Professor, Rensselaer Polytechnic Institute, Troy, NY

Abstract：

Symmetry dictates the physical properties of materials. The symmetry of the Bravais lattice defines the set of points, lines, and planes over which sets of planewaves are degenerate, upon which atomic symmetry determines the interaction potentials which may lift such degeneracies. This results in wavefunctions which are single planewaves throughout the BZ, except in the vicinity of the removed degeneracies. As optical transitions between any two planewaves are forbidden, only regions of the Brillouin zone (BZ) near these lifted degeneracies contribute to optical properties. Application to optical response of Si and other semiconductors reveals that a single band transition, with only two planewaves, well describes their dielectric properties. Further, it provides a framework to understand non-linear optical response which is demonstrated to arise from higher order degeneracy existing along high symmetry lines/points of the BZ.

Brief CV of Prof.Zhang, Shengbai：

NAME: Zhang, Shengbai

POSITION TITLE: Professor, Emeritus

INSTITUTION: Rensselaer Polytechnic Institute

PROFESSIONAL PREPARATION

Jilin University Changchun, Jilin, Semiconductor Physics and Electronics BS 1982

University of California at Berkeley, Berkeley, California, Condensed Matter Physics MA 1985

University of California at Berkeley, Berkeley, California, Condensed Matter Physics PHD 1989

Xerox PARC Palo Alto, California, Electronic Materials Postdoctoral Fellow 1989 – 1991

APPOINTMENTS

2008 – 2025/06/30 Professor, Rensselaer Polytechnic Institute, Troy, NY

2008 – 2025/06/30 Senior Kodosky Constellation Chair, Rensselaer Polytechnic Institute, Troy, NY

2000 - 2007 Senior Scientist II, National Renewable Energy Laboratory, Golden, CO

1997 - 2000 Senior Scientist I, National Renewable Energy Laboratory, Golden, CO

1994 - 1997 Staff Scientist, National Renewable Energy Laboratory, Golden, CO

1991 - 1994 Research Associate, National Renewable Energy Laboratory, Golden, CO

RECENT REPRESENTATIVE PUBLICATIONS

1. Y Liang, D West, S Chen, J Liu, T Li, S Zhang, Semiconductor-compatible topological digital alloys, Materials Today https://doi.org/10.1016/j.mattod.2025.03.017 (2025).

2. Y Liang, S Chen, X Jin, D West, SQ Yu, T Li, S Zhang, Group IV topological quantum alloy and the role of short-range order: the case of Ge-rich Ge1-xPbx, npj Comp. Mat. 10, 82 (2024).

3. Choe DH, West D, Zhang S. Revealing the vacuum level in an infinite solid by real-space potential unfolding. Phys Rev B 103, 235202 (2021).

4. Choe DH, West D, Zhang S. Band alignment and the built-in potential of solids. Phys Rev Lett. 121, 196802 (2018).

5. Z Jiang, D West, S Zhang, Bond dipole based geometric theory of band alignment, Featured Article, Appl. Phys. Rev. 12, 011411 (2025).

6. H Shang, Z Jiang, Y Sun, D West, S Zhang, Revisiting the formulation of charged defect in solids, Editor’s Suggestion, Phys. Rev. Lett. 134, 066401 (2025).

7. D. Wang, D. Han, X.-B. Li, S.-Y. Xie, N.-K. Chen, W. Q. Tian, D. West, H.-B. Sun, and S. B. Zhang, Determination of formation and ionization energies of charged defects in two-dimensional materials, Phys. Rev. Lett. 114, 196801 (2015).

8. Z. Jiang, Y. Li, S. Zhang, and W. Duan, Realizing an intrinsic excitonic insulator by decoupling exciton binding energy from the minimum band gap, Phys. Rev. B 98, 081408(R) (2018).

9. Z. Jiang, Y. Li, W. Duan, S. Zhang, Half-excitonic insulator: A single-spin Bose-Einstein condensate”, Phys. Rev. Lett. 122, 236402 (2019).

10. Jiang Z, Lou W, Liu Y, Li Y, Song H, Chang K, Duan W, Zhang S. Spin-triplet excitonic insulator: The case of semihydrogenated graphene. Phys Rev Lett. 124,166401 (2020).

11. M Cai, M-P Miao, Y Liang, Z Jiang, Z-Y Liu, W-H Zhang, X Liao, L-F Zhu, D West, S Zhang, Y-S Fu, Manipulating single excess electrons in monolayer transition metal dihalide, Nat. Comm. 14, 3691 (2023).

12. YT Huang, ZZ Li, NK Chen, Y Wang, HB Sun, S Zhang, XB Li, Complex charge density waves in simple electronic systems of two-dimensional III2–VI3 materials, Nat. Comm. 15, 9983 (2024).

HIGHLIGHTS OF THE RECENT WORKS

In Refs. [1] and [2], we predict 3D topological materials, including topological triple-point and Weyl semimetals, weak and strong topological insulators, can be made of ordinary semiconductors with full compatibility to today’s semiconductor industry. In Refs. [3] and [4], we uncovered the vacuum level position in periodic solids. Using the vacuum level as common reference, we made breakthroughs in the everlasting quests on the physics of band alignment at interface [5] and charged defect formation energy [6]. In Ref. [5], we show atoms in a solid not only are charge neutral but also pertain local symmetries of the crystal and tessellate space. It leads to the discovery of interfacial bond dipoles and a completely new geometric theory of band alignment, which explains all the experiments and first-principles results that in isotropic systems, the band alignment is nearly orientation independent. In Ref. [6], we developed the most efficient yet most accurate formalism for the calculation of converged energy of charged defects. Currently, we are pushing the limit to resolve the issue of calculating charged defects in a few-layers two-dimension (2D) systems and 2D on a substrate, even though we have already solved the issue strictly for 2D free-standing systems [7]. In Refs. [8-10], we pointed out the broad importance of dark excitons in 2D materials and established the conditions in various materials at which the dark excitons can precipitate into various excitonic insulator ground states. In a couple of such materials, electronic excitation, via the creation of excitons, opposed to phonons, also gives rise to the formation of small polarons seen by experiment [11]. Other recent work includes the study of complex charge density waves in 2D materials [12].

邀请人：翁红明   研究员

联系人：于乐乐   yulele@iphy.ac.cn

报告地点：物理所中关村园区M楼830会议室