Speaker: Prof. Shengbai Zhang, professer from the Rensselaer Polytechnic Institute

Title: ond Dipole-Based Geometric Theory of Band Alignment - A New Insight on the Particle-Wave Duality in Solids

Time: 15:00 September 3rd, 2025 (Wednesday)

Venue: No.6 conference room on the 3rd floor, Building No.5

Host: Prof. Xingfa Gao

Abstract

Study of band alignment is plagued by the lack of a common reference for periodic systems. Typically, average potential is used as the reference. One may truncate a bulk to expose the vacuum level [1]. However, with respect to such a level, the average potential is strongly orientation dependent [2]. This happens because the average potential is a projection of a nonintuitive bulk quadrupole tensor in the given direction [3]. By introducing Wigner-Seitz atoms (WSA), which are charge neutral, maintain local crystal symmetry, and tessellate space, one can however reduce the tensor to the expected scalar quantity, whereby setting the stage for a universal intrinsic band alignment [4]. The WSA approach further allows for an evaluation from classical electrostatics of the charge transfer at the interface, which manifests itself as the formation of (sometimes sizable) interfacial bond dipoles. In general, therefore, band alignment consists of two parts: (1) intrinsic contribution of bulk and (2) extrinsic contribution due to interfacial bond polarization. We discover that for interface between isotropic systems, the potential shift due to interface charge transfer is only a function of bulk crystal structure and strictly interface orientation independent in line with experiments [4].

[1] D.-H. Choe, D. West, S. Zhang, Phys. Rev. Lett. 121, 196802 (2018).

[2] L. Kleinman, Phys. Rev. B 24, 7412 (1981).

[3] D.-H. Choe, D. West, S. Zhang, Phys. Rev. B 103, 235202 (2021).

[4] Z. Jiang, D. West, and S. Zhang, Featured Article, Appl. Phys. Rev. 12, 011411 (2025).

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