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Ge two-dimensional hole gases (2DHG) formed in strained, modulation-doped quantum-wells are highly suitable for future spintronic applications due to their good electronic transport properties. For electrical spin injection into a Ge 2DHG, the ferromagnetic alloy Mn 5 Ge 3 can be used as a contact material. The Mn 5 Ge 3 layer can be grown as an interlayer by interdiffusion between an evaporated Mn layer and the Ge 2DHG. In this paper, we report on the growth of a ferromagnetic Mn 5 Ge 3 thin film directly on the strained Ge. To this end, the Si 20 Ge 80 capping layer covering the channel was selectively removed using Ar+ ion milling. We investigate the magnetic properties of Mn 5 Ge 3 grown on a Ge (111) 2DHG by superconducting quantum interference device magnetometry and compare the results to an unetched Mn 5 Ge 3 on Ge (111) reference. Furthermore, temperature-dependent Hall measurements using the Mn 5 Ge 3 contacts on the Ge (111) 2DHG confirm the electrical contact to the high mobility 2DHG. These results are an important step towards electrical spin injection into a Ge 2DHG which is a promising material for future spintronic applications.

We report on the first synthesis of a Mn based ferromagnet on SixGe(1-x-y)Sny lattice matched on Ge with Sn content up to 15 %. The ferromagnetic layers were grown using interdiffusion of evaporated Mn and epitaxially grown SixGe(1-x-y)Sny. The Si to Sn ratio of the epitaxial layer is fixed to allow lattice matched growth on Ge. The possibility to grow the ferromagnetic layer directly on a semiconductor opens up the opportunity for large scale manufacturing using a selfaligned interdiffusion process. The compound exhibits a ferromagnetic phase for all samples studied. The observed Curie temperature remains around room temperature and shows no decisive trend with increasing Sn content. The samples show an increasing coercive field and decreasing saturation magnetization with increasing Sn content. This makes Mn-SixGe(1-x-y)Sny an interesting alternative to Mn5Ge3 as a ferromagnetically harder material for spintronics applications.

The anisotropic magnetoresistance (AMR) of ferromagnetic ${\mathrm{Mn}}_{5}{\mathrm{Ge}}_{3}{\mathrm{C}}_{x}\phantom{\rule{4pt}{0ex}}(0\ensuremath{\le}x\ensuremath{\le}1)$ and ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}{\mathrm{C}}_{x}\phantom{\rule{4pt}{0ex}}(0.5\ensuremath{\le}x\ensuremath{\le}1)$ thin films was investigated and compared with density functional theory calculations from which the spin-split electronic density of states at the Fermi level and the spin polarization were obtained. The isostructural compounds exhibit different AMR behavior. While only ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}{\mathrm{C}}_{0.5}$ shows a positive AMR ratio and a positive spin polarization, the negative AMR ratio of all other compounds is due to a negative spin polarization. The correlation between the sign of the AMR and the degree of spin polarization is in agreement with theoretical calculations of the AMR ratio indicating that the magnetoelectronic transport in both compounds is dominated by minority-spin conduction. The dominating role of minority-spin conduction remains unaffected even after incorporation of carbon into the crystalline lattice which weakens both AMR and spin polarization.

Low-temperature magnetoresistance measurements of n- and p-doped germanium-tin (Ge

We report on the structure and magnetic properties of Mn based ferromagnetic layers on the semiconductor SixGe1-x-ySny with Sn content up to y = 0.15 in comparison with layers on Ge and Si0.75Ge0.25. The ferromagnetic layers grow by interdiffusion between an evaporated Mn layer and molecular-beam-epitaxy grown semiconductor layers. This approach enables the preparation of Mn based layers, e. g., as a ferromagnetic contact material for SixGe1-x-ySny using a self-aligned interdiffusion process, opening up the opportunity for large-scale manufacturing. The samples show a clear phase separation into Si-rich and Ge-rich Mn compounds. All samples are ferromagnetic and exhibit a decrease in saturation magnetization and an increase in coercive field with increasing Si content x. The Curie temperature shows no decisive trend with increasing Si content with values around room temperature. Based on the composition, structure and magnetic properties, we propose a two-layer model to correlate the structure and composition with the observed magnetic properties. We show that the changes in magnetic behavior can be explained solely by considering the Si content of the SixGe1-x-ySny substrates with the Sn being largely passive.

