arXiv subjects

Eli Rotenberg

Publications and source records attributed to Eli Rotenberg.

At least 127 records · Page 7Linked to original sources

arXiv2016

A Novel Quasi-One-Dimensional Topological Insulator in Bismuth Iodide $β$-Bi$_4$I$_4$

Recent progress in the field of topological states of matter(1,2) has largely been initiated by the discovery of bismuth and antimony chalcogenide bulk topological insulators (TIs)(3-6), followed by closely related ternary compounds(7-16) and predictions of several weak TIs(17-19). However, both the conceptual richness of Z$_2$ classification of TIs as well as their structural and compositional diversity are far from being fully exploited. Here, a new Z$_2$ topological insulator is theoretically predicted and experimentally confirmed in the $β$-phase of quasi-one-dimensional bismuth iodide Bi$_4$I$_4$. The electronic structure of $β$-Bi$_4$I$_4$, characterized by Z$_2$ invariants (1;110), is in proximity of both the weak TI phase (0;001) and the trivial insulator phase (0;000). Our angle-resolved photoemission spectroscopy measurements on the (001) surface reveal a highly anisotropic band-crossing feature located at the point of the surface Brillouin zone and showing no dispersion with the photon energy, thus being fully consistent with the theoretical prediction.

cond-mat.mtrl-sci↗

arXiv2015

Latent Instabilities in Metallic LaNiO3 Films by Strain Control of Fermi-Surface Topology

Strain control is one of the most promising avenues to search for new emergent phenomena in transition-metal-oxide films. Here, we investigate the strain-induced changes of electronic structures in strongly correlated LaNiO3 (LNO) films, using angle-resolved photoemission spectroscopy and the dynamical mean-field theory. The strongly renormalized eg-orbital bands are systematically rearranged by misfit strain to change its fermiology. As tensile strain increases, the hole pocket centered at the A point elongates along the kz-axis and seems to become open, thus changing Fermi-surface (FS) topology from three- to quasi-two-dimensional. Concomitantly, the FS shape becomes flattened to enhance FS nesting. A FS superstructure with Q1 = (1/2,1/2,1/2) appears in all LNO films, while a tensile-strained LNO film has an additional Q2 = (1/4,1/4,1/4) modulation, indicating that some instabilities are present in metallic LNO films. Charge disproportionation and spin-density-wave fluctuations observed in other nickelates might be their most probable origins.

cond-mat.str-el↗

arXiv2014

Hallmarks of the Mott-Metal Crossover in the Hole Doped J=1/2 Mott insulator Sr2IrO4

The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among possible competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. We investigate the evolution of electronic structure and dynamics of the hole-doped J=1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple exotic features previously observed in doped cuprates - pseudogaps, Fermi "arcs", and marginal-Fermi-liquid-like electronic scattering rates, despite different mechanisms that forbid electron double-occupancy. We argue these universal features of the Mott-metal crossover are not related to preformed electron pairing, quantum criticality or density-wave formation as most commonly discussed. Instead, short-range antiferromagnetic correlations may play an indispensible role.

cond-mat.str-el↗

arXiv2013

Dimensional crossover of the electronic structure in LaNiO3 ultrathin films: Orbital reconstruction, Fermi surface nesting, and the origin of the metal-insulator transition

Dimensionality control in the LaNiO3 (LNO) heterostructure has attracted attention due to its two-dimensional (2D) electronic structure was predicted to have an orbital ordered insulating ground state, analogous to that of the parent compound of high-Tc cuprate superconductors [P. Hansmann et al., Phys. Rev. Lett. 103, 016401 (2009)]. Here, we directly measured the electronic structure of LNO ultrathin films using in situ angle-resolved photoemission spectroscopy (ARPES). We recognized the dimensional crossover of the electronic structure around 3-unit cells (UC)-thick LNO film and observed the orbital reconstruction. However, complete orbital ordering was not achieved. Instead, we observed that the Fermi surface nesting effect became strong in the 2D LNO ultrathin film. These results indicated that the orbital reconstruction should be described by taking into account the strong nesting effect to search for the novel phenomena, such as superconductivity in 2D LNO heterostructure. In addition, the APRES spectra showed that the Fermi surface existed down to a 1-UC-thick film, which showed insulating behavior in transport measurements. We suggested that the metal-insulator transition in the transport properties may originate from Anderson localization.

