[Paper Review] Tunable intrinsic ferromagnetic topological phases in bulk van der Waals crystal MnSb6Te10

Xin Zhang, Shihao Zhang+15 more|arXiv (Cornell University)|Nov 9, 2021

Topological Materials and Phenomena4 citations

TL;DR

This study identifies MnSb6Te10, a van der Waals bulk crystal, as a tunable intrinsic ferromagnetic topological material exhibiting multiple topological phases. By tuning temperature, magnetic field, or hole doping, it transitions between ferromagnetic, ferrimagnetic, Z2 antiferromagnetic topological insulator, axion insulator, and Weyl semimetal phases, with strong intrinsic anomalous Hall effect confirming its topological nature.

ABSTRACT

Intrinsic ferromagnetism is a crucial ingredient to realize quantum anomalous Hall effect in quasi two dimensional materials, thus the search of intrinsic ferromagnetic topological materials is one of the most concerned issues in the field of topological phases of matter. In this work, combining magnetotransport measurements, first principles calculations, and angle-resolved photoemission spectroscopy studies, we find that in MnSb6Te10, the n = 2 member of the MnSb2Te4/(Sb2Te3)n family, the strong magnetic competition realizes a fragile ferromagnetic ground state, which whereas easily enters into ferrimagnetic and the Z_2 antiferromagnetic topological insulator phase with warming to higher temperature. Interestingly, the system stays in an inversion-symmetry-protected axion insulator phase in the ferromagnetic ground state as well as in the external magnetic field driven spin-polarized FM phase and can be converted into a Weyl semimetal with multiple Weyl nodes in the valence bands with hole doping, which are manifested by the measured notable intrinsic anomalous Hall effect. Our work thus provides an intrinsic magnetic topological material which is highly tunable into versatile topological phases by temperature, magnetic field, as well as carrier doping.

Motivation & Objective

• To identify intrinsic ferromagnetic topological materials capable of hosting the quantum anomalous Hall effect.
• To explore the role of magnetic competition in stabilizing fragile ferromagnetic ground states in van der Waals materials.
• To demonstrate tunability of topological phases in a single bulk crystal via external parameters such as temperature, magnetic field, and carrier doping.
• To establish MnSb6Te10 as a platform for realizing multiple topological states, including axion insulator and Weyl semimetal phases.

Proposed method

• Conducting magnetotransport measurements to probe anomalous Hall effect and magnetic phase transitions.
• Performing first-principles electronic structure calculations to determine band topology and magnetic ground states.
• Applying angle-resolved photoemission spectroscopy (ARPES) to directly observe surface states and band dispersion.
• Systematically varying temperature and external magnetic field to access different magnetic and topological phases.
• Introducing hole doping via chemical substitution to drive transitions into Weyl semimetal phases.
• Analyzing symmetry protection and topological invariants to confirm axion insulator behavior in ferromagnetic and spin-polarized states.

Experimental results

Research questions

• RQ1 Can intrinsic ferromagnetism in a bulk van der Waals crystal stabilize topological phases with potential for quantum anomalous Hall effect?
• RQ2 How does magnetic competition in MnSb6Te10 lead to a fragile ferromagnetic ground state that is sensitive to temperature and magnetic field?
• RQ3 What topological phases can be accessed in MnSb6Te10 through tuning temperature, magnetic field, or carrier doping?
• RQ4 Is the ferromagnetic state of MnSb6Te10 protected by inversion symmetry and capable of hosting axion insulator behavior?
• RQ5 Can hole doping induce a Weyl semimetal phase with multiple Weyl nodes in the valence band, as evidenced by transport and spectroscopic measurements?

Key findings

• MnSb6Te10 exhibits a fragile ferromagnetic ground state stabilized by strong magnetic competition, confirmed by magnetotransport and first-principles calculations.
• The material transitions into a ferrimagnetic phase and a Z2 antiferromagnetic topological insulator phase upon heating, indicating thermally driven magnetic reconfiguration.
• In both the ferromagnetic ground state and the field-induced spin-polarized FM phase, MnSb6Te10 hosts an inversion-symmetry-protected axion insulator phase.
• Hole doping drives the system into a Weyl semimetal phase with multiple Weyl nodes in the valence band, as evidenced by a notable intrinsic anomalous Hall effect.
• The observed anomalous Hall signal is intrinsic and robust, indicating strong spin-momentum locking and topological band structure.
• The material's ability to host multiple topological phases—ferromagnetic, axion insulator, Weyl semimetal—within a single bulk crystal highlights its high tunability via external parameters.