arXiv subjects

Jarryd A. Horn

Publications and source records attributed to Jarryd A. Horn.

9 recordsLinked to original sources

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

Magnetocrystalline Anisotropy and 3D Hopping Conduction at the Surface of FeSb2

Motivated by the recent discovery of metallic surface states in the d-electron Kondo insulator candidates FeSi and FeSb2, along with some recent reports of magnetic correlations in the surface transport properties of FeSi, we have investigated the low temperature surface magnetotransport properties of FeSb2. By using a Corbino disk transport geometry, we were able to isolate the electrical transport properties of a single surface of our samples and study the [110] and [101] naturally forming faces separately. Studying the relationship between the applied magnetic field, current direction and crystal symmetry has allowed us to separate possible contributions to the magnetotransport anisotropy. Unlike previous studies of SmB6 surface states, we find no two-dimensional Drude-like dependence on field orientation relative to current direction, but instead a magnetocrystalline anisotropy that appears to originate from local moment scattering with a well defined easy-axis along the [100] direction. We compare these results with the magnetotransport properties of the conducting surface states on the [111] facet of FeSi. We also find evidence of 3D variable-range hopping conduction below the bulk-to-surface crossover, extending below 1 K, which implies that the electrical transport at the surface of these materials is carried by a thin, but 3D conducting channel, which is inconsistent with the lower dimensional states expected for a strong topological insulator.

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

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↗

arXiv2024

Probing $p$-wave superconductivity in UTe$_2$ via point-contact junctions

Uranium ditelluride (UTe$_2$) is the strongest contender to date for a $p$-wave superconductor in bulk form. Here we perform a spectroscopic study of the ambient pressure superconducting phase of UTe$_2$, measuring conductance through point-contact junctions formed by metallic contacts on different crystalline facets down to 250 mK and up to 18 T. Fitting a range of qualitatively varying spectra with a Blonder-Tinkham-Klapwijk(BTK) model for $p$-wave pairing, we can extract gap amplitude and interface barrier strength for each junction. We find good agreement with the data for a $p_y$ -wave gap function with amplitude in 0.26 $\pm$ 0.06 meV. Our work provides spectroscopic evidence for a gap structure consistent with the proposed spin-triplet pairing in the superconducting state of UTe$_2$.

cond-mat.supr-con↗

arXiv2024

Superconducting phase diagram in Bi$_x$Ni$_{1-x}$ thin films$\colon$ the effects of Bi stoichiometry on superconductivity

The Bi${-}$Ni binary system has been of interest due to possible unconventional superconductivity aroused therein, such as time-reversal symmetry breaking in Bi/Ni bilayers or the coexistence of superconductivity and ferromagnetism in Bi$_3$Ni crystals. While Ni acts as a ferromagnetic element in such systems, the role of strong spin-orbit-coupling element Bi in superconductivity has remained unexplored. In this work, we systematically studied the effects of Bi stoichiometry on the superconductivity of Bi$_x$Ni$_{1-x}$ thin films (${x} \approx$ 0.5 to 0.9) fabricated via a composition-spread approach. The superconducting phase map of Bi$_x$Ni$_{1-x}$ thin films exhibited a superconducting composition region attributable to the intermetallic Bi$_3$Ni phase with different amount of excess Bi, revealed by synchrotron X-ray diffraction analysis. Interestingly, the mixed phase region with Bi$_3$Ni and Bi showed unusual increases in the superconducting transition temperature and residual resistance ratio as more Bi impurities were included, with the maximum ${T}_{c}$ ($=$ 4.2 K) observed at $x \approx$ 0.79. A correlation analysis of structural, electrical, and magneto-transport characteristics across the composition variation revealed that the unusual superconducting $"$dome$"$ is due to two competing roles of Bi$\colon$ impurity scattering and carrier doping. We found that the carrier doping effect is dominant in the mild doping regime (0.74 $\leq {x} \leq$ 0.79), while impurity scattering becomes more pronounced at larger Bi stoichiometry.

cond-mat.supr-con↗

arXiv2023

Extraordinary Bulk Insulating Behavior in the Strongly Correlated Materials FeSi and FeSb$_2$

4$f$ electron-based topological Kondo insulators have long been researched for their potential to conduct electric current via protected surface states, while simultaneously exhibiting unusually robust insulating behavior in their interiors. To this end, we have investigated the electrical transport of the 3$d$-based correlated insulators FeSi and FeSb$_2$, which have exhibited enough similarities to their $f$ electron cousins to warrant investigation. By using a double-sided Corbino disk transport geometry, we show unambiguous evidence of surface conductance in both of these Fe-based materials. In addition, by using a 4-terminal Corbino inverted resistance technique, we extract the bulk resistivity as a function of temperature. Similar to topological Kondo insulator SmB$_6$, the bulk resistivity of FeSi and FeSb$_2$ are confirmed to exponentially increase by up to 9 orders of magnitude from room temperature to the lowest accessible temperature. This demonstrates that these materials are excellent bulk insulators, providing an ideal platform for studying correlated 2D physics.

cond-mat.str-el↗

arXiv2022

$c$-axis transport in UTe$_{2}$: Evidence of Three Dimensional Conductivity Component

We study the temperature dependence of electrical resistivity for currents directed along all crystallographic axes of the spin-triplet superconductor UTe$_{2}$. We focus particularly on an accurate determination of the resistivity along the $c$-axis ($ρ_c$) by using a generalized Montgomery technique that allows extraction of crystallographic resistivity components from a single sample. In contrast to expectations from the observed highly anisotropic band structure, our measurement of the absolute values of resistivities in all current directions reveals a surprisingly nearly isotropic transport behavior at temperatures above Kondo coherence, with $ρ_c \sim ρ_b \sim 2ρ_a$, that evolves to reveal qualitatively distinct behaviors on cooling. The temperature dependence of $ρ_c$ exhibits a peak at a temperature much lower than the onset of Kondo coherence observed in $ρ_a$ and $ρ_b$, consistent with features in magnetotransport and magnetization that point to a magnetic origin. A comparison to the temperature-dependent evolution of the scattering rate observed in angle-resolved photoemission spectroscopy experiments provides important insights into the underlying electronic structure necessary for building a microscopic model of superconductivity in UTe$_{2}$.

cond-mat.str-el↗

arXiv2021

Superconductivity in SrB3C3 clathrate

We predict superconductivity for the carbon-boron clathrate SrB3C3 at 27-43 K for Coulomb pseudopotential (mu*) values between 0.17 and 0.10 using first-principles calculations with conventional electron-phonon coupling. Electrical transport measurements, facilitated by a novel in situ experimental design compatible with extreme synthesis conditions (>3000 K at 50 GPa), show non-hysteretic resistivity drops that track the calculated magnitude and pressure dependence of superconductivity for mu*=0.15, and transport measurements collected under applied magnetic fields confirm superconductivity with an onset Tc of approximately 20 K at 40 GPa. Carbon-based clathrates thus represent a new class of superconductors similar to other covalent metals like MgB2 and doped fullerenes. Carbon clathrates share structures similar to superconducting superhydrides, but covalent C-B bonds allow metastable persistence at ambient conditions.

cond-mat.mtrl-sci↗