Evidence of non-degenerated, non-reciprocal and ultra-fast spin-waves in the canted antiferromagnet {\alpha}-Fe2O3

Spin-waves in antiferromagnets hold the prospects for the development of faster, less power-hungry electronics, as well as new physics based on spin-superfluids and coherent magnon-condensates. For both these perspectives, addressing electrically coherent antiferromagnetic spin-waves is of importance, a prerequisite that has so far been elusive, because unlike ferromagnets, antiferromagnets couple weakly to radiofrequency fields. Here, we demonstrate the electrical detection of ultra-fast non-reciprocal spin-waves in the dipolar-exchange regime of a canted antiferromagnet. Using time-of-flight spin-wave spectroscopy on hematite (alpha-Fe2O3), we find that the magnon wave packets can propagate as fast as 30 km/s for reciprocal bulk spin-wave modes and up to 10 km/s for surface-spin waves propagating parallel to the antiferromagnetic N\'eel vector. The electrical detection of coherent non-reciprocal antiferromagnetic spin waves holds makes hematite a versatile platform where most of the magnonic concepts developed for ferromagnet can be adapted paving the way for the development antiferromagnetic and altermagnet-based magnonic devices

Introducing coherent time control to cavity magnon-polariton modes

By connecting light to magnetism, cavity magnon-polaritons (CMPs) can link quantum computation to spintronics. Consequently, CMP-based information processing devices have emerged over the last years, but have almost exclusively been investigated with single-tone spectroscopy. However, universal computing applications will require a dynamic and on-demand control of the CMP within nanoseconds. Here, we perform fast manipulations of the different CMP modes with independent but coherent pulses to the cavity and magnon system. We change the state of the CMP from the energy exchanging beat mode to its normal modes and further demonstrate two fundamental examples of coherent manipulation. We first evidence dynamic control over the appearance of magnon-Rabi oscillations, i.e., energy exchange, and second, energy extraction by applying an anti-phase drive to the magnon. Our results show a promising approach to control building blocks valuable for a quantum internet and pave the way for future magnon-based quantum computing research

Antiferromagnetic cavity magnon polaritons in collinear and canted phases of hematite

Cavity spintronics explores light-matter interactions at the interface between spintronic and quantum phenomena. Until now, studies have focused on the hybridization between magnons in ferromagnets and cavity photons. Here, we realize antiferromagnetic cavity magnon polaritons. Hybridization arises from the interaction of the collective spin motion in single hematite crystals (α- Fe 2 O 3 ) and the microwave field of integrated cavities operating between 18 and 45 GHz. We show theoretically and experimentally that the photon-magnon coupling in the collinear phase is mediated by the dynamic Néel vector and the weak magnetic moment in the canted phase by measuring across the Morin transition. We show that the coupling strength, ~ g , scales with the anisotropy field in the collinear phase and with the Dzyaloshinskii-Moriya field in the canted phase. We reach the strong-coupling regime in both canted (cooperativity C > 70 for selected modes at 300 K) and noncollinear phases (C > 4 at 150 K), and thus, towards coherent information-exchange-harnessing antiferromagnetic cavity magnon polaritons. These results provide evidence for a generic strategy to achieve cavity magnon polaritons in antiferromagnets for different symmetries, opening the field of cavity spintronics to antiferromagnetic materials

Financial services and the urban system: an exploration

Financial services have come to represent an increasingly important sector in the economies of developed nations. Although a substantial literature has accumulated on this topic, relatively little attention has been given to the locational aspects of � nancial services. An attempt is made here to examine the spatial structure of this sector in terms of the urban system, drawing on the principles of central-place theory, the limitations and applicability of which are considered. This is followed by a discussion of the salient features of financial services within the overall urban system. After describing the differentiation of financial services in frequency terms, the hierarchical structure of the UK urban system is outlined. These two aspects are then related, in order to demonstrate the ordered nature of the spatial structure of financial services. There follows a brief discussion of the findings and their implications for future wor