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1. Strain-tuned topological phase transition and unconventional Zeeman effect in ZrTe5 microcrystals

   https://doi.org/10.1038/s43246-022-00316-5  

   Gaikwad, Apurva; Sun, Song; Wang, Peipei; Zhang, Liyuan; Cano, Jennifer; Dai, Xi; Du, Xu (December 2022, Communications Materials)

   Abstract The geometric phase of an electronic wave function, also known as Berry phase, is the fundamental basis of the topological properties in solids. This phase can be tuned by modulating the band structure of a material, providing a way to drive a topological phase transition. However, despite significant efforts in designing and understanding topological materials, it remains still challenging to tune a given material across different topological phases while tracing the impact of the Berry phase on its quantum transport properties. Here, we report these two effects in a magnetotransport study of ZrTe 5 . By tuning the band structure with uniaxial strain, we use quantum oscillations to directly map a weak-to-strong topological insulator phase transition through a gapless Dirac semimetal phase. Moreover, we demonstrate the impact of the strain-tunable spin-dependent Berry phase on the Zeeman effect through the amplitude of the quantum oscillations. We show that such a spin-dependent Berry phase, largely neglected in solid-state systems, is critical in modeling quantum oscillations in Dirac bands of topological materials. 

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2. New magnetic topological materials from high-throughput search

   https://doi.org/10.1126/sciadv.adv8780  

   Robredo, Iñigo; Xu, Yuanfeng; Jiang, Yi; Felser, Claudia; Bernevig, B Andrei; Elcoro, Luis; Regnault, Nicolas; Vergniory, Maia G (October 2025, Science Advances)

   We conducted a high-throughput search for topological magnetic materials across 522 new, experimentally reported commensurate magnetic structures from MAGNDATA, doubling the number of available materials on the Topological Magnetic Materials database. This brings up to date the previous studies. For each material, we performed first-principles electronic calculations and diagnosed the topology as a function of the HubbardUparameter. Our high-throughput calculation led us to the prediction of 250 experimentally relevant topologically nontrivial materials, which represent 47.89% of the newly analyzed materials. We present five remarkable examples of these materials, each showcasing a different topological phase: Mn₂AlB₂(BCSID 1.508), which exhibits a nodal line semimetal to topological insulator transition as a function of SOC; CaMnSi (BCSID 0.599), a narrow gap axion insulator; UAsS (BCSID 0.594), a 5f-orbital Weyl semimetal; CsMnF₄(BCSID 0.327), a material presenting a new type of quasi-symmetry protected closed nodal surface; and FeCr₂S₄(BCSID 0.613), a symmetry-enforced semimetal with double Weyls and spin-polarized surface states. 

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3. Bonding Interactions Can Drive Topological Phase Transitions in a Zintl Antiferromagnetic Insulator

   https://doi.org/10.1002/adfm.202415610  

   Berry, Tanya; Moya, Jaime M; Smiadak, David; Lee, Scott B; Aharon, Sigalit; Zevalkink, Alexandra; McQueen, Tyrel M; Schoop, Leslie M (February 2025, Advanced Functional Materials)

   Abstract While ∼30% of materials are reported to be topological, topological insulators are rare. Magnetic topological insulators (MTI) are even harder to find. Identifying crystallographic features that can host the coexistence of a topological insulating phase with magnetic order is vital for finding intrinsic MTI materials. Thus far, most materials that are investigated for the determination of an MTI are some combination of known topological insulators with a magnetic ion such as MnBi₂Te₄. Motivated by the recent success of EuIn₂As₂, the role of chemical pressure on topologically trivial insulator is investigated, Eu₅In₂Sb₆via Ga substitution. Eu₅Ga₂Sb₆is predicted to be topological but is synthetically difficult to stabilize. The intermediate compositions between Eu₅In₂Sb₆and Eu₅Ga₂Sb₆are observed through theoretical works to explore a topological phase transition and band inversion mechanism. The band inversion mechanism is attributed to changes in Eu–Sb hybridization as Ga is substituted for In due to chemical pressure. Eu₅In_4/3Ga_2/3Sb₆is also synthesized, the highest Ga concentration in Eu₅In_2‐xGa_xSb₆, and report the thermodynamic, magnetic, transport, and Hall properties. Overall, the work paints a picture of a possible MTI via band engineering and explains why Eu‐based Zintl compounds are suitable for the co‐existence of magnetism and topology. 

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4. Gate‐Tunable Spin‐To‐Charge Conversion in Topological Insulator‐Magnetic Insulator Heterostructures at Room Temperature

   https://doi.org/10.1002/adfm.202501880  

   Sun, Wenxuan; Chen, Yequan; Xu, Ruijie; Zhuang, Wenzhuo; Wang, Di; Liu, Long; Song, Anke; Xing, Guozhong; Xu, Yongbing; Zhang, Rong; et al (March 2025, Advanced Functional Materials)

   Abstract Over the past decade, topological insulators have received enormous attention for their potential in energy‐efficient spin‐to‐charge conversion, enabled by strong spin‐orbit coupling and spin‐momentum locked surface states. Despite extensive research, the spin‐to‐charge conversion efficiency, usually characterized by the spin Hall angle (θ_SH), remains relatively low at room temperature. In this work, pulsed laser deposition is employed to fabricate high‐quality ternary topological insulator (Bi_0.1Sb_0.9)₂Te₃thin films on magnetic insulator Y₃Fe₅O₁₂. It is found that the value ofθ_SHreaches ≈0.76 at room temperature and increases to ≈0.9 as the Fermi level is tuned to cross topological surface states via electrical gating. These findings provide an innovative approach to tailoring the spin‐to‐charge conversion in topological insulators and pave the way for their applications in energy‐efficient spintronic devices. 

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5. Non-equilibrium states and interactions in the topological insulator and topological crystalline insulator phases of NaCd4As3

   https://doi.org/10.1063/4.0000273  

   Kafle, Tika R; Zhang, Yingchao; Wang, Yi-yan; Shi, Xun; Li, Na; Sapkota, Richa; Thurston, Jeremy; You, Wenjing; Gao, Shunye; Dong, Qingxin; et al (January 2025, Structural Dynamics)

   Topological materials are of great interest because they can support metallic edge or surface states that are robust against perturbations, with the potential for technological applications. Here, we experimentally explore the light-induced non-equilibrium properties of two distinct topological phases in NaCd4As3: a topological crystalline insulator (TCI) phase and a topological insulator (TI) phase. This material has surface states that are protected by mirror symmetry in the TCI phase at room temperature, while it undergoes a structural phase transition to a TI phase below 200 K. After exciting the TI phase by an ultrafast laser pulse, we observe a leading band edge shift of >150 meV that slowly builds up and reaches a maximum after ∼0.6 ps and that persists for ∼8 ps. The slow rise time of the excited electron population and electron temperature suggests that the electronic and structural orders are strongly coupled in this TI phase. It also suggests that the directly excited electronic states and the probed electronic states are weakly coupled. Both couplings are likely due to a partial relaxation of the lattice distortion, which is known to be associated with the TI phase. In contrast, no distinct excited state is observed in the TCI phase immediately or after photoexcitation, which we attribute to the low density of states and phase space available near the Fermi level. Our results show how ultrafast laser excitation can reveal the distinct excited states and interactions in phase-rich topological materials. 

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