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Non-reciprocal devices are key components in modern electronics covering broad applications ranging from transistors to logic circuits thanks to the output rectified signal in the direction parallel to the input. In this work, we propose a transverse Cooper-pair rectifier in which a non-reciprocal current is perpendicular to the driving field, when inversion, time reversal, and mirror symmetries are broken simultaneously. The Blonder-Tinkham-Klapwijk formalism is developed to describe the transverse current-voltage relation in a normal-metal/superconductor tunneling junction, where symmetry constraints are achieved by an effective built-in supercurrent manifesting in an asymmetric and anisotropic Andreev reflection. The asymmetry in the Andreev reflection is induced when inversion and time reversal symmetry are broken by the supercurrent component parallel to the junction while the anisotropy occurs when the mirror symmetry with respect to the normal of the junction interface is broken by the perpendicular supercurrent component to the junction. Compared to the conventional longitudinal one, the transverse rectifier supports fully polarized diode efficiency and colossal nonreciprocal conductance rectification, completely decoupling the path of the input excitation from the output rectified signal. This work provides a formalism for realizing transverse non-reciprocity in superconducting junctions, which is expected to be achieved by modifying current experimental setups and may pave the way for future low-dissipation superconducting electronics., Comment: 8 + 10 pages, 3 + 4 figures

Recent breakthroughs in Josephson diodes dangle the possibility of extending conventional non-reciprocal electronics into the realm of superconductivity. While a strong magnetic field is recognized for enhancing diode efficiency, it concurrently poses a risk of undermining the essential superconductivity required for non-dissipative devices. To circumvent the need for magnetic-based tuning, we propose a field-effect Josephson diode based on the electrostatic gate control of finite momentum Cooper pairs in asymmetric spin-momentum-locking states. We propose two possible implementations of our gate-controlled mechanism: (i) a topological field-effect Josephson diode in time-reversal-broken quantum spin Hall insulators; and (ii) semiconductor-based field-effect Josephson diodes attainable in current experimental setups involving a Zeeman field and spin-orbit coupling. Notably, the diode efficiency is highly enhanced in the topological field-effect Josephson diode because the current carried by the asymmetric helical edge states is topologically protected and can be tuned by local gates. In the proposed Josephson diode, the combination of gates and asymmetric spin-momentum-locking nature is equivalent to that of a magnetic field, thus providing an alternative electrical operation in designing nonreciprocal superconducting devices., Comment: 24 pages, 14 figures

We study the optical response of nanoribbons made from the $\alpha-T_3$ lattice under a weak magnetic field in the terahertz to far-infrared regime. It is found that the magnetic field can open a gap in the band structure and induce a new absorption peak with much reduced frequency in metallic armchair ribbons and a class of zigzag ribbons with particular boundaries. This tunable magneto-optical modulation effect is attributed to the interband transitions between the flat band and the propagating bands. By contrast, this magnetic modulation of gap opening and optical conductance is much weaker in metallic armchair graphene ribbons (the case of $\alpha=0$) in which the flat band is absent. The enhancement in the $\alpha-T_3$ model is analytically investigated and explained within the perturbation theory for metallic armchair ribbons. The magnetic field induced valley degeneracy lifting and valley splitting of the absorption peak are also discussed in the case of zigzag ribbons. These findings pave the way for magneto-optics devices based on the $\alpha-T_3$ model materials., Comment: 7 pages, 7 figures; accepted by Physical Review B

Weyl semimetals are a three dimensional topological phase of matter with linearly dispersed Weyl points which appear in pairs and carry opposite chirality. The separation of paired Weyl points allows charge transfer between them in the presence of parallel electric and magnetic fields, which is known as the chiral anomaly. In this paper, we theoretically study the influence of the chiral anomaly induced chiral charge imbalance on the Josephson current in a Weyl superconductor-Weyl semimetal-Weyl superconductor junction. In Weyl superconductors, two types of pairings are considered, namely, zero momentum BCS-like pairing and finite momentum FFLO-like pairing. For BCS-like pairing, we find that the Josephson current exhibits $0$-$\pi$ transitions and oscillates as a function of $\lambda_{0} L $, where $\lambda_{0}$ is the chirality imbalance induced by the parallel electric and magnetic fields and $L$ is the length of the Weyl semimetal. The amplitude of the Josephson current also depends on the angle $\beta$ between the line connecting two paired Weyl points and the transport direction along the junction. For FFLO-like pairing, the chirality imbalance induced periodic oscillations are absent and the Josephson current is also independent of the angle $\beta$. These findings are useful in detecting the chiral anomaly and distinguishing the superconducting pairing mechanism of Weyl semimetals., Comment: 7 pages, 6 figures; accepted by PRB

We propose wideband bandpass filters based on multipole resonances of spoof localized surface plasmons (SLSPs). The resonance characteristics and geometric tunability of SLSPs are investigated under microstrip excitations. Strong coupling with interlayer microstrip lines is proposed to join discrete multipole resonances into a continuous and flat passband. The SLSP filters exhibit wide passbands in compact sizes and well-balanced shapes, while holding satisfactory spurious rejection bands, group delays, and geometric tunability. This work exposes the SLSPs' application potential in filters as novel resonators.

