Program

DAY 1 (January 17, 2022) Quantum Hall anyons

Session Chair: Heung-Sun Sim

Talk 1 [05:00 PM - 05:40 PM (Korea)] [09:00 AM - 09:40 AM (Paris)]

Speaker: D. Christian Glattli (CEA Saclay)

Title: Anyonic relation in circuit QED

Abstract: We show that anyonic relations are ubiquitous for all one-dimensional systems described by a collection of bosonic harmonic oscillators. We focus on the case of QED circuits where we show that, generally the field displacement operators (here the charge creation operator), obey anyonic relations. We apply these results to the case of composite fermions in the FQHE regime.

Talk 2 [05:50 PM - 06:30 PM (Korea)] [09:50 AM - 10:30 AM (Paris)]

Speaker: Christophe Mora (Univ. de Paris)

Title: Fractionalization and anyonic statistics in the integer quantum Hall collider

Abstract: Under strong magnetic fields, electrons that are confined to two spatial dimensions can exhibit a fractional quantum Hall state where the elementary particles carry only a fraction of the electron charge. These exotic excitations, called anyons, moreover behave under the interchange of two individuals neither as fermions nor as bosons but are characterized instead by a non-trivial exchange phase. The experimental proof of these anyons and their exchange phase was performed only recently, in 2020. Here, we show that anionic excitations could also be engineered in the integer quantum Hall regime, requiring weaker magnetic fields, with the additional ingredient of a coupled metallic island.

By coupling a set of edge-propagating channels of the integer quantum Hall effect to an electrically gated metallic island, we identify an emission of fractional elementary charges. The full statistics of the charge emission is obtained in agreement with a simple picture where each electron entering the island is fractionalized democratically between the many edge channels. In addition, we find that the elementary charges behave as anyons under exchange. This last property can be revealed in a cross-correlation measurement at the output of a beam splitter geometry, similarly to the recent 2020 experiment demonstrating anyons. Interestingly, we also revisit the physical interpretation of this experiment and find that it is a direct signature of anyon braiding and not of anyon bunching as previously proposed.

Our work highlights a novel platform for investigating anyons and their unconventional statistics. It opens many perspectives, from the realization of unprecedented fractions to the mixing of beams of non-identical anyons or time-dependent electronic excitations.

Talk 3 [07:30 PM - 08:10 PM (Korea)] [11:30 AM - 12:10 PM (Paris)]

Speaker: Gwendal Feve (Sorbonne Univ)

Title: Fractional statistics of anyons in mesoscopic colliders

Abstract: In three-dimensional space, elementary particles are divided between fermions and bosons according to the properties of symmetry of the wave function describing the state of the system when two particles are exchanged. When exchanging two fermions, the wave function acquires a phase, φ=π. On the other hand, in the case of bosons, this phase is zero, φ=0. This difference leads to deeply distinct collective behaviors between fermions, which tend to exclude themselves, and bosons which tend to bunch together. The situation is different in two-dimensional systems which can host exotic quasiparticles, called anyons, which obey intermediate quantum statistics characterized by a phase φ varying between 0 and π [1,2].

For example in the fractional quantum Hall regime, obtained by applying a strong magnetic field perpendicular to a two-dimensional electron gas, elementary excitations carry a fractional charge [3,4] and have been predicted to obey fractional statistics [1,2] with an exchange phase φ=π/m (where m is an odd integer) for Laughlin states corresponding to a fractional filling υ=1/m of the first Landau level. I will present how fractional statistics of anyons can be demonstrated in this system by implementing and studying anyon collisions at a beam-splitter [5,6,7]. The collisions are first studied in the low magnetic field regime, where the elementary excitations are electrons which obey the usual fermionic statistics. It leads to the observation of an antibunching effect in an electron collision: electrons systematically exit in two different arms of the beam-splitter. The observed result is completely different in the fractional quantum Hall regime at filling factor υ=1/3. Fractional statistics lead to a suppression of the antibunching effect and quasiparticles tend to bunch together in larger packets of charge in a single output of the splitter. This effect leads to the observation of negative correlations of the current fluctuations [6] in perfect agreement with recent theoretical predictions [5].

