SiGeSn ternaries are grown on Ge‐buffered Si wafers incorporating Si or Sn contents of up to 15 at%. The ternaries exhibit layer thicknesses up to 600 nm, while maintaining a high crystalline quality. Tuning of stoichiometry and strain, as shown by means of absorption measurements, allows bandgap engineering in the short‐wave infrared range of up to about 2.6 µm. Temperature‐dependent photoluminescence experiments indicate ternaries near the indirect‐to‐direct bandgap transition, proving their potential for ternary‐based light emitters in the aforementioned optical range. The ternaries' layer relaxation is also monitored to explore their use as strain‐relaxed buffers, since they are of interest not only for light emitting diodes investigated in this paper but also for many other optoelectronic and electronic applications. In particular, the authors have epitaxially grown a GeSn/SiGeSn multiquantum well heterostructure, which employs SiGeSn as barrier material to efficiently confine carriers in GeSn wells. Strong room temperature light emission from fabricated light emitting diodes proves the high potential of this heterostructure approach.

We introduce a highly compact fiber-optic Fabry-Pérot refractive index sensor integrated with a fluid channel that is fabricated directly near the tip of a 32 μm in diameter single-mode fiber taper. The focused ion beam technique is used to efficiently mill the microcavity from the fiber side and finely polish the end facets of the cavity with a high spatial resolution. It is found that a fringe visibility of over 15 dB can be achieved and that the sensor has a sensitivity of ∼1731 nm/RIU (refractive index units) and a detection limit of ∼5.78 × 10−6 RIU. This miniature integrated all-in-fiber optofludic sensor may find use in minimal-invasive biomedical applications.

The temperature and field dependence of harmonics in voltage V n = V n − iV n using the screening technique have been measured for YBa 2 Cu 3 O 7−δ superconducting thin films. Using the Sun model we obtained the curves for the temperature-dependent critical current density J c (T). In addition, we applied the criterion proposed by Acosta et al. to compute J c (T). Also, we made used of the empirical law J c ∝ (1 − T /T c) n as an input in our calculations to reproduce experimental harmonic generation up to the fifth harmonic. We found that most models fit well the fundamental voltage but higher harmonics are poorly reproduced. Such behavior suggests the idea that higher harmonics contain information concerning complex processes like flux creep or thermally assisted flux flow.

We have fabricated ultra-thin YBa2Cu3O7-x nanowires with a high critical current density and studied their voltage switching behavior in the 4.2 -90 K temperature range. A comparison of our experimental data with theoretical models indicates that, depending on the temperature and nanowire cross section, voltage switching originates from two different mechanisms: hotspot-assisted suppression of the edge barrier by the transport current and the appearance of phase-slip lines in the nanowire. Our observation of hotspot-assisted voltage switching is in good quantitative agreement with predictions based on the Aslamazov-Larkin model for an edge barrier in a wide superconducting bridge. I. INTRODUCTIONOver the last decade, superconducting nanowires have attracted attention because of their promising applications in quantum sensing and computing [1][2][3]. Abrupt voltage switching is a characteristic feature of superconducting nanowires and is used to investigate superconductivity in low-dimensional structures, as well as for practical applications. Voltage switching is observed in both low-temperature (low-Tc) and high-temperature (high-Tc) current-biased superconducting bridges [4][5][6][7][8][9][10][11][12][13][14][15][16]. Voltage switching in conventional low-Tc superconducting bridges is well understood [4][5][6][7][16][17][18]. However, there is no consensus for explaining the origin of voltage switching in high-Tc cuprate superconductors. Several mechanisms have been considered to explain discontinuities in the current-voltage (IV) characteristics of high-Tc superconducting bridges, including flux-flow instabilities [8,[13][14][15], a phase-slip process [11], hotspot effects [8,12], and fluctuating charge stripe domains [10]. In wide and thick bridges, all of these mechanisms can coexist within the same current range, which complicates the analysis of experimental data. However, the identification of voltage switching mechanisms is possible in superconducting wires whose dimensions approach the characteristic length scales of the superconducting state. As a result of the *

A novel device that can be used as a tunable support-free phase plate for transmission electron microscopy of weakly scattering specimens is described. The device relies on the generation of a controlled phase shift by the magnetic field of a segment of current-carrying wire that is oriented parallel or antiparallel to the electron beam. The validity of the concept is established using both experimental electron holographic measurements and a theoretical model based on Ampere’s law. Computer simulations are used to illustrate the resulting contrast enhancement for studies of biological cells and macromolecules.