Search results for "tunne"

Spatially resolved measurement of nonequilibrium quasiparticle relaxation in superconducting Al

2011

Spatially resolved relaxation of nonequilibrium quasiparticles in a superconductor at ultralow temperatures was experimentally studied. It was found that the quasiparticle injection through a tunnel junction results in the modification of the shape of the I-V characteristic of a remote ``detector'' junction. The effect depends on the temperature, injection current, and proximity to the injector. The phenomena can be understood in terms of the creation of quasiparticle charge and energy disequilibrium characterized by two different length scales ${\ensuremath{\Lambda}}_{{Q}^{*}}~5$ and ${\ensuremath{\Lambda}}_{{T}^{*}}~40$ $\ensuremath{\mu}$m. The findings are in good agreement with existing…

Field dependence of the vortex core size probed by scanning tunneling microscopy

2016

We study the spatial distribution of the density of states (DOS) at zero bias N(r) in the mixed state of single and multigap superconductors. We provide an analytic expression for N(r) based on deGennes' relationship between DOS and the order parameter that reproduces well scanning tunneling microscopy (STM) data in several superconducting materials. In the single gap superconductor β-Bi2Pd, we find that N(r) is governed by a length scale ξH=φ0/2πH, which decreases in rising fields. The vortex core size C, defined via the slope of the order parameter at the vortex center, C (dΔ/dr|r→0)-1, differs from ξH by a material dependent numerical factor. The new data on the tunneling conductance and…

Heavy-fermion superconductivity induced by antiferromagnetic spin fluctuations

2007

Superconductivity is caused by an attractive interaction between electrons at the Fermi level that induces the pairing of time-reversed electron states to Cooper pairs. Conventionally this attractive interaction is mediated by phonons. Theoretically, non-phonon mediated coupling seems to be likely for heavy-fermion superconductors whose low-temperature dynamics is dominated by antiferromagnetic spin correlations. However, evidence for spin-fluctuation coupling has not yet been experimentally observed. One of the most direct methods of investigation of the superconducting state is tunneling spectroscopy. We prepared cross-type tunneling junctions composed of the heavy-fermion superconductor …

Evidence for eight node mixed-symmetry superconductivity in a correlated organic metal

2015

We report a combined theoretical and experimental investigation of the superconducting state in the quasi-two-dimensional organic superconductor $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br. Applying spin-fluctuation theory to a low-energy material-specific Hamiltonian derived from ab initio density functional theory we calculate the quasiparticle density of states in the superconducting state. We find a distinct three-peak structure that results from a strongly anisotropic mixed-symmetry superconducting gap with eight nodes and twofold rotational symmetry. This theoretical prediction is supported by low-temperature scanning tunneling spectroscopy on in situ cleaved single crystals of $\kappa$-(ET)$_2$…

Josephson junctions and superconducting field effect transistors based on epitaxial Bi2Sr2Can-1CunO2(n+2) thin films

1998

Abstract Josephson junctions based on thin films of the Bi2Sr2Ca2Cu3O10+δ compound show IcRn products compatible with YBa2Cu3O7−δ samples. Using quasiparticle tunneling experiments we found evidence for a superconductor–insulator–superconductor tunneling process via localized states in the barrier. The Bi2Sr2CaCu2O8+δ compound is investigated regarding possible applications in superconducting field effect devices. We present thin films of four unit cells thickness that are superconducting at 58 K. An inverted metal–insulator–superconductor structure was prepared. From the modulation of the normal state resistance we estimate a carrier density of 7×1019 cm−3 for a superconducting sample. The…

Investigation of Many‐Body Effects in the Quasi‐Two‐Dimensional Electronic System of Organic Charge‐Transfer Salts

2019

Spatial development of multiple-gap states in nonequilibrium superconductors

1985

We have studied the gap instability in a superconductor under tunneling injection at high voltages by probing the spatial distribution of the phonon emission. A high sensitivity was achieved by using the fountain pressure of superfluid helium for detecting the phonons. Spatial structures were observed at gap depressions as small as 2%. From their spatial development we find that the quasiparticles diffuse into regions where their density is higher.

Effect of carrier transfer on the PL intensity in self-assembled In (Ga) As/GaAs quantum rings

2006

We present results concerning the carrier transfer between In(Ga)As quantum rings in a stacked multilayer structure, which is characterised by a bimodal size distribution. This transfer of carriers explains the observed temperature behaviour of diode lasers based on that kind of stacked layer structures. The inter-ring carrier transfer can be possible by phonon assisted tunnelling from the ground state of the smallring family towards the big-ring family of the bimodal size distribution. This process is thermally activated in the range 40–80 K.

Morphology and electronic structure of bcc Co(110) and fcc/hcp Co(111) on Fe(110) investigated by STM and STS

2009

Abstract We report on the growth of ultrathin epitaxial Co films on Fe(1 1 0) examined by scanning tunneling microscopy and spectroscopy (STM and STS). At room temperature Co forms pseudomorphic, ideally ordered body-centered cubic (bcc) layers for the first two monolayers as confirmed by atomically resolved STM images. This is in contrast to the related case of Co/Cr(1 1 0) where a superstructure occurs in the second layer. The third monolayer forms a close-packed structure and causes a transformation of the buried second monolayer into a close-packed structure. The Fe(1 1 0) substrate strongly influences the electronic structure of the first Co monolayer as concluded from the dI / dU spec…

Enhanced CDW Transitions in Nb3X4(X = S, Se, Te): Intercalation and Surface Effects

2004

A x Nb 3 X 4 (A = In, Tl, ZnHg; X = S, Se, Te) compounds show CDW instabilities dependent on the type and concentration of intercalate. Tl or In intercalation flattens the Fermi surfaces and supports CDW formation. In the corresponding DOS spectrum the Fermi level is shifted towards coincidence with a small peak, derived mainly from the Nb dz 2 orbital. Localized modulated regions observed in STM images of Nb 3 X 4 at room temperature represent precursor effects to full CDW formation.