Disentangling surface and bulk photoemission using circularly polarized light

We show that in angle resolved photoemission spectroscopy (ARPES), near-surface induced fields can be useful for disentangling the surface and bulk related emission. The jump of the dielectric function at the interface results in a nonzero term $\mathrm{div}\mathbf{A}$ in the photoemission matrix element. The term happens to be significant approximately within the first unit cell and leads to circular dichroism for the states localized therein. As an example we use ARPES spectra of an $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ crystal to distinguish between the overdoped surface related component and its bulk counterparts.

Figure 1

(Color online) Experimental geometry. (a) Linear dependence of the circular dichroism in photoelectron intensity $D=I^{\mathrm{cr}}-I^{\mathrm{cl}}$ on the angle $\eta$. The red-white-blue color scale denotes the strength of the dichroism. (b) Decomposition of a circularly polarized wave in two linearly polarized ones with polarization vectors ${\mathbf{A}}_{\mathrm{S}}$ and ${\mathbf{A}}_{\mathrm{C}}$ with a phase shift of $\pi ∕2$.

Figure 2

(Color online) (a), (b) Left to right: position of the energy-momentum cuts in the reciprocal space, sum of the spectra measured with opposite circular polarizations, their difference, extracted bulk component, extracted surface component. Color scale bars show the absolute intensity. In the block (a) the process of disentangling the surface related antibonding band and the chain band is demonstrated ($h\nu =50\mathrm{eV}$, $k_x^{\text{slit}}\approx -1.82{\mathrm{\AA }}^{-1}$). (b) The same procedure, but for the surface and bulk components of the bonding band ($h\nu =55\mathrm{eV}$, $k_y^{\text{slit}}\approx -0.70{\mathrm{\AA }}^{-1}$). The antibonding band in this case is suppressed by the unfavorable matrix elements. (c) Structure of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ near the cleavage plane.