Investigating the thermoelectric properties of ferromagnets is important for the development of future microelectronic devices for efficient energy conversion purposes. Ferromagnetic Mn$_5$Ge$_3$C$_x$ thin films with a Curie temperature up to $T_{\rm C}$ = 450 K well above room temperature are potential candidates for spintronic applications by integration into CMOS heterostructures. In this work, the thermoelectric power, in particular, the anomalous Nernst effect (ANE) has been investigated experimentally for magnetron sputtered thin films on sapphire (11-20) substrates. The ANE gradually increases with increasing carbon content x up to a maximum value obtained for x=0.8 in line with earlier investigations of the magnetization and anomalous Hall effect. The ANE is strongly enhanced by a factor three compared to the parent Mn$_5$Ge$_3$ compound. However, for x=0.8 we observe a clear deviation of the calculated ANE from the measured values., Comment: 6 pages, 4 figures

The antiperovskite Mn 3 Zn 0.77 Mn 0.19 N 0.94 was investigated by in situ neutron powder diffraction (NPD) in the temperature region 5–300 K. Here, a noncollinear-antiferromagnetic/collinear-ferrimagnetic phase separation (PS) showing different lattice parameters was firstly revealed in antiperovskites. The NPD results prove that the noncollinear antiferromagnetic phase, even coexisting with the collinear ferrimagnetic phase, could be responsible for the zero thermal expansion behavior of Mn 3 Zn 0.77 Mn 0.19 N 0.94 below 110 K. These findings suggest that Mn 3 ZnN based materials could open a new avenue for further exploring the noncollinear magnetic PS and correlated physical properties of antiperovskites.

The electronic structure and the domain wall width of industrial (Nd,Dy)$_{2}$Fe$_{14}$B hard magnets were investigated using low-temperature, spin-polarized scanning tunneling microscopy (STM) in ultra-high vacuum. In a first step, atomically clean and flat surfaces were prepared. The flat terraces were separated by monatomic steps. Surface termination was identified as the Fe c layer from atomically resolved STM imaging. The electronic density of states and its spin polarization agree well with ab initio predictions of the Fe c layer. High-resolution spin-polarized STM images allowed to finally resolve the domain wall width w of only 3.2 ± 0.4 nm.

Superconducting granular aluminum is attracting increasing interest due to its high kinetic inductance and low dissipation, favoring its use in kinetic inductance particle detectors, superconducting resonators or quantum bits. We perform switching current measurements on DC-SQUIDs, obtained by introducing two identical geometric constrictions in granular aluminum rings of various normal-state resistivities in the range from ρ n = 250–5550 μΩ cm. The relative high kinetic inductance of the SQUID loop, in the range of tens of nH, leads to a suppression of the modulation in the measured switching current versus magnetic flux, accompanied by a distortion towards a triangular shape. We observe a change in the temperature dependence of the switching current histograms with increasing normal-state film resistivity. This behavior suggests the onset of a diffusive motion of the superconducting phase across the constrictions in the two-dimensional washboard potential of the SQUIDs, which could be caused by a change of the local electromagnetic environment of films with increasing normal-state resistivities.

Measuring the anomalous Nernst effect of magnetically ordered thin films on substrates is often hampered by the mismatch between different thermal conductivities and the unknown temperature gradient in the film. Here, we demonstrate that for ferromagnetic films deposited on a semiconducting substrate, the Nernst effect of the semiconductor can serve as an internal reference for estimating the local temperatures present in the film and substrate. The Nernst effect in semiconductors is particularly large in the temperature region above 200 K where the semiconductor shows a strong change in the charge carrier concentration. As an example, we have studied the anomalous Nernst effect of 28 nm thick ferromagnetic Mn5Ge3C0.8 films deposited on p-type Ge(111) substrates with the temperature gradient oriented either parallel or perpendicular to the film plane. From the additional contribution of the Nernst effect arising from the substrate and comparison with theory, we estimate the temperature gradient in the substrate and thin film for both configurations and determine the thermoelectric coefficients of the film.

