We studied the $c$-axis transport of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ (Bi2212) cross-whisker junctions formed by annealing “naturally” formed whisker crosses. These frequently appear during growth when the $ab$ faces of neighboring whiskers come in contact. We obtained Fraunhofer patterns of the cross-junction critical currents in a parallel magnetic field, and found a sharp increase in the quasiparticle tunneling conductance at $V_g=50–60\mathrm{mV}$, indicating high junction quality. For our weak junctions, the interface critical current density is about 3% of the critical current density across the stack of bulk intrinsic junctions, as is the room-temperature conductivity, and both are independent of the twist angle, in contrast to most of the data reported on “artificial” cross-whisker junctions [Y. Takano et al., Phys. Rev. B 65, 140513(R) (2002)]. As a minimum, our results provide strong evidence for incoherent tunneling at least at the interface, and for at least a small $s$-wave order-parameter component in the bulk of Bi2212 for $T⩽T_c$. They are also consistent with the bicrystal twist experiments of Li et al. [Phys. Rev. Lett. 83, 4160 (1999)].

We report on direct observation of microscopic solitons in single electronic processes of the coherent interlayer tunneling in charge density waves. Special nanoscale devices were fabricated from the chain compound ${\mathrm{NbSe}}_3$ using focused ion beams. The spectra were drastically refined by working at high (up to 27 T) magnetic fields. Internal quantum tunneling of electrons can go through solitons that are energetically more favorable quantum particles than electrons. In addition to the interband tunneling across the gap $2\Delta$, we observe a clear peak at the intermediate voltage $\approx 2\Delta /3$, which we associate with the creation of microscopic solitons, the energy of which must be $2\Delta /\pi$. These solitons might correspond to the long sought special quasiparticle—the spinon.

We present the generation and detection of spin currents by using magnetoelastic resonance excitation in a magnetoelectric composite high overtone bulk acoustic wave (BAW) resonator (HBAR) formed by a Al-ZnO-Al-GGG-YIG-Pt structure. Transversal BAW drives magnetization oscillations in YIG film at a given resonant magnetic field, and the resonant magneto-elastic coupling establishes the spin-current generation at the Pt/YIG interface. Due to the inverse spin Hall effect (ISHE) this BAW-driven spin current is converted to a dc voltage in the Pt layer. The dependence of the measured voltage both on magnetic field and frequency has a resonant character. The voltage is determined by the acoustic power in HBAR and changes its sign upon magnetic field reversal. We compare the experimentally observed amplitudes of the ISHE electrical field achieved by our method and other approaches to spin current generation that use surface acoustic waves and microwave resonators for ferromagnetic resonance excitation, with the theoretically expected values.

Tunneling spectra of chain materials ${\mathrm{NbSe}}_3$ and ${\mathrm{TaS}}_3$ were studied in nanoscale mesa devices. Current-voltage $I\mathrm{\text{−}}V$ characteristics related to all charge density waves (CDWs) reveal universal spectra within the normally forbidden region of low $V$, below the electronic CDW gap $2\Delta$. The tunneling always demonstrates a threshold $V_t\approx 0.2\Delta$, followed, for both CDWs in ${\mathrm{NbSe}}_3$, by a staircase fine structure. $T$ dependencies of $V_t(T)$ and $\Delta (T)$ scale together for each CDW, while the low $T$ values $V_t(0)$ correlate with the CDWs’ transition temperatures $T_p$. Fine structures of CDWs perfectly coincide when scaled along $V/\Delta$. The results evidence the sequential entering of CDW vortices (dislocations) in the junction area with the tunneling current concentrated in their cores. The subgap tunneling proceeds via the phase channel: coherent phase slips at neighboring chains.

We report on the experimental observation of excitation and detection of parametric spin waves and spin currents in the bulk acoustic wave resonator. The hybrid resonator consists of a ZnO piezoelectric film, yttrium iron garnet (YIG) films on a gallium gadolinium garnet substrate, and a heavy metal Pt layer. Shear bulk acoustic waves are electrically excited in the ZnO layer due to piezoeffect at the resonant frequencies of the resonator. The magnetoelastic interaction in the YIG film emerges magnons (spin waves) excitation by acoustic waves either on resonator's eigenfrequencies or the half-value frequencies at supercritical power. We investigate the acoustic pumping of magnons at the half-value frequencies and acoustic spin pumping from parametric magnons, using the inverse spin Hall effect in the Pt layer. The constant electric voltage in the Pt layer, depending on the frequency, the magnetic field, and the pump power, was systematically studied. We explain the low threshold obtained ($\sim 0.4$ mW) by the high efficiency of electric power transmission into the acoustic wave in the resonator.