scholarly journals DOPING INDUCED ELECTRONIC PHASE SEPARATION AND COULOMB BUBBLES IN LAYERED SUPERCONDUCTORS

2009 ◽  
Vol 23 (20n21) ◽  
pp. 4198-4215 ◽  
Author(s):  
M. SAARELA ◽  
F. V. KUSMARTSEV
Keyword(s):  
Coulomb Interaction ◽  
Coulomb Force ◽  
Charge Carriers ◽  
Localized States ◽  
Scanning Tunneling ◽  
Many Body ◽  
Trap Charge ◽  
Electronic Phase ◽  
Competing Orders ◽  
Coulomb Fluids

We study properties of charge fluids with random impurities or heavy polarons using a microscopic Hamiltonian with the full many-body Coulomb interaction. At zero temperature and high enough density the bosonic fluid is superconducting, but when density decreases the Coulomb interaction will be strongly over-screened and impurities or polarons begin to trap charge carriers forming bound quasiparticle like clusters, which we call Coulomb bubbles or clumps. These bubbles are embedded inside the superconductor and form nuclei of a new insulating state. The growth of a bubble is terminated by the Coulomb force. The fluid contains two groups of charge carriers associated with free and localized states. The insulating state arises via a percolation of the insulating islands of bubbles, which cluster and prevent the flow of the electrical supercurrent through the system. Our results are applicable to HTSC. There the Coulomb fluids discussed in the paper correspond to mobile holes located on Cu sites and heavy polarons or charged impurities located on Oxygen sites. As a result of our calculations the following two-componet picture of two competing orders in cuprates arise. The mobile and localized states are competing with each other and their balance is controlled by doping. At high doping a large Fermi surface is open. There the density of real charge carriers is significantly larger than the density of the doped ones. When doping decreases more and more carriers are localized as Coulomb clumps which are creating around heavy polarons localized on Oxygen sites and forming a regular lattice. The picture is consistent with the Gorkov and Teitelbaum (GT) analysis 1,2 of the transport, Hall effect data and the ARPES spectra as well as with nanoscale superstructures observed in Scanning Tunneling Microscope(STM) experiments [3-8]. The scenario of the clump formation may be also applicable to pnictides, where two types of clumps may arise even at very high temperatures.

scholarly journals Probing resonating valence bond states in artificial quantum magnets

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kai Yang ◽  
Soo-Hyon Phark ◽  
Yujeong Bae ◽  
Taner Esat ◽  
Philip Willke ◽  
...  
Keyword(s):  
Quantum Information Processing ◽  
Energy Levels ◽  
Finite Size ◽  
Valence Bond ◽  
Exchange Interactions ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Many Body ◽  
Quantum Magnets ◽  
Resonating Valence Bond

AbstractDesigning and characterizing the many-body behaviors of quantum materials represents a prominent challenge for understanding strongly correlated physics and quantum information processing. We constructed artificial quantum magnets on a surface by using spin-1/2 atoms in a scanning tunneling microscope (STM). These coupled spins feature strong quantum fluctuations due to antiferromagnetic exchange interactions between neighboring atoms. To characterize the resulting collective magnetic states and their energy levels, we performed electron spin resonance on individual atoms within each quantum magnet. This gives atomic-scale access to properties of the exotic quantum many-body states, such as a finite-size realization of a resonating valence bond state. The tunable atomic-scale magnetic field from the STM tip allows us to further characterize and engineer the quantum states. These results open a new avenue to designing and exploring quantum magnets at the atomic scale for applications in spintronics and quantum simulations.

scholarly journals Many-Body State Description of Single-Molecule Electroluminescence Driven by a Scanning Tunneling Microscope

Nano Letters ◽  
2019 ◽  
Vol 19 (5) ◽  
pp. 2803-2811 ◽  
Author(s):  
Kuniyuki Miwa ◽  
Hiroshi Imada ◽  
Miyabi Imai-Imada ◽  
Kensuke Kimura ◽  
Michael Galperin ◽  
...  
Keyword(s):  
Single Molecule ◽  
Scanning Tunneling Microscope ◽  
Scanning Tunneling ◽  
Many Body ◽  
Tunneling Microscope ◽  
Body State

Stm Studies at Electrochemically Controlled Interfaces

1994 ◽  
Vol 332 ◽  
Author(s):  
S.M. Lindsay ◽  
J. Pan ◽  
T.W. Jing
Keyword(s):  
Electron Tunneling ◽  
Point Contact ◽  
Localized States ◽  
Scanning Tunneling ◽  
Zero Field ◽  
Tunneling Microscopy ◽  
Dna Oligomers ◽  
Synthetic Dna ◽  
Quantum Point

ABSTRACTWe use electrochemical methods to control the adsorption of molecules onto an electrode for imaging in-situ by scanning tunneling microscopy. Measurements of the barrier for electron tunneling show that the mechanism of electron transfer differs from vacuum tunneling. Barriers depend upon the direction of electron tunneling, indicating the presence of permanently aligned dipoles in the tunnel gap. We attribute a sharp dip in the barrier near zero field to induced polarization. We propose a ‘tunneling’ process consisting of two parts: One is delocalization of quantum-coherent states in parts of the molecular adlayer that hybridize strongly (interaction ≥ kT) with Bloch states in the metal. This gives rise to a quantum-point-contact conductance, Gc ≤ 2e2/h at a height zo. The other part comes from the exponential decay of the tails of localized states, G = Gc exp{−2K(z − z0)}. Because measured decay lengths, (2K‘)−1, are small (≈ 1 Å), STM contrast is dominated by the contour along which G[z0 (x,y)] = Gc. Measured changes in z0 are used to calculate images which are in reasonable agreement with observations. We illustrate this with images of synthetic DNA oligomers.

