Enhanced superconductivity in restacked TaS 2 nanosheets

Transcription

1 Supplementary Information for Enhanced superconductivity in restacked TaS 2 nanosheets Jie Pan, 1,2,3 Chenguang Guo, 1,2,3 Changsheng Song, 1 Xiaofang Lai, 3 Hui Li, 4 Wei Zhao, 1 Hui Zhang, 6 Gang Mu, 6 Kejun Bu, 1,2,3 Tianquan Lin, 1 * Xiaoming Xie, 6 Mingwei Chen, 4,5, Fuqiang Huang 1,3 * 1 State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai , P. R. China 2 University of Chinese Academy of Sciences, Beijing , China 3 State Key Laboratory of Rare Earth Materials Chemistry and Applications, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing , P.R. China 4 State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai , P.R. China 5 WPI Advanced Institute for Materials Research, Tohoku University, Sendai , Japan 6 State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai , P.R. China List of contents: 1. Materials and methods 1) Preparation of TaS 2 2) Preparation of Li x TaS 2 3) Chemical exfoliation of Li x TaS 2 4) Purification treatment of single-layer TaS 2 nanosheets 5) Preparation of restacked TaS 2 sheets 6) Superconducting measurement 2. Theoretical calculation details 3. Supplementary figures S1

2 1. Materials and Methods Preparation of TaS 2 Raw powder of TaS 2 was synthesized by stoichiometric elements of Ta (99.9%, Alfa Aesar) and S (99.999%, Alfa Aesar) in an evacuated quartz tube at 900 C for 3 days. Then the evacuated quartz tube cooled down to 800 C at the rate of 0.5 C/min, keeping 800 C for 7 days. Finally, the evacuated quartz tube cooled down to room temperature for another 7 days. Preparation of Li x TaS 2 The obtained 0.1 g 2H-TaS 2 polycrystalline was soaked in 20 ml of 1.6 M n-butyllithium in hexane for 3 days. Then the powders were washed by hexane for three times. Finally the powders were dried under evacuated condition. Chemical exfoliation of Li x TaS 2 Obtained LiTaS 2 polycrystalline was soaked in the distilled water and sonicated for 30 min with stirring. After sonication, exfoliated TaS 2 nanosheets was produced and a transparent dispersion solution was formed without any sediments inside. Centrifugalization was not needed and super high yield was realized in this work. Purification treatment of single-layer TaS 2 nanosheets a. The obtained transparent dispersion containing exfoliated TaS 2 nanosheets was centrifuged at the rate of 2000 rpm for 15 min. b. Then the supernatant was centrifuged at the rate of rpm for 10 min in order to precipitate most of single-layer TaS 2 nanosheets. c. Keep the sediments, and add distill water following the sonication process. d. Repeat the b and c steps for three times for removing the ions in the dispersion solution. Preparation of restacked TaS 2 sheets First, the obtained uniform dispersion solution of single-layer TaS 2 nanosheets is S2

3 dialyzed repeatedly to ensure to remove the ions in the solution further. Then through simple air pump filtration, we can obtain TaS 2 films with different thickness dependent on the amount of TaS 2 sheets. Superconducting measurement Temperature-dependent magnetic susceptibility measurement was conducted under a magnetic field of 10 Oe, containing field-cooling and zero field-cooling processes. Magnetic field-dependent magnetic susceptibility measurement was taken at 2K, and the resistivity measurement as the function of temperature was conducted under different magnetic fields. Specific heat test data were collected using the thermal relaxation method. Abovementioned measurements were performed in a physical property measurement system (PPMS) of Quantum Design. 2. Theoretical calculation details Theoretical calculations have been performed within the framework of density functional theory (DFT) as implemented by the Vienna an initio Simulation Package (VASP) [S1, S2]. The exchange-correlation energy was treated in the generalized-gradient approximation (GGA) using Perdew-Burke-Ernzerhof (PBE)-D2 method [S3] that includes vdw interactions. The cutoff energy of plane wave was chosen at 400 ev. For the structure optimizations, Monkhorst-Pack (MP) grids were used. The changes in total energies between two successive iteration steps were less than 10-5 ev, and all the Hellmann-Feynman force acting on each atoms was lower than 0.01 ev /Å. The twisted bilayers were modeled using accidental angular commensurations [S4]. In a hexagonal lattice whose basis vector is a 1 and a 2, a skewed supercell with basis vector (na 1 + ma 2 ) has a corresponding skewed angle, θ = tan -1 ( 3 m/2n+m). We investigate the twisted TaS 2 bilayers, which are produced by stacking a pair of oppositely skewed TaS 2 Supercells. We have considered twisted TaS 2 bilayers with the same periodicity, where a Ta atom in the top layer S3

4 superimposes on a Ta atom in the bottom layer. S3

5 References [S1] P. E. Blo chl, Phys. Rev. B 1994, 50, [S2] G. Kresse, and J. Furthmu ller, Phys. Rev. B 1996, 54, [S3] M. C. Payne, M. P. Teter, D. C. Allan, T. A. Arias, J. D. Joannopoulos, Rev. Mod. Phys. 1992, 64, [S4] A. Kolmogorov, V. Crespi, Phys. Rev. B 2005, 71, Supplementary Figures Figure S1. PXRD pattern of as-prepared 2H-TaS 2 polycrystalline and Li x TaS 2 polycrystalline. S4

6 Figure S2. a, Schematic illustration of lithium-deintercalation exfoliation for preparation of TaS 2 single-layers. b, Uniform dispersion solution of TaS 2 nanosheets. Figure S3. a, the Raman spectra of bulk 2H-TaS 2 and single-layer TaS 2 nanosheets. b, the Raman spectra of bulk 2H-TaS 2 and restacked TaS 2 nanosheets. S5

7 Figure S4. SEM image of restacked TaS 2 nanosheets. Figure S5. a, HAADF STEM image, and b, corresponding SAED pattern of TaS 2 sheets restacked by TaS 2 single layers. S5

8 Figure S6. Temperature dependence of derivative of resistance, ranging from 15 K to 100 K. S6

9 Figure S7. Temperature dependence of magnetic susceptibility of freeze-dried exfoliated single-layer TaS 2 powders under the magnetic field of 10 Oe, with zero-field-cooling curve (black) and field-cooling curve (red). Figure S8. PXRD pattern of freeze-dried monolayer TaS 2 sample. S7

10 Figure S9. Relationship between superconducting temperature and critical magnetic field. Figure S10. Crystal structures of untwisted 2H-TaS 2 and twisted TaS 2 with different twisted angles. S8

11 Figure S11. DFT band structure of untwisted 2H-TaS 2 and twisted TaS 2 with different twisted angles. S9

12 Figure S12. DFT calculated density of states (DOS) with different twisted angles. Figure S13. Difference charge density for 2H-TaS 2 a and twisted TaS 2 b. S10