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E W Plummer

Publications and source records attributed to E W Plummer.

At least 19 recordsLinked to original sources
PubMed2006

Giant discrete steps in metal-insulator transition in perovskite manganite wires.

Optical lithography is used to fabricate LPCMO wires starting from a single (La(5/8-0.3)Pr(0.3))Ca3/8MnO3 (LPCMO) film epitaxially grown on a LaAlO3(100) substrate. As the width of the wires is decreased, the resistivity of the LPCMO wires exhibits giant and ultrasharp steps upon varying temperature and magnetic field in the vicinity of the metal-insulator transition. The origin of the ultrasharp transitions is attributed to the effect of spatial confinement on the percolative transport in manganites.

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PubMed2006

Surface reconstructions of TiO2(110) driven by suboxides.

Scanning tunneling microscopy and density functional theory are used to develop a new structural model for surface reconstructions driven by Ti interstitials on TiO2(110). Ti interstitials form the edge- or face-sharing octahedra that serve as building blocks for (1 x 1) reconstruction. Thus, contrary to conventional wisdom, the 1 x 1 periodicity is insufficient to establish the correct surface stoichiometry. Furthermore, in our structural and compositional model the reversible oxidation or reduction between (1 x 1) and (1 x 2) is entirely achieved by transfer of the added rows.

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PubMed2006

Dopant-induced nanoscale electronic inhomogeneities in Ca(2-x)Sr(x)RuO4.

Ca(2-x)Sr(x)RuO4 single crystals with 0.1 < or = x < or = 2.0 have been studied systematically using scanning tunneling microscopy (STM) and spectroscopy, low-energy electron diffraction, and angle resolved photoelectron spectroscopy (ARPES). In contrast with the well-ordered lattice structure, the local density of states at the surface clearly shows a strong doping dependent nanoscale electronic inhomogeneity, regardless of the fact of isovalent substitution. Remarkably, the surface electronic roughness measured by STM and the inverse spectral weight of quasiparticle states determined by ARPES are found to vary with x in the same manner as the bulk in-plane residual resistivity, following the Nordheim rule. For the first time, the surface measurements--especially those with STM--are shown to be in good agreement with the bulk transport results, all clearly indicating a doping-induced electronic disorder in the system.

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PubMed2005

"Live" surface ferromagnetism in Fe nanodots/Cu multilayers on Cu(111).

We investigate the crossover behavior from two-dimensional (2D) to three-dimensional in multilayers of magnetic nanodots grown by stacking 2D Fe nanodot assemblies on Cu(111) single crystal substrate with a Cu spacing layer. Using an in situ magneto-optical Kerr effect, we have observed a striking ferromagnetic to spin-glass-like phase transition with an increasing number of Fe dot layers. The topmost layer of the Fe dots survives the phase transition and remains ferromagnetic. This unusual surface ferromagnetism is likely caused by a surface-state-mediated coupling which is stronger than the coupling in bulk layers. This is confirmed by the fact that the critical temperature of the surface ferromagnetism is considerably higher than that of the bulk spin-glass phase in the system.

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PubMed2005

Visualization of localized holes in manganite thin films with atomic resolution.

The magnetic and transport behaviors of manganites are critically related to the spatial distribution and correlation of doped holes. Using in situ scanning tunneling microscopy, we have imaged both occupied and unoccupied states simultaneously in a hole-doped (La(5/8-0.3)Pr0.3)Ca(3/8)MnO3 epitaxial thin film grown by laser molecular beam epitaxy. Doped holes localized on Mn4+ ion sites were directly observed with atomic resolution in the paramagnetic state at room temperature. In contrast to a random distribution, these doped holes show strong short-range correlation and clear preference of forming nanoscale CE-type charge-order-like clusters. The results provide direct visualization of the nature of intriguing electronic inhomogeneity in transition metal oxides.

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PubMed2005

Non-fermi-liquid behavior in quasi-one-dimensional Li0.9Mo6O17.

