Quantum oscillations and anisotropic magnetoresistance in the quasi-two-dimensional Dirac nodal line superconductor $\mathrm{YbSb_2}$

TL;DR

The paper addresses the challenge of finding materials that host non-trivial band topology together with superconductivity in a type I system. It combines AMR, quantum oscillations (SdH and dHvA), DFT+U calculations, Wannier reconstruction, and ARPES to map the normal-state Fermi surface of YbSb2 and identify Dirac nodal-line pockets. The results show multiple Dirac nodal-line-derived Fermi pockets and a magnetic-breakdown orbit; angle-resolved measurements reveal non-monotonic AQO and AMR that reflect a complex, quasi-two-dimensional Fermi-surface morphology, with experimental frequencies aligning well with DFT predictions. The findings establish YbSb2 as a promising platform to explore the interplay between band topology and superconductivity in a type I material, with implications for realizing unconventional or topological superconducting states.

Abstract

Recent interest in quantum materials has focused on systems exhibiting both superconductivity and non-trivial band topology as material candidates to realize topological or unconventional superconducting states. So far, superconductivity in most topological materials has been identified as type II. In this work, we present magnetotransport studies on the quasi-two-dimensional type I superconductor $\mathrm{YbSb_2}$. Combined ab initio DFT calculations and quantum oscillation measurements confirm that $\mathrm{YbSb_2}$ is a Dirac nodal line semimetal in the normal state. The complex Fermi surface morphology is evidenced by the non-monotonic angular dependence of both the quantum oscillation amplitude and the magnetoresistance. Our results establish $\mathrm{YbSb_2}$ as a candidate material platform for exploring the interplay between band topology and superconductivity.

Figures (8)

• Figure 1: Crystal structure, band structure, and Fermi surface of $\mathrm{YbSb_2}$. (a) Crystal structure of $\mathrm{YbSb_2}$. (b) First Brillouin zone of $\mathrm{YbSb_2}$. The direction of the Dirac nodal line is highlighted in orange. (c) Electronic band structure of $\mathrm{YbSb_2}$ from DFT calculations. The bands that cross the Fermi energy are highlighted in red, green, and cyan. (d) Calculated Fermi pockets of $\mathrm{YbSb_2}$ with SOC included. The colors of the Fermi pockets match those in (c), and the labels represent the QO frequencies as shown in Fig. \ref{['fig:2']}-\ref{['fig:5']}. (e) Calculated Fermi surface of $\mathrm{YbSb_2}$ in the first Brillouin zone, illustrating the positions of the Fermi pockets in (c). (f) Magnetic breakdown orbit $\delta$ formed by $\alpha_3$ and $\beta_2$ cross-sections.
• Figure 2: Resistivity, susceptibility, and magnetoresistance (MR) of $\mathrm{YbSb_2}$. (a) Zero field resistivity of $\mathrm{YbSb_2}$ as a function of temperature. The inset is the susceptibility of $\mathrm{YbSb_2}$ illustrating the bulk superconductivity. (b) Magnetoresistance (MR) of $\mathrm{YbSb_2}$ at different temperatures for current along c-axis and magnetic field along b-axis.
• Figure 3: Shubnikov-de Haas (SdH) oscillations of $\mathrm{YbSb_2}$ with $\mathbf{H} \parallel \mathbf{b}$. (a,b) SdH oscillations of $\mathrm{YbSb_2}$ as a function of magnetic field $\mu_0 H$ (a) and inverse magnetic field $1/\mu_0 H$ (b) at different temperatures. (c) Fast Fourier transform (FFT) spectra of (b). The inset shows the fit to the Lifshitz-Kosevich (LK) thermal damping term to extract the effective masses of different frequencies. (d) LK fitting (red line) to the SdH oscillations (purple symbols) at 1.8 K. The inset shows the high-frequency SdH oscillations and fitting in the region enclosed by the grey box.
• Figure 4: de Haas-van Alphen (dHvA) oscillations of $\mathrm{YbSb_2}$ with $\mathbf{H} \parallel \mathbf{b}$. (a,b) dHvA oscillations of $\mathrm{YbSb_2}$ as a function of magnetic field $\mu_0 H$ (a) and inverse magnetic field $1/\mu_0 H$ (b) at different temperatures. (c) FFT spectra of (b). The inset shows the fit to the LK thermal damping term to extract the effective masses corresponding to the $\alpha_3$ frequencies. (d) LK fitting (red line) to the dHvA oscillations (purple symbols) at 2.5 K. The inset shows the dHvA oscillations and fitting in the region enclosed by the grey box.
• Figure 5: Angle-dependent quantum oscillations (AQO) of $\mathrm{YbSb_2}$ with the magnetic field in the bc-plane. (a) Waterfall plot of the SdH oscillations after background subtraction. A vertical offset is applied for better visualization. The oscillations highlighted in the magenta rectangle show a non-sinusoidal-like waveform. The dotted lines divide the oscillations into three regions depending on the QO amplitude. (b) Contour plot of the FFT spectra of (a) with the calculated cross-sectional area from DFT (symbols). The contour represents the FFT intensities, from low (blue) to high (red). (c) SdH oscillations at different temperatures for $\theta = 32.5^\circ$. The inset shows the measurement setup for AQO. (d) FFT spectra of (c). The inset shows the fit to the Lifshitz-Kosevich (LK) thermal damping term used to extract the effective masses of $\alpha_1$ and its higher harmonics. (e) LK fitting (red line) to the SdH oscillations (purple symbols) at 1.8 K.