High-temperature superconductivity in cuprates arises from an electronic state that remains poorly understood. We report the observation of a related electronic state in a noncuprate material, strontium iridate (Sr2IrO4), in which the distinct cuprate fermiology is largely reproduced. Upon surface electron doping through in situ deposition of alkali-metal atoms, angle-resolved photoemission spectra of Sr2IrO4 display disconnected segments of zero-energy states, known as Fermi arcs, and a gap as large as 80 millielectron volts. Its evolution toward a normal metal phase with a closed Fermi surface as a function of doping and temperature parallels that in the cuprates. Our result suggests that Sr2IrO4 is a useful model system for comparison to the cuprates.

We used the Linac Coherent Light Source free-electron x-ray laser to probe the electronic structure of CO molecules as their chemisorption state on Ru(0001) changes upon exciting the substrate by using a femtosecond optical laser pulse. We observed electronic structure changes that are consistent with a weakening of the CO interaction with the substrate but without notable desorption. A large fraction of the molecules (30%) was trapped in a transient precursor state that would precede desorption. We calculated the free energy of the molecule as a function of the desorption reaction coordinate using density functional theory, including van der Waals interactions. Two distinct adsorption wells-chemisorbed and precursor state separated by an entropy barrier-explain the anomalously high prefactors often observed in desorption of molecules from metals.

We give experimental and theoretical evidence of the Rashba effect at the magnetic rare-earth metal surface Gd(0001). The Rashba effect is substantially enhanced and the Rashba parameter changes its sign when a metal-oxide surface layer is formed. The experimental observations are quantitatively described by ab initio calculations that give a detailed account of the near-surface charge density gradients causing the Rashba effect. Since the sign of the Rashba splitting depends on the magnetization direction, the findings open up new opportunities for the study of surface and interface magnetism.PACS numbers: 71.70. Ej, A key issue in condensed-matter research aiming at future spintronic devices [1] is to control and manipulate the electron spin in a two-dimensional electron gas (2DEG) of semiconductor systems without the need of applying an external magnetic field. Rashba had realized early on [2] that this can be achieved by an electric field which acts as a magnetic field in the rest frame of a moving electron. The interaction between the spin s of a moving electron of momentumhk with an electric field oriented along the z-axis e z is described by the Rashba HamiltonianThe Rashba parameter α R is proportional to the electric field and depends on the effective, material-dependent spin-orbit coupling (SOC) strength. In nonmagnetic systems the Rashba effect lifts the spin-degeneracy of the energy dispersion ǫ(k) of an electronic state, and the energy difference between ǫ ↑ (k) and ǫ ↓ (k) is called Rashba splitting ∆ǫ(k) = α R |k|. Even though spintronic research currently focuses on spin-polarized electrons in semiconductors [3,4], it is important to explore the Rashba effect in other material classes as well. A necessary condition for the Rashba effect to occur is the absence of inversion symmetry and, while in the proposed FET-type spin transistor [5] a gate voltage must be applied to break inversion symmetry of the 2DEG, this condition is naturally fulfilled by the structural inversion asymmetry (SIA) existing at any crystal surface or interface. Owing to SIA, electrons in a two-dimensional surface or interface state experience an effective crystal potential gradient perpendicular to their plane of propagation, hereby optimizing (e z × k) in Eq. (1). One should expect that the Rashba effect is a general surface and interface phenomenon, but up to now Rashba splittings have only been observed for surface states at Au(111) [6,7] and W(110) [8,9]. Recently relativistic density functional theory (DFT) calculations were able to reproduce the observed splitting of the Au sp-like surface state [10] and the analogy to a 2DEG has been pointed out [11]. Yet, it is still a challenging task to give a physical picture of the Rashba effect from the electronic structure point of view.This Letter presents the first experimental and theoretical evidence of a Rashba splitting of exchange-split two-dimensional electron states. Using the surface state of ferromagnetic Gd metal as example we report on the novel finding of a k-depe...