Crystal growth and magnetic structure of MnBi2Te4

Abstract

Millimeter-sized MnBi2Te4 single crystals are grown out of a BiTe flux and characterized using magnetic, transport, scanning tunneling microscopy, and spectroscopy measurements. The magnetic structure of MnBi2Te4 below TN is determined by powder and single-crystal neutron diffraction measurements. Below TN = 24 K, Mn2+ moments order ferromagnetically in the ab plane but antiferromagnetically along the crystallographic c axis. The ordered moment is 4.04(13)μB/Mn at 10 K and aligned along the crystallographic c axis in an A-type antiferromagnetic order. Below TN, the electrical resistivity drops upon cooling or when going across the metamagnetic transition in increasing magnetic fields. A critical scattering effect is observed in the vicinity of TN in the temperature dependence of thermal conductivity, indicating strong spin-lattice coupling in this compound. However, no anomaly is observed in the temperature dependence of thermopower around TN. Fine tuning of the magnetism and/or electronic band structure is needed for the proposed topological properties of this compound. The growth protocol reported in this work might be applied to grow high-quality crystals where the electronic band structure and magnetism can be finely tuned by chemical substitutions.

Axion coupling in the hybrid Wannier representation

“…To date the closest to a physical realization seems to the antiferromagnetic topological insulator 28 MnBi 2 Te 4 , which has been the subject of much recent interest. [29][30][31][32][33][34] Other symmetry operations also reverse the sign of θ, and thus support an axion Z 2 classification. These include simple mirrors and glide mirrors, rotoinversions, and time-reversed rotations and screws.…”

“…The double prime on the first sum in Eq. (34) indicates that all terms coming from within a DR are to be omitted, and in Eq. (35) it excludes terms where both bands lie in the same DR in the same cell; these omissions are compensated by the second term in Eq.…”

“…Then θ zΩ reduces to the first term of Eq. (34). This in turn can be broken into two contributions: one from the blue region z n (k) ∈ [z nom (k) + δ, z nom (k) + c − δ], and another from the red region z n (k) ∈ [z nom (k) + c − δ, z nom (k) + c + δ], in Fig.…”

Universal gapless Dirac cone and tunable topological states in (MnBi2Te4)m(

“…In the newly discovered magnetic topological insulator MnBi2Te4 [1][2][3][4][5][6][7][8], both axion insulator state and quantized anomalous Hall effect (QAHE) have been observed by tuning the magnetic structure [9][10][11]. The related (MnBi2Te4)m(Bi2Te3)n heterostructures with increased tuning knobs, are predicted to be a more versatile platform for exotic topological states [12][13][14][15][16].…”

“…The first thing is to understand the universal gapless TSSs. The magnetic moments in the ground state of (MnBi2Te4)m(Bi2Te3)n are ferromagnetically ordered within a Mnplane along the z-direction, but antiferromagnetically coupled between layers [6,37,38]. In theory, this so-called A-type antiferromagnetic order would inevitably induce a sizable magnetic gap in the possibility is the co-existence of multiple short-range magnetic orders (presumably in different domains), such that the global magnetic moment in each layer could be zero.…”