Imaging Doped Holes in a Cuprate Superconductor with High-Resolution Compton Scattering

The high-temperature superconducting cuprate La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) shows several phases ranging from antiferromagnetic insulator to metal with increasing hole doping. To understand how the nature of the hole state evolves with doping, we have carried out high-resolution Compton scattering measurements at room temperature together with first-principles electronic structure computations on a series of LSCO single crystals in which the hole doping level varies from the underdoped (UD) to the overdoped (OD) regime [1]. Holes in the UD system are found to primarily populate the O 2px/py orbitals. In contrast, the character of holes in the OD system is very different in that these holes mostly enter Cu d orbitals. High-resolution Compton scattering provides a bulk-sensitive method for imaging the orbital character of dopants in complex materials. \\[4pt] [1] Y. Sakurai \textit{et al.} Science {\bf 332}, 698 (2011).