effects of ex-situ annealing in a high pressure furnace under an oxygen-rich environment. Transport measurements show that the La$_3$Ni$_2$O$_7$ thin films on LAO(001) exhibit Fermi liquid-like metallic behavior with a slight Kondo-like upturn at low temperatures, which evolves with the application of modest hydrostatic pressures toward non-Fermi liquid behavior with a temperature dependence of resistance approaching $\sim$ T$^{1.4}$ at 1.41 GPa. The ability to tune the normal state resistivity of La$_3$Ni$_2$O$_7$ films to display non-Fermi liquid behavior under such a modest hydrostatic pressure range - only 6 - 8 % of that typically applied via diamond anvil cell (DAC) in La$_3$Ni$_2$O$_7$ single crystals to achieve comparable effects - is both noteworthy and unexpected. These findings imply the strong tunability of La$_3$Ni$_2$O$_7$ in thin film form and the likely proximity of a strongly fluctuating ordered state leading to non-Fermi liquid behavior under even modest applied pressures.

cond-mat.str-el↗

arXiv2026

Anisotropic magnetism at the surface of a non-magnetic bulk insulator

The potential for topological Kondo insulating behavior in d-electron systems has attracted interest in studying the surface states of the correlated insulators FeSb2 and FeSi. While detailed studies and theoretical description of a spin-orbit coupled ferromagnetic surface state have been applied to FeSi, the magnetic properties of the surface states of FeSb2 have not been addressed. Here, we report on the surface magnetic properties of FeSb2, utilizing the surface area dependence of magnetic susceptibility to separate the surface Curie-Weiss temperature dependence from the bulk spin-gap susceptibility. We use these results to further extract the surface magnetic anisotropy of a thin, rough-surfaced single-crystal FeSb2 to compare with the observed magnetotransport anisotropy, and find good agreement between the anisotropy in the surface magnetization and surface magnetotransport. We conclude with evidence of an anomalous Hall contribution to the low-temperature surface transport.

cond-mat.str-el↗

arXiv2025

Dilute Paramagnetism and Non-Trivial Topology in Quasicrystal Approximant Fe$_4$Al$_{13}$

A very fundamental property of both weakly and strongly interacting materials is the nature of its magnetic response. In this work we detail the growth of crystals of the quasicrystal approximant Fe$_4$Al$_{13}$ with an Al flux solvent method. We characterize our samples using electrical transport and heat capacity, yielding results consistent with a simple non-magnetic metal. However, magnetization measurements portray an extremely unusual response for a dilute paramagnet and do not exhibit the characteristic Curie-Weiss behavior expected for a weakly interacting material at high temperature. Electronic structure calculations confirm metallic behavior, but also indicate that each isolated band near the Fermi energy hosts non-trivial topologies including strong, weak and nodal components, with resultant topological surface states distinguishable from bulk states on the (001) surface. With half-filled flat bands apparent in the calculation but absence of long-range magnetic order, the unusual paramagnetic response suggests the dilute paramagnetic behavior in this quasicrystal approximant is surprising and may serve as a test of the fundamental assumptions that are taken for granted for the magnetic response of weakly interacting systems.

cond-mat.str-el↗

arXiv2024

Quasi-two-dimensional Antiferromagnetic Spin Fluctuations in the Spin-triplet Superconductor Candidate CeRh$_2$As$_2$

The tetragonal heavy-fermion superconductor CeRh$_2$As$_2$ ($T_{\rm c}=0.3$ K) exhibits an exceptionally high critical field of 14 T for $\textbf{B} \parallel \textbf{c}$. It undergoes a field-driven first-order phase transition between superconducting (SC) states, potentially transitioning from spin-singlet to spin-triplet superconductivity. To elucidate the underlying pairing mechanism, we probe spin fluctuations in CeRh$_2$As$_2$ using neutron scattering. We find dynamic $(π,π)$ antiferromagnetic spin correlations with an anisotropic quasi-two-dimensional correlation volume. Our data place an upper limit of 0.31 $μ_{\rm B}$ on the staggered magnetization of corresponding Néel orders at $T=0.08$ K. Density functional theory (DFT) calculations, treating Ce $4f$ electrons as core states, show that the AFM wave vector connects significant areas of the Fermi surface. Our findings show the dominant excitations in CeRh$_2$As$_2$ for $\hbarω< 1.2$~meV are magnetic and indicate superconductivity in CeRh$_2$As$_2$ is mediated by AFM spin fluctuations associated with a proximate quantum critical point.

cond-mat.str-el↗

arXiv2024

Disordered 2D ferromagnetism at the surface of FeSi

FeSi is a curious example of a $d$-electron system that manifests many of the same phenomena associated with $f$-electron Kondo insulators, including conducting surface states with potentially non-trivial topology. Here we investigate the magnetization and magnetotransport of these surface states and how a 2D ferromagnetic state at the surface of FeSi influences the surface conductivity. We confirm the 2D ferromagnetism via a systematic study of magnetization on groups of filtered fragments with increasing surface area-to-volume ratios, identifying characteristic temperatures and magnetic fields associated with the ordered state. The paramagnetic to ferromagnetic transition appears broadened, suggesting disorder, which allows spin fluctuations to manifest up to at least 9 T at 2 K. This highlights the need to understand the relation between the disorder of the 2D ferromagnetism and the surface conductivity in FeSi.

cond-mat.str-el↗