We present intrinsic tunneling spectroscopy measurements on small ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+x}$ mesas. The tunnel conductance curves show both sharp peaks at the superconducting gap voltage and broad humps representing the $c$-axis pseudogap. The superconducting gap vanishes at $T_c$, while the pseudogap exists both above and below $T_c$. Our observation implies that the superconducting and pseudogaps represent different coexisting phenomena.

Diode is one of the basic electronic components. It has a nonreciprocal current response, associated with a broken space/time reversal symmetry. Here we demonstrate prototypes of superconducting diodes operational at zero magnetic field. They are based on conventional niobium planar Josephson junctions, in which space/time symmetry is broken by a combination of self-field effect from nonuniform bias and stray fields from a trapped Abrikosov vortex. We demonstrate that nonreciprocity of critical current in such diodes can reach an order of magnitude and rectification efficiency can exceed 70%. Furthermore, we can easily change the diode polarity and switch nonreciprocity on/off by changing the bias configuration and by trapping/removing of a vortex. This facilitates a memory functionality. We argue that such a diode-with-memory can be used for a future generation of in-memory superconducting computers.

A microscopic model of the proximity effect in superconductor-insulator-superconductor (SS’IS’ ’S) Josephson tunnel junctions has been developed for the general case of the finite critical temperature of the S’ (S’ ’) metal, arbitrary SS’ (SS’ ’) boundary transparency and the strength of the proximity effect between S and S’ (respectively S and S’ ’). The metals are assumed to be in the dirty limit and the thickness of the proximity layer is assumed to be small compared to its coherence length. The electrical properties of the SS’IS’ ’S junction are calculated as a function of the strength of the proximity effect, boundary transparency, critical temperature ratio, and temperature. The experimentally determined electrical characteristics of a series of Nb/${\mathrm{Al}}_1$, Al oxide, ${\mathrm{Al}}_2$/Nb junctions with varying thickness ${\mathit{d}}_1$ of the ${\mathrm{Al}}_1$ layer were interpreted with this model. The current-voltage characteristics and the temperature dependence of the critical current and sum-gap voltage could be described quantitatively well without any other correction than the non-BCS ratio ${\mathrm{\Delta }}_0$/${\mathit{k}}_{\mathit{B}}$ ${\mathit{T}}_{\mathit{c}}$≊1.93 of Nb. Deviations from the model for the junctions with the largest ${\mathit{d}}_1$ are attributed to the fact that the Nb and Al are not fully in the dirty limit and ${\mathit{d}}_1$ is not small compared to the coherence length.

Superconducting digital devices can be advantageously used in future supercomputers because they can greatly reduce the dissipation power and increase the speed of operation. Non-volatile quantized states are ideal for the realization of classical Boolean logics. A quantized Abrikosov vortex represents the most compact magnetic object in superconductors, which can be utilized for creation of high-density digital cryoelectronics. In this work we provide a proof of concept for Abrikosov-vortex-based random access memory cell, in which a single vortex is used as an information bit. We demonstrate high-endurance write operation and two different ways of read-out using a spin valve or a Josephson junction. These memory cells are characterized by an infinite magnetoresistance between 0 and 1 states, a short access time, a scalability to nm sizes and an extremely low write energy. Non-volatility and perfect reproducibility are inherent for such a device due to the quantized nature of the vortex.

Intrinsic tunneling spectroscopy in high magnetic field ( $H$) is used for a direct test of superconducting features in the quasiparticle density of states of pure Bi2212 and intercalated ${\mathrm{HgBr}}_2$-Bi2212 high- $T_c$ superconductors. We were able to distinguish with great clarity two coexisting gaps: (i) the superconducting gap, which closes as $H\to H_{c2\mathrm{}}\left(T\right)$, and (ii) the $c$-axis pseudogap, which does not change either with $H$ or with $T$. Strikingly different $H$ dependencies, together with previously observed different temperature dependencies of the two gaps, speak against a superconducting origin of the pseudogap.

Mesa structures made of Bi₂Sr₂CaCu₂O_8+δ high-temperature superconductor represent stacks of atomic scale intrinsic Josephson junctions. They can be used for generation of high-frequency electromagnetic waves. Here we analyze Josephson emission from small-but-high mesas (with a small area, but containing many stacked junctions). We have found strong evidence for tunable terahertz emission with a good efficacy in a record high-frequency span 1–11 THz, approaching the theoretical upper limit for this superconductor. Emission maxima correspond to in-phase cavity modes in the mesas, indicating coherent superradiant nature of the emission. We conclude that terahertz emission requires a threshold number of junctions N ~ 100. The threshold behavior is not present in the classical description of stacked Josephson junctions and suggests importance of laser-like cascade amplification of the photon number in the cavity.