Takashi Komesu

Effective surface Debye temperature for NiMnSb(100) epitaxial films

The surface Debye temperature of the NiMnSb (100) epitaxial films has been obtained using low energy electron diffraction, inverse photoemission, and core-level photoemission. The normal dynamic motion of the (100) surface results in a value for the effective surface Debye temperature of 145±13 K. This is far smaller than the bulk Debye temperature of 312±5 K obtained from wave vector dependent inelastic neutron scattering. The large difference between these measures of surface and bulk dynamic motion indicates a soft and compositionally different (100) surface.

Increasing the Néel temperature of magnetoelectric chromia for voltage-controlled spintronics

Boron doped chromia (Cr2O3) thin films with substitutional doping levels between zero and 3% are grown using pulsed laser deposition in borane background gases. Magnetometry reveals a tunable increase in the Neel temperature of the (0001) textured Cr2BxO3−x thin films at a rate of about 10% with 1% oxygen site substitution preserving a net boundary magnetization. Spin resolved inverse photoemission measured after magnetoelectric annealing in subsequently reversed electric fields evidences voltage-controlled reversal of boundary magnetization and thus magnetoelectricity of Cr2BxO3−x. Conservation of magnetoelectricity far above room temperature makes ultra-low power voltage-controlled spintronic devices feasible.

Spin-orbit coupling in the band structure of monolayer WSe2.

We used angle-resolved photoemission spectroscopy (ARPES) to map out the band structure of single-layer WSe2. The splitting of the top of the valence band because of spin-orbit coupling is 513 ± 10 meV, in general agreement with theoretical predictions and in the same range as that of bulk WSe2. Overall, our density functional theory (DFT) calculations of the band structure are in excellent agreement with the ARPES results. We have verified that the few discrepancies between theory and experiment are not due to the effect of strain. The differences between the DFT-calculated band structure using local density approximation (LDA) and that using the generalized gradient approximation (GGA), for single-layer WSe2, are caused mainly by differences in the respective charge densities.

The surface phases of the La0.65Pb0.35MnO3 manganese perovskite surface

Abstract We have studied the surface composition and structure of colossal magneto-resistive perovskite thin films of La0.65Pb0.35MnO3. Depending on the annealing treatments, the thin film surface exhibits wildly different behavior and composition. With a gentle annealing procedure, the surface is dominated by appreciable Pb segregation, whereas a heavily annealed surface undergoes an irreversible restructuring into a Ruddlesden–Popper phase (La1−xPbx)2MnO4. The measured effective Debye temperatures of the two surfaces shows that the Pb-rich La0.65Pb0.35MnO3 surface region is softer than the surface of the Ruddlesden–Popper phase.

THE OCCUPIED AND UNOCCUPIED ELECTRONIC STRUCTURE OF ADSORBED FERROCENE

Abstract We have studied both the occupied and unoccupied molecular orbitals of adsorbed ferrocene. The occupied molecular orbitals have been identified using a combination of photoemission selection rules and resonant photoemission. Ferrocene adsorbs with a strong preferential molecular orientation on Mo(112) at 150 K, like metallocenes on many other surfaces. Though the ferrocene molecular axis is largely parallel with the Mo(112) surface there is very little perturbation of the molecular orbitals relative to the gas phase.

Occupied and unoccupied electronic structure of Na doped MoS2(0001)

The influence of sodium on the band structure of MoS2(0001) and the comparison of the experimental band dispersion with density functional theory show excellent agreement for the occupied states (angle-resolved photoemission) and qualitative agreement for the unoccupied states (inverse photoemission spectroscopy). Na-adsorption leads to charge transfer to the MoS2 surface causing an effect similar to n-type doping of a semiconductor. The MoS2 occupied valence band structure shifts rigidly to greater binding with little change in the occupied state dispersion. Likewise, the unoccupied states shift downward, approaching the Fermi level, yet the amount of the shift for the unoccupied states is greater than that of the occupied states, effectively causing a narrowing of the MoS2 bandgap.

Temperature dependent induced spin polarization in Cr2O3 overlayers on epitaxial CrO2 films

Abstract Spin-resolved inverse photoemission investigations show that the native Cr 2 O 3 surface is antiferromagnetically coupled to the CrO 2 thin film substrate, with a temperature dependent induced polarization. The Cr 2 O 3 exhibits the characteristic behavior of a rigid band/spin mixing behavior (non-Stoner) of a local moment paramagnet. The strong shifts of the conduction band edge from room temperature to low temperature suggests that the extent of the induced polarization of the Cr 2 O 3 oxide surface, by the CrO 2 substrate, may be partly related to Coulomb blockade effects identified in CrO 2 /Cr 2 O 3 /CrO 2 junctions.

Comparing inverse photoemission and X-ray absorption spectroscopies

Abstract The comparison of inverse photoemission with X-ray absorption spectra is possible. We discuss some of the similarities and differences that must be considered in both techniques. Two examples of such comparison are given: the NiMnSb half-Heusler alloy and the La0.65Pb0.35MnO3 perovskite. We briefly present the dipole and symmetry selection rules which can be used for the interpretation of inverse photoemission as well as the absorption spectra. Due to the symmetry constraints imposed by the initial state, the selection rules in inverse photoemission are more restrictive than in the case of X-ray absorption.

The origin of enhanced magnetization in strained gadolinium

Abstract From combined spin-resolved photoemission and spin-polarized inverse photoemission, the experimental spin-resolved band structure of gadolinium on Mo(112) has been constructed. The occupied spin dependent electronic structure near the Fermi level is dominated by shallow dispersion of a spin minority band with considerable surface weight. There is an occupied spin majority bulk band straddling the Fermi level whose spin minority counterpart remains largely on the unoccupied side of the Fermi level. This results in large spin majority weight in the occupied band structure relative to spin minority.

Symmetry-resolved surface-derived electronic structure of MoS2(0 0 0 1)

We find a wave vector dependence of the band symmetries for MoS(2)(0 0 0 1) in angle-resolved photoemission. The band structures are found to be significantly different for states of even and odd reflection parities, despite the absence of true mirror plane symmetry away from Γ, the Brillouin zone center, along the line to the K point, at the Brillouin zone edge. Our measurements agree with density functional theory (DFT) calculations for each band symmetry, with the notable exception of the Mo 4d(x(2)-y(2)) contributions to the valence band structure of MoS(2)(0 0 0 1). The band structure is indicative of strong S 3p and Mo 4d hybridization. In particular, the top of the valence band is predominantly composed of Mo 4d(3z(2)-r(2)) derived states near Γ, whereas near K Mo 4d(x(2)-y(2)) as well as Mo 4d(xy) dominate. In contrast, the bottom of the valence band is dominated by Mo 5s and S 3p(z) contributions.