The upper critical field and its anisotropy in RbCr$_{3}$As$_{3}$

TL;DR

This study investigates the temperature dependence and anisotropy of the upper critical field in RbCr₃As₃ single crystals, revealing high critical fields exceeding the Pauli limit and anisotropic pair-breaking effects.

Contribution

The paper provides detailed measurements of $H_{c2}$ anisotropy in RbCr₃As₃, showing how the critical fields surpass the BCS limit and differ with magnetic field orientation, highlighting strong paramagnetic effects.

Findings

$H_{c2}$ exceeds the Pauli limit for both directions.

Anisotropy parameter $b (b=H_{c2}^{ot c}/H_{c2}^{\u03c4 c})$ increases from 0.5 to 1.6 as temperature decreases.

Paramagnetic pair breaking is significant for $H \uparrow c$ but negligible for $H \uparrow b c$.

Abstract

The temperature dependence of the upper critical field ($H_{c2}$) in RbCr$% _{3}$As$_{3}$ single crystals ($T_{c}\approx $ 7.3 K) has been determined by means of magnetoresistance measurements with temperature down to 0.35 K in static magnetic fields up to 38 T. The magnetic field was applied both for directions parallel ($H\parallel c $, $H_{c2}^{\parallel c}$) and perpendicular ($H\perp c$, $H_{c2}^{\perp c}$) to the Cr chains. The curves $H_{c2}^{\parallel c}(T)$ and $H_{c2}^{\perp c}(T)$ cross at $\sim $ 5.5 K. As a result, the anisotropy parameter $\gamma (T)=H_{c2}^{\perp c}/H_{c2}^{\parallel c}(T)$ increases from 0.5 near $T_{c}$ to 1.6 at low temperature. Fitting with the Werthamer-Helfand-Hohenberg (WHH) model yields zero-temperature critical fields of $\mu_0H_{c2}^{\parallel c}(0)\approx $ 27.2 T and $\mu_0H_{c2}^{\perp c}(0)\approx $ 43.4 T, both exceeding the BCS weak-coupling Pauli limit $\mu_0H_{p}=1.84T_{c}=13.4$ T. The results indicate that the paramagnetic pair breaking effect is strong for $H \parallel c$ but absent for $H \perp c$, which was further confirmed by the angle dependent magnetoresistance and $H_{c2}$ measurements.