Chiral phonon-polaritonic states are of interest for handedness-dependent light-matter interactions, yet their realization and magnetic control remain challenging, while direct magneto-optical tunability of phonon-polaritonic media is limited. Here, we propose a hybrid platform in which an hBN phonon polariton couples to a chiral bound state in the continuum supported by a magneto-optical photonic crystal, enabling strong and selective photonic coupling. The interaction gives rise to pronounced mode splitting and the formation of hybrid states, and their modal composition is quantified by phonon-proportion analysis and described by a coupling theory. Importantly, the hybridization can be controlled by magnetic bias through the magneto-optical response of the photonic component, providing control over the modal composition and spectral response. In addition, the hybrid states exhibit handedness-selective absorption under circularly polarized excitation. This work offers a feasible route toward magnetically tunable chiral phonon-polaritonic devices and hybrid polaritonic functionalities

Abstract We theoretically investigate the Josephson effect of massive pseudospin-1 fermions in the ferromagnetic α - T 3 model, which includes the S z - and U -type fermions, via the modulation of parameter α . Our results first reveal that the non-ferromagnetic junction is invariably in the 0 state, with the supercurrent vanishing when the mass magnitude m or the junction length L is sufficiently large. In the ferromagnetic junction, the 0 − π state transition can be induced by varying the value of α , with this state transition strongly influenced by m and the Fermi energy E F . Particularly, a large m is shown to cause the disappearance of both the 0 − π state transition and the supercurrent itself. Furthermore, we demonstrate the distinctive supercurrent properties that characterize the S z - and U -type fermions. These results may provide valuable insights for developing quantum electronic devices based on the superconducting properties of α - T 3 materials with massive pseudospin-1 fermions.

We investigate the Josephson effect of pseudospin-1 fermions in a superconductor/normal/superconductor (S/N/S) junction based on the dice lattice, where the supercurrent is mediated by topological edge states. Two types of staggered magnetizations are applied in the middle N region, respectively. It is shown that, for the A-B-C lattice staggered magnetization, the 0 - pi state transition can be realized by modulating the magnetization strength M. However, a larger M may inhibit the occurrence of the 0 - pi state transition and even the supercurrent. For the A-C lattice staggered magnetization, the oppositely flowing critical supercurrents are asymmetric, indicating a Josephson diode effect (JDE), which is due to spin-resolved edge states possessing different Fermi velocities in opposite directions. In particular, the JDE efficiency can increase from zero to approximately 24% by modulating M, giving rise to a high nonreciprocity. Our results not only uncover the unique supercurrent features of pseudospin-1 fermions in the topological dice lattice but also provide an alternative approach for generating the 0 - pi state transition and an efficient JDE.

We theoretically investigate the Josephson effect of massive pseudospin-1 fermions in the ferromagneticmodel, which includes the- and-type fermions, via the modulation of parameter. Our results first reveal that the non-ferromagnetic junction is invariably in thestate, with the supercurrent vanishing when the mass magnitudeor the junction lengthis sufficiently large. In the ferromagnetic junction, thestate transition can be induced by varying the value of, with this state transition strongly influenced byand the Fermi energy. Particularly, a largeis shown to cause the disappearance of both thestate transition and the supercurrent itself. Furthermore, we demonstrate the distinctive supercurrent properties that characterize the- and-type fermions. These results may provide valuable insights for developing quantum electronic devices based on the superconducting properties ofmaterials with massive pseudospin-1 fermions.

Topological phases and modes, including pseudospin-Hall-selective edge transport and corner states, provide robust control of wave propagation and modal confinement in classical wave platforms. Under a tight-binding framework, we theoretically investigate two lattice designs derived from the kagome lattice. These extended kagome lattices support a series of localized modes, including pseudospin-Hall-like topological edge states and corner modes in different bandgaps and frequencies, which were not only achieved under lower lattice symmetries than Wu-Hu lattices, but also enable more degrees of freedom in topological and localized modes. By introducing two types of extended kagome lattices with different topological properties, multiple interesting phenomena, including newly emerged multiple groups of corner states, parametric tunable pseudospin Hall effect, and type-II corner states without long-range interactions, are found in theoretical models, which are possible and viable to achieve in artificial classical systems such as photonic, acoustic, or electrical circuits.

We theoretically study the antiferromagnetism-involved Andreev reflection (AR) in a graphenebased ferromagnet/superconductor/antiferromagnet hybrid structure, with the ferromagnetic exchange field rotated in the ferromagnet region. The local and nonlocal ARs are considerably characterized by the spin polarization of the antiferromagnet region. A switching effect of perfect spin-singlet nonlocal AR processes can be achieved by conversion from the parallel to the antiparallel configuration for the ferromagnetic and antiferromagnetic exchange fields. Particularly, under the noncollinear scenario, a quasiperfect oblique-spin nonlocal AR process can be realized. It could bring about novel spin quantum entanglement, which cannot be lost in the presence of only one stray field and has scarcely been explored thus far.

