Direct imaging of the two-dimensional Fermi contour: Fourier-transform STM

Petersen, L.; Sprunger, P. T.; Hofmann, Philip; Lægsgaard, Erik; Briner, B. G.; Doering, Marcus; Rust, Hans-Peter; Bradshaw, Alexander M.; Besenbacher, Flemming; Plummer, E. W.

doi:10.1103/physrevb.57.r6858

Cited by 153 publications

(149 citation statements)

References 20 publications

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“…This is confirmed in the FT of the image, see Fig. 1(f), that shows an incomplete circle positioned around the center of the spectrum, indicating that the SW pattern is given by energy-resolved Friedel oscillations [22]. From Fig.…”

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confidence: 60%

Room-Temperature Self-Assembly of Equilateral Triangular Clusters via Friedel Oscillations

et al. 2008

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We report on the formation of equilateral triangular clusters hollow inside with 5-6 atoms per side, selfassembled on Ni adislands grown on Rh(111). The observation of standing wave patterns on the Ni adislands and the Rh(111) indicates that the self-assembly is mediated by Friedel oscillations. In this context, we propose a model based on the energy of interaction between adsorbates, which explains the formation of the clusters as a result of the assembly of rows of 5-6 adatoms.

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confidence: 60%

Room-Temperature Self-Assembly of Equilateral Triangular Clusters via Friedel Oscillations

et al. 2008

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“…27 The interference of incoming and reflected waves gives rise to a modulation in the local density of states with a periodicity of 2k F , i.e., with the vector connecting the two states. A twodimensional Fourier transformation of conductance images taken with small tunneling voltages is therefore closely related to the two-dimensional Fermi surface, 28 a relationship which has led to several applications. 21,[28][29][30][31][32][33][34][35] However, this simple picture is only correct when the state at k F and the state at −k F have the same spin.…”

Section: Scanning Tunneling Microscopymentioning

confidence: 99%

Evidence against a charge density wave on Bi(111)

et al. 2005

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The Bi͑111͒ surface was studied by scanning tunneling microscopy ͑STM͒, transmission electron microscopy ͑TEM͒, and angle-resolved photoemission spectroscopy ͑ARPES͒ in order to verify the existence of a recently proposed surface charge-density wave ͑CDW͒ ͓Ch. R. Ast and H. Höchst, Phys. Rev. Lett. 90, 016403 ͑2003͔͒. The STM and TEM results do not support a CDW scenario at low temperatures. Furthermore, the quasiparticle interference pattern observed in STM confirms the spin-orbit split character of the surface states which prevents the formation of a CDW, even in the case of good nesting. The dispersion of the electronic states observed with ARPES agrees well with earlier findings. In particular, the Fermi contour of the electron pocket at the center of the surface Brillouin zone is found to have a hexagonal shape. However, no gap opening or other signatures of a CDW phase transition can be found in the temperature-dependent data.

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“…A charged impurity inside a Fermi sea is known to generate Friedel oscillations. Interference between oscillations produced by neighbouring impurities is detectable by scanning tunnelling microscopy (STM) 27 . Now, a calcium ion rattling inside its cage in a Fermi sea would generate two superimposed sets of Friedel oscillations, as illustrated in Fig.…”

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A ferroelectric quantum phase transition inside the superconducting dome of Sr1−xCaxTiO3−δ

Rischau¹,

Lin²,

Grams³

et al. 2017

Nature Phys

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SrTiO 3 , a quantum paraelectric 1 , becomes a metal with a superconducting instability after removal of an extremely small number of oxygen atoms 2 . It turns into a ferroelectric upon substitution of a tiny fraction of strontium atoms with calcium 3 . The two orders may be accidental neighbours or intimately connected, as in the picture of quantum critical ferroelectricity 4 . Here, we show that in Sr 1−x Ca x TiO 3−δ (0.002 < x < 0.009, δ < 0.001) the ferroelectric order coexists with dilute metallicity and its superconducting instability in a finite window of doping. At a critical carrier density, which scales with the Ca content, a quantum phase transition destroys the ferroelectric order. We detect an upturn in the normal-state scattering and a significant modification of the superconducting dome in the vicinity of this quantum phase transition. The enhancement of the superconducting transition temperature with calcium substitution documents the role played by ferroelectric vicinity in the precocious emergence of superconductivity in this system, restricting possible theoretical scenarios for pairing.A perovskite of the ABO 3 family, SrTiO 3 is a quantum paraelectric whose dielectric constant rises to ∼20,000 at low temperature 1 , but avoids long-range ferroelectric order. It becomes a metal by substituting Sr with La, Ti with Nb, or by removing O. It has been known for half a century that this metal is a superconductor at low temperatures 2 . More recently, a sharp Fermi surface and a superconducting ground state have been found to persist down to a carrier concentration of 10 17 cm −3 in SrTiO 3−δ (refs 5,6 However, mobile electrons screen polarization and therefore only insulating solids are expected to host a ferroelectric order. Hitherto, as a paradigm, ferroelectric quantum criticality, in contrast to its magnetic counterpart, was deprived of an experimental phase diagram in which a superconducting phase and a ferroelectric order share a common boundary.Here, we produce such a phase diagram in the case of Sr 1−x Ca x TiO 3−δ . The main new observations are the following: metallic Sr 1−x Ca x TiO 3−δ hosts a phase transition structurally indistinguishable from the ferroelectric phase transition in insulating Sr 1−x Ca x TiO 3 ; the coexistence between this ferroelectric-like order and superconductivity ends beyond a threshold carrier concentration; and, in the vicinity of this quantum phase transition, calcium substitution enhances the superconducting critical temperature and induces an upturn in the normal-state resistivity.Figure 1 summarizes what we know about the emergence of ferroelectricity, metallicity and superconductivity in this system. When a small fraction of Sr atoms (x > 0.002) is replaced with isovalent Ca, Sr 1−x Ca x TiO 3 becomes ferroelectric 3 , with a Curie temperature steadily increasing with Ca content in the dilute limit 0.002 < x < 0.02 (refs 3,13,14). Macroscopic polarization below the Curie temperature has been observed in dielectric and linear birefringence measurements, a...

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Direct imaging of the two-dimensional Fermi contour: Fourier-transform STM

Cited by 153 publications

References 20 publications

Room-Temperature Self-Assembly of Equilateral Triangular Clusters via Friedel Oscillations

Room-Temperature Self-Assembly of Equilateral Triangular Clusters via Friedel Oscillations

Evidence against a charge density wave on Bi(111)

A ferroelectric quantum phase transition inside the superconducting dome of Sr1−xCaxTiO3−δ

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