We report a theoretical study of the quantized spin pump in a traditional two-parameter quantum pump device that is based on the helical edge states of a quantum spin Hall insulator. By introducing two time-dependent magnetizations out of phase as the pumping parameters, we found that when the Fermi energy resides in the energy gap opened by magnetization, an integer number of charges or spins can be pumped out in a pumping cycle and ascribed to the possible topological interface state born in between the two pumping potentials. The quantized pump current can be fully spin-polarized, spin-unpolarized, or pure spin current while its direction can be abruptly reversed by some system parameters such as the pumping phase and local gate voltage. Our findings may shed light on generation of a quantized spin pump., Comment: 7pages, 5 figures

Usually, the superconducting quantum interference device (SQUID) consists of two Josephson junctions and the interference therein is modulated by a magnetic flux. In this work, we propose an electrically modulated SQUID consisting of single Josephson junction coupled by a time-reversal breaking Weyl semimetal thin film. For a low Fermi energy, the Josephson current is only mediated by Fermi arc surface states, and has an arbitrary ground-state phase difference \phi0 which is directly proportional to the product of the transverse electric field and the cross section area of the junction.For a suitable Fermi energy, the bulk states make comparable contributions to the Josephson current with the current-phase relation of a 0-junction. The interference between the surface channel and the bulk channel results in an electrically modulated SQUID with single Josephson junction, which provides an experimental proposal to identify magnetic Weyl semimetals and may have potential applications in superconducting quantum computation., Comment: 5 figures

Under more consideration, it seems that bulk valley current mediated nonlocal resistance is inconsistent with Landau-Buttiker formalism. We believe Landau-Buttiker formalism is right and the declared bulk valley current mediated nonlocal resistance is questionable and the experimental signal should be attributed to other origins., Comment: It seems that bulk valley current mediated nonlocal resistance is nconsistent with Landau-Buttiker formalism

We show that the two-band nature of noncentrosymmetric superconductors leads naturally to an anomalous Josephson current appearing at zero phase difference in a clean noncentrosymmetric superconductor/ferromagnet/noncentrosymmetric superconductor junction. The two-band nature provides two sets of Andreev bound states which carry two supercurrents with different amplitudes. When the magnetization direction of the ferromagnet is suitably chosen, two supercurrents experience opposite phase shifts from the conventional sinusoidal current-phase relation. Then the total Josephson current results in a continuously tunable ground-state phase difference by adjusting the ferromagnet parameters and the triplet-singlet ratio of noncentrosymmetric superconductors. The physics picture and analytical results are given on the basis of the $s$+$p$ wave, while the numerical results are reported on both $s$+$p$ and $d$+$p$ waves. For the $d$+$p$ wave, we find novel states in which the supercurrents are totally carried by continuous propagating states instead of discrete Andreev bound states. Instead of carrying supercurrent, the Andreev bound states which here only appear above the Fermi energy block the supercurrent flowing along the opposite direction. These novel states advance the understaning of the relation between Andreev bound states and the Josephson current. And the ground-state phase difference serves as a tool to determine the triplet-singlet ratio of noncentrosymmetric superconductors., Comment: 10pages, 6figures

We studied the anomalous Josephson current appearing at zero phase difference in junctions coupled with a ferromagnetic trilayer which has noncoplanar magnetizations. A $\pi/2$ junction with an equilibrium phase difference $\pi/2$ is obtained under suitable conditions. The equilibrium phase difference and the amplitude of the supercurrent are all tunable by the structure parameters. In addition to calculating the anomalous current using the Bogoliubov-de Gennes equation, we also developed a clear physical picture explaining the anomalous Josephson effect in the structure. We show that the triplet proximity correlation and the phase shift in the anomalous current-phase relation all stem from the spin precession in the first and third ferromagnet layers., Comment: 7 pages, 8 figures, accepted to PRB

We investigate the enhancement of spin polarization in a quantum wire in the presence of a constriction and a spin-orbit coupling segment. It is shown that the spin-filtering effect is significantly heightened in comparison with the configuration without the constriction. It is understood in the studies that the constriction structure plays a critical role in enhancing the spin filtering by means of confining the incident electrons to occupy one channel only while the outgoing electrons occupy two channels. The enhancement of spin-filtering has also been analyzed within the perturbation theory. Because the spin polarization arises mainly from the scattering between the constriction and the segment with spin-orbit coupling, the sub-band mixing induced by spin-orbit interaction in the scattering process and the interferences result in higher spin-filtering effect., Comment: 8 pages, 7 figures