Abstract：

　In this talk I will discuss a series of insights into non-equilibrium phenomena involving the orbital angular momentum (OAM) of Bloch electron systems. Recent years have witnessed a surge of interest in the orbital angular momentum of Bloch electrons, motivated by its emerging applications in spintronics and magnetic memory [1].  I will first show that disorder plays a crucial role in the orbital Hall effect, at least when the OAM current is evaluated according to the conventional prescription of multiplying the matrix elements of the OAM by those of the velocity [2]. Building on this insight I will show that, more importantly, the conventional evaluation of the orbital Hall effect suffers from a fundamental flaw. Evaluations of the orbital Hall effect have only retained inter-band matrix elements of the position operator. I will outline the correct way to evaluate the OHE including all matrix elements of the position operator, including the technically challenging intra-band elements [3]. They also give rise to a giant OHE in the bulk states of topological insulators, which greatly exceeds spin-related effects [4]. Finally I will discuss our recent insights into the orbital magneto-electric effect. I will show that the OME is partly the result of a non-equilibrium dipole moment generated via Zitterbewegung and proportional to the quantum metric. Our results suggest quantum metric engineering as a route towards maximizing orbital torques [5]. In closing I will give an overview of outstanding questions in the field which include the full role of disorder, inhomogeneities, and the non-conservation of the OAM due to intrinsic mechanisms, which our group has also identified [6].

1.      Rhonald Burgos Atencia, Amit Agarwal, and Dimitrie Culcer, Advances in Physics X 9, 2371972 (2024).

2.      Hong Liu and Dimitrie Culcer, Phys. Rev. Lett. 132, 186302 (2024).

3.      Hong Liu, James H. Cullen, Daniel P. Arovas, and Dimitrie Culcer, Phys. Rev. Lett. 134, 036304 (2025).

4.      James H. Cullen, Hong Liu, and Dimitrie Culcer, NPJ Spintronics 3, 22 (2025).

5.      James H. Cullen, Daniel P. Arovas, Roberto Raimondi, and Dimitrie Culcer, arXiv:2505.02911.

6.      Rhonald Burgos Atencia, Daniel P. Arovas, and Dimitrie Culcer, Phys. Rev. B 110, 035427 (2024).

Biosketch：

 Dimitrie Culcer obtained his PhD from the University of Texas at Austin in 2005. He worked as a postdoctoral research fellow first at Argonne National Laboratory between 2006-2008, and subsequently at the University of Maryland, College Park, 2008-2010. He became a faculty member at the University of Science and Technology of China in Hefei in 2010, where he was a member of the International Center for Quantum Design of Functional Materials. In 2013 he moved to the University of New South Wales in Sydney where he is currently a Professor. In 2019 he was awarded a Future Fellowship by the Australian Research Council.

Dimi Culcer's research interests include quantum computing, spin-orbit coupling and topological effects in condensed matter physics, quantum transport theory and nonlinear electrical and optical effects, with a focus on topological materials. He is actively working in all these areas.