cond-mat.str-el↗

arXiv2013

Visualizing Atomic-Scale Negative Differential Resistance in Bilayer Graphene

We investigate the atomic-scale tunneling characteristics of bilayer graphene on silicon carbide using the scanning tunneling microscopy. The high-resolution tunneling spectroscopy reveals an unexpected negative differential resistance (NDR) at the Dirac energy, which spatially varies within the single unit cell of bilayer graphene. The origin of NDR is explained by two near-gap van Hove singularities emerging in the electronic spectrum of bilayer graphene under a transverse electric field, which are strongly localized on two sublattices in different layers. Furthermore, defects near the tunneling contact are found to strongly impact on NDR through the electron interference. Our result provides an atomic-level understanding of quantum tunneling in bilayer graphene, and constitutes a useful step towards graphene-based tunneling devices.

cond-mat.mtrl-sci↗

arXiv2012

Small scale rotational disorder observed in epitaxial graphene on SiC(0001)

Interest in the use of graphene in electronic devices has motivated an explosion in the study of this remarkable material. The simple, linear Dirac cone band structure offers a unique possibility to investigate its finer details by angle-resolved photoelectron spectroscopy (ARPES). Indeed, ARPES has been performed on graphene grown on metal substrates but electronic applications require an insulating substrate. Epitaxial graphene grown by the thermal decomposition of silicon carbide (SiC) is an ideal candidate for this due to the large scale, uniform graphene layers produced. The experimental spectral function of epitaxial graphene on SiC has been extensively studied. However, until now the cause of an anisotropy in the spectral width of the Fermi surface has not been determined. In the current work we show, by comparison of the spectral function to a semi-empirical model, that the anisotropy is due to small scale rotational disorder ($\sim\pm$ 0.15$^{\circ}$) of graphene domains in graphene grown on SiC(0001) samples. In addition to the direct benefit in the understanding of graphene's electronic structure this work suggests a mechanism to explain similar variations in related ARPES data.

cond-mat.mes-hall↗

arXiv2012

Extraordinary epitaxial alignment of graphene islands on Au(111)

Pristine, single-crystalline graphene displays a unique collection of remarkable electronic properties that arise from its two-dimensional, honeycomb structure. Using in-situ low-energy electron microscopy, we show that when deposited on the (111) surface of Au carbon forms such a structure. The resulting monolayer, epitaxial film is formed by the coalescence of dendritic graphene islands that nucleate at a high density. Over 95% of these islands can be identically aligned with respect to each other and to the Au substrate. Remarkably, the dominant island orientation is not the better lattice-matched 30^{\circ} rotated orientation but instead one in which the graphene [01] and Au [011] in-plane directions are parallel. The epitaxial graphene film is only weakly coupled to the Au surface, which maintains its reconstruction under the slightly p-type doped graphene. The linear electronic dispersion characteristic of free-standing graphene is retained regardless of orientation. That a weakly interacting, non-lattice matched substrate is able to lock graphene into a particular orientation is surprising. This ability, however, makes Au(111) a promising substrate for the growth of single crystalline graphene films.

cond-mat.mtrl-sci↗

arXiv2011

Magnetic-Order Induced Spectral-Weight Redistribution in a Triangular Surface System

The Sn-induced $\sqrt3 \times \sqrt3$ surface reconstruction on Si(111) has been investigated by material-specific many-body calculations and by angle-resolved photoelectron spectroscopy (ARPES). This triangular surface system in the low adatom coverage regime is governed by rather localized dangling bond orbitals with enhanced electronic correlations and it is prone to exhibit magnetic frustration. We find a rather good overall agreement of the spectral function and its temperature-dependence between theory and experiment. Changes in the ARPES band topology in comparison to the density functional calculations can be explained as a spectral weight redistribution with respect to an additional symmetry which is not due to any geometrical change. This new symmetry corresponds to a magnetic order, which is found to be more complex than the canonical $120^{\circ}$ anti-ferromagnetic order on a triangular lattice with nearest-neighbor coupling only.

cond-mat.str-el↗

arXiv2011

Electronic structure of graphene on single crystal copper substrates

The electronic structure of graphene on Cu(111) and Cu(100) single crystals is investigated using low energy electron microscopy, low energy electron diffraction and angle resolved photoemission spectroscopy. On both substrates the graphene is rotationally disordered and interactions between the graphene and substrate lead to a shift in the Dirac crossing of $\sim$ -0.3 eV and the opening of a $\sim$ 250 meV gap. Exposure of the samples to air resulted in intercalation of oxygen under the graphene on Cu(100), which formed a ($\sqrt{2} \times 2\sqrt{2}$)R45$^{\rm o}$ superstructure. The effect of this intercalation on the graphene $π$ bands is to increase the offset of the Dirac crossing ($\sim$ -0.6 eV) and enlarge the gap ($\sim$ 350 meV). No such effect is observed for the graphene on Cu(111) sample, with the surface state at $Γ$ not showing the gap associated with a surface superstructure. The graphene film is found to protect the surface state from air exposure, with no change in the effective mass observed.

