Sangkook Choi (KIAS): TBA

 

 

 

Moonjip Park (PCS IBS): Twisted bilayer magnet CrI3

Recent experiments with twisted bilayer materials have provided a versatile platform for the realization of exotic phases of matter. In this talk, we are going to expand the theory of moire systems to spin systems. Starting from the brief review of twisted bilayer graphene, we develop a concrete theory of twisted bilayer magnetism. Based on the first-principles calculations of two-dimensional honeycomb magnet CrI3, we construct the generic spin models that represent a broad class of twisted bilayer magnetic systems. Using the Monte-Carlo method, we discover a variety of non-collinear magnetic order that has been overlooked in previous theoretical and experimental studies. Finally, we show that the twisted magnets can be a promising candidate for the discovery of topological