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Register a new userTopological phase transition in layered magnetic compound MnSb2Te4: Spin-orbit coupling and interlayer coupling dependeces
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Based on the first-principles calculations and theoretical analysis, we investigate the electronic structures, topological phase transition (TPT) and topological properties of layered magnetic compound MnSb2Te4. It has the similar crystal and magnetic structure as the magnetic topological insulator MnBi2Te4. We find that when the spin-orbit coupling (SOC) is considered, the band structure of MnSb2Te4 in antiferromagnetic (AFM) state has no band inversion at {Gamma}. This is due to the SOC strength of Sb is less than that of Bi. The band inversion can be realized by increasing the SOC of Sb by 0.3 times, which drives MnSb2Te4 from a trivial AFM insulator to an AFM topological insulator (TI) or axion insulator. Uniaxial compressive strain along the layer stacking direction is another way to control the band inversion. The interlayer distance shorten by 5% is needed to drive the similar TPT. For the ferromagnetic (FM) MnSb2Te4 with experimental crystal structure, it is a normal FM insulator. The band inversion can happen when SOC is enhanced by 0.1 times or the interlayer distance is decreased by more than 1%. Thus, FM MnSb2Te4 can be tuned to be the simplest type-I Weyl semimetal with only one pair of Weyl nodes on the three-fold rotational axis. These two Weyl nodes are projected onto (1-10) surface with one Fermi arc connecting them.
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As a sister compound and isostructural of MnBi2Te4, the high quality MnSb2Te4 single crystals are grown via solid-state reaction where prolonged annealing and narrow temperature window play critical roles on account of its thermal metastability. X-ray diffraction analysis on MnSb2Te4 single crystals reveals pronounced cation intermixing, 28.9(7)% Sb antisite defects on the Mn (3a) site and 19.3(6)% Mn antisite defects on the Sb (6c) site, compared with MnBi2Te4. Unlike antiferromagnetic (AFM) nature MnBi2Te4, MnSb2Te4 contains magnetic and antiferromagnetic competition and exhibits a spin glass (SG) state below 24 K. Its magnetic hysteresis, anisotropy, and relaxation process are investigated in detail with DC and AC magnetization measurements. Moreover, anomalous Hall effect as a p-type conductor is demonstrated through transport measurements. This work grants MnSb2Te4 a possible access to the future exploration of exotic quantum physics by removing the odd/even layer number restraint in intrinsic AFM MnBi2Te4-family materials as a result of the crossover between its magnetism and potential topology in the Sb-Te layer.
Intrinsic magnetic topological insulators provide an ideal platform to achieve various exciting physical phenomena. However, this kind of materials and related research are still very rare. In this work, we reported the electronic and structural phase transitions in intrinsic magnetic topological insulator MnSb2Te4 driven by hydrostatic pressure. Electric transport results revealed that temperature dependent resistance showed a minimum value near short-range antiferromagnetic (AFM) ordering temperature TN, the TN values decline with pressure, and the AFM ordering was strongly suppressed near 10 GPa and was not visible above 11.5 GPa. The intensity of three Raman vibration modes in MnSb2Te4 declined quickly starting from 7.5 GPa and these modes become undetectable above 9 GPa, suggesting possible insulator-metal transition, which is further confirmed by theoretical calculation. In situ x-ray diffraction (XRD) demonstrated that an extra diffraction peak appears near 9.1 GPa and MnSb2Te4 started to enter an amorphous-like state above 16.6 GPa, suggesting the structural origin of suppressed AFM ordering and metallization. This work has demonstrated the correlation among interlayer interaction, magnetic ordering, and electric behavior, which could be benefit for the understanding of the fundamental properties of this kind of materials and devices.
We investigate the effect of spin-orbit coupling on the behavior of magnetic impurity at the edge of a zigzag graphene ribbon by means of quantum Monte Carlo simulations. A peculiar interplay of Kane-Mele type spin-orbit and impurity-host coupling is found to affect local properties such as the impurity magnetic moment and spectral densities. The special helical nature of the topological insulator on the edge is found to affect nonlocal quantities, such as the two-particle and spin-spin correlation functions linking electrons on the impurity with those in the conduction band.
The discovery of an ever increasing family of atomic layered magnetic materials, together with the already established vast catalogue of strong spin-orbit coupling (SOC) and topological systems, calls for some guiding principles to tailor and optimize novel spin transport and optical properties at their interfaces. Here we focus on the latest developments in both fields that have brought them closer together and make them ripe for future fruitful synergy. After outlining fundamentals on van der Waals (vdW) magnetism and SOC effects, we discuss how their coexistence, manipulation and competition could ultimately establish new ways to engineer robust spin textures and drive the generation and dynamics of spin current and magnetization switching in 2D materials-based vdW heterostructures. Grounding our analysis on existing experimental results and theoretical considerations, we draw a prospective analysis about how intertwined magnetism and spin-orbit torque (SOT) phenomena combine at interfaces with well-defined symmetries, and how this dictates the nature and figures-of-merit of SOT and angular momentum transfer. This will serve as a guiding role in designing future non-volatile memory devices that utilize the unique properties of 2D materials with the spin degree of freedom.
The bulk Rashba semiconductors BiTeX (X=I, Cl and Br) with intrinsically enhanced Rashba spin-orbit coupling provide a new platform for investigation of spintronic and magnetic phenomena in materials. We theoretically investigate the interlayer exchange interaction between two ferromagnets deposited on opposite surfaces of a bulk Rashba semiconductor BiTeI in its trivial and topological insulator phases. In the trivial phase BiTeI, we find that for ferromagnets with a magnetization orthogonal to the interface, the exchange coupling is reminiscent of that of a conventional three-dimensional metal. Remarkably, ferromagnets with a magnetization parallel to the interface display a magnetic exchange qualitatively different from that of conventional three-dimensional metal due to the spin-orbit coupling. In this case, the interlayer exchange interaction acquires two periods of oscillations and decays as the inverse of the thickness of the BiTeI layer. For topological BiTeI, the magnetic exchange interaction becomes mediated only by the helical surface states and acts between the one-dimensional spin chains at the edges of the sample. The surface state-mediated interlayer exchange interaction allows for the coupling of ferromagnets with non-collinear magnetization and displays a decay power different from that of trivial BiTeI, allowing the detection of the topological phase transition in this material. Our work provides insights into the magnetic properties of these newly discovered materials and their possible functionalization.
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