cond-mat.mes-hall↗

arXiv2011

Effective screening and the plasmaron bands in Graphene

Electron-plasmon coupling in graphene has recently been shown to give rise to a "plasmaron" quasiparticle excitation. The strength of this coupling has been predicted to depend on the effective screening, which in turn is expected to depend on the dielectric environment of the graphene sheet. Here we compare the strength of enviromental screening for graphene on four different substrates by evaluating the separation of the plasmaron bands from the hole bands using Angle Resolved PhotoEmission Spectroscopy. Comparison with G0W-RPA predictions are used to determine the effective dielectric constant of the underlying substrate layer. We also show that plasmaron and electronic properties of graphene can be independently manipulated, an important aspect of a possible use in "plasmaronic" devices.

cond-mat.str-el↗

arXiv2011

Highly p-doped graphene obtained by fluorine intercalation

We present a method for decoupling epitaxial graphene grown on SiC(0001) by intercalation of a layer of fluorine at the interface. The fluorine atoms do not enter into a covalent bond with graphene, but rather saturate the substrate Si bonds. This configuration of the fluorine atoms induces a remarkably large hole density of p \approx 4.5 \times 1013 cm-2, equivalent to the location of the Fermi level at 0.79 eV above the Dirac point ED .

cond-mat.mtrl-sci↗

arXiv2010

In-plane orientation effects on the electronic structure, stability and Raman scattering of monolayer graphene on Ir(111)

We employ angle-resolved photoemission spectroscopy (ARPES) to investigate the electronic structures of two rotational variants of epitaxial, single-layer graphene on Ir(111). As grown, the more-abundant R0 variant is nearly charge-neutral, with strong hybridization between graphene and Ir bands near the Fermi level. The graphene Fermi surface and its replicas exactly coincide with Van Hove singularities in the Ir Fermi surface. Sublattice symmetry breaking introduces a small gap-inducing potential at the Dirac crossing, which is revealed by n-doping the graphene using K atoms. The energy gaps between main and replica bands (originating from the moiré interference pattern between graphene and Ir lattices) is shown to be non-uniform along the mini- zone boundary due to hybridization with Ir bands. An electronically mediated interaction is proposed to account for the stability of the R0 variant. The variant rotated 30° in-plane, R30, is p-doped as grown and K doping reveals no band gap at the Dirac crossing. No replica bands are found in ARPES measurements. Raman spectra from the R30 variant exhibit the characteristic phonon modes of graphene, while R0 spectra are featureless. These results show that the film/substrate interaction changes from chemisorption (R0) to physisorption (R30) with in-plane orientation. Finally, graphene-covered Ir has a work function lower than the clean substrate but higher than graphite.

cond-mat.mtrl-sci↗

arXiv2010

Uniaxial "nematic-like" electronic structure and Fermi surface of untwinned CaFe2As2

Obtaining the electronic structure of the newly discovered iron-based superconductors is the key to understanding the mechanism of their high-temperature superconductivity. We used angle-resolved photoemission spectroscopy (ARPES) to make direct measurements of the electronic structure and Fermi surface (FS) of the untwinned uniaxial state of CaFe2As2, the parent compound of iron-based superconductors. We observed unequal dispersions and FS geometries along the orthogonal Fe-Fe bond directions. More importantly, unidirectional straight and flat FS segments are observed near the zone center, which indicates the existence of a unidirectional nematic charge density wave order, strengthening the case for a quantum electronic liquid crystalline "nematic" phase. Further, the doping dependence extrapolates to a possible quantum critical point of the disappearance of this order in the heavily overdoped regime of these materials.

cond-mat.supr-con↗

arXiv2010

Giant Faraday rotation in single- and multilayer graphene

Optical Faraday rotation is one of the most direct and practically important manifestations of magnetically broken time-reversal symmetry. The rotation angle is proportional to the distance traveled by the light, and up to now sizeable effects were observed only in macroscopically thick samples and in two-dimensional electron gases with effective thicknesses of several nanometers. Here we demonstrate that a single atomic layer of carbon - graphene - turns the polarization by several degrees in modest magnetic fields. The rotation is found to be strongly enhanced by resonances originating from the cyclotron effect in the classical regime and the inter-Landau-level transitions in the quantum regime. Combined with the possibility of ambipolar doping, this opens pathways to use graphene in fast tunable ultrathin infrared magneto-optical devices.