The International Conference on Magnetism 2009 (ICM 2009) was held in Karlsruhe, Germany, from 26 to 31 July 2009. Previous conferences in this series were organized in Edinburgh, UK (1991), Warsaw, Poland (1994), Cairns, Australia (1997), Recife, Brazil (2000), Rome, Italy (2003), and Kyoto, Japan (2006). As with previous ICM conferences, the annual Conference on Strongly Correlated Electron Systems (SCES) was integrated into ICM 2009. The topics presented at ICM 2009 were strongly correlated electron systems, quantum and classical spin systems, magnetic structures and interactions, magnetization dynamics and micromagnetics, spin-dependent transport, spin electronics, magnetic thin films, particles and nanostructures, soft and hard magnetic materials and their applications, novel materials and device applications, magnetic recording and memories, measuring techniques and instrumentation, as well as interdisciplinary topics. We are grateful to the International Advisory Committee for their help in coordinating an attractive program encompassing practically all aspects of magnetism, both experimentally and theoretically. The Program Committee comprised A Loidl, Germany (Chair), M A Continentino, Brazil, D E Dahlberg, USA, D Givord, France, G Guntherodt, Germany, H Mikeska, Germany, D Kaczorowski, Poland, Ching-Ray Chang, South Korea, I Mertig, Germany, D Vollhardt, Germany, and E F Wassermann, Germany. E F Wassermann was also head of the National Organizing Committee. His help is gratefully acknowledged. The scientific program started on Monday 27 July 2009 with opening addresses by the Conference Chairman, the Deputy Mayor of Karlsruhe, Ms M Mergen and the Chairman of the Executive Board of Forschungszentrum Karlsruhe, E Umbach. ICM 2009 was attended by the Nobel Laureates P W Anderson, A Fert and P Grunberg who gave plenary talks. A special highlight was the presentation of the Magnetism Award and Neel Medal to S S P Parkin who also presented his newest results in a plenary talk. The IUPAP Young Scientist Award on Magnetism was presented to S O Valenzuela, E Saitoh and T Kimura. The sessions were held in the Stadthalle Karlsuhe operated by the Karlsruher Messe- und Kongress-GmbH (KMK). We are grateful to Ms M Makelburg (KMK) for organizing the conference site impeccably. The conference was attended by 1552 participants from 48 countries, with approximately 50 per cent from overseas. The program entailed six plenary talks (40 min each), with 16 half-plenary and 41 invited talks (30 min) and 298 contributed talks (15 min). Extended lunch breaks and evenings were devoted to poster sessions, with a total of 1632 posters presented. All submitted papers were reviewed in order to meet the standards of Journal of Physics: Condensed Matter and Journal of Physics: Conference Series. The referees made every effort to ensure that the manuscripts submitted for publication in the proceedings reached a high standard. The tremendous work in organizing the paper classification and refereeing procedures was carried out by the Publication Committee which was headed by J Wosnitza, and comprised, in addition, Th Pruschke, M Richter and L Schultz. We also thank G Douglas, IOP Publishing, for his support with the preparation of these proceedings. We gratefully acknowledge the help of L Behrens, E Maass and B Schelske in preparing the conference. The conference would not have been possible without G Goll (conference secretary) and C Surgers (finances). I thank them for their help. Thanks also go to the many students in blue t-shirts who helped to manage the conference. We are grateful for the financial support of Universitat Karlsruhe (TH) and Forschungszentrum Karlsruhe (both institutions merged to form the Karlsruhe Institute of Technology (KIT) as of 1 October 2009), the International Union of Pure and Applied Physics (IUPAP), the City of Karlsruhe, Deutsche Forschungsgemeinschaft (German National Science Foundation), and the European Commission through COST MPNS Action P16. Hilbert v Lohneysen Conference Chairman of ICM 2009 Karlsruhe Institute of Technology, Germany

Thermoelectric effects can be surprisingly large in superconductor-ferromagnet tunnel junctions when the superconductor is subject to a spin-splitting field. The spin splitting can be provided by an applied magnetic field, but can also be created by exchange coupling to a ferromagnetic insulator. Here, it is shown that thermoelectric effects in superconductor-ferromagnet tunnel junctions can be enhanced by boosting the spin splitting with an intrinsic exchange field provided by a ferromagnetic insulator. These findings could lead to more precise local electron thermometry or efficient microrefrigerators.

