The observation by scanning tunnelling spectroscopy (STS) of Abrikosov vortex cores in the hightemperature superconductor YBa2Cu3O7−δ (Y123) has revealed a robust pair of electron-hole symmetric states at finite subgap energy. Their interpretation remains an open question because theory predicts a different signature in the vortex cores, characterised by a strong zero-bias conductance peak. We present STS data on very homogeneous Y123 at 0.4 K revealing that the subgap features do not belong to vortices: they are actually observed everywhere along the surface with high spatial and energy reproducibility, even in the absence of magnetic field. Detailed analysis and modelling show that these states remain unpaired in the superconducting phase and belong to an incoherent channel which contributes to the tunnelling signal in parallel with the superconducting density of states.

In CRESST-III, 10 cryogenic detector modules optimized for low energy thresholds were operated for almost two years (May 2016 - February 2018). Together with this document we are publishing data from the best performing detector module which has a nuclear recoil threshold of 30.1eV. With this data-set we were able to set limits on the cross-section for spin-dependent and spin-independent elastic scattering of dark matter particles off nuclei at dark matter masses down to 160MeV/c$^2$. We publish the energies of all events after data selection as well as of all events within the acceptance region for dark-matter searches. In this document we describe how to use these data sets.

The observation by scanning tunnelling spectroscopy of Abrikosov vortex cores in the high-temperature superconductor YBa2Cu3O7-δ (Y123) has revealed a robust pair of electron-hole symmetric states at finite subgap energy. Their interpretation remains an open question because theory predicts a different signature in the vortex cores, characterized by a strong zero-bias conductance peak. Here, we present scanning tunnelling spectroscopy data on very homogeneous Y123 at 0.4 K revealing that the subgap features do not belong to vortices: they are actually observed everywhere along the surface with high spatial and energy reproducibility, even in the absence of magnetic field. Detailed analysis and modelling show that these states remain unpaired in the superconducting phase and belong to an incoherent channel, which contributes to the tunnelling signal in parallel with the superconducting density of states.

We study the vortex phase diagram of the single-layer Bi2Sr2CuO6+d (Bi2201) superconductor by means of bulk magnetization measurements on high-quality oxygen-overdoped crystals. In striking contrast with the results found in the moderately-doped two and three-layer Bi-based cuprates, Bi2201 exhibits a strong temperature-dependent second-peak effect. By means of measurements of the in and out-of-plane first-penetration field we provide direct evidence that this phenomenon is mainly associated to an increase of the electromagnetic anisotropy on warming. The effect of oxygen-doping d on the vortex phase diagram results in both the irreversibility and second-peak lines shifting to higher temperatures and fields. This enhanced stability of the Bragg glass phase suggests that the interlayer coupling between Cu-O layers increases with d. In addition, we found that the critical temperature follows the parabolic relation with the number of holes per Cu-O plane that holds for most single and two-layer cuprates.

Manufacturing superconducting circuits out of ultrathin films is a challenging task when it comes to patterning complex compounds, which are likely to be deteriorated by the patterning process. With the purpose of developing high-T(c) superconducting photon detectors, we designed a novel route to pattern ultrathin YBCO films down to the nanometric scale. We believe that our method, based on a specific use of a focused-ion beam, consists of locally implanting Ga(3+) ions and/or defects instead of etching the film. This protocol could be of interest for engineering high-T(c) superconducting devices (SQUIDS, SIS/SIN junctions and Josephson junctions), as well as to treat other sensitive compounds.

We present temperature-dependent scanning tunneling spectroscopy measurements on $La_{1-x}Ca_{x}MO_{3}$ ($x\sim0.33$) films with different degrees of biaxial strain. A depletion in normalized conductance around the Fermi level is observed both above and below the insulator-to-metal transition temperature $T_{MI}$, for weakly as well as highly-strained films. This pseudogap-like depletion globally narrows on cooling. The zero-bias conductance decreases on cooling in the insulating phase, reaches a minimum close to $T_{MI}$ and increases on cooling in the metallic phase, following the trend of macroscopic conductivity. These results support a recently proposed scenario in which dynamical short-range antiferromagnetic/charge order correlations play a preeminent role in the transport properties of colossal magnetoresistive manganites [R. Yu \textit{et al}., Phys. Rev. B \textbf{77}, 214434 (2008)].

The major drawback for the commercialization of fault current limiter (FCL) made of YBCO on sapphire is their expensive price. In the recent years, coated conductors (CC) have been extensively developed and, due to their lower prices, have been recently tested for current limitation application. One weakness of these CC is the very low electric fields they can sustain, typically below 1 V/cm as compared to 20-40 V/cm observed in YBCO films grown on sapphire. The limitation of this electric field in CC comes certainly from the very low propagation velocities of the dissipative state, a property which might be correlated with the poor thermal behavior of the architecture of these materials. Both the thermal conductivities of the Hastelloy substrate and of the conducting bilayer (superconducting DyBCO and Ag conducting layer) influence the thermal behavior of the CC and therefore have to be optimized to get the best performance. We have then investigated the thermal and electrical behavior and the propagation velocities in CC during constant current pulses above Jc . The comparison with the results obtained on YBCO films grown on sapphire shows several differences. In CC, the flux flow resistivities are 2-3 orders of magnitude higher than in film grown on sapphire and quench propagation velocities are 2-3 orders of magnitude lower (of the order of cm/s). The propagation velocities in CC and in films on sapphire are analysed with a simple adiabatic model.

