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

/pdf/the-current-phase-relation-in-josephson-junctions-40zrgv4v2s.pdf

The current-phase relation in Josephson junctions

This review presents an overview of the thermal properties of mesoscopic structures. The discussion is based on the concept of electron energy distribution, and, in particular, on controlling and probing it. The temperature of an electron gas is determined by this distribution: refrigeration is equivalent to narrowing it, and thermometry is probing its convolution with a function characterizing the measuring device. Temperature exists, strictly speaking, only in quasiequilibrium in which the distribution follows the Fermi-Dirac form. Interesting nonequilibrium deviations can occur due to slow relaxation rates of the electrons, e.g., among themselves or with lattice phonons. Observation and applications of nonequilibrium phenomena are also discussed. The focus in this paper is at low temperatures, primarily below $4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, where physical phenomena on mesoscopic scales and hybrid combinations of various types of materials, e.g., superconductors, normal metals, insulators, and doped semiconductors, open up a rich variety of device concepts. This review starts with an introduction to theoretical concepts and experimental results on thermal properties of mesoscopic structures. Then thermometry and refrigeration are examined with an emphasis on experiments. An immediate application of solid-state refrigeration and thermometry is in ultrasensitive radiation detection, which is discussed in depth. This review concludes with a summary of pertinent fabrication methods of presented devices.

/pdf/opportunities-for-mesoscopics-in-thermometry-and-10z63yzsh2.pdf

Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications

Spin photocurrents generated by homogeneous optical excitation with circularly polarized radiation in quantum wells (QWs) are reviewed. The absorption of circularly polarized light results in optical spin orientation due to the transfer of the angular momentum of photons to electrons of a two-dimensional electron gas. It is shown that in QWs belonging to one of the gyrotropic crystal classes a non-equilibrium spin polarization of uniformly distributed electrons causes a directed motion of electrons in the plane of the QW. A characteristic feature of this electric current, which occurs in unbiased samples, is that it reverses its direction upon changing the radiation helicity from left-handed to right-handed and vice versa. Two microscopic mechanisms are responsible for the occurrence of an electric current linked to a uniform spin polarization in a QW: the spin polarization-induced circular photogalvanic effect and the spin-galvanic effect. In both effects the current flow is driven by an asymmetric distribution of spin-polarized carriers in k-space of systems with lifted spin degeneracy due to k-linear terms in the Hamiltonian. Spin photocurrents provide methods to investigate spin relaxation and to reach a conclusion as regards the in-plane symmetry of QWs. The effect can also be utilized to develop fast detectors for determining the degree of circular polarization of a radiation beam. Furthermore, spin photocurrents under infrared excitation were used to demonstrate and investigate monopolar spin orientation of free carriers.

/pdf/spin-photocurrents-in-quantum-wells-5eyotdi33h.pdf

Spin photocurrents in quantum wells

Several research groups have been actively pursuing antimonide-based electronic devices in recent years. The advantage of narrow-bandgap Sb-based devices over conventional GaAs- or InP-based devices is the attainment of high-frequency operation with much lower power consumption. This paper will review the progress on three antimonide-based electronic devices: high electron mobility transistors (HEMTs), resonant tunneling diodes (RTDs), and heterojunction bipolar transistors (HBTs). Progress on the HEMT includes the demonstration of Ka- and W-band low-noise amplifier circuits that operate at less than one-third the power of similar InP-based circuits. The RTDs exhibit excellent figures of merit but, like their InP- and GaAs-based counterparts, are waiting for a viable commercial application. Several approaches are being investigated for HBTs, with circuits reported using InAs and InGaAs bases.

Antimonide-based compound semiconductors for electronic devices: A review

In this review paper, we summarize the performance (in particular the magnetic field resolution), micro-fabrication technologies and applications of micrometer sized Hall effect devices. Additionally, our activities in this domain are briefly described.

Micro-Hall devices: performance, technologies and applications

Modulation-doped In0.5Ga0.5As/In0.5Al0.5As quantum well structures grown by molecular beam epitaxy on GaAs substrates using a relaxed AlGaAsSb buffer showed carrier mobilities of 8500 cm2/V s for a sheet concentration of 3.5×1012 cm−2 at room temperature. The crystallinity of the quaternary buffer layer was verified by x-ray diffractometry. Transistors with 0.25×100 μm2 gates demonstrated transconductance values as high as 800 mS/mm. S-parameter measurements revealed a cutoff frequency fT of 87 GHz and a maximum oscillation frequency fMAX of 140 GHz (both extrinsic values).

Metamorphic InGaAs/InAlAs quantum well structures grown on GaAs substrates for high electron mobility transistor applications

Hall sensors with high sensitivity and excellent temperature stability were fabricated from quantum wells based on an InAs/Al 0.2 Ga 0.8 Sb heterostructure. The layers were grown on semi-insulating GaAs substrates by molecular beam epitaxy (MBE). Maximum Hall mobilities of 29.500 cm 2 V -1 s -1 with sheet electron concentrations of 2 × 10 12 cm -2 were measured at room temperature for an undoped quantum well structure. For a cross-shaped sensor, these excellent transport properties resulted in sensitivities of 0.9 T -1 (for voltage drive) and 300 V A -1 T -1 (for current drive). Additional doping of the InAs quantum well leads to an improvement of the temperature stability of the input resistance and sensitivity in the temperature range of - 100°C to + 150°C.

InAs/Al0.2Ga0.8Sb quantum well Hall effect sensors

This paper reports on the fabrication and characterization of Hall and magnetoresistive sensors with high sensitivity and good temperature stability, InAs/AlGaSb quantum well structures grown by molecular beam epitaxy (MBE) on semiinsulating GaAs substrates were used as active layers for magnetic field sensing. The excellent transport properties (electron mobilities up to 30,000 cm/sup 2/Ns at room temperature) resulted in high sensitivity for room temperature operation of magnetoresistors (relative sensitivity of 0.46%/mT) and Hall elements (magnetic sensitivity of 5.5 V/T),.

InAs/(Al,Ga)Sb quantum well structures for magnetic sensors

We investigated the magnetotransport properties of high-mobility InAs/GaSb antidot lattices. For samples with large antidot diameter, we found a broad maximum of classical origin around 2.5 T in addition to the usual commensurability features at low magnetic fields. The broad maximum can be ascribed to a class of orbits involving multiple reflections on a single antidot. This is shown by both a simple transport calculation based on a classical Kubo formula and an analysis of the Poincare sections at different magnetic-field values. At low temperatures we observe weak 1/B- periodic oscillations superimposed on the classical maximum.

/pdf/skipping-orbits-and-enhanced-resistivity-in-large-diameter-11ftanmtkr.pdf

Skipping orbits and enhanced resistivity in large-diameter InAs/GaSb antidot lattices

High quality InAs/Al/sub 0.2/Ga/sub 0.8/Sb quantum well structures were grown on Germanium substrates by molecular beam epitaxy. The excellent transport properties resulted in sensitivities of 0.85 T/sup -1/ (voltage drive) and 370 V/A/T (current drive) for a cross-shaped sensor at room temperature. The results show that the performance of Hall sensors on germanium and on GaAs substrates is comparable in terms of sensitivity and temperature stability.

High-performance InAs quantum well Hall sensors on germanium substrates

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