In order to facilitate IR absorption measurements, we have upgraded our Bruker IFS66v/S Fourier-transform infrared (FTIR) spectrometer. A synthetic diamond beam splitter without compensator plate and UHV diamond viewports was installed. We have also modified the IR detector chamber to allow measurements with 5 different detectors. As a result we can now obtain FT absorption spectra from 12 000 cm

We have studied controlled electromigration (EM) in free-standing copper wires. Besides electrical characterization by voltage–current measurements, structural analyses have been performed by means of scanning electron microscopy and cross-sectional microprobe measurements. We have found that oxidation during the EM in air stabilizes the free-standing wire against uncontrolled blowing, making it possible to thin the conductive part of the wire down to a conductance of a few conductance quanta $$G_0=2e^2{/}h$$ . The decisive influence of oxidation by air on the EM process was confirmed by control experiments performed under ultra-high vacuum conditions. In line with these findings, free-standing Au wires were difficult to thin down reproducibly to a conductance of a few $$G_0$$ . Estimates of the local temperature in the free-standing wire are obtained from finite element method calculations.

The anomalous Hall effect in an antiferromagnet can be switched on and off using an electric field to alter the strain in the material.

We investigate the properties of Mn5Ge3C0.8 contacts on Ge (100) and (111) with varying doping type and doping concentrations with the aim of fabricating low-resistance contacts. Specific contact resistivities on Ge (100) are very high in all cases. The lowest specific contact resistivity (1.25·10-4 Ω·cm2) was obtained for Mn5Ge3C0.8 contacts on n++-Ge (111) with N D = 1∙1020 cm-3. We discuss means to further reduce specific contact resistivities.

In this communication, we investigate the thermoelectric properties of a charge density wave material TiSe2 upon Cu intercalation. Polycrystalline Cu x TiSe2 (x=0–0.11) alloys were synthesized using solid state sintering process and their morphological and structural properties were investigated. The material grows in layered morphology and the c-lattice parameter increases linearly with x. The temperature dependent resistivity measured in the 300–5 K range, shows that increasing x leads to a systematic transition from charge density wave state to the metallic state. For x=0.11, the room temperature thermoelectric figure-of-merit is found to be 0.104, which is higher by seven orders in magnitude (i.e. 1.93×10−8) measured for pristine TiSe2 and comparable to the other reported thermoelectric materials. These results show that Cu x TiSe2 are a potential material for the low temperature thermoelectric applications.

In order to facilitate IR absorption measurements of mass-selected ions isolated in cryogenic matrices, we have upgraded an ion beam deposition apparatus encompassing a Bruker IFS66v/S FTIR spectrometer. A synthetic diamond beam splitter without compensator plate and UHV diamond viewports were installed. We have also modified the IR detector chamber to allow measurements with 5 different detectors. As a result we can now obtain FT absorption spectra from 12000 cm$^{-1}$ to 15 cm$^{-1}$ with the same sample held under ultrahigh vacuum conditions, simply by switching between appropriate IR detectors. We demonstrate performance of the upgraded FTIR spectrometer by presenting measurements of matrix isolated fullerene ions and an adhesive tape.

Cerium is a fascinating element exhibiting, with its different phases, long-range magnetic order and superconductivity in bulk form. The coupling of the 4f electron to sd conduction electrons and to the lattice is responsible for unique structural and electronic properties like the isostructural first-order solid-solid transition from the cubic $\gamma$ phase to the cubic $\alpha$ phase, which is accompanied by a huge volume collapse of 14 %. While the $\gamma - \alpha$ phase transition has been investigated for decades, experiments aiming at disentangling the 4f contribution to the electric conductance of the different phases have not been performed. Here we report on the strongly enhanced conductance of single-atom Ce contacts. By controlling the content of $\alpha$-Ce employing different rates of cooling, we find a strong correlation between the fraction of $\alpha$-Ce and the magnitude of the last conductance plateau before the contact breaks. We attribute the enhanced conductance of $\alpha$-Ce to the additional contribution of the 4f level., Comment: 3 Figures

We demonstrate the utilization of the giant magnetostriction of Tb 0.3 DY 0.7 Fe 1.95 in a mechanically controlled break-junction device to control the conductance in a remote way by variation of an applied magnetic field $H$ at room temperature. The Tb 0.3 DY 0.7 Fe 1.95 grain-oriented compound was obtained by employing a modified Bridgman method. The rod was grown with a preferred crystallographic orientation with axes along the rod axis. Reproducible switching of the electrical conductance was observed at room temperature with the externally applied magnetic field perpendicularly to the wire long axis. Below 70 K, we observe a hysteresis for the conductance switching which is attributed to the pinning of domain walls. The switching of the conductance is distinctly different when the magnetic field is applied in the parallel or perpendicular direction with respect to the long wire axis, which is attributed to the different magnetic anisotropy in the two orientations. We also discuss about the tunneling characteristics of the Tb 0.3 DY 0.7 Fe 1.95 nanocontacts at 10 K. These results are important for developing a device based on a nano-electromechanical system operating at room temperature.