We study the extent of the reversible region in the vortex phase diagram of recently available RbOs2O6 single crystals [Rogacki , Phys. Rev. B 77, 134514 (2008)] by means of bulk magnetization measurements. We found that the irreversible magnetic response sets in at a field H-irr(T)similar to 0.3H(c2)(T) for 0.5 less than or similar to T/T-c less than or similar to 0.8 yielding a reversible vortex region that is wide in comparison with other low-T-c materials. The relevance of thermal fluctuations is limited since we estimate a Ginzburg number G(i)=5x10(-7). However, the relevance of quenched disorder is low since the critical-current density ratio at low fields and temperatures is of the order of that found in high T-c's. We therefore conclude that an intrinsically low bulk pinning magnitude favors the existence of an unexpectedly wide reversible vortex region in RbOs2O6.

In two dimensions the noninteracting density of states displays a van Hove singularity (VHS) which introduces an intrinsic electron-hole asymmetry, absent in three dimensions. We show that due to this VHS the strong-coupling analysis of tunneling spectra in high-Tc superconductors must be reconsidered. Based on a microscopic model which reproduces the experimental data with excellent accuracy, we elucidate the peculiar role played by the VHS in shaping the tunneling spectra, and show that more conventional analysis of strong-coupling effects can lead to severe errors.

We study the extent of the reversible region in the vortex phase diagram of recently available RbOs_2O_6 single crystals by means of bulk magnetization measurements. We found that the irreversible magnetic response sets in at a field H_ irr(T) ∼ 0.3 H_ c2(T) for 0.5 ≲ T/T_ c≲ 0.8, yielding a reversible vortex region that is uncommonly wide in comparison with typical low-T_ c materials. The relevance of thermal fluctuations is limited since we estimate a Ginzburg number G_ i = 5 × 10^-7. However, the relevance of quenched disorder is unconventionally low since the critical-current density ratio at low fields and temperatures is of the order of that found in high-T_ c's. We therefore conclude that an intrinsically low bulk pinning magnitude favors the existence of an unexpectedly wide reversible vortex region that seems to be generic to β-pyrochlores.

We report low-temperature scanning tunneling microscopy and spectroscopy on high quality Bi2Sr2Ca2Cu3O10+δ crystals. We present atomic-resolution topography and show spectroscopic data acquired on two different samples. In one case, we obtained an extremely homogeneous sample with Tc=109K and a transition width of only 1K, and with Δ¯p=60meV over at least 50nm. In the other case, the respective parameters were Tc=111K and ΔTc=1.7K, it yielded a slightly less homogeneous sample with Δ¯p=45meV. We evidence strong similarities with Bi2Sr2CaCu2O8+δ and discuss the doping level of our samples.

Control of the density of mobile charge carriers using electric fields is widely used in a variety of metal–insulator–semiconductor structures and is the governing principle behind the operation of field-effect transistors. Ferroelectric materials possessing a switchable and non-volatile polarization field can be used as insulating layers, revealing new opportunities for device applications1,2. Advances in material processing and in particular complex oxide thin-film growth mean that high-quality field-effect devices can be based on ferroelectric/metallic oxide heterostructures3,4,5,6,7,8,9,10,11. In addition, advances in local probe techniques such as atomic force microscopy allow them to be used in the imaging and study of small ferroelectric domain structures in bulk crystals12 and thin films13,14,15,16,17,18,19,20. Meanwhile, scanning tunnelling microscopy and spectroscopy have established themselves as powerful techniques for atomic manipulation and nanometre-resolution electron tunnelling spectroscopy21,22. Here, a scanning tunnelling microscope is used to investigate the ferroelectric field effect in all-perovskite heterostructures. Scanning tunnelling spectroscopy allows us to probe the local electronic properties of the polarized channel of a ferroelectric field-effect device as a function of the field orientation. This technique can be used to read and write ferroelectric field-induced regions with a size as low as 20 nm.