[1] B. I. Halperin, Phys. Rev. Lett. 52, 1583–1586 (1984).

[2] D. Arovas, J. R. Schrieffer, F. Wilczek, Phys. Rev. Lett. 53, 722–723 (1984).

[3] R. de Picciotto et al., Nature 389, 162–164 (1997).

[4] L. Saminadayar, D. C. Glattli, Y. Jin, B. Etienne, Phys. Rev. Lett. 79, 2526–2529 (1997)

[5] B. Rosenow, I. P. Levkivskyi, B. I. Halperin, Phys. Rev. Lett. 116, 156802 (2016).

[6] H. Bartolomei, M. Kumar et al. Science 368, 173-177 (2020).

[7] T. Morel et al., arXiv:2110.13925 (2021)

Talk 4 [08:20 PM - 09:00 PM (Korea)] [12:20 PM - 01:00 PM (Paris)]

Speaker: Heung-Sun Sim (KAIST)

Title: Non-Abelian anyon collider

Abstract: TBA

DAY 2 (January 19, 2022) Emerging Quantum Spintronics

Session Chair: Kab-Jin Kim

Talk 1 [09:40 AM - 10:20 AM (Korea, Japan)] [08:40 AM - 09:20 AM (China, Singapore)]

Speaker: Hiroaki Ishizuka (TIT)

Title: Anomalous Hall effect and nonreciprocal transport phenomena due to magnetic multiple scattering

Abstract: Magnetic textures, such as skyrmions and helix, bring about unconventional transport phenomena when they couple to itinerant electrons. Anomalous Hall effect (AHE) in skyrmion crystal is one of such phenomena that is intensively studied over last couple of decades. The common interpretation of this effect is that it is a Hall effect due to the effective magnetic field originating from the spin Berry phase. The relation between spin Berry phase and spin chirality connects the skyrmions to this effect. Namely, it is an intrinsic AHE. On the other hand, recent theoretical studies points out that the thermal fluctuation of spins also contributes to an AHE related to the spin chirality, which is described by the magnetic multiple scattering [1,2].

Inspired by these developments and the intrinsic/extrinsic crossover of anomalous Hall effect in ferromagnets, we studied the physics and their experimental consequences of the magnetic multiple scattering mechanism. We find that the multiple magnetic scattering leads to anomalous Hall effect with features distinct from the intrinsic counterpart: It gives a large Hall angle and scaling different from the intrinsic counterpart [3,4]. Further implications of the theory and its application to recent experiments [5] will also be discussed. In addition to the anomalous Hall effect, the multiple scattering also causes a nonreciprocal response [7], namely, the left/right asymmetry of resistivity as in semiconductor diodes. Our calculation reproduces the trends of experimentally observed temperature-magnetic field phase diagram of helical magnets [8,9], and is consistent with the enhanced nonreciprocity at the phase boundaries [10]. The results shed light onto the rich transport phenomena in magnetic metals and shows a potential for designing functional materials through novel mechanism.

[1] H. Ishizuka et al., Sci. Adv. 4, eaap9962 (2018).

[2] Y. Kato et al., Phys. Rev. Appl. 12, 021001 (2019).

[3] H. Ishizuka et al., Phys. Rev. B 103, 235148 (2021).

[4] Y. Fujishiro et al., Nat. Commun. 12, 317 (2021).

[5] M. Uchida et al., Sci. Adv. 7, Abl5381 (2021).

[6] S.-Y. Yang et al., Sci. Adv. 6, eaab5003 (2020).

[7] H. Ishizuka et al., Nat. Commun. 11, 2986 (2020).

[8] T. Yokouchi et al., Nat. Commun. 8, 866 (2017).

[9] R. Aoki et al., Phys. Rev. Lett. 122, 057206 (2019).

[10] A. Kitaori et al., Phys. Rev. B 103, L220410 (2021).