We present temperature dependent scanning tunneling spectroscopy data of the quasi-one-dimensional conductor Li0.9Mo6O17. The differential tunneling current in our low-temperature spectra shows a power-law behavior around the Fermi energy, which is expected for a clean Luttinger liquid. The power-law exponent is found to be 0.6. Spectra for a temperature range of 5 to 55 K can be fitted fairly well with a model for tunneling into a Luttinger liquid at the appropriate temperature. A fit with a model based on a zero bias anomaly is significantly worse compared to the Luttinger liquid model. No signature of a phase transition at T = 24 K is observed in our temperature dependent data.

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PubMed2005

Real-space observation of nanoscale inhomogeneities and fluctuations in a phase transition of a surface quasi-one-dimensional system: In/Si(111).

We report direct visualizations of the fluctuation and condensation phenomena in a phase transition of a one-dimensional (1D) In/Si(111) system using scanning tunneling microscopy. The high-temperature (HT) and low-temperature (LT) phases are found to coexist on the nanometer scale near Tc. Above Tc, 1D LT-phase stripes fluctuate in the HT phase and coalesce into 2D islands with decreasing temperature. They condense to make the LT phase below Tc. Small areas of the HT phase also exist below Tc. The observed temperature-dependent evolution of the nanoscale inhomogeneities is consistent with the theoretical predictions for a second-order phase transition.

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PubMed2005

Multiple bosonic mode coupling in the electron self-energy of (La2-xSrx)CuO4.

High resolution angle-resolved photoemission spectroscopy data along the (0,0)-(pi,pi) nodal direction with significantly improved statistics reveal fine structure in the electron self-energy of the underdoped (La2-xSrx)CuO4 samples in the normal state. Fine structure at energies of (40-46) meV and (58-63) meV, and possible fine structure at energies of (23-29) meV and (75-85) meV, have been identified. These observations indicate that, in (La2-xSrx)CuO4, more than one bosonic modes are involved in the coupling with electrons.

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PubMed2005

Intertwined electronic and structural phase transitions in the In/Si(111) interface.

The structural (4 x 1) to (8 x 2) transition and the electronic metal to semimetal transition at the In/Si interface are studied with scanning tunneling microscopy and spectroscopy. Both transitions are gradual, resulting in a complex domain structure in the transition temperature regime. At these intermediate temperatures, the metallic (4 x 1) and semimetallic (8 x 2) domains coexist with each other and with new nanophases. By probing the two intertwined but distinguishable transitions at the atomic level, the interaction between different phases is visualized directly.

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PubMed2005

Frozen low-spin interface in ultrathin Fe films on Cu(111).

In ultrathin film systems, it is a major challenge to understand how a thickness-driven phase transition proceeds along the cross-sectional direction of the films. We use ultrathin Fe films on Cu(111) as a prototype system to demonstrate how to obtain such information using an in situ scanning tunneling microscope and the surface magneto-optical Kerr effect. The magnetization depth profile of a thickness-driven low-spin to high-spin magnetic phase transition is deduced from the experimental data, which leads us to conclude that a low-spin Fe layer at the Fe/Cu interface stays live upon the phase transition. The magnetically live low-spin phase is believed to be induced by a frozen fcc Fe layer that survives a thickness-driven fcc-->bcc structural transition.

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PubMed2005

Low temperature disordered phase of alpha-Pb/Ge(111).

A new structural phase transition has been observed at low temperature for the one-third of a monolayer (alpha phase) of Pb on Ge(111) using a variable-temperature scanning tunneling microscope. The well-known (sqrt[3] x sqrt[3])R30 degrees to (3 x 3) transition is accompanied by a new structural phase transition from (3 x 3) to a disordered phase at approximately 76 K. The formation of this "glasslike" phase is a consequence of competing interactions on different length scales.

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PubMed2004

Fermi surface topology of Ca1.5Sr0.5RuO4 determined by angle-resolved photoelectron spectroscopy.

