From spin-orbital entanglement in Sr2RuO4 to spin-orbit controlled MIT in Sr2IrO4

Beyond the direct correspondence between experimental intensity and the electronic removal spectral function, angle-resolved photoemission spectroscopy (ARPES) provides an unparalleled depth of information regarding the electronic structure of solids. In particular, the strict selection rules associated with the photoemitting dipole operator provide further access to both spin and orbital structure of the electronic eigenstates. I will discuss our application of these concepts to the development of various experiments directed towards unraveling the role of spin-orbit coupling in unconventional superconductivity and metal-insulator transitions. I will present our results utilizing circularly-polarized spin-ARPES (CPS-ARPES) for the study of spin-orbit coupling in unconventional superconductors such as Sr2RuO4 [1,2], as well as LiFeAs and FeSe [3]. In doing so, we have established a vectorial description of the relative alignment of spin and orbital vectors and their variation through momentum space, raising important questions regarding the nature of pairing in these materials, and the dramatic modification of the wavefunctions imbued by relativistic effects. I will then conclude by showcasing how similar approaches can be utilized to demonstrate the spin-orbit-controlled nature of the metal insulator transition in Sr2IrO4 [4].

[1] M.W. Haverkort et al., Phys. Rev Lett. 101, 026406 (2008).
[2] C.N. Veenstra et al., Phys. Rev Lett. 112, 127002 (2014).
[3] R.P. Day et al., Phys. Rev Lett. 121, 076401 (2018).
[4] B. Zwartsenberg et al., Nat. Phys. 16, 290 (2020).