Two-dimensional Dirac fermions and quantum magnetoresistance in CaMnBi${}_{2}$

Rapid Communication

Two-dimensional Dirac fermions and quantum magnetoresistance in CaMnBi $_{2}$

Kefeng Wang (王克锋), D. Graf, Limin Wang (王莉敏), Hechang Lei (雷和畅), S. W. Tozer, and C. Petrovic

Phys. Rev. B 85, 041101(R) – Published 18 January 2012

Abstract

We report two-dimensional Dirac fermions and quantum magnetoresistance in single crystals of CaMnBi $_{2}$ . The nonzero Berry's phase, small cyclotron resonant mass, and first-principles band structure suggest the existence of the Dirac fermions in Bi square nets. The in-plane transverse magnetoresistance exhibits a crossover at a critical field $B^{*}$ from semiclassical weak-field $B^{2}$ dependence to the high-field unsaturated linear magnetoresistance ( $\sim$ $120 %$ in 9 T at 2 K) due to the quantum limit of the Dirac fermions. The temperature dependence of $B^{*}$ satisfies quadratic behavior, which is attributed to the splitting of linear energy dispersion in high field. Our results demonstrate the existence of two-dimensional Dirac fermions in CaMnBi $_{2}$ with Bi square nets.

Received 30 December 2011

DOI:https://doi.org/10.1103/PhysRevB.85.041101

Authors & Affiliations

Kefeng Wang (王克锋)¹, D. Graf², Limin Wang (王莉敏)¹, Hechang Lei (雷和畅)¹, S. W. Tozer², 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

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 85, Iss. 4 — 15 January 2012

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Crystal structures of CaMnBi $_{2}$ . Bi atoms in 2D square nets are shows by red balls. Ca atoms are denoted by green balls. Another location of Bi atoms is denoted by purple balls. Mn atoms are denoted by orange balls. Blue lines define the unit cell. (b) Temperature dependence of the in-plane resistivity $ρ_{a b} (T)$ (open symbols) and $c$ -axis resistivity $ρ_{c} (T)$ (solid symbols) of the CaMnBi $_{2}$ single crystal in the $B = 0$ T (squares) and $B = 9$ T (circles) magnetic fields, respectively. (c) Magnetization ( $M$ ) in $B = 1$ T field applied parallel (open symbols) and perpendicular (solid symbols) to the $c$ axis in both ZFC (squares) and FC (circles) runs. (d) The total DOS and local DOS from Ca, Mn, Bi square nets (Bi1) and Bi in MnBi $_{4}$ tetrahedron (Bi2) for AFM CaMnBi $_{2}$ . The dotted line indicates the position of the Fermi energy. (e) The band structure for CaMnBi $_{2}$ . The heavy lines with circles denote the bands from Bi square nets and the dotted line indicates the position of the Fermi energy.Reuse & Permissions
Figure 2
(a) In-plane resistivity $ρ$ vs the tilt angle $θ$ from $0^{\circ}$ to $360^{\circ}$ at $B = 9$ T and $T = 2$ K for CaMnBi $_{2}$ . The red solid line is the fitting curve using $| \cos (θ) |$ (see text). The inset shows the configuration of the measurement. (b) In-plane resistivity $ρ$ vs magnetic field $B$ of the CaMnBi $_{2}$ crystal with different tilt angles $θ$ between the magnetic field and the sample surface ( $a b$ plane) at 2 K. (c) $ρ$ vs the tilt angle $θ$ in the fixed magnetic fields (3, 6, and 9 T) and 2 K.Reuse & Permissions
Figure 3
(a) Magnetic field dependence of resistance of CaMnBi $_{2}$ crystal and (b) magnetoresistant SdH oscillations $Δ R_{x x} = R_{x x} - 〈 R_{x x} 〉$ as a function of $1 / B$ below 35 T. (c) Temperature dependence of the oscillation amplitude (Osc. Amp.) in magnetoresistant SdH oscillations. The red (light gray) line is the fitting results giving cyclotron mass. The inset shows the Fourier transform spectrum of the SdH oscillation. (d) The integer Landau levels as a function of inverse field. The inset shows the oscillation of $Δ R_{x x}$ at 0.36 K, where the arrows indicate the positions of the estimated LL index $n$ labeled by the numbers.Reuse & Permissions
Figure 4
(a) The magnetic field ( $B$ ) dependence of the in-plane MR at different temperatures. (b) The field derivative of in-plane MR at different temperatures, respectively. The lines in the high-field regions were fitting results using $MR = A_{1} B + O (B^{2})$ , and the lines in the low-field regions using $MR = A_{2} B^{2}$ . (c) Temperature dependence of the critical field $B^{*}$ (black squares) and the effective MR mobility $μ_{MR}$ extracted from the weak-field MR (blue circles). The red solid line is the fitting results of $B^{*}$ using $B^{*} = \frac{1}{2 e ℏ v_{F}^{2}} {(E_{F} + k_{B} T)}^{2}$ .Reuse & Permissions

Physical Review B

covering condensed matter and materials physics