Alberto De la Torre

Spin-orbit splitting of the Shockley surface state on Cu(111)

We present angle-resolved photoemission data from Cu(111). Using a focused 6 eV continuous-wave laser for photoexcitation, we achieve a high effective momentum resolution, enabling detection of the Rashba spin splitting in the Shockley surface state on Cu(111). The magnitude of the spin splitting of Δk∼0.006 A−1 is surprisingly large and exceeds values predicted for the analogous surface state on Ag(111), but is reproduced by first-principles calculations. We further resolve a kink in the dispersion, which we attribute to electron-phonon coupling.

Carrier-Density Control of the SrTiO3 (001) Surface 2D Electron Gas studied by ARPES.

The origin of the 2D electron gas (2DEG)stabilized at the bare surface of SrTiO3 (001) is investigated. Using high-resolution angle-resolved photoemission and core-level spectroscopy, it is shown conclusively that this 2DEG arises from light-induced oxygen vacancies. The dominant mechanism driving vacancy formation is identified, allowing unprecedented control over the 2DEG carrier density.

Second Harmonic Generation Spectroscopy of Hidden Phases

Second harmonic generation (SHG), a frequency doubling process through the second order nonlinear light-matter interactions, provides essential symmetry information of the matter that light interacts with. Recently, SHG, owing to its enhanced capability of symmetry, spectral and spatial resolutions and its compatibility of extreme sample environments such as low temperature, magnetic and electric fields, is exploited to probe complex electronic phases in correlated electron systems. In particular, SHG has shown its unique advantages in revealing hidden electronic phases that are invisible to many experimental probes because of their unconventional order parameters, or preserved translational symmetry as the underlying lattice, or small domain size of degenerate states. In this review, we describe the advances in the SHG based techniques that have enabled their applications in searching for the hidden electronic phases. We discuss successful examples of a toroidal order in a magnetoelectric insulator LiCoPO 4 , a parity-broken nematic order in a correlated metal Cd 2 Re 2 O 7 , and a loop-current or magnetic-quadrupole order in a cuprate analogue Sr 2 IrO 4 and in a cuprate high-Tc superconductor YBa 2 Cu 3 O y . Finally, we briefly survey the prospects of second order nonlinear optical responses in addition to SHG in studying hidden phases.