We show how the second-order nonlinear optical properties of nanolaminates fabricated by atomic-layer deposition can be controlled and enhanced. An optimized metamaterial shows a second-order nonlinear susceptibility of χ(2) zzz = −4.47 pm/V.

Metallic antiferromagnets with noncollinear orientation of magnetic moments provide a playground for investigating spin-dependent transport properties by analysis of the anomalous Hall effect. The intermetallic compound Mn5Si3 is an intinerant antiferromagnet with collinear and noncollinear magnetic structures due to Mn atoms on two inequivalent lattice sites. Here, magnetotransport measurements on polycrystalline thin films and a single crystal are reported. In all samples, an additional contribution to the anomalous Hall effect attributed to the noncollinear arrangment of magnetic moments is observed. Furthermore, an additional magnetic phase between the noncollinear and collinear regimes above a metamagnetic transition is resolved in the single crystal by the anomalous Hall effect., 7 pages, 4 figures

A spin-aligner that shows ferromagnetism at room temperature is indispensable for spintronic applications. Diluted magnetic semiconductors are prospective candidates for a spin-aligner. We show that Cu-doped group-III nitrides show ferromagnetic behavior at room temperature although Cu is an intrinsic non-magnetic material. Problems with the building of magnetic secondary phases like in Mn- or Gd-doped nitrides are avoided by using Cu. The formation of Cu-group-III metal compounds is observed. However, these compounds will not affect the ferromagnetic properties and 90% of them can be removed by etching with HIVO 3 for 5 min.

Electroresistance has become a stimulating research topic because of its potential applications in next-generation nonvolatile memory technology. Here, an electroresistance-like behavior of the antiperovskite Mn3GaC compound around the antiferromagnetic–intermediate phase transition is reported. A high sensing current significantly decreases the fraction of the antiferromagnetic phase of higher resistivity relative to the intermediate phase of lower resistivity upon warming, showing a resistivity change up to 50 %. Through extensive studies of the resistivity at different sample locations and of the magnetization under applied current, it is unambiguously shown that this electroresistance-like behavior originates from the local Joule heating of the sample due to high-resistive lead contacts and not from an intrinsic effect. These findings open an available avenue to explore electroresistance-like behavior by achieving phase coexistence of a high- and low-resistivity phase under the driving force of local Joule heating.

Metallic hybrid structures comprizing superconducting and ferromagnetic materials are interesting objects for studying the mutual influence between superconductivity and ferromagnetic order. We focus on two particular systems that have been studied during the last few years. In superconducting spin-valves the transition temperature of a superconductor squeezed between two ferromagnetic layers depends on the relative orientation of the two magnetization directions. Results have been obtained for systems with in-plane and out-of-plane magnetizations. Furthermore, we report on the electronic transport through superconductor/ferromagnet nanocontacts that allow a determination of the current spin-polarization which is related to the bulk spin polarization.

Top-contact organic field-effect transistors based on poly(3-hexylthiophene) (P3HT) active layer were fabricated using gate dielectric (SiO 2 ) modified with 3-aminopropyltrimethoxysilane (APTMS) multilayers. It has been demonstrated that the treatment of dielectric with APTMS enhances the field-effect mobility as well as the on/off ratio of the devices by nearly two orders of magnitude. This is attributed to conformational changes as well as to an improved uniformity of the spin coat P3HT films on the APTMS-modified substrate as revealed by atomic force microscopy, Fourier transform infrared spectroscopy and UV–Vis measurements.

The π-conjugated oligomer consisting of ethynyl interlinked thiophene and benzene subunits C114H158O8S2Si2 has been deposited on clean Cu(111) substrates at room temperature using the pulse-injection method with tetrahydrofuran (THF) as solvent. Scanning tunneling microscopy measurements in ultrahigh vacuum at room temperature demonstrate that the CHOSSi and THF molecules coadsorb on the copper surface. The solvent molecules form ordered structures with distinct orientations and domain boundaries, suggesting a strong interaction of THF with the substrate. Individual and small clusters of CHOSSi molecules appear randomly distributed on the surface with no apparent correlation with the solvent molecules. Subsequent thermal treatment removing the solvent causes a degradation of the CHOSSi oligomers which aggregate forming fractal nanostructures.