We theoretically propose an antiferromagnetic silicene/superconductor hybrid structure, which unveils unconventional Andreev reflections (ARs) due to the Rashba spin-orbit and interface couplings. They are characterized by perfect spin- or/and valley-triplet pairing states with the spin or/and valley being fully polarized. Of the most striking is the spin-valley-triplet (intravalley equal-spin) AR induced by the combination of spin-flip and valley-mixing scatterings, which is an alternative pairing process. The tunability of spin and valley polarizations in antiferromagnetic silicene enables a spin-valley pairing switch between three types of triplet (intervalley equal-spin, intravalley opposite-spin, and intravalley equal-spin) pairing AR processes. It is also demonstrated that the corresponding subgap conductance spectra for each type exhibits distinct characteristic features, which can be directly tested experimentally using scanning tunnel microscope measurements and/or point-contact spectroscopy. Our findings may pave the way for the application of silicene in spin-valleytronics.

Topological photonic crystals have attracted tremendous attention due to their promise of robust optical properties and great potential for applications in on-chip devices. Numerous successful experimental demonstrations have shown or proved their topological properties, however, many of them turn out to have a nature of fragile topological phases. Here, using theoretical methods of fragile topology, we analyze two cases of topological photonic crystals with preserved time reversal symmetry, which utilize (1), the intrinsic duality and bi-anisotropy, and (2), accidental duality and structural bi-anisotropy respectively to induce their topological order. Our results show that the former case belongs to a Wannier-obstructed type of topological phase, indicating strong topological protection in their edge states. However, the latter meta-waveguide designs with structural bi-anisotropy widely implemented in experiments are Wannierizable, implying the fragile properties of their topology and gapped edge spectra. Our results provide new insights into the topological properties of photonic crystals as well as other bosonic systems with time-reversal symmetry.

We theoretically study the valley-polarized subgap transport and intravalley pairing states in silicene-based antiferromagnet/superconductor (AF/SC) junctions. It is found that in the absence of an electric field, the antiferromagnetic order induced in silicene can give rise to valley-polarized states that strongly affect the subgap conductance. With the increasing antiferromagnetic exchange field, the gap-edge Andreev-resonant peak is replaced by broadened features for the homo-SC model whereas by a sharp conductance dip for the bulk-SC one. This significant difference arises from the intravalley Andreev reflection caused by the valley-mixing scattering in the bulk-SC model, which can be enhanced by the antiferromagnetic order. Particularly, this intravalley pairing process can be switched on or off by adjusting the spin polarization through the electric field applied in the AF region. Our findings not only pave a new road to employ antiferromagnetic materials in valleytronics, but also facilitate the verification and detection of potential intravalley pairing state and valley polarization in silicene.

Anomalous Floquet topological superconductivity with chirality can be achieved by applying a dc-bias voltage across the Josephson junction with a sandwiched magnetic topological insulator (TI), in which the intrinsic Josephson phase provides a time-dependent periodic driving [R.-X. Zhang and S. Das Sarma, Phys. Rev. Lett. 127, 067001 (2021)]. In this work, we remove the bias voltage and connect the magnetic TI to an external AC voltage source to modulate the chemical potential, thus bringing about an explicit-time Floquet periodic driving. In the context of the driving, the system is similarly found to convert into a two-dimensional anomalous Floquet topological superconductor with chirality. By tuning the AC voltage source's frequency, we obtain a rich variety of novel Floquet topological superconducting phases with chirality. Particularly, by manipulating such static parameters as Zeeman field and superconducting pairing potential, a series of topological superconducting phase transitions are also exhibited, accompanied by exotic Floquet topological superconducting phases with chirality.

Current theoretical and experimental endeavors to realize an anomalous Floquet chiral topological superconductor (TSC), which is characterized by chiral Majorana edge modes independent of the Chern number, remain insufficient. Herein, we propose a new scheme that involves jointly tuning dynamic driving and static parameters within a magnetic topological insulator-superconductor sandwich structure to achieve this goal. The Josephson phase modulation induced by an applied bias voltage across the structure is utilized as a Floquet periodic drive. It is found that the interplay between the two kinds of tunings can bring about a lot more exotic Floquet TSC phases than those caused by only tuning the dynamic driving parameter (frequency omega or period tau). More importantly, just tuning static parameters (the chemical potential mu, Zeeman field gz , and proximity-induced superconducting energy gap Delta b ) also can induce a series of novel topological phase transitions. Particularly, the features in the context of the three tunings are different from each other, originating from the combination of intrinsic and different extrinsic mechanisms. In addition, jointly tuning tau and mu (gz ) can have its own unique TSC phases. The proposed scheme should be readily accessible in experiments, and thus the family of anomalous Floquet TSC phases may be considerably enriched.