MER Michel DECROUX, Alfred MANUEL Postdocs Louis ANTOGNAZZA, Morten ESKILDSEN, Isabelle JOUMARD, Edmond KOLLER, Olivier KUFFER, Martin KUGLER, Ivan MAGGIO-APRILE, Serge REYMOND, Shukichi TANAKA PhD students Laurent BESSON, Cédric DUBOIS, Bart HOOGENBOOM, Pascal REINERT, Emmanuel TREBOUX Diploma students Estelle DE CHAMBRIER, Daniel GUTIERREZ RIOS Technicians Paul-Emile BISSON, Jean-Gabriel BOSCH, Arthur STETTLER

We present a detailed study of vortex-core spectroscopy in slightly overdoped Bi2Sr2CaCu2O8+delta using a low-temperature scanning tunneling microscope. Inside the vortex core, we observe a fourfold symmetric modulation of the local density of states with an energy-independent period of (4.3 +/- 0.3)a0. Furthermore, we demonstrate that this square modulation is related to the vortex-core states which are located at +/-6 meV. Since the core-state energy is proportional to the superconducting gap magnitude , our results strongly suggest the existence of a direct relation between the superconducting state and the local electronic modulations in the vortex core.

Recent angle-resolved photoemission and neutron scattering data have provided new ingredients for the interpretation of scanning tunneling spectra on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. We analyze the low-temperature tunneling spectra, from oxygen overdoped to underdoped samples, including details about the bilayer splitting and the neutron resonance peak. Two van Hove singularities are identified: the first is integrated in the coherence peaks, the second is heavily broadened at higher binding energy. The shape of the tunneling spectra suggests a strong coupling of the quasiparticles with a collective mode, and a comparison with photoemission shows that the scattering rate in tunneling is an order of magnitude smaller than in ARPES. Finally, the theoretical spectra calculated with an isotropic tunneling matrix element are in better agreement with the experimental data than those obtained with anisotropic matrix elements.

During past years, scanning tunneling spectroscopy (STS) investigations of high temperature superconductors have revealed unusual characteristics of the superconducting gap. We present here the temperature dependence of the tunneling conductance spectra on YBa2Cu3O7−δ and Bi2Sr2CaCu2O8+δ single crystals. We discuss similarities and differences between these two compounds. In particular we note that while in Bi2Sr2CaCu2O8+δ a pseudogap is observed above the critical temperature, even in overdoped samples, we find no indication of a pseudogap in optimally doped YBa2Cu3O7−δ above Tc. This is consistent with other striking differences between the two systems and supports the interpretation of the pseudogap in terms of strong superconducting correlations.

We present scanning tunneling spectroscopy (STS) investigations of high temperature superconductors illustrating the very unusual characteristics of the superconducting gap, and the intimate relation existing between the superconducting and the normal-state gap (pseudogap). A unique feature of STS is to probe the local density of quasiparticle states bound to individual vortices. The vortex core spectroscopy sheds new light on the pseudogap and the microscopic nature of HTS. The experiments reviewed here suggest that HTS are in a regime very different from BCS, approaching the crossover to Bose-Einstein condensation.

Tunneling spectroscopy has played a central role in the experimental verification of the microscopic theory of superconductivity in classical superconductors. Initial attempts to apply the same approach to high-temperature superconductors were hampered by various problems related to the complexity of these materials. The use of scanning tunneling microscopy and spectroscopy (STM and STS) on these compounds allowed the main difficulties to be overcome. This success motivated a rapidly growing scientific community to apply this technique to high-temperature superconductors. This paper reviews the experimental highlights obtained over the last decade. The crucial efforts to gain control over the technique and to obtain reproducible results are first recalled. Then a discussion on how the STM and STS techniques have contributed to the study of some of the most unusual and remarkable properties of high-temperature superconductors is presented: the unusually large gap values and the absence of scaling with the critical temperature, the pseudogap and its relation to superconductivity, the unprecedented small size of the vortex cores and its influence on vortex matter, the unexpected electronic properties of the vortex cores, and the combination of atomic resolution and spectroscopy leading to the observation of periodic local density of states modulations in the superconducting and pseudogap states and in the vortex cores.

Ballistic electron emission microscopy (BEEM) has been used to study metal-oxide-semiconductor (MOS) structures such as Au/SiO2/n-type Si(100) and Ir/SiO2/n-type Si(100), with the thin SiO2 layer varying from 10 to 30 Angstrom. As expected, the presence of a 30-Angstrom oxide layer at the interface induces much higher electronic barriers than in the case of Schottky diodes. Samples with Au show a barrier height of similar to 4.1 eV, while those with Ir have a barrier as high as 5.6 eV. When the interface oxide-layer thickness is reduced to similar to 10 Angstrom, the BEEM spectra behavior is different. For Au/SiO2/Si junctions, although a clear threshold is always observed around 4 eV, showing that a high barrier is already formed at these small thicknesses, a leakage current is often detected below this threshold. In the case of Ir/SiO2/Si structures, the BEEM spectra display an anomalous behavior. Below the high-energy threshold around 5.5-6 eV, a first threshold (similar to 1.5 eV) and a broad peak (similar to 4 eV) are observed. These structures could result from a resonant tunneling effect through the oxide layer. A striking result is also observed in the reverse BEEM (RBEEM) mode. In contrast to what is normally observed, where the RBEEM current is much weaker than the BEEM current, for these ultrathin barriers we find a broad peak at 4 eV with approximately the same intensity in RBEEM as in BEEM.