The magnetic properties of Mn5Si3Cx and Mn5Ge3Cx films prepared by magnetron cosputtering or C+-ion implantation are studied. The carbon-doped films exhibit ferromagnetic properties with Curie temperatures TC well above room temperature and metallic conductivity, making them possible candidates for future magnetic semiconductor-based devices. In Mn5Si3Cx, the carbon gives rise to a lattice expansion and a concomitant change of the magnetic order from antiferromagnetic Mn5Si3 to ferromagnetic Mn5Si3C0.8 with TC = 350 K. Likewise, TC of ferromagnetic Mn5Ge3 is strongly enhanced in Mn5Ge3C0·8. However, in this case the lattice is slightly compressed by carbon. This demonstrates that the effect of carbon on the magnetic behaviour in these compounds is not simply due to a change of the various interatomic distances by carbon but also due to a modification of the electronic band structure.

We present a detailed study on the growth and characterization of iron phthalocyanine (FePc) nanostructures using molecular beam epitaxy. FePc films of nominal thickness varying between 30 and 500 nm have been deposited as a function of substrate temperature (25–300 °C) and deposition rate (0.02–0.07 nm/s). Several interesting results have been observed. (1) For a growth temperature up to 200 °C, FePc grows in α-phase; while at growth temperatures >200 °C formation of β-phase also takes place. (2) Film thickness has a profound influence on the morphology: for thickness ⩽60 nm well-defined nanorods with crystallographic a-axis orientated normal to the substrate plane are formed, while for higher thicknesses a-axis oriented nanarods coalescence to each other which results in the random grain growth. (3) The morphology of a 60 nm α-phase film, at a growth temperature of 200 °C, can be tuned from nanobrush (nearly parallel nanorods aligned normal to the substrate plane) to nanoweb (nanowires forming a web-like structure in the plane of the substrate) by changing the deposition rate from 0.02 to 0.07 nm/s. (4) Both α-FePc nanobrush and nanoweb morphology turn into polycrystalline β-phase on annealing at 225 °C for prolonged durations. We propose growth mechanisms of nanoweb and nanobrush morphology based on the van der Waals (vdW) epitaxy.

Superconductors (S) can be employed to probe the spin polarization of ferromagnetic metals (F) by virtue of Andreev reflection. Using nanocontacts defined by e-beam lithography, the spin-polarization of the current across an S/F interface can be determined reliably. Via non-local Andreev reflection, an incident electron from a nanocontact is retroreflected as a hole in an adjacent contact, forming spatially separated but entangled Einstein–Podolski–Rosen pairs. Finally, the proximity-induced superconductivity can be probed by magnetization measurements.

We investigate the superconducting transition temperature Tc of epitaxial ferromagnet/superconductor/ferromagnet (FSF) triple layers with perpendicular magnetic anisotropy. Due to the different coercive fields of the top and bottom F layers (F=[Co/Pt] multilayer) different magnetized states can be achieved: a fully magnetized state where the F layer magnetizations are parallel oriented, a state DM where one layer is demagnetized, and a state DD where both layers are demagnetized. Tc is maximum in the fully magnetized state and decreases consecutively from the DM to the DD state due to the different contributions from magnetic stray fields originating from the domain walls present in the demagnetized layers. The role of the proximity effect and the effect of the stray fields on the superconductivity in the S layer can be distinguished by analyzing the temperature dependence of the upper critical field and by comparison with data taken on an FISIF multilayer where I is an insulating SiO2 barrier. Hence, we demonstrate that Tc can be manipulated by the intentional creation of different stray-field configurations in the F layers.

We use epitaxial strain to shift the energy of the two-dimensional Ag(111) surface states of Ag islands on Nb(110) substrates, allowing to spatially tune the bottom of the surface-state band $E_{\rm SS}$ through the Fermi level $E_{\rm F}$. Bulk and surface-state contributions to the Ag(111) local density of states (LDOS) can be separated with scanning tunneling spectroscopy. For thick islands ($\approx$\, 20 nm), the Ag surface states are decoupled from the Ag bulk states via orthogonality, and the superconductive gap induced by proximity to Nb is due to bulk states only. However, for thin islands (3-4 nm), surface-state electrons develop superconducting correlations as identified by a complete energy gap in the LDOS when $E_{\rm F}$ is smaller than but close to $E_{\rm F}$. The induced superconductivity in this case is of two-band nature and appears to occur when the surface-state wave function reaches down to the Ag/Nb interface., Comment: 5 pages, 4 figures

