There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

This book presents the conceptual framework underlying the atomistic theory of matter, emphasizing those aspects that relate to current flow. This includes some of the most advanced concepts of non-equilibrium quantum statistical mechanics. No prior acquaintance with quantum mechanics is assumed. Chapter 1 provides a description of quantum transport in elementary terms accessible to a beginner. The book then works its way from hydrogen to nanostructures, with extensive coverage of current flow. The final chapter summarizes the equations for quantum transport with illustrative examples showing how conductors evolve from the atomic to the ohmic regime as they get larger. Many numerical examples are used to provide concrete illustrations and the corresponding Matlab codes can be downloaded from the web. Videostreamed lectures, keyed to specific sections of the book, are also available through the web. This book is primarily aimed at senior and graduate students.

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Quantum Transport: Atom to Transistor

Advanced gravitational wave interferometers, currently under realization, will soon permit the detection of gravitational waves from astronomical sources. To open the era of precision gravitational wave astronomy, a further substantial improvement in sensitivity is required. The future space-based Laser Interferometer Space Antenna and the third-generation ground-based observatory Einstein Telescope (ET) promise to achieve the required sensitivity improvements in frequency ranges. The vastly improved sensitivity of the third generation of gravitational wave observatories could permit detailed measurements of the sources' physical parameters and could complement, in a multi-messenger approach, the observation of signals emitted by cosmological sources obtained through other kinds of telescopes. This paper describes the progress of the ET project which is currently in its design study phase.

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The Einstein Telescope: a third-generation gravitational wave observatory

The Advanced LIGO gravitational wave detectors are next generation instruments which will replace the existing initial LIGO detectors. They are currently being constructed and installed. Advanced LIGO strain sensitivity is designed to be about a factor 10 better than initial LIGO over a broad band and usable to 10 Hz, in contrast to 40 Hz for initial LIGO. This is expected to allow for detections and significant astrophysics in most categories of gravitational waves. To achieve this sensitivity, all hardware subsystems are being replaced with improvements. Designs and expected performance are presented for the seismic isolation, suspensions, optics and laser subsystems. Possible enhancements to Advanced LIGO, either to resolve problems that may arise and/or to allow for improved performance, are now being researched. Some of these enhancements are discussed along with some potential technology being considered for detectors beyond Advanced LIGO.

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Advanced LIGO: the next generation of gravitational wave detectors

This review provides a theoretical basis for understanding the current-phase relation (CPhiR) for the stationary (dc) Josephson effect in various types of superconducting junctions The authors summarize recent theoretical developments with an emphasis on the fundamental physical mechanisms of the deviations of the CPhiR from the standard sinusoidal form A new experimental tool for measuring the CPhiR is described and its practical applications are discussed The method allows one to measure the electrical currents in Josephson junctions with a small coupling energy as compared to the thermal energy A number of examples illustrate the importance of the CPhiR measurements for both fundamental physics and applications

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The current-phase relation in Josephson junctions

Texture and electrical dynamics of micrometer and submicrometer bridges in misalignedTl2Ba2CaCu2O8films

Step edge Josephson junctions and DC superconducting quantum interference devices (SQUIDs) made of laser ablated and sputtered YBaCuO (YBCO) films and grain boundary junctions in polycrystalline TlBaCaCuO (TBCCO) films have been investigated Bridges on the micrometer scale have been structured by laser or ion beam etching as well as by the inhibit-layer technique The Josephson junctions are characterized comparing I-V measurements under microwave irradiation to calculations within the resistively shunted junction (RSJ) model with finite capacitance and white noise The dependence of the I/sub C/R/sub N/ product on temperature can be fitted to the microscopic theory of superconductor-normal insulator-normal superconductor (SNINS) or superconductor-normal conductor-superconductor (SNS) junctions with additional temperature-independent pair breaking Flux modulation and noise properties of the DC SQUIDs at 77 K are shown >

High-T/sub c/ Josephson junctions and DC SQUIDs

Mesa structures were produced from different highly anisotropic HTS thin films showing the intrinsic Josephson effect in c -direction. We observed clear dependencies of the critical current on both external magnetic field and microwave field. For the first time we were able to detect the modulation of the critical current of BSCCO thin film mesas in external magnetic field. For BSCCO as well as for TBCCO we found modulation periods in the Tesla range which is in good agreement with the lateral dimensions of the junctions. In the current-voltage characteristics of TBCCO mesas we found subgap structures and measured their dependence on temperature, external magnetic field and microwave irradiation.

One-dimensional intrinsic Josephson arrays based on HTS thin films

We tested oxidized titanium layers as barriers for hybrid Josephson junctions with high IcRn-products and for the preparation of junctions for tunneling spectroscopy. For that we firstly prepared junctions with conventional superconductor electrodes, such as lead and niobium, respectively. By tuning the barrier thickness, we were able to change the junction's behavior from a Josephson junction to tunnel-like behavior applicable for quasi-particle spectroscopy. Subsequently, we transferred the technology to junctions using Co-doped BaFe2As2 thin films prepared by pulsed laser deposition as base electrode and evaporated Pb as counter electrode. For barriers with a thickness of 1.5 nm, we observe clear Josephson effects with IcRn≈90 μV at 4.2 K. These junctions behave SNS'-like (SNS: superconductor-normal conductor-superconductor) and are dominated by Andreev reflection transport mechanism. For junctions with barrier thickness of 2.0 nm and higher, no Josephson but SIS'- (SIS: superconductor-insulator-superc...

Investigation of TiO x barriers for their use in hybrid Josephson and tunneling junctions based on pnictide thin films

We have designed and constructed a split type of a four-valve pulse tube refrigerator (FVPTR) in order to cool high-Tc Superconducting Quantum Interference Devices1 (SQUIDs). A SQUID, in particular, places rigorous upper limits on the tolerable levels of magnetic interference, vibrations and temperature fluctuations. The pressure wave in the system is generated by means of a commercial He-compressor in combination with a rotary valve. In order to protect the cold head from disturbances generated by the valve gear and the compressor, it is useful to separate those parts spatially. Reduction of interference signals from the compressor and the rotary valve is accomplished using flexible tubes between the rotary valve and the cold head. Most parts of the cold head, including the regenerator, were made of non-metallic, electrically insulating, and non-magnetic materials to minimize eddy currents and local magnetic fields, which interfere the sensor directly.

Paul Seidel

Papers

Texture and electrical dynamics of micrometer and submicrometer bridges in misalignedTl2Ba2CaCu2O8films

High-T/sub c/ Josephson junctions and DC SQUIDs

One-dimensional intrinsic Josephson arrays based on HTS thin films

Investigation of TiO x barriers for their use in hybrid Josephson and tunneling junctions based on pnictide thin films

Low Noise Cold Head of a Four-Valve Pulse Tube Refrigerator