Electron-hole asymmetry, Dirac fermions, and quantum magnetoresistance in ${\mathrm{BaMnBi}}_{2}$

Electron-hole asymmetry, Dirac fermions, and quantum magnetoresistance in ${BaMnBi}_{2}$

Lijun Li (黎丽君), Kefeng Wang (王克锋), D. Graf, Limin Wang (王莉敏), Aifeng Wang (王爱峰), and C. Petrovic

Phys. Rev. B 93, 115141 – Published 28 March 2016

Abstract

We report two-dimensional quantum transport and Dirac fermions in ${BaMnBi}_{2}$ single crystals. ${BaMnBi}_{2}$ is a layered bad metal with highly anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, small cyclotron mass, and the first-principles band structure calculations indicate the presence of Dirac fermions in Bi square nets. Quantum oscillations in the Hall channel suggest the presence of both electron and hole pockets, whereas Dirac and parabolic states coexist at the Fermi level.

Received 4 February 2016

DOI:https://doi.org/10.1103/PhysRevB.93.115141

Physics Subject Headings (PhySH)

Dirac fermions Geometric & topological phases Magnetoresistance Quantum transport

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Lijun Li (黎丽君)^1,*, Kefeng Wang (王克锋)^1,†, D. Graf², Limin Wang (王莉敏)^1,†, Aifeng Wang (王爱峰)¹, and C. Petrovic¹

¹Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
²National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4005, USA

^*Present address: Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, Peoples Republic of China.
^†Present address: Department of Physics, University of Maryland, College Park, MD 20742-4111, USA.

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Vol. 93, Iss. 11 — 15 March 2016

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Figure 1
(a) Powder XRD patterns and refinement results. The data were shown by (+), fitting and difference curves are given by the red and green solid line, respectively. (b) Crystal structure of ${BaMnBi}_{2}$ . (c, d) Temperature dependence of the in-plane resistivity $ρ_{a b} (T)$ and $c$ -axis resistivity $ρ_{c} (T)$ of the ${BaMnBi}_{2}$ single crystal in the $B = 0 T$ (solid symbols) and $B = 12 T$ (open symbols) magnetic fields, respectively. (e) Temperature dependence of magnetization $M (T)$ for applied magnetic field parallel and perpendicular to the $a b$ plane in both zero-field-cooling (ZFC, solid symbols) and field-cooling (FC, open symbols). The inset in (e) shows temperature dependence of heat capacity. (f) Magnetization hysteresis loops M(H) of ${BaMnBi}_{2}$ , at 300 K, 100 K, and 2 K.
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Figure 2
The crystal was fixed on a rotating stage so that the tilt angle $θ$ between the crystal surface ( $a b$ plane) and the magnetic field can be continuously changed and the current is flowing in the $a b$ plane perpendicular to magnetic field. (a) Tilt angle $θ$ (from $0^{\circ}$ to $360^{\circ}$ ) dependence of in-plane resistivity ( $ρ_{a b}$ ) at $B = 16 T$ as $T = 2 K$ . The black dash line is the $| cos (θ) |$ curve. The inset shows the configuration of the measurement. (b) In-plane resistivity $ρ_{a b}$ vs. magnetic field $B$ at different tilt angles $θ$ at 2 K ( $- 15^{\circ}$ to $90^{\circ}$ ).
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Figure 3
(a) In plane $ρ_{a b} - B$ and (b) $c$ -axis resistivity $ρ_{c} - B$ of ${BaMnBi}_{2}$ crystal measured at different temperatures. (c) Magnetic field dependence of Hall resistance. (d) The integer Landau levels as a function of inverse field; the arrows indicate the positions of the estimated LL index $n$ labeled by the numbers. Insets in (a) and (c) present magnetoresistant SdH oscillations of $Δ R_{i} = R_{i} - 〈 R_{i} 〉$ as a function of B where $i = a b, c$ .
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Figure 4
(a) The Fourier transform spectrum of the SdH oscillation at $T = 1.55 K$ . (b) Temperature dependence of the temperature divided oscillation amplitude ( $Osc.Amp. / T - T$ ) in magnetoresistant SdH oscillations, the black balls are obtained from $Δ R_{a b}$ data, and the red squares are obtained from $Δ R_{H}$ data. The red line is the fitting results giving cyclotron mass $m^{*} \sim 0.105 m_{e}$ . (c) In-plane low-field magnetoresistance ( $M R_{a b}$ ) for $T = 1.9 K$ (blue solid squares) and $T = 50 K$ (red solid circles); the lines are fitting results of $M R = A_{2} \times B^{2}$ . (d) Temperature dependence of the critical field $B^{*}$ (purple solid squares) and the effective $M R$ mobility (orange solid circles) $μ_{M R}$ obtained by fitting the low-field $M R_{a b}$ . The red solid line is the fitting results of $B^{*}$ using $B^{*} = \frac{1}{2 e ℏ ν_{F}^{2}} {(E_{F} + κ_{B} T)}^{2}$ .
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Figure 5
(a) The band structure for ${BaMnBi}_{2}$ with antiferromagnetic order but without spin-orbit coupling. (b, c) The total and local density of states from Mn, Ba, and Bi atoms for AFM ${BaMnBi}_{2}$ . The dotted line indicates the position of the Fermi energy. In the calculation, the moments of Mn atoms are arranged in an antiferromagnetic order in the $a b$ plane but the Mn layers are ferromagnetically stacked along the $c$ axis.
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Physical Review B

covering condensed matter and materials physics

Electron-hole asymmetry, Dirac fermions, and quantum magnetoresistance in ${BaMnBi}_{2}$

Lijun Li (黎丽君), Kefeng Wang (王克锋), D. Graf, Limin Wang (王莉敏), Aifeng Wang (王爱峰), and C. Petrovic

Phys. Rev. B 93, 115141 – Published 28 March 2016

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Physical Review B

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Electron-hole asymmetry, Dirac fermions, and quantum magnetoresistance in BaMnBi2

Lijun Li (黎丽君), Kefeng Wang (王克锋), D. Graf, Limin Wang (王莉敏), Aifeng Wang (王爱峰), and C. Petrovic

Phys. Rev. B 93, 115141 – Published 28 March 2016

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Electron-hole asymmetry, Dirac fermions, and quantum magnetoresistance in ${BaMnBi}_{2}$