Proximity effect and strong-coupling superconductivity in nanostructures built with an STM (original) (raw)

Phase Controlled Superconducting Proximity Effect Probed by Tunneling Spectroscopy

Physical Review Letters, 2008

Using a dual-mode STM-AFM microscope operating below 50 mK we measured the Local Density of States (LDoS) along small normal wires connected at both ends to superconductors with different phases. We observe that a uniform minigap can develop in the whole normal wire and in the superconductors near the interfaces. The minigap depends periodically on the phase difference. The quasiclassical theory of superconductivity applied to a simplified 1D model geometry accounts well for the data.

Phase sensitive electron-phonon coupling in a superconducting proximity structure

Physical Review B, 2009

We study the role of the superconducting proximity effect on the electron-phonon energy exchange in diffusive normal metals (N) attached to superconductors (S). The proximity effect modifies the spectral response of the normal metal, in particular the local density of states. This leads to a weakening of the electron-phonon energy relaxation. We show that the effect is easily observable with modern thermometry methods, and predict that it can be tuned in structures connected to multiple superconductors by adjusting the phase difference between superconducting order parameters at the two NS interfaces.

Superconducting nanostructures fabricated with the scanning tunnelling microscope

Journal of Physics: Condensed Matter, 2004

The properties of nanoscopic superconducting structures fabricated with a scanning tunnelling microscope are reviewed, with emphasis on the effects of high magnetic fields. These systems include the smallest superconducting junctions which can be fabricated, and they are a unique laboratory in which to study superconductivity under extreme conditions. The review covers a variety of recent experimental results on these systems, highlighting their unusual transport properties, and theoretical models developed for their understanding.

Electron-phonon interaction in high-temperature superconductors

Physics-Uspekhi, 1993

The results of experimental studies of the interaction between electrons and crystal lattice vibrations in high-temperature superconducting metal oxides are presented. Attention is directed mainly toward a critical analysis of the data obtained by means of tunneling spectroscopy.

Electron Phonon Interactions and Superconductivity

Electron–Phonon Interactions and Superconductivity in (Cu 0.5 Tl 0.5)Ba 2 Ca 3 (Cu 4−y Ti y)O 12−δ (y = 0, 0.25, 0.50, 0.75, 1.0) Abstract We have used two-step solid state reaction method for the synthesis of (Cu 0.5 Tl 0.5)Ba 2 Ca 3 (Cu 4−y Ti y) O 12−δ (y = 0, 0.25, 0.50, 0.75, 1.0) superconductors at 880 • C. The oxygen contents in the samples were optimized by carrying out self-doping which is accomplished by post-annealed in flowing oxygen environment at 500 • C for approximately 5 h. The superconducting properties of all the samples were improved, after the self-doping of the carriers in the conducting planes. In the x-ray diffraction scans of the samples, the a-axis length of tetragonal unit cell increases whereas the c-axis decreases with increased Ti doping in the final compound. The Fourier transform infrared spectrometer (FTIR) absorption measurements of these samples have shown that the apical oxygen mode at 548 cm −1 and the pla-nar oxygen mode at 596 cm −1 are softened with increased Ti doping. The origin of softening of planar oxygen mode lies in increase bond lengths of apical oxygen atoms promoted by larger covalent radius of Ti (1.32Å) atoms relative to Cu (1.17Å) atoms that in turn promotes the softening of the apical oxygen modes. Doped Ti (47.90 amu) atoms at the Cu (63.54 amu) sites initiate the an-harmonic oscillations resulting into the suppression of density of phonon modes. The suppression in the values of superconductiv-ity parameters with Ti doping at the Cu sites shows the essential role of phonon in mechanism of high T c supercon-ductivity and hence the electron–phonons interactions. The excess conductivity analyses (FIC) of conductivity data of oxygen-post-annealed samples have shown decrease in the mean field critical temperature, coherence length along the c-axis, interlayer coupling, and Fermi velocity with increase Ti doping. However, the values of B c , B c1 , and J c(0) increase with Ti doping, showing increase in the population of the pinning centers.

Electron tunneling study of phonon structures in superconducting La1.85Sr0.15CuO4

Physica C: Superconductivity, 1993

Presented quasiparticle tunneling measurements of superconducting La~.ssSro.asCuO4 have shown that the fine structures in the second derivative of the tunneling current -d21/d V ~ are strong enough to be observed, and the energy positions of the peaks and valleys in -d21/d V 2 measured from the gap edge of 7 meV correlate with the generalized phonon density of states obtained by inelastic neutron spectroscopy. This fact suggests that phonons participate in the electron-pairing interaction in this superconductor.

Tunneling spectroscopy of bound and resonant states in superconducting proximity structures

Applied Surface Science, 1999

Scanning tunneling microscopy and spectroscopy are employed in order to map with nanometer resolution the local quasi-particle density of states in superconducting proximity structures. Our experimental configuration is unique, in that the tunneling current flows in parallel to the interfaces between different materials. We focus here on the measurement of bound and resonant states, arising from multiple Andreev reflections of quasi-particles propagating in a plane perpendicular to the tunneling current. q

Pseudo-gap in tunneling spectra as a signature of inhomogeneous superconductivity in oxide interfaces

Superconductor Science and Technology, 2015

= 626 mK, γ = 128 mK, w = 0.72, x = 0.1); Box (T min c = 255 mK, T max c = 580 mK, w = 0.58, x = 0.1). c = 661 mK, γ = 81 mK, w = 0.5, x = 0.1); Box (T min c = 278 mK, T max c = 661 mK, w = 0.42, x = 0.1).

Direct evidence for predominantly phonon-mediated pairing in high-temperature superconductors

The spectra of the second derivative of tunneling current d 2 I/dV 2 in the high-temperature superconductors YBa2Cu3O 7−δ and Bi2Sr2CaCu2O 8+δ show clear dip and peak features due to strong coupling to the bosonic modes mediating electron pairing. The energy positions of nearly all the peaks in −d 2 I/dV 2-like spectra match precisely with those in the phonon density of states obtained by inelastic neutron scattering. The results demonstrate that the bosonic modes mediating the electron pairing are phonons and that high-temperature superconductivity should arise primarily from strong coupling to multiple phonon modes.