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

Yun Suk Eo, Shouzheng Liu+14 more|arXiv (Cornell University)|Jan 8, 2021

Rare-earth and actinide compounds7 citations

TL;DR

This study measures the electrical resistivity of UTe₂ along all three crystallographic axes using a generalized Montgomery technique, revealing unexpectedly isotropic c-axis transport above Kondo coherence. The c-axis resistivity exhibits a distinct peak at ~10 K, indicating a magnetic scattering mechanism unrelated to Kondo screening, suggesting multiple transport channels and a magnetic crossover scale critical to understanding superconductivity in this spin-triplet material.

ABSTRACT

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$_{2}$.

Motivation & Objective

• To determine the absolute resistivity along all three crystallographic axes (a, b, c) in UTe₂ with high precision.
• To resolve the long-standing ambiguity in c-axis transport by applying a generalized Montgomery technique to a single crystal.
• To investigate the origin of anomalous resistivity behavior in the c-axis direction, particularly its deviation from expected anisotropy.
• To link resistivity anomalies to magnetic excitation spectra and scattering mechanisms via comparison with magnetotransport and ARPES data.
• To provide critical normal-state electronic structure data for building a microscopic theory of spin-triplet superconductivity in UTe₂.

Proposed method

• Employed a generalized Montgomery technique to extract individual resistivity components (ρₐ, ρ_b, ρ_c) from a single anisotropic crystal using four-terminal measurements with controlled current and voltage orientations.
• Measured temperature-dependent resistivity for currents along the a, b, and c axes using high-quality single crystals of UTe₂ grown via the floating-zone method.
• Conducted magnetotransport measurements at 14 T to probe field-dependent resistivity and extract magnetoresistance (MR) and magnetic susceptibility (ΔM/H) for H ∥ a and H ∥ b.
• Compared resistivity data with angle-resolved photoemission spectroscopy (ARPES) results to analyze temperature-dependent scattering rates.
• Analyzed magnetization and magnetic response data to identify energy scales associated with magnetic fluctuations.
• Used Curie-Weiss analysis to extract high-temperature magnetic susceptibility and assess antiferromagnetic interactions.

Experimental results

Research questions

• RQ1 Why does the c-axis resistivity (ρ_c) remain surprisingly high and isotropic with ρ_a and ρ_b despite strong electronic anisotropy in the band structure?
• RQ2 What causes the distinct peak in ρ_c at ~10 K, which occurs at a temperature much lower than the Kondo coherence temperature observed in ρ_a and ρ_b?
• RQ3 How do the c-axis transport properties differ qualitatively from those along the a- and b-axes, and what does this imply about the underlying transport channels?
• RQ4 What is the nature of the magnetic scattering mechanism responsible for the ρ_c peak, and how does it relate to the magnetic excitation spectrum?
• RQ5 How do the observed resistivity anomalies correlate with features in magnetization, magnetoresistance, and ARPES-derived scattering rates?

Key findings

• The c-axis resistivity ρ_c is found to be nearly isotropic with ρ_a and ρ_b at high temperatures, with ρ_c ≈ ρ_b ≈ 2ρ_a, contrary to expectations from the highly anisotropic band structure.
• ρ_c exhibits a pronounced peak at ~10 K, which is significantly lower than the Kondo coherence temperature (~30–40 K) observed in ρ_a and ρ_b.
• The peak in ρ_c coincides with minima in magnetoresistance (MR) and ΔM/H for H ∥ a, indicating a magnetic crossover scale near 10 K that dominates c-axis transport.
• The temperature dependence of ρ_c is inconsistent with Kondo screening and instead points to a non-Kondo-like magnetic scattering mechanism with an energy scale of ~10 K.
• The observed crossover is consistent with quantum critical scaling of magnetization (M/T ∝ H/T¹.⁵) and suggests a change in the fluctuation spectrum near 15 K.
• ARPES data show a temperature-dependent scattering rate that correlates with the ρ_c peak, supporting a link between electronic correlations and magnetic fluctuations in the normal state.