In Nb/Ag layers, the induced superconductivity in Ag by Nb gives rise to diamagnetic screening currents in the Ag layer well below the transition temperature of the superconductor. By investigating the position dependence of the individual diamagnetic transitions of Nb and Ag with a gradiometer in a nearly parallel magnetic field, we find that the screening of the Ag layer is remarkably different compared to the Nb layer. While for the Nb layer a strong out-of-plane contribution is observed due to the large demagnetization factor, such a contribution is absent for the Ag layer. This can be explained by the partial overscreening of the magnetic field, i.e. a reduced diamagnetic response of the Ag layer, as suggested by the theory for the clean limit.

The Si(557)-Au one-dimensional surface structure, with two types of characteristic protrusions denominated as alternating chains and rows oriented parallel to the [ 10] direction, is investigated at room temperature by scanning tunneling microscopy and spectroscopy in order to determine the local electronic properties. Tunneling spectra taken with atomic resolution above the two substructures are different which demonstrates that they arise from different contributions of the surface band-structure, i.e. Si adatoms and step edges. We find no evidence for features originating from Au atoms, indicating that these are completely embedded in the surface, in agreement with recent structure models.

Experimental investigations of superconductor/ferromagnet (S/F) interfaces which probe the penetration of the superconducting pairing amplitude into the ferromagnet are reviewed. The microscopic basis for this proximity effect is the process of Andreev reflection which can be used to extract the current spin-polarization in F from current-voltage characteristics. Initial studies focused on S/F layers and multilayers, while more recent experiments investigated nanostructured point contacts in local and nonlocal configurations. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The morphology and electronic transport of ultrathin Au films with thicknesses d = 1 − 5 monolayers (ML) deposited on Si(111)7 × 7 surfaces is investigated by in situ scanning tunneling microscopy and electrical resistance measurements for temperatures T = 2 − 300 K. With decreasing film thickness, i.e. decreasing sheet conductance Gs, a transition from a weakly conducting regime described by a logarithmic temperature dependence to an insulating regime occurs. In the insulating regime, the temperature dependence is described by Gs ∝ exp[−(T0/T)n] with an exponent n which gradually changes from 0.69 to 1 with decreasing film thickness. In contrast, for the Si(111)6 × 6-Au reconstruction obtained after annealing, an exponent n = 1/2 is found suggesting the formation of a soft Coulomb gap due to electron-electron interaction.

The electronic transport through nanostructured bismuth nanobridges has been investigated at low temperatures (T K ) and in magnetic fields B up to 8.5 T . The samples show reproducible resistance fluctuations as a function of B, superimposed on a large magnetoresistance of up to 50%. In addition, time-dependent resistance fluctuations in zero magnetic field demonstrate the presence of bistable scatterers in the constriction region of our samples, which are described by two-level systems. Their dynamics are shown to be sensitive to subtle modifications of the static scatterer configuration in their vicinity, which cannot be detected in the sample magnetofingerprint.

The electronic properties of single P- and B-dopants at the cleaved Si(1 1 1) surface of Czochralski-grown single crystals are investigated by scanning tunneling microscopy (STM) and spectroscopy at room temperature. Both types of dopants (donors or acceptors) can be identified by a specific voltage-dependent image contrast. The local variation of the electronic structure is confirmed by tunneling spectra taken at and away from the dopant site. Furthermore, Au-induced chainlike structures on vicinal Si(1 1 1) substrates are prepared by deposition of submonolayer coverages of gold. The tunneling spectra exhibit distinct features on the different types of protrusions which suggests that they arise from different types of atoms, i.e. Si or Au.

We report on an ultra-high vacuum (UHV) compatible method for fabricating devices of sub-micrometer size by virtue of a non-organic evaporation mask of high thermal and mechanical stability. As an application we describe the superconducting properties of mesoscopic superconductor=normal-metal and superconductor=ferromagnet=superconductor hybrid structures. In particular, we report on the observation of the DC-Josephson e9ect in Nb=Cu=Co=Cu=Nbstructures prepared in UHV. The Josephson coupling between the two superconductors through the very thin (5 nm) magnetic and metallic weak link is con;rmed by the magnetic ;eld dependence of the critical current Ic, which displays a Fraunhofer-like interference pattern.