Talk 2 [10:20 AM - 11:00 AM (Korea, Japan)] [09:20 AM - 10:00 AM (China, Singapore)]

Speaker: Se Kwon Kim (KAIST)

Title: Nonreciprocal thermal transport realized by spin superfluids

Abstract: In chiral magnets with intrinsic inversion-symmetry breaking, it has been predicted that two spin waves propagating along a particular direction and the opposite direction can propagate with different velocities. This novel phenomenon, called magnetochiral nonreciprocity, allows for efficient magnonic logic device applications such as a spin-wave diode. Here we theoretically demonstrate that the spin-wave nonreciprocity can be non-locally induced in easy-cone magnets with no inversion-symmetry breaking [1]. We show that the non-local injection of the spin current into the easy-cone magnet leads to the Doppler shift of the spin-wave spectrum on top of a spin superfluid and produces the spin-wave nonreciprocity in the bulk. The resultant nonreciprocal thermal transport driven by a temperature gradient, which realized a thermal diode, is discussed as a practical application.

[1] G. Go, S. Lee, and S. K. Kim, "Generation of Nonreciprocity of Gapless Spin Waves by Chirality Injection," arXiv:2110.01867

Talk 3 [11:20 AM - 12:00 PM (Korea, Japan)] [10:20 AM - 11:00 AM (China, Singapore)]

Speaker: Wanjun Jiang (Tsinghua Univ)

Title: Skyrmion Topological Spintronics

Abstract: Symmetry breaking together with a strong spin-orbit interaction give rise to many exciting opportunities for the condensed matter physics community. Topologically protected magnetic skyrmions are one of the examples. Skyrmions are particle-like topological spin textures stabilized by the Dzyaloshinskii-Moriya interaction, which have recently stimulated great interests in spintronics community[1-3].

In this talk, I will first present our experimental results in the electric creation and manipulation of skyrmions at room temperature in the interfacially asymmetric magnetic multilayers. This is enabled by the inhomogeneous current induced spin-orbit torques in a Ta/CoFeB/TaOx trilayer [4-6]. I will demonstrate experimentally a spin-topology-driven dynamics of magnetic skyrmion – the skyrmion Hall effect [6-7]. Namely, an accumulation of skyrmions at the transverse side of the device is experimentally achieved.

Secondly, I will discuss the thermodynamical physics associated with skyrmions. In particular, an intriguing topology dependent Brownian gyromotion, together with a nonlinear temperature-dependent diffusion behavior will be discussed [8]. Subsequently, thermal generation, manipulation and detection of nanoscale skyrmions in an integrated/on-chip device will be discussed [9].

Subsequently, I will discuss the possibility of realizing 20nm skyrmions by using current-induced spoin torque at room temperature in [Pt/Co/Ir] multilayer[10]. Finally, some open questions and future focus points will be addressed.

References:

[1] A. Fert, et al., Nature Nanotechnology, 8, 152 (2013).

[2] N. Nagaosa, et al., Nature Nanotechnology 8, 899-911 (2013).

[3] W. Jiang, et al., Physics Reports, 704, 1-49 (2017).

[4] W. Jiang, et al., Science 349, 283 (2015).

[5] W. Jiang, et al., AIP Advances 6, 055602 (2016).

[6] W. Jiang, et al., Nature Physics,13, 162 (2017).

[7] K. Litzius, et al., Nature Physics,13, 170 (2017).

[8] L. Zhao, et al., W. Jiang, Phys. Rev. Letts. 125，027206 (2020).

[9] Z. Wang, et al., W. Jiang, Nature Electronics, 3,672-679 (2020).

[10] J. Liu., et al., W. Jiang, Chinese Physics Letters 39(1), 17501 (2022).