Coulomb interaction among transporting charge carriers confined in two dimensions

2008 ◽  
Vol 104 (8) ◽  
pp. 083716 ◽  
Author(s):  
G. H. Buh ◽  
Ji-Yong Park ◽  
Young Kuk
Keyword(s):  
Coulomb Interaction ◽  
Two Dimensions ◽  
Charge Carriers

Scanning Tunneling Microscopy and Spectroscopy of Semiconductor Surfaces

1986 ◽  
Vol 77 ◽  
Author(s):  
J. E. Demuth ◽  
R. J. Hamers ◽  
R. M. Tromp
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Local Structure ◽  
Localized States ◽  
Silicon Surfaces ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Geometric Information ◽  
Charge Densities ◽  
Surface Electronic Structure ◽  
New Information

ABSTRACTThe principles of scanning tunneling microscopy and its application to study silicon surfaces are briefly reviewed. Scanning tunneling microscopy “topographs” contain both geometric information about the locations of atoms at the surface as well as about the charge densities of surface localized states. We describe procedures by which these two components can be distinguished so as to produce images of the surface electronic states with atomic resolution. This ability to spatially resolve the surface electronic structure provides new information to understand the local structure and nature of bonding, and in some cases can be used as a means to chemically image specific features of the surface.

scholarly journals C-, N-, S-, and F-Doped Anatase TiO2 (101) with Oxygen Vacancies: Photocatalysts Active in the Visible Region

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Julio César González-Torres ◽  
Enrique Poulain ◽  
Víctor Domínguez-Soria ◽  
Raúl García-Cruz ◽  
Oscar Olvera-Neria
Keyword(s):  
Visible Light ◽  
Conduction Band ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Visible Region ◽  
Charge Carriers ◽  
Localized States ◽  
Similar Process ◽  
Visible Radiation ◽  
C Doping

Anatase TiO2 presents a large bandgap of 3.2 eV, which inhibits the use of visible light radiation (λ > 387 nm) for generating charge carriers. We studied the activation of TiO2 (101) anatase with visible light by doping with C, N, S, and F atoms. For this purpose, density functional theory and the Hubbard U approach are used. We identify two ways for activating the TiO2 with visible light. The first mechanism is broadening the valence or conduction band; for example, in the S-doped TiO2 (101) system, the valence band is broadened. A similar process can occur in the conduction band when the undercoordinated Ti atoms are exposed on the TiO2 (101) surface. The second mechanism, and more efficient for activating the anatase, is to generate localized states in the gap: N-doping creates localized empty states in the bandgap. For C-doping, the surface TiO2 (101) presents a “cleaner” gap than the bulk TiO2, resulting in fewer recombination centers. The dopant valence electrons determine the number and position of the localized states in the bandgap. The formation of charge carriers with visible light is highly favored by the oxygen vacancies on TiO2 (101). The catalytic activity of C-doping using visible radiation can be explained by its high absorption intensity generated by oxygen vacancies on the surface. The intensity of the visible absorption spectrum of doped TiO2 (101) follows the order: C > N > F > S dopant.

scholarly journals A new view on the origin of zero-bias anomalies of Co atoms atop noble metal surfaces

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Juba Bouaziz ◽  
Filipe Souza Mendes Guimarães ◽  
Samir Lounis
Keyword(s):  
Density Functional ◽  
Degrees Of Freedom ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Many Body ◽  
Magnetic Anisotropy Energy ◽  
Zero Bias ◽  
Relativistic Time ◽  
Wide Range ◽  
Spin Excitations

AbstractMany-body phenomena are paramount in physics. In condensed matter, their hallmark is considerable on a wide range of material characteristics spanning electronic, magnetic, thermodynamic and transport properties. They potentially imprint non-trivial signatures in spectroscopic measurements, such as those assigned to Kondo, excitonic and polaronic features, whose emergence depends on the involved degrees of freedom. Here, we address systematically zero-bias anomalies detected by scanning tunneling spectroscopy on Co atoms deposited on Cu, Ag and Au(111) substrates, which remarkably are almost identical to those obtained from first-principles. These features originate from gaped spin-excitations induced by a finite magnetic anisotropy energy, in contrast to the usual widespread interpretation relating them to Kondo resonances. Resting on relativistic time-dependent density functional and many-body perturbation theories, we furthermore unveil a new many-body feature, the spinaron, resulting from the interaction of electrons and spin-excitations localizing electronic states in a well defined energy.

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