Topological boundary modes in electronic and classical-wave systems exhibit fascinating properties. In photonics, topological nature of boundary modes can make them robust and endows them with an additional internal structure—pseudo-spins. Here, we introduce heterogeneous boundary modes, which are based on mixing two of the most widely used topological photonics platforms—the pseudo-spin–Hall-like and valley-Hall photonic topological insulators. We predict and confirm experimentally that transformation between the two, realized by altering the lattice geometry, enables a continuum of boundary states carrying both pseudo-spin and valley degrees of freedom (DoFs). When applied adiabatically, this leads to conversion between pseudo-spin and valley polarization. We show that such evolution gives rise to a geometrical phase associated with the synthetic gauge fields, which is confirmed via an Aharonov-Bohm type experiment on a silicon chip. Our results unveil a versatile approach to manipulating properties of topological photonic states and envision topological photonics as a powerful platform for devices based on synthetic DoFs.

The nonreciprocity of critical supercurrents in a Josephson device, termed the Josephson diode effect (JDE), has drawn considerable interest recently. Herein, we present possible spin-resolved and charge JDEs in a Josephson junction based on the alpha- T-3 lattice, due to different spin-resolved Fermi velocities in opposite directions for the distorted flat bands and edge states. Two mechanisms are exhibited, which are characterized by a topological phase with an anisotropic parameter alpha . One is that the JDE only originates from distorted flat bands, corresponding to the topological phase (0 < alpha < 0 . 5), the other simultaneously from edge states in the topological phase (0.5 . 5 < alpha < 1). Particularly, the charge JDE only manifests in the context of magnetization and its efficiency can range from - 45% to 39%, suggesting a high nonreciprocity. More importantly, both the magnitude and polarity of the charge JDE from edge states and distorted flat bands can be strongly adjusted by the magnetization strength.

We investigate the quantum interference of the electron–hole conversions from the two interfaces in a Weyl semimetal (WSM)-based hybrid structure, in which a superconducting WSM is sandwiched in between two normal ones. The quantum interference is characterized by the chirality-anomaly-manipulation (CAM). It is found that only low energy is in favor for s-wave BCS pairing states. The Andreev reflection (AR) chirality blockade can be tuned by the stagger angle α for the relative orientation of paired Weyl points, accompanied by an AR bipolar chirality diode. Thus, a strong CAM is indicated for the electron–hole conversion. However, the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) pairing states have no energy preference, with the weak and strong CAMs being near and far away from the zero energy, respectively. More interestingly, a perfect AR with the normal reflection suppressed thoroughly can be obtained at any α as a result of the FFLO paring with the same chirality. In addition, the conductance or noise power, which incorporates the contributions of the two paired Weyl nodes, not only, in turn, embodies the respective features of their contributions but also can be experimentally measured to discern between the BCS and FFLO paring states.

Our research investigates the magnon bands and their topological characteristics in a ferromagnetic pyrochlore lattice, with the Dzyaloshinskii-Moriya (DM) interaction playing a significant role. Given its kagome AB bilayer structure, the ferromagnetic exchange couplings, which may differ among the AB triangles, are further considered for their implications on the system's magnetic properties. By employing the non-equilibrium Green's function method, we explicitly demonstrate that the one-way chiral edge magnon transport is indeed regulated by the DM interaction direction ( D ->-D) and the exchange interaction of J(1) and J(2) ( J(1)<-> J(2)). Moreover, we demonstrate that the topological edge state predominantly resides along the edges and exhibits an oscillatory decay as it penetrates into the bulk in a non-equilibrium state. Although the chiral edge magnons and the corresponding energy current tend to travel along one edge from the hot region to the cold one, in the bulk, however, the energy current flows reversely from the cold to the hot region. The valley magnon Hall effects and chiral edge transport proposed here may be realized in the thin films of the insulating ferromagnet, such as Lu2V2O7. Thus, it will pave the way for a more extensive use of magnonics in future technologies. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC) license

We theoretically study the Josephson effect of massive pseudospin-1 fermions in a superconductor/ferromagnet/superconductor (S/F/S) junction based on the dice lattice, including S z- and + U-type mass terms with the magnitude m . For the S z-type fermions, it is found that, in the absence of ferromagnetic exchange field h , the supercurrent is effectively inhibited by m or the junction length L . In the presence of h , 0 - state transition can be realized by modulating h , m , or L . The m-induced state transition occurs more frequently for a larger h or L . Particularly, the inhibition of supercurrent caused by m still remains for a large m . In the doping case, corresponding to a nonzero E F , the m-induced state transition may disappear for a large h or L . With EF increased, the inhibition caused by m diminishes for a small h whereas intensifies for a large h . In addition, the supercurrent features for the + U-type fermions distinct from those for the S z-type fermions are demonstrated.

We propose an adiabatic superconducting charge pump based on massive Dirac electrons. A superconductor is sandwiched in between two pumping sources, which are formed by introducing the time-dependent and out-of-phase staggered potentials in graphene as pumping parameters. The pump is shown to be characterized by not only the topological interface state (TIS) but also the non-topologically quasi interface state (QIS). Hereafter, our attention is focused on the pumping currents I L NR and I L AR from the normal and Andreev reflections, respectively, which predominate by making the electron energy reside in the effective energy gap. It is found that modulating the energy E , superconductor length L 0 , and pumping source length L P results in the considerable variation of competitive behaviors between I L NR and I L AR . In particular, the reversal effect of current direction can be realized by tuning L P . More interestingly, the current-phase relationship exhibits the platform behaviors, which can be manipulated by L P and the pumping strength. All the above pumping properties are attributed to the adiabatic evolution of TIS and non-topologically QIS, particularly the conversion between each other is the crucial origin. We also obtain the quantized pumping current by adjusting L P and L 0 , and present the corresponding qualitative explanation through the pumping contour circled by the two parameters. In addition, we discuss the features of pumping current based on the armchair graphene as well.

Valley coupling is proposed to construct a spatially separated two-parameter pump based on the O-or Yshaped Kekule (Kek) graphene superlattices (GSs) with a sandwiched graphene layer. It is shown that for the O-shaped Kek GS pumping structure, pumped charges with an integer number can be obtained in a pumping cycle at the Fermi energy residing in the effective energy gap. Particularly, this quantization only from the contribution of intervalley reflection is thoroughly different from the one in previous two-parameter pumps only with the intravalley reflection. This stems from the Hamiltonian of an antiunitary symmetry, leading to a phase analogous to a topological superconductor and thus a perfect pseudo-Andreev reflection in the valley version. The quantization also can be attributed to the topological interfacial state (TIS) arising in between the two pumping sources due to different quantum valley Hall insulator (QVHI) phases. However, for the Y-shaped Kek GS one, the current coming from both the intravalley and intervalley reflections is nonquantized. This is due to the time-dependent coupling term between two valleys only emerging in the A sublattice, which induces no QVHI and no resultant TISs. Our findings may not only pave a new road to design the quantized charge pump device based on the GS, but also provide a sharp experimental signature to detect the O-shaped one and distinguish between the two GSs.

The zigzag graphene nanoribbon (ZR) is characterized by the distinct pseudoparity combined with valley-selection rule, which could feature exotic transport phenomena, especially in ZR-based superconducting spintronic devices. However, the ZR with superconductivity induced by proximity of a bulk superconductor (SC) on it still keeps original band properties. Herein, we present a superconducting heterostructure with an SC directly coupling to two ZRs, which is characteristic of pseudoparity-mixing, resulting in pseudoparity nonconservation elastic cotunneling (EC) and crossed Andreev reflection (CAR) processes. It is shown that the mixing leads to the switch effect of the EC and CAR processes manipulated by the SC length, particularly the full spin polarization. In the context of only one magnetized ZR lead, a novel bipolar spin diode behavior on a scale of small SC length and unipolar spin entanglement pairing at some large SC lengths, are both exhibited on a large scale of forward and/or reverse bias voltages. More importantly, the spin-diode can be combined with the quantum spin Hall (QSH) insulator to provide smoking gun evidence for the helical spin texture of the (QSH) insulator, which is still lacking.

We report novel topological polaritonic states of half-light and half-phonon character in a topological mid-infrared metasurface integrating hexagonal boron nitride (hBN). A custom-built Fourier-space imaging microscope was used to investigate a three-dimensional band diagram of the photonic topological phonon-polaritonic states in our system for the first time. Our Fourier- and real-space imaging experimental findings, supported by theoretical models, demonstrate that topological properties of photonic modes are transcribed to the in-plane lattice vibrations (phonons) supported by hBN. As a result, the observed topological phonon-polaritons exhibit unidirectional propagation with the helical nature of vibrations and the resilience of the modes to sharp bends.