Quantum oscillations and transport properties of layered single-crystal SrCu$_4$As$_2$

TL;DR

The paper addresses the electronic structure and transport of layered SrCu4As2, aiming to map its Fermi-surface topology and identify Dirac-like carriers in a nonmagnetic pnictide. It combines high-field transport and quantum oscillations up to $60~\mathrm{T}$ with density functional theory to characterize the Fermi-surface pockets and their dimensionality. A structural-distortion-type transition at $T_P = 59~\mathrm{K}$ accompanies a dominant hole-like Hall response and a large linear magnetoresistance, indicating a tunable multiband semimetal. Quantum oscillations reveal five low-mass frequencies consistent with Dirac-like carriers, broadly supported by the DFT results, highlighting SrCu4As2 as a platform for Dirac physics in layered pnictides.

Abstract

We report a systematic investigation of the physical properties and Fermi-surface topology of layered single-crystal \ce{SrCu4As2} using electrical transport, magnetotransport, and quantum-oscillation experiments plus band-structure calculations. The temperature-dependent electrical resistivity reveals a hysteretic phase transition at $T_P$ = 59 K, most likely associated with a structural change. Hall resistivity data suggest a marked change in the average hole density resulting from the latter phase transition near $T_P$. A large, linear, and nonsaturating magnetoresistance is observed at low temperatures in \ce{SrCu4As2}, likely attributable to the multipocket Fermi surface. Quantum-oscillation data measured in magnetic fields of up to 60 T show several oscillation frequencies exhibiting low effective masses, indicating the presence of Dirac-like band dispersion in \ce{SrCu4As2}, as suggested by the band structure calculations.

Figures (4)

• Figure 1: The unit cell of SrCu4As2 shown using rhombohedral (a) and hexagonal axes (b). There are two symmetry-inequivalent Cu positions in the structure: Cu(1) and Cu(2). Note the [0001] direction in the hexagonal cell is equivalent to the [111] direction in the rhombohedral one.
• Figure 2: Electrical resistivity and magnetotransport properties of SrCu4As2: (a) The temperature dependence of the zero-field electrical resistivity from 2 to 300 K with the current applied in the ab plane of the crystal. The inset shows the first-order derivative of the resistivity data, the peak occurring at the phase transition. (b) Cooling and heating curves for the electrical resistivity near the phase transition temperature at 0 and 9 T. (c) Field dependence of the magnetoresistance measured up to 9 T for various temperatures ($H \parallel c$). (d) The first-order derivative of the MR as a function of magnetic field for temperatures of 2 K and 50 K. (e) The field-dependent Hall resistivity measured between 2 and 200 K. The inset shows the linear fit up to 6 T at 2 K. (f) and (g) display the temperature variation of the hole concentration and the average mobility estimated from the Hall resistivity data.
• Figure 3: Quantum oscillations in SrCu4As2 observed via PDO measurements: (a) The field dependence of PDO frequency as a function for rising and falling fields at 690 mK. (b) PDO data as a function of 1/$\mu_0H$ after polynomial background subtraction in the field range 25-60 T at 690 mK for $H\parallel c$. (c) FFTs of background subtracted PDO data at 690 mK. (d) The temperature variation of the FFT amplitudes fitted using Eq. \ref{['LK']}. (e) Quantum oscillations at 690 mK for various angles of the magnetic field with respect to the c-axis of the crystal, as shown in the inset diagram. The corresponding FFTs are shown in (f). (g) The angular dependences of the FFT frequencies. The dotted curves represent 1/$\cos{\theta}$ fits. (h) FFTs at 1.5 K for 0$^\circ$ and ±2.5$^\circ$
• Figure 4: (a) Band structure of SrCu4As2 with the contribution of the two inequivalent Cu atoms (Cu(1) & Cu(2)) and As marked by the thickness of the red, green, and blue lines, respectively. Panel (b) shows the electronic density of states (DOS). Inset shows a close-up of the DOS around the Fermi energy, $E_F$ . Panel (c) shows the band dispersion around the Fermi energy. The 5 bands forming the Fermi surface are highlighted. Panel (d) shows the dispersion of the 5 bands along the $\Gamma$-$Z$ line, with band indices labeled using colors consistent with panel (c) and the Fermi-surface section coloring in panel (e). Panel (e) shows the Fermi surface of SrCu4As2 and its cross-section along the hexagonal [0001] direction[(the section plane is shown in gray]. Panel (f) shows theoretical SdH frequencies plotted against the angle between the hexagonal $c$ axis (parallel to the rhombohedral [111] direction) and $a$.