We report angle-resolved photoelectron spectroscopy results of the Fermi surface of Ca1.5Sr0.5RuO4, which is at the boundary of magnetic/orbital instability in the phase diagram of the Ca-substituted Sr ruthenates. Three t(2g) energy bands and the corresponding Fermi surface sheets are observed, which are also present in the Ca-free Sr2RuO4. We find that while the Fermi surface topology of the alpha,beta (d(yz,zx)) sheets remains almost the same in these two materials, the gamma (d(xy)) sheet exhibits a holelike Fermi surface in Ca1.5Sr0.5RuO4 in contrast to being electronlike in Sr2RuO4. Our observation of all three volume conserving Fermi surface sheets clearly demonstrates the absence of orbital-selective Mott transition, which was proposed theoretically to explain the unusual transport and magnetic properties in Ca1.5Sr0.5RuO4.

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PubMed2004

Ferromagnetic stability in Fe nanodot assemblies on Cu(111) induced by indirect coupling through the substrate.

We report collective ferromagnetic behavior with high Curie temperatures (T(c)) in Fe dot assemblies supported by the Cu(111) surface. Our ability to tune the average size and spacing of the individual dots allows us to conclude that enhanced magnetic anisotropy cannot account for this high-T(c) ferromagnetic order. Because our Monte Carlo simulations have ruled out the dipolar interaction as the dominant factor in this system, we attribute the origin of the ferromagnetic order to indirect exchange coupling via the Cu(111) substrate.

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PubMed2004

Direct extraction of the Eliashberg function for electron-phonon coupling: a case study of Be(10(-)10).

We propose a systematic procedure to directly extract the Eliashberg function for electron-phonon coupling from high-resolution angle-resolved photoemission measurement. The procedure is successfully applied to the Be(10(-)10) surface, providing new insights into electron-phonon coupling at this surface. The method is shown to be robust against imperfections in experimental data and suitable for wider applications.

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PubMed2003

Surface phase transitions induced by electron mediated adatom-adatom interaction.

We propose that the indirect adatom-adatom interaction mediated by the conduction electrons of a metallic surface is responsible for the sqrt[3]xsqrt[3]<==>3x3 structural phase transitions observed in Sn/Ge (111) and Pb/Ge (111). When the indirect interaction overwhelms the local stress field imposed by the substrate registry, the system suffers a phonon instability, resulting in a structural phase transition in the adlayer. Our theory is capable of explaining all the salient features of the sqrt[3]xsqrt[3]<==>3x3 transitions observed in Sn/Ge (111) and Pb/Ge (111), and is in principle applicable to a wide class of systems whose surfaces are metallic before the transition.

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PubMed2001

Jahn-Teller phonon anomaly and dynamic phase fluctuations in La0.7Ca0.3MnO3.

Inelastic neutron scattering was used to study the temperature (T) dependence of the lattice excitations in La 0.7Ca 0.3MnO (3). An optical Jahn-Teller phonon exhibits continuous but anomalous damping with increasing temperature in the ferromagnetic-metallic phase and collapses above the Curie temperature T(C) (240 K). We attribute this anomaly to the growing dynamic phase segregation as T-->T(C), thus providing evidence of local fluctuations associated with the short-range polaron or charge/orbital ordering in the ferromagnetic-metallic state.

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PubMed2001

Shape of the quantum diffusion front.

We show that quantum diffusion has well-defined front shape. After an initial transient, the wave packet front (tails) is described by a stretched exponential P(x,t) = A(t)exp(-absolute value of [x/w](gamma)), with 1 < gamma < infinity, where w(t) is the spreading width which scales as w(t) approximately t(beta), with 0 < beta < or = 1. The two exponents satisfy the universal relation gamma = 1/(1-beta). We demonstrate these results through numerical work on one-dimensional quasiperiodic systems and the three-dimensional Anderson model of disorder. We provide an analytical derivation of these relations by using the memory function formalism of quantum dynamics. Furthermore, we present an application to experimental results for the quantum kicked rotor.

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