We have combined a stand-alone Bi2Sr2CaCu2O8 intrinsic Josephson junction stack, emitting terahertz radiation, with a YBa2Cu3O7 grain boundary Josephson junction acting as detector. The detector is mounted on a lens, positioned 1.2 cm away from the emitter on a similar lens. With the emitter radiating at 0.5 THz, we observed up to 7 Shapiro steps on the current-voltage characteristic of the detector. The ac current induced in this junction was 0.9 mA, and the dissipated power was 1.8 μW. The setup, although far from being optimized, may be considered as a first step towards an integrated high-Tc receiver.

We report on Bi 2 Sr 2 CaCu 2 O 8 (BSCCO) intrinsic Josephson junction stacks with improved cooling, allowing for a remarkable increase in emission frequency compared to the previous designs. We started with a BSCCO stack embedded between two gold layers. When mounted in the standard way to a single substrate, the stack emits in the range of 0.43-0.82 THz. We then glued a second, thermally anchored substrate onto the sample surface. The maximum voltage of this better cooled and dimension-unchanged sample was increased and, accordingly, both the emission frequencies and the tunable frequency range were significantly increased up to 1.05 THz and to 0.71 THz, respectively. This double sided cooling may also be useful for other "hot" devices, e.g., quantum cascade lasers. V C 2014 AIP Publishing LLC. [http://dx.

We used one-dimensional coupled sine-Gordon equations combined with heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a 300 µm long intrinsic Josephson junction stack consisting of N = 700 junctions. The junctions in the stack are combined to M segments where we assume that inside a segment all junctions behave identically. Most simulations are for M = 20. For not too high bath temperatures there is the appearence of a hot spot at high bias currents. In terms of electromagnetic properties, robust standing wave patterns appear in the current density and electric field distributions. These patterns come together with vortex/antivortex lines across the stack that correspond to π kink states, discussed before in the literature for a homogeneous temperature distribution in the stack. We also discuss scaling of the thermal and electromagnetic properties with M , on the basis of simulations with M between 10 and 350.

Recently, it has been found that, when operated at large input power, the linewidth f of terahertz radiation emitted from intrinsic Josephson junction stacks can be as narrow as some megahertz. In this high-bias regime, a hot spot coexists with regions which are still superconducting. Surprisingly, f was found to decrease with increasing bath temperature. We present a simple model describing the dynamics of the stack in the presence of a hot spot by two parallel arrays of pointlike Josephson junctions and an additional shunt resistor in parallel. Heat diffusion is taken into account by thermally coupling all elements to a bath at temperature T b . We present current-voltage characteristics of the coupled system and calculations of the linewidth of the radiation as a function of T b . In the presence of a spatial gradient of the junction parameters' critical current and resistance, f deceases with increasing T b , similar to the experimental observation.

The internal friction of partially Sr-substituted Y(Ba 1−x Sr x ) 2 Cu 3 O 7−δ (Y123) ceramics was measured by the vibrating-reed method from liquid nitrogen temperature to room temperature at kilohertz frequencies. The intensity of the internal friction peak, which appears around 220 K, decreases upon Sr doping while the peak position shows no systematic change. Our results do not support the previous oxygen order-disorder explanation; we present another approach relating this peak to the crossover in charge-carrier dynamics, and its evolution with Sr doping is discussed in terms of release of internal strain and electron-phonon coupling.

We used 2D coupled sine-Gordon equations combined with 3D heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a 250 × 70 µm 2 intrinsic Josephson junction stack. The 700 junctions are grouped to 20 segments; we assume that in a segment all junctions behave identically. At large input power a hot spot forms in the stack. Resonant electromagnetic modes, oscillating either along the length ((0, n) modes) or the width ((m, 0) modes) of the stack or having a more complex structure, can be excited both with and without a hot spot. At fixed bath temperature and bias current several cavity modes can coexist in the absence of a magnetic field. The (1, 0) mode, considered to be the most favorable mode for THz emission, can be stabilized by applying a small magnetic field along the length of the stack. A strong field-induced enhancement of the emission power is also found in experiment, for an applied field around 5.9 mT.

We report on a liquid-nitrogen-cooled compact source for continuous terahertz (THz) emission. The emitter is a Bi 2 Sr 2 CaCu 2 O 8þδ intrinsic Josephson-junction stack embedded between two gold layers and sandwiched between two MgO substrates. The radiation is emitted to free space through a hollow metallic tube acting as a waveguide. The maximum emission power is 1.17 μW. The tunable emission frequency bandwidth is up to 100 GHz with a maximum emission power at 0.311 THz. Since the operation voltage is about 1 V and the current is less than 30 mA, we are able to drive this terahertz source at 77 K with only one commercial 1.5-V battery, just like a torch. This convenient and economical setup may find applications in fields like tracer-gas detection or nondestructive evaluation.

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