cond-mat.mes-hall↗

arXiv2010

Critical change in the Fermi surface of iron arsenic superconductors at the onset of superconductivity

The phase diagram of a correlated material is the result of a complex interplay between several degrees of freedom, providing a map of the material's behavior. One can understand (and ultimately control) the material's ground state by associating features and regions of the phase diagram, with specific physical events or underlying quantum mechanical properties. The phase diagram of the newly discovered iron arsenic high temperature superconductors is particularly rich and interesting. In the AE(Fe1-xTx)2As2 class (AE being Ca, Sr, Ba, T being transition metals), the simultaneous structural/magnetic phase transition that occurs at elevated temperature in the undoped material, splits and is suppressed by carrier doping, the suppression being complete around optimal doping. A dome of superconductivity exists with apparent equal ease in the orthorhombic / antiferromagnetic (AFM) state as well as in the tetragonal state with no long range magnetic order. The question then is what determines the critical doping at which superconductivity emerges, if the AFM order is fully suppressed only at higher doping values. Here we report evidence from angle resolved photoemission spectroscopy (ARPES) that critical changes in the Fermi surface (FS) occur at the doping level that marks the onset of superconductivity. The presence of the AFM order leads to a reconstruction of the electronic structure, most significantly the appearance of the small hole pockets at the Fermi level. These hole pockets vanish, i. e. undergo a Lifshitz transition, at the onset of superconductivity. Superconductivity and magnetism are competing states in the iron arsenic superconductors. In the presence of the hole pockets superconductivity is fully suppressed, while in their absence the two states can coexist.

cond-mat.supr-con↗

arXiv2010

Structure and Correlation Effects in Semiconducting SrTiO$_{3}$

We have investigated the effects of structure change and electron correlation on SrTiO$_{3}$ single crystals using angle-resolved photoemission spectroscopy. We show that the cubic to tetragonal phase transition at 105$^\circ$K is manifested by a charge transfer from in-plane ($d_{yz}$ and $d_{zx}$) bands to out-of-plane ($d_{xy}$) band, which is opposite to the theoretical predictions. Along this second-order phase transition, we find a smooth evolution of the quasiparticle strength and effective masses. The in-plane band exhibits a peak-dip-hump lineshape, indicating a high degree of correlation on a relatively large (170 meV) energy scale, which is attributed to the polaron formation.

cond-mat.mtrl-sci↗

arXiv2009

Bilayer splitting and c-axis coupling in bilayer manganites showing colossal magnetoresistance

By performing angle-resolved photoemission spectroscopy of the bilayer colossal magnetoresistive (CMR) manganite, $La_{2-2x}Sr_{1+2x}Mn_{2}O_{7}$, we provide the complete mapping of the Fermi level spectral weight topology. Clear and unambiguous bilayer splitting of the in-plane 3d$_{x^2-y^2}$ band, mapped throughout the Brillouin zone, and the full mapping of the 3d$_{3z^2-r^2}$ band are reported. Peculiar doping and temperature dependencies of these bands imply that as transition from the ferromagnetic metallic phase approaches, either as a function of doping or temperature, coherence along the c-axis between planes within the bilayer is lost, resulting in reduced interplane coupling. These results suggest that interplane coupling plays a large role in the CMR transition.

cond-mat.str-el↗

arXiv2009

Energy-dependent scaling of incoherent spectral weight and the origin of the waterfalls in high-Tc cuprates

The exotic physics in condensed matter systems, such as high-Tc superconductivity in cuprates, is due to the properties of the elementary excitations and their interactions. The dispersion of the electronic states revealed by angle-resolved photoemission spectroscopy (ARPES) provides a chance to understand these excitations. Recently, a "high energy anomaly" or "waterfall-like" feature in cuprates' dispersion has been reported and studied theoretically. Most of the current views argue that it is the result of some many-body effect at a specific high energy scale (e.g. ~ 0.3eV), though there are other arguments that this is an artificial effect. Here, we report a systematic ARPES study on the "high energy anomaly" in Bi2212 samples over multiple Brillouin zones and with a large variety of ARPES matrix elements. We find that the incoherent weight of the electron spectral function at high binding energy is intimately linked to the energy of the dispersive coherent weight through an unexpected but simple relationship with no special energy scales. This behavior in concert with strong k-dependent matrix element effects gives rise to the heavily studied "waterfall" behavior.

cond-mat.supr-con↗