Talk 4 [12:00 PM - 12:40 PM (Korea, Japan)] [11:00 AM - 11:40 AM (China, Singapore)]

Speaker: Peng Yan (UESTC)

Title: Exceptional magnetic sensitivity of PT-symmetric cavity magnon polaritons

Abstract: Achieving magnetometers with ultrahigh sensitivity at room temperature is an outstanding problem in physical sciences and engineering. Recently developed non-Hermitian cavity spintronics offers new possibilities. In this work we predict an exceptional magnetic sensitivity of cavity magnon polaritons with the peculiar parity-time (PT) symmetry. Based on the input-output formalism, we demonstrate a “Z”-shape spectrum including two sideband modes and a dark-state branch with an ultranarrow linewidth in the exact PT phase. The spectrum evolves to a step function when the polariton touches the third-order exceptional point, accompanied by an ultrahigh sensitivity with respect to the detuning. The estimated magnetic sensitivity can approach 10−15 THz−1/2 in the strong coupling region, which is two orders of magnitude higher than that of the state-of-the-art magnetoelectric sensor. Possible experiments to realize our proposal are discussed.

Talk 5 [12:40 PM - 01:20 PM (Korea, Japan)] [11:40 AM - 12:20 PM (China, Singapore)]

Speaker: Jiang Xiao (Fudan Univ)

Title: Antiferromagnetic Resonance Revisited: a spectrum of level attraction

Abstract: We found that the antiferromagnetic resonance spectrum can be viewed as a result of the level attraction between the two eigenmodes from the two magnetic sublattices. This is a surprise because the antiferromagnet is a closed Hermitian system, which typically shows the level repulsion. And the level attraction is a characteristic behavior often observed in non-Hermitian systems. This counter intuitive behavior does not linked to any dissipation or openness of the system, but is caused by the PT-symmetric antiferromagnetic ground state. This new understanding on antiferromagnetic resonance also explains the mysterious enhancement of antiferromagnetic damping rate. Being effectively non-Hermitian, antiferromagnetic magnons can be used for quantum entanglement generation without introducing a third party like external parametric pumping.

Session Chair: Se Kwon Kim

Talk 6 [02:20 PM - 03:00 PM (Korea, Japan)] [01:20 AM - 02:00 PM (China, Singapore)]

Speaker: Satoru Hayami (The Univ of Tokyo)

Title: Skyrmion crystals in centrosymmetric magnets

Abstract: A magnetic skyrmion, which is characterized by a nontrivial topological spin texture in magnets, have been attracting much interest in condensed matter physics. Since the discovery of a skyrmion crystal, which corresponds to a periodic array of the skyrmion spin textures, in 2009, noncentrosymmetric magnets with the spin-orbit coupling have been good platforms of hosting the skyrmion crystals. Meanwhile, recent theoretical and experimental studies have clarified several different origins of the skyrmion crystals in centrosymmetric magnets by introducing the frustrated exchange interaction in localized magnets and the multiple-spin interaction arising from the spin-charge coupling in itinerant magnets. In the presentation, we discuss the stabilization mechanisms of the skyrmion crystals on the basis of the microscopic spin model with the symmetric and antisymmetric anisotropic interactions. We present important interactions and magnetic anisotropy to stabilize the square- and triangular-shaped skyrmion crystals in the ground state in centrosymmetric magnets.

Talk 7 [03:00 PM - 03:40 PM (Korea, Japan)] [02:00 AM - 02:40 PM (China, Singapore)]

Speaker: Kab-Jin Kim (KAIST)

Title: Phase-transition-induced large spin current generation and the universality class of skyrmion motion

Abstract: In this talk, I will discuss two topics which we recently obtained. First, I will present the large spin current generation induced by the magnetic-phase-transition. We demonstrate that during the metamagnetic transition of FeRh from antiferromagnetic to ferromagnetic state, the alloy pumps a large spin current into the adjacent layer. The burst of spin current is detected by measuring the real-time inverse-spin Hall-effect voltage. This voltage exceeds those recorded during conventional spin pumping by at least two orders of magnitude.

The second topic is the universality of thermally activated skyrmion motion. We investigate the dynamics of weakly driven magnetic skyrmions and compare its scaling law with the motion of a magnetic domain wall (DW) creep. We find that the skyrmion does not follow the scaling law of the DW creep in 2-dimensional space but instead shows a hopping behavior similar to that of the particle-like DW in 1-dimensional confinement. In addition, the hopping law satisfies even when a topological charge of the skyrmion is removed. The origin of this distinct scaling law will be discussed.

