As a new type of topological materials, ZrTe 5 shows many exotic properties under extreme conditions. Using resistance and ac magnetic susceptibility measurements under high pressure, while the resistance anomaly near 128 K is completely suppressed at 6.2 GPa, a fully superconducting transition emerges. The superconducting transition temperature T c increases with applied pressure, and reaches a maximum of 4.0 K at 14.6 GPa, followed by a slight drop but remaining almost constant value up to 68.5 GPa. At pressures above 21.2 GPa, a second superconducting phase with the maximum T c of about 6.0 K appears and coexists with the original one to the maximum pressure studied in this work. In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopy combined with theoretical calculations indicate the observed two-stage superconducting behavior is correlated to the structural phase transition from ambient Cmcm phase to high-pressure C2/m phase around 6 GPa, and to a mixture of two high-pressure phases of C2/m and P-1 above 20 GPa. The combination of structure, transport measurement, and theoretical calculations enable a complete understanding of the emerging exotic properties in 3D topological materials under extreme environments.high pressure | Dirac semimetals | superconductivity | synchrotron X-ray diffraction S ince the first report of topological insulator, an extensive attention in recent years has been focused on newly emergent Dirac materials including topological insulators (1-3), Dirac semimetals (4, 5), and Weyl semimetals (5-7) for their unique quantum phenomena. ZrTe 5 has been studied for a long time due to its large thermoelectric power (8, 9), resistivity anomaly (10, 11), and large positive magnetoresistance (12). Recent theoretical works (13,14) have proposed that single-layer ZrTe 5 is a large gap quantum spin hall insulator, but the bulk ZrTe 5 behaves between the strong and weak topological insulator. These predictions spark the renewed interest in the investigation of its Dirac and topological characters. Indeed, the magnetotransport experiments (15) have observed the chiral magnetic effect, both angle-resolved photoemission spectroscopy (15) and magneto-infrared spectroscopy (16, 17) study show the electronic structure of ZrTe 5 is similar with other three-dimensional (3D) Dirac semimetals like Na 3 Bi (18-20) and Cd 3 As 2 (21-25). These results suggest that ZrTe 5 is a very promising system that hosts topological properties and might help to pave a new way for further experimental studies of topological phase transitions.As one of the fundamental state parameters, high pressure is an effective, clean way to tune lattice as well as electronic states, especially in quantum states (26)(27)(28). In this work, by performing resistance and ac magnetic susceptibility measurements on ZrTe 5 single crystal at various pressures up to 68.5 GPa, a superconducting transition at 1.8 K was first noticed at a pressure of 6.2 GPa. It was interesting to notice that the occurrence of the metallic pha...
Tungsten ditelluride (WTe 2 ) has attracted significant attention due to its interesting electronic properties, such as the unsaturated magnetoresistance and superconductivity. Recently, it has been proposed to be a new type of Weyl semimetal, which is distinguished from other transition metal dichalcogenides (TMDs) from a topological prospective. Here, we study the structure of WTe 2 under pressure with a crystal structure prediction and ab initio calculations combined with high pressure synchrotron X-ray diffraction and Raman spectroscopy measurements. We find that the ambient orthorhombic structure (Td) transforms into a monoclinic structure (1T') at around 4-5 GPa. As the transition pressure is very close to the critical point in recent high-pressure electrical transport measurements, the emergence of superconductivity in WTe 2 under pressure is attributed to the Td-1T' structure phase transition, which associates with a sliding mechanism of the TMD layers and results in a shorter Te-Te interlayer distance compared to the intralayer ones. These results highlight the critical role of the interlayer stacking and chalcogen interactions on the electronic and superconducting properties of multilayered TMDs under hydrostatic strain environments.
Strain can be used as an effective tool to tune the crystal structure of materials and hence to modify their electronic structures, including topological properties. Here, taking Na3Bi as a paradigmatic example, we demonstrated with first-principles calculations and k · p models that the topological phase transitions can be induced by various types of strains. For instance, the Dirac semimetal phase of ambient Na3Bi can be tuned into a topological insulator (TI) phase by uniaxial strain along the 100 axis. Hydrostatic pressure can let the ambient structure transfer into a new thermodynamically stable phase with Fm3m symmetry, coming with a perfect parabolic semimetal having a single contact point between the conduction and valence bands, exactly at Γ point on the Fermi level like α-Sn. Furthermore, uniaxial strain in the 100 direction can tune the new parabolic semimetal phase into a Dirac semimetal, while shear strains in both the 100 and 111 directions can take the new parabolic semimetal phase into a TI. k · p models are constructed to gain more insights into these quantum topological phase transitions. At last, we calculated surface states of Fm3m Na3Bi without and with strains to verify these topological transitions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.