Pressure-Induced Changes in Structure, Magnetic Order and Development of Superconductivity in the Ferromagnetic Topological Insulator MnBi8Te13

We report a comprehensive study of pressure-induced evolution of the magnetism and development of superconductivity (SC) in MnBi8Te13, a promising ambient pressure, ferromagnetic (FM) topological insulator candidate. By employing high-pressure electrical transport, magnetoresistance, DC magnetic susceptibility, and X-ray diffraction measurements, we construct a detailed temperature-pressure phase diagram. At ambient pressure, MnBi8Te13 exhibits FM ordering with an easy-axis along the c-axis which is progressively suppressed under pressure and replaced by an antiferromagnetic (AFM) order. Density functional theory calculations predicted an evolution from FM to a G-type AFMg2 phase near 5 GPa. Above 16.6 GPa, a bulk SC state emerges with a maximum transition temperature ~6.8 K, as confirmed by resistance and magnetic susceptibility measurements. This pressure-induced SC may co-exist with another AFM dome that shows a weak anomaly in the transport data. In contrast, our work on MnBi6Te10 shows no SC up to 40 GPa. Indeed, in contrast to MnBi8Te13, the MnBi2Te4(Bi2Te3)n compounds with n < 3, didn’t exhibit SC, highlighting the crucial role of Mn concentration in stabilizing SC. The observation of pressure-induced FM-AFM-SC transitions in MnBi8Te13 not only establishes it as a rare Mn-based SC but also provides a platform to study the interplay between magnetism, SC, and potentially nontrivial band topology in correlated magnetic materials.

💡 Research Summary

The authors present a comprehensive high‑pressure investigation of MnBi₈Te₁₃, a ferromagnetic (FM) topological‑insulator candidate, focusing on the evolution of its crystal structure, magnetic order, and the emergence of superconductivity (SC). Using a combination of electrical transport, magnetoresistance, dc magnetic susceptibility, and synchrotron X‑ray diffraction up to ~40 GPa, they construct a detailed temperature–pressure (T–p) phase diagram.

At ambient conditions MnBi₈Te₁₃ adopts a rhombohedral R‑3m structure and exhibits FM order with the easy axis along the c‑direction. Upon compression the FM transition temperature (T_C) continuously decreases and disappears around 4 GPa. Density‑functional‑theory (DFT) calculations predict a change to a G‑type antiferromagnetic (AFM) “AFMg₂” configuration near 5 GPa, which is supported experimentally by the appearance of a weak resistance anomaly near 6 K and a flattening of the R(T) curves between 4 and 8 GPa. The anomaly resembles a magnetic super‑zone gap, suggesting a modulated or incommensurate AFM state rather than a simple A‑type AFM.

Structural measurements reveal two successive pressure‑induced transitions: (i) rhombohedral → monoclinic (A2/m) around 10 GPa, and (ii) monoclinic → cubic (Im‑3m) near 16 GPa. The first transition coincides with a marked increase in overall resistance and a suppression of temperature‑dependent scattering, indicating a reconstruction of the electronic band structure. The second transition is accompanied by a dramatic drop in resistance. At 16.6 GPa a non‑zero‑resistance drop appears, marking the onset of a nascent superconducting state. Between 19 and 27 GPa the resistance reaches near‑zero, and the superconducting transition temperature (T_c) peaks at ~6.8 K. Magnetic susceptibility measured under 0.2 kOe at 19.6 and 24.1 GPa shows an unsaturated diamagnetic response with an estimated shielding fraction of ~50 % at 2 K, indicating bulk‑like but not yet fully percolating superconductivity. The broad transition width is attributed to pressure inhomogeneity and possible exfoliation of the layered crystal.

A parallel study on MnBi₆Te₁₀, which contains fewer Mn atoms, shows a monotonic suppression of its ambient‑pressure AFM order (T_N ≈ 10 K) down to ~3.7 K at 8.8 GPa, but no superconductivity is detected up to 40 GPa. This contrast underscores the crucial role of Mn concentration and Mn–Mn spacing in stabilizing the superconducting phase. The authors also note that other members of the MnBi₂Te₄(Bi₂Te₃)_n series with n < 3 do not become superconducting under pressure, whereas MnBi₈Te₁₃ (n = 3) does, suggesting that the additional Bi₂Te₃ spacer layers enhance structural resilience and reduce magnetic exchange enough to allow Cooper pairing.

The work establishes MnBi₈Te₁₃ as a rare Mn‑based superconductor and provides a unique platform where ferromagnetism, antiferromagnetism, and superconductivity can be tuned continuously by pressure. This enables future investigations of the interplay between magnetic order, topological surface states, and unconventional pairing mechanisms, including the possible emergence of Majorana modes. The authors propose that high‑pressure neutron diffraction or μSR experiments, together with ARPES and STM under pressure, will be essential to resolve whether superconductivity coexists microscopically with AFM order and to elucidate the underlying pairing glue.