Talk 8 [04:00 PM - 04:40 PM (Korea, Japan)] [03:00 AM - 03:40 PM (China, Singapore)]

Speaker: Qiming Shao (HKUST)

Title: Spin-orbit torques with quantum materials and systems

Abstract: Ubiquitous smart devices and the internet of things create tremendous data every day, shifting computing diagrams towards data-driven. Traditional computers' computing and memory units are physically separated, which leads to substantial energy costs and time delays. Novel computer architectures bring computing and memory units together for data-intensive applications. These units preferably need to be fast, energy-efficient, scalable, and nonvolatile. We work on spin-orbit torque devices and employ quantum materials and systems to enable potentially unprecedented technological advances. The highest energy efficiency of magnetic memory requires the largest charge-to-spin conversion efficiency that allows the minimum power to manipulate the magnetization. We utilize topological insulators and two-dimensional materials and aim to generate giant and unconventional spin-orbit torques. To have the best scaling performance, we investigate emerging topological skyrmions in magnetic thin films, arguably the smallest spin texture in nature. We introduce first room temperature chiral spin interactions and topological Hall effect in magnetic insulator-based heterostructures. Besides, we demonstrate the magnetic dynamics of these ferrimagnetic insulators can be efficiently manipulated by spin-orbit torques from the heavy metal layer.

Talk 9 [04:40 PM - 05:20 PM (Korea, Japan)] [03:40 AM - 04:20 PM (China, Singapore)]

Speaker: Yan Zhou (CUHK)

Title: Topological spintronics

Abstract: Recently, tremendous attention has been focused on the continuous scaling of Moore’s law as well as the advanced non-von Neumann computing architecture. Spintronics may go beyond classical electronics and offer low power logic/computing components to further increase the performance of modern information and communication technologies meanwhile reducing the energy consumption. In particular, magnetic skyrmions – topologically non-trivial spin nanostructures, have been endowed with great expectations as promising candidates for next-generation spintronic device applications. However, there is a major roadblock for skyrmionics device applications – the skyrmion Hall effects, which may lead to skyrmions annihilation at the sample edge. In this talk, Dr. Yan Zhou will discuss his recent work of eliminating/suppressing the skyrmion Hall effects, which may overcome the main bottleneck of practical applications of skyrmionic racetrack memory and logic devices. In the last part of his talk, he will discuss some novel device concepts based on these intriguing topological spin textures (such as neuromorphic or skyrmionics computing etc).

Talk 10 [05:20 PM - 06:00 PM (Korea, Japan)] [04:20 AM - 05:00 PM (China, Singapore)]

Speaker: Anjan Soumyanarayanan (NUS)

Title: Creating and Manipulating Magnetic Skyrmions

Abstract: Magnetic skyrmions are topological spin structures emerging from the interplay of atomic-scale magnetic interactions. Their room temperature stability and tunability in multilayer films has spawned a fascinating research field witnessing rapid progress in fundamental science and device applications [1]. Practical technologies require nanoscale skyrmions stable under ambient conditions, along with electrical manipulation and detection capabilities within device configurations.

We begin by establishing a multilayer platform where skyrmion properties (e.g., size, density) can be smoothly tuned by modulating interfacial chiral interactions [2]. We further show that these interactions gradually induce transitions in key microscopic skyrmion characteristics and formation mechanism [3]. Next, we present a distinct thermodynamic marker associated with ZF skyrmion stability in films and nanostructures [4, 5]. We conclude with efforts to electrically write, delete, and move skyrmions in nanowire devices [6, 7].

References

[1] A. Soumyanarayanan et al., Nature (2016) 539, 509.

[2] A. Soumyanarayanan et al., Nature Materials (2017) 16, 898.

[3] X. Chen et al., Advanced Science (2021) 202103978.

[4] P. Ho et al., Physical Review Applied (2019) 11, 024064.

[5] A.K.C. Tan et al., Physical Review Materials (2020) 4, 114419.

[6] S. Je, D. Thian et al., Nano Letters (2021) 21(3), 1253.

[7] A.K.C. Tan, P. Ho et al., Nature Communications (2021) 12, 4252.