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Electronic Topological Transition in Ag2Te at High-pressure.

Zhang Y, Li Y, Ma Y, Li Y, Li G, Shao X, Wang H, Cui T, Wang X, Zhu P - Sci Rep (2015)

Bottom Line: Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag2Te at 1.8 GPa.This result indicates that the best bulk insulating character and topological nature in Ag2Te can be obtained at this pressure.A pressure-induced metallization in Ag2Te is confirmed by the results of temperature-dependent resistivity measurements.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China.

ABSTRACT
Recently, Ag2Te was experimentally confirmed to be a 3D topological insulator (TI) at ambient pressure. However, the high-pressure behaviors and properties of Ag2Te were rarely reported. Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag2Te at 1.8 GPa. Before ETT, the positive pressure coefficient of bulk band-gap, which is firstly found in TIs family, is found by both first-principle calculations and in situ high-pressure resistivity measurements. The electrical resistivity obtained at room temperature shows a maximum at 1.8 GPa, which is nearly 3.3 times to that at ambient pressure. This result indicates that the best bulk insulating character and topological nature in Ag2Te can be obtained at this pressure. Furthermore, the high-pressure structural behavior of Ag2Te has been investigated by in situ high-pressure synchrotron powder X-ray diffraction technique up to 33.0 GPa. The accurate pressure-induced phase transition sequence is firstly determined as P21/c → Cmca → Pnma. It is worth noting that the reported isostructural P21/c phase is not existed, and the reported structure of Cmca phase is corrected by CALYPSO methodology. The second high-pressure structure, a long puzzle to previous reports, is determined as Pnma phase. A pressure-induced metallization in Ag2Te is confirmed by the results of temperature-dependent resistivity measurements.

No MeSH data available.


Calculated band structures of Ag2Te at (a) ambient pressure, (b) 1.0 GPa, and (c) 2.0 GPa, respectively. Total DOS and PDOS results of Ag2Te at (d) ambient pressure, (e) 1.0 GPa, and (f) 2.0 GPa, respectively.
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f4: Calculated band structures of Ag2Te at (a) ambient pressure, (b) 1.0 GPa, and (c) 2.0 GPa, respectively. Total DOS and PDOS results of Ag2Te at (d) ambient pressure, (e) 1.0 GPa, and (f) 2.0 GPa, respectively.

Mentions: As shown in Fig. 4(a,b), bulk Ag2Te is an indirect band-gap semiconductor at ambient pressure and at 1.0 GPa, with the valence-band maximum (VBM) located around D point and the conduction-band minimum (CBM) at Γ point. However, as shown in Fig. 4c, Ag2Te is a direct band-gap semiconductor at 2.0 GPa with VBM and CBM at Γ point. At ambient pressure, the band inversion of surface states at Γ point is the origin of the topological nature, as discussed by Zhang et al.6. The partial electron density of state (PDOS) and sum DOS results of Ag2Te at ambient pressure, 1.0, and 2.0 GPa, respectively, indicate that VBM are mainly composed by the hybridization of Ag-4d and Te-5p electrons, as shown in Fig. 4(d–f). The orbital composition is almost invariant under selective pressures. This indicates that the TI character should be stable under pressure26. On the other hand, it is found that the increasing interlayer spin-orbit coupling and the fluctuation of LEP activity35 under pressure caused a positive pressure coefficient of indirect band-gap and a reduction in the direct band-gap at Γ point, which result in an indirect-to-direct transition36. Given this indirect-to-direct transformation of Ag2Te, the above assumption of a pressure-induced ETT appears reasonable2537.


Electronic Topological Transition in Ag2Te at High-pressure.

Zhang Y, Li Y, Ma Y, Li Y, Li G, Shao X, Wang H, Cui T, Wang X, Zhu P - Sci Rep (2015)

Calculated band structures of Ag2Te at (a) ambient pressure, (b) 1.0 GPa, and (c) 2.0 GPa, respectively. Total DOS and PDOS results of Ag2Te at (d) ambient pressure, (e) 1.0 GPa, and (f) 2.0 GPa, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588579&req=5

f4: Calculated band structures of Ag2Te at (a) ambient pressure, (b) 1.0 GPa, and (c) 2.0 GPa, respectively. Total DOS and PDOS results of Ag2Te at (d) ambient pressure, (e) 1.0 GPa, and (f) 2.0 GPa, respectively.
Mentions: As shown in Fig. 4(a,b), bulk Ag2Te is an indirect band-gap semiconductor at ambient pressure and at 1.0 GPa, with the valence-band maximum (VBM) located around D point and the conduction-band minimum (CBM) at Γ point. However, as shown in Fig. 4c, Ag2Te is a direct band-gap semiconductor at 2.0 GPa with VBM and CBM at Γ point. At ambient pressure, the band inversion of surface states at Γ point is the origin of the topological nature, as discussed by Zhang et al.6. The partial electron density of state (PDOS) and sum DOS results of Ag2Te at ambient pressure, 1.0, and 2.0 GPa, respectively, indicate that VBM are mainly composed by the hybridization of Ag-4d and Te-5p electrons, as shown in Fig. 4(d–f). The orbital composition is almost invariant under selective pressures. This indicates that the TI character should be stable under pressure26. On the other hand, it is found that the increasing interlayer spin-orbit coupling and the fluctuation of LEP activity35 under pressure caused a positive pressure coefficient of indirect band-gap and a reduction in the direct band-gap at Γ point, which result in an indirect-to-direct transition36. Given this indirect-to-direct transformation of Ag2Te, the above assumption of a pressure-induced ETT appears reasonable2537.

Bottom Line: Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag2Te at 1.8 GPa.This result indicates that the best bulk insulating character and topological nature in Ag2Te can be obtained at this pressure.A pressure-induced metallization in Ag2Te is confirmed by the results of temperature-dependent resistivity measurements.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China.

ABSTRACT
Recently, Ag2Te was experimentally confirmed to be a 3D topological insulator (TI) at ambient pressure. However, the high-pressure behaviors and properties of Ag2Te were rarely reported. Here, a pressure-induced electronic topological transition (ETT) is firstly found in Ag2Te at 1.8 GPa. Before ETT, the positive pressure coefficient of bulk band-gap, which is firstly found in TIs family, is found by both first-principle calculations and in situ high-pressure resistivity measurements. The electrical resistivity obtained at room temperature shows a maximum at 1.8 GPa, which is nearly 3.3 times to that at ambient pressure. This result indicates that the best bulk insulating character and topological nature in Ag2Te can be obtained at this pressure. Furthermore, the high-pressure structural behavior of Ag2Te has been investigated by in situ high-pressure synchrotron powder X-ray diffraction technique up to 33.0 GPa. The accurate pressure-induced phase transition sequence is firstly determined as P21/c → Cmca → Pnma. It is worth noting that the reported isostructural P21/c phase is not existed, and the reported structure of Cmca phase is corrected by CALYPSO methodology. The second high-pressure structure, a long puzzle to previous reports, is determined as Pnma phase. A pressure-induced metallization in Ag2Te is confirmed by the results of temperature-dependent resistivity measurements.

No MeSH data available.