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Toward Tunable Magnetic Dirac Semimetals: Mn Doping of Cd$_3$As$_2$

Anthony D. Rice, Ian Leahy, Herve Ness, Andrew G. Norman, Karen N. Heinselman, Chun-Sheng Jiang, David Graf, Alexey Suslov, Stephan Lany, Mark Van Schilfgaarde, Kirstin Alberi

TL;DR

This work addresses the challenge of tuning the electronic topology of Cd3As2, a Dirac semimetal, by dilute magnetic doping with Mn to break time-reversal symmetry and drive a Dirac-to-Weyl transition. The authors demonstrate uniform Mn incorporation (>10%) in Cd3As2 thin films grown by MBE under As-rich, (001)-oriented conditions while preserving high electron mobilities, enabling transport and spectroscopic probing of the dopant's effects. They observe evolving magnetization, absence of Mn-rich secondary phases, and the emergence of a second quantum oscillation frequency in Hall measurements, consistent with Mn-induced Dirac point splitting and Weyl-like band structure changes. The results establish a viable path toward tunable magnetic topological semimetals and lay groundwork for exploring Mn_i/Mn_Cd site physics and device concepts based on Berry-curvature control.

Abstract

Magnetic impurities provide a route toward increasing functionality in electronic materials, often enabling new device concepts and architectures. In the case of topological semimetals, dilute magnetic doping presents a particularly attractive approach for inducing a Dirac to Weyl phase change via time reversal symmetry breaking. However, efforts to realize changes in the electronic structure have been limited by challenges in incorporating magnetic impurities into crystals with sufficiently high electron mobilities to detect them via transport or spectroscopic techniques. Here, we demonstrate incorporation of Mn into Cd$_3$As$_2$ Dirac semimetal thin films grown by molecular beam epitaxy (MBE). Using As-rich growth conditions and [001] oriented thin films, Mn compositions of >10% are achieved. Films contain uniform distributions of Mn with no evidence of secondary phases and exhibit electron mobilities greater than 10,000-30,000 cm$^2$/Vs up to 5% Mn. An evolution in the magnetization behavior along with the emergence of a second quantum oscillation frequency at low Mn concentrations provide preliminary evidence of Mn-induced changes in the electronic structure that are consistent with a Weyl phase. This work demonstrates the potential of magnetically doping topological semimetal thin films and a pathway for synthesizing them.

Toward Tunable Magnetic Dirac Semimetals: Mn Doping of Cd$_3$As$_2$

TL;DR

This work addresses the challenge of tuning the electronic topology of Cd3As2, a Dirac semimetal, by dilute magnetic doping with Mn to break time-reversal symmetry and drive a Dirac-to-Weyl transition. The authors demonstrate uniform Mn incorporation (>10%) in Cd3As2 thin films grown by MBE under As-rich, (001)-oriented conditions while preserving high electron mobilities, enabling transport and spectroscopic probing of the dopant's effects. They observe evolving magnetization, absence of Mn-rich secondary phases, and the emergence of a second quantum oscillation frequency in Hall measurements, consistent with Mn-induced Dirac point splitting and Weyl-like band structure changes. The results establish a viable path toward tunable magnetic topological semimetals and lay groundwork for exploring Mn_i/Mn_Cd site physics and device concepts based on Berry-curvature control.

Abstract

Magnetic impurities provide a route toward increasing functionality in electronic materials, often enabling new device concepts and architectures. In the case of topological semimetals, dilute magnetic doping presents a particularly attractive approach for inducing a Dirac to Weyl phase change via time reversal symmetry breaking. However, efforts to realize changes in the electronic structure have been limited by challenges in incorporating magnetic impurities into crystals with sufficiently high electron mobilities to detect them via transport or spectroscopic techniques. Here, we demonstrate incorporation of Mn into CdAs Dirac semimetal thin films grown by molecular beam epitaxy (MBE). Using As-rich growth conditions and [001] oriented thin films, Mn compositions of >10% are achieved. Films contain uniform distributions of Mn with no evidence of secondary phases and exhibit electron mobilities greater than 10,000-30,000 cm/Vs up to 5% Mn. An evolution in the magnetization behavior along with the emergence of a second quantum oscillation frequency at low Mn concentrations provide preliminary evidence of Mn-induced changes in the electronic structure that are consistent with a Weyl phase. This work demonstrates the potential of magnetically doping topological semimetal thin films and a pathway for synthesizing them.
Paper Structure (8 sections, 4 figures, 1 table)

This paper contains 8 sections, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Results
  3. Enhanced Mn Incorporation Via Tailored Growth Conditions
  4. Magnetization
  5. Electrical Transport
  6. Discussion
  7. Conclusion
  8. Methods

Figures (4)

  • Figure 1: Summary of thin film growth a) Survey XRD scan of a (Mn$_{0.05}$Cd$_{0.95}$)$_3$As$_2$ and b) XRD scans around the (0016) (Mn,Cd)$_3$As$_2$ peak as a function of Mn BFM flux. c) AFM of a 1x1 $\mu$m area and (d-e) STEM HAADF image and Mn EDS elemental map of the film stack. Films are smooth, with a gradual shift in lattice parameter in the (Mn,Cd)$_3$As$_2$ peaks, no visible secondary peaks, and uniform Mn content through the bulk of the layer. For higher Mn content, the ZnCdTe(004) buffer layer peak may be visible near 58$\degree$.
  • Figure 2: Investigations of short range ordering of Mn. a) Cross-sectional high resolution STEM HAADF image near layer surface. b) Higher magnification STEM HAADF image. c) Comparison of a "random" (non-channeling) and channeling axis spectra and d) RBS channeling crystal image of the Cd signal from a $8\%$ Mn film. Higher intensity indicates higher backscattered yield.
  • Figure 3: Magnetization of (Mn,Cd)$_3$As$_2$ films with varying Mn concentrations at 2 K. A linear diamagnetic background from the substrate has been removed. a) Magnetization vs. Field loops for films with different Mn concentrations. A clear hysteresis loop is only observed at high Mn concentrations. The vertical scale is broken and loops are offset for clarity. Light colored boxes represent error in the magnetization measurement. b) Value of the magnetization at 1 T vs. Mn concentration. At low Mn concentrations, the moment per Mn atom is largest. The moment per Mn rapidly decreases with increasing Mn concentration.
  • Figure 4: 2 K a) Fractional magnetoresistance and b) Hall resistivity for (Mn,Cd)$_3$As$_2$ films at 2 K for $H\perp I$. c) Electron density and d) Mobility as a function of Mn percentage. e) Fourier transforms of quantum oscillations extracted from $\partial_H^2\rho_{xx}$ for $H\parallel I$. Arrows denote the bulk oscillations which split at low Mn doping.