20 research outputs found
Character of eigenstates of the 3D disordered Anderson Hamiltonian
We study numerically the character of electron eigenstates of the three
dimensional disordered Anderson model. Analysis of the statistics of inverse
participation ratio as well as numerical evaluation of the electron-hole
correlation function confirm that there are no localized states below the
mobility edge, as well as no metallic state in the tail of the conductive band.
We discuss also finite size effects observed in the analysis of all the
discussed quantities.Comment: 7 pages, 9 figures, resubmitted to Physical Review
Transport in the 3-dimensional Anderson model: an analysis of the dynamics on scales below the localization length
Single-particle transport in disordered potentials is investigated on scales
below the localization length. The dynamics on those scales is concretely
analyzed for the 3-dimensional Anderson model with Gaussian on-site disorder.
This analysis particularly includes the dependence of characteristic transport
quantities on the amount of disorder and the energy interval, e.g., the mean
free path which separates ballistic and diffusive transport regimes. For these
regimes mean velocities, respectively diffusion constants are quantitatively
given. By the use of the Boltzmann equation in the limit of weak disorder we
reveal the known energy-dependencies of transport quantities. By an application
of the time-convolutionless (TCL) projection operator technique in the limit of
strong disorder we find evidence for much less pronounced energy dependencies.
All our results are partially confirmed by the numerically exact solution of
the time-dependent Schroedinger equation or by approximative numerical
integrators. A comparison with other findings in the literature is additionally
provided.Comment: 23 pages, 10 figure
The Role of Power-Law Correlated Disorder in the Anderson Metal-Insulator Transition
We study the influence of scale-free correlated disorder on the
metal-insulator transition in the Anderson model of localization. We use
standard transfer matrix calculations and perform finite-size scaling of the
largest inverse Lyapunov exponent to obtain the localization length for
respective 3D tight-binding systems. The density of states is obtained from the
full spectrum of eigenenergies of the Anderson Hamiltonian. We discuss the
phase diagram of the metal-insulator transition and the influence of the
correlated disorder on the critical exponents.Comment: 6 pages, 3 figure
Promoting Atoms into Delocalized Long-Living Magnetically Modified State Using Atomic Force Microscopy
We
report on a low-temperature atomic force microscropy manipulation
of Co atoms in ultrahigh vacuum on an oxidized copper surface in which
the manipulated atom is kept delocalized above several surface unit
cells over macroscopic times. The manipulation employed, in addition
to the ubiquitous short-range tip-generated chemical forces, also
long-range forces generated via Friedel oscillations of the metal
charge density due to Co nanostructures prearranged on the surface
by lateral manipulation. We show that our manipulation protocol requires
mechanical control of the spin state of the Co atom
Colossal band gap response of single-layer phosphorene to strain predicted by quantum Monte Carlo
Straintronics is an emerging field enabling novel tuneable functionalities of electronic, optical, magnetic, or spin devices with advances being fuelled by new developments in van der Walls (vdW) heterostructure engineering and materials design. Here we show, using state-of-the-art quantum Monte Carlo (QMC) methods, that a single phosphorene monolayer exhibits outstanding straintronics functionalities due to discovered colossal strain tunability of its semiconducting electronic gap. First, we determine the equilibrium atomic structure that differs appreciably from available bulk phosphorene experimental data. That enables us to precisely analyze the quasiparticle band gaps for any uniaxial (armchair and zigzag) and biaxial strains which we describe by a quadrivariate paraboloid function of lattice and internal structure parameters. Using the fixed-node QMC calculations fitted by analytical formulas we localize the following excited state crossings: (i) between the direct (Γ→Γ) and direct but reordered (Γ→Γ′) excitations that also imply substantial differences of corresponding transport properties; and (ii) between the direct Γ→Γ and indirect Γ→X excitations. Based on this highly accurate many-body treatment, we predict the gauge factor ≈100 meV/% and an unusual behavior with the band gap remaining direct even if strained by several percent. Consequently, we suggest there is a colossal band gap tunability window, larger by an order of magnitude when compared to quintessential straintronic materials such as MoS2. In addition, we ascertain that the ground state deformation energies exhibit an out-of plane negative Poisson's ratio and auxetic behavior
Critical Importance of van der Waals Stabilization in Strongly Chemically Bonded Surfaces: Cu(110):O
We
provide strong evidence that different reconstructed phases
of the oxidized Cu(110) surface are stabilized by the van der Waals
(vdW) interactions. These covalently bonded reconstructed surfaces
feature templates that are an integral part of the surfaces and are
bonded on the bare metal surface by a combination of chemical and
physical bonding. The vdW stabilization in this class of systems affects
predominantly the intertemplate Cu–O interactions in structures
sparsely populated by these templates. The conventional dispersionless
density functional theory (DFT) methods fail to model such systems.
We find a failure to describe the thermodynamics of the different
phases that are formed at different oxygen exposures and spurious
minima on the potential energy surface of a diffusing surface adatom.
To overcome these issues, we employ a range of different DFT methods
that account for the missing vdW correlations. Surprisingly, despite
vast conceptual differences in the different formulations of these
methods, they yield physically identical results for the Cu(110):O
surface phases, provided the massive screening effects in the metal
are taken into account. Contrary, the vibrational contribution does
not consistently stabilize the experimentally observed surface structures.
The van der Waals surface stabilization, so far deemed to play only
a minor role in hard-bonded surfaces, is suggested to be a more general
key feature for this and other related surfaces