Quasi-Two-Dimensional Antiferromagnetic Spin Fluctuations in the Spin-Triplet Superconductor Candidate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>CeRh</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>As</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math>

Abstract

The tetragonal heavy-fermion superconductor ${\mathrm{CeRh}}_{2}{\mathrm{As}}_{2}$ (${T}_{\mathrm{c}}=0.3\text{ }\text{ }\mathrm{K}$) exhibits an exceptionally high critical field of 14 T for $\mathbf{B}\ensuremath{\parallel}\mathbf{c}$. It undergoes a field-driven first-order phase transition between superconducting states, potentially transitioning from spin-singlet to spin-triplet superconductivity. To further understand these superconducting states and the role of magnetism, we probe spin fluctuations in ${\mathrm{CeRh}}_{2}{\mathrm{As}}_{2}$ using neutron scattering. We find dynamic $(\ensuremath{\pi},\ensuremath{\pi})$ antiferromagnetic (AFM) spin correlations with an anisotropic quasi-two-dimensional correlation volume. Our data place an upper limit of $0.31\text{ }\text{ }{\ensuremath{\mu}}_{\mathrm{B}}$ on the staggered magnetization of corresponding N\'eel orders at $T=0.08\text{ }\text{ }\mathrm{K}$. Density functional theory calculations, treating Ce $4f$ electrons as core states, show that the AFM wave vector connects significant areas of the Fermi surface. Our findings indicate that the dominant excitations in ${\mathrm{CeRh}}_{2}{\mathrm{As}}_{2}$ for $\ensuremath{\hbar}\ensuremath{\omega}&lt;1.2\text{ }\text{ }\mathrm{meV}$ are magnetic and suggest that superconductivity in ${\mathrm{CeRh}}_{2}{\mathrm{As}}_{2}$ is mediated by AFM spin fluctuations associated with a proximate quantum critical point.

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