TECHNICAL FIELD

[0001] The present disclosure relates to topologically protected surface magnon states. In particular, the present disclosure provides a means to measure topologically protected surface magnon states.

BACKGROUND

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] The non-trivial topology of quasiparticle wavefunctions are now known to manifest themselves in the form of observable surface states. Since electronic topology can be probed relatively easily using standard spectroscopy and electronic transport techniques, most advances have been in the area of electronic materials. For instance, a number of potential (electronic and/or optical) devices and sensors based on topological electronic materials have been proposed. However, topological properties are not restricted to electronic systems alone. Another area where topology is expected to be important, is magnetic materials, where the topology of the magnon band structure could result in interesting phenomena and device applications. However, the existence of topologically protected magnon surface states remains to be experimentally demonstrated.

OBJECTS OF THE PRESENT DISCLOSURE

[0004] An object of the present disclosure relates to topologically protected surface magnon states. In particular, the present disclosure provides a means to measure topologically protected surface magnon states.

[0005] Another object of the present disclosure is to provide a device capable of detecting and characterizing topologically protected surface magnons.

[0006] Yet another object of the present disclosure is to utilize the measurement geometry comprising a metal layer on top of a ferromagnetic material and the physical mechanism of interfacial magnon drag enables the electrical detection and exploration of the unique properties of topological magnons. SUMMARY

[0007] The present disclosure relates in general, to topologically protected surface magnon states. In particular, the present disclosure provides a means to measure topologically protected surface magnon states. The main objective of the present disclosure is to overcome the drawback, limitations, and shortcomings of the existing device and solution, by providing a device designed for the detection of topologically protected surface magnons.

[0008] The device consists of a measurement geometry featuring a metal layer deposited on the surface of a ferromagnetic material. By utilizing the phenomenon of interfacial magnon drag, wherein a magnon spin current on the magnet surface exerts a dragging force on the charge carriers in the adjacent material, an electrical voltage is generated. This device provides a means to electrically detect and measure topologically protected surface magnons, offering valuable insights into their properties and behavior. The interplay between the metal layer and the ferromagnet enables the observation and analysis of these unique magnonic states, opening up possibilities for the development of magnon-based devices and applications.

[0009] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF DRAWINGS

[0010] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0011] FIG. 1 illustrates a schematic view of a device for measuring magnon currents, according to an embodiment of the present disclosure;

[0012] FIGs. 2A and 2B illustrate exemplary plots depicting variation in thermopower developed in the metal layer with change in applied magnetic field H, when the metal layer is platinum and tungsten, respectively;

[0013] FIGs. 3A and 3B illustrate exemplary plots depicting variation in thermopower developed in the metal layer with change in applied magnetic field H, when the metal layer is platinum and tungsten, respectively; and [0014] FIG. 4 illustrates a schematic representation of the device indicating interfacial magnon drag, according to an embodiment of the present disclosure.

[0015] FIG. 5 illustrates a flow chart of the method for detecting topologically protected surface magnons, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0016] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such details as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[0017] Magnons refer to a quanta of collective spin wave excitations. Magnons may be used to develop a platform where a topology of a magnon band structure may manifest itself in the form of observable surface states which are distinct from the bulk. Such topological magnons may have properties distinct from their bulk counterparts and may thus have important implications in magnon based spintronic devices. The existence of topologically protected magnon (surface) states remains to be experimentally demonstrated, owing to the fact that conventional measurement techniques, such as inelastic neutron scattering, or Brillouin light scattering, are relatively insensitive to surface magnon states.

[0018] In some embodiments, the present disclosure provides a means to demonstrate the existence of topologically protected surface magnons using an electrical based detection methodology. This is achieved by the means of a new physical mechanism of interfacial magnon drag, where the magnon currents in a surface of a material is detected by means of a force imposed by the magnon currents on charge carriers of an adjacent layer.

[0019] In some embodiments, the present disclosure further provides a device for detecting the topologically protected surface magnons. The device used to infer the presence of magnon surface states includes a measurement geometry including a metal deposited on top of a ferromagnet. The device may utilize the phenomena of interfacial magnon drag, wherein a magnon spin current on the magnet surface drags the charge carriers in the adjoining material, thereby giving rise to an electrical voltage. Generally, the magnon band structure in a number of quantum materials may exhibit topologically protected attributes. Being able to infer magnon topology using electrical means may have far reaching applications in many areas, including that of dissipation-less spin transport, magnonic crystals, light-induced magnonic phenomena, and magnon-based quantum information processing.

[0020] FIG. 1 illustrates a schematic view of a device 100 for measuring magnon currents, according to an embodiment of the present disclosure.

[0021] The device includes a conducting layer 102 disposed on top of a magnetic layer 104. The conducting layer 102 disposed on top of a magnetic layer 104 to define a measurement geometry. An energy source configured to apply a magnetic field to induce magnon spin currents on the surface of the magnetic layer 104, where the magnon spin current on the surface of the magnetic layer 104 exerts a dragging force on the charge carriers in the conducting layer 102, resulting in the generation of an electrical voltage. The energy source in the present disclosure can encompass various forms, including temperature gradients, microwaves, acoustic waves, light, electric fields, or any combination thereof.

[0022] The conducting layer 102 facilitates the collection of charge carriers affected by the dragging force exerted by the magnon spin currents on the magnet surface, where the interfacial magnon drag gives rise to the electrical voltage indicative of the strength and direction of the magnon spin currents. The electrical voltage generated as a result of the interfacial magnon drag is measured to characterize the magnon spin currents.

[0023] In some embodiments, the conducting layer 102 may include any material, such as a metal or a semi-conductor that includes a finite number of charge carriers, such as platinum, tungsten, etc.

[0024] The magnetic layer 104 comprises ferromagnetic material. The ferromagnetic material selected from topologically protected magnon surface states, including pyrochlores, transition metal halides, layered ferromagnetic semiconductors, Kagome compounds and their variants, hexagonal closed packed (HCP) magnets, Skyrmion crystals or Skyrmion host materials, honeycomb lattice materials, and Kitaev magnets. As can be appreciated, the present disclosure is not limited to ferromagnetic materials and can be extended to include other magnetic materials, such as ferro, antiferro, or ferri-magnetic materials.

[0025] In some embodiments, the magnetic layer 104 may include the material that possesses the topologically protected magnon surface states. Some examples of the materials may include, without limitations, pyrochlores (such as Y2V2O7), transition metal halides (such as CrF, CrBr , layered ferromagnetic semiconductors (such as CrSiTcs, CrGcTcs), Kagome compounds and their variants (such as YMneSne, FeSn), HCP magnets such as Gd, Skyrmion crystals or Skyrmion host materials, honeycomb lattice materials (such as CoTiOs), Kitaev magnets, etc. [0026] In some embodiments, a magnetic field H is applied orthogonal to a thermal gradient ATzz, and a thermal gradient ATzx is obtained that is orthogonal to both the applied magnetic field H and the applied thermal gradient ATzz. In order to determine the thermal gradient ATzx, a thin metal layer is deposited over the magnetic layer 104 and measuring a thermopower which develops across the metal layer. In some embodiments, the thermopower measured using such a set up may have favorable signal-to-noise ratio.

[0027] FIGs. 2A and 2B illustrate exemplary plots 200, 250 depicting variations in thermopower developed in the metal layer with change in applied magnetic field H, when the metal layer is platinum and tungsten, respectively. The measurements were performed with the magnetic field H applied along a crystallographic [100] direction. The voltage is asymmetric as a function of the applied magnetic field H, and in accordance with the magnon Hall effect expected in the pyrochlore system.

[0028] FIGs. 3A and 3B illustrate exemplary plots 300, 350 depicting variations in thermopower developed in the metal layer with change in applied magnetic field H, when the metal layer is platinum and tungsten, respectively. In some cases, when the magnetic field H is not along the crystallographic [100] direction, some pyrochlore materials may support topologically protected surface magnon states. The voltages measured with the magnetic field applied along the crystallographic [111] direction is shown in FIGs. 3 A and 3B. As is evident, the signals look quite different from the earlier case. An additional (symmetric) voltage may be seen to have been added to the (antisymmetric) voltage arising from the magnon Hall effect. Interestingly, this voltage changes its sign, when a tungsten layer (bottom panel) is used instead of a platinum layer (top panel), owing to the difference in the material properties between platinum and tungsten.

[0029] FIG. 4 illustrates a schematic representation of the device 100 indicating interfacial magnon drag, according to an embodiment of the present disclosure. This additional voltage arising may be due to the interfacial magnon drag, wherein a magnon current is detected by means of the force they exert on the charge carriers of an adjacent material. In some embodiments, such a phenomenon may be exhibited with a number of different capping layers.

[0030] FIG. 5 illustrates a flow chart of the method for detecting topologically protected surface magnons, according to an embodiment of the present disclosure.

[0031] The method 500 for detecting topologically protected surface magnons. The method at block 502 includes depositing a conducting layer on top of a magnetic layer to define a measurement geometry. At block 504, the energy source configured to apply magnetic field to induce magnon spin currents on the surface of the magnetic layer and at block 506, detecting an electrical voltage generated as a result of the interfacial magnon drag, wherein the magnon spin current on the surface of the magnetic layer exerts a dragging force on the charge carriers in the conducting layer, resulting in the generation of the electrical voltage.

[0032] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprise” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C . . . .and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.

[0033] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions, or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art. ADVANTAGES OF THE PRESENT INVENTION

[0034] The present invention provides a device that provides an electrical means of detecting and characterizing topological magnons, allowing for precise measurements and analysis. [0035] The present invention provides the use of interfacial magnon drag as a detection mechanism enables the generation of an electrical voltage, providing a clear and measurable signal for the presence of topologically protected surface magnons.

[0036] The present invention provides the device that opens up possibilities for the development of magnon-based spintronic devices that utilize the unique properties and behavior of topological magnons.

[0037] The present invention contributes to the advancement of magnon-based research and technology, with potential implications for future applications in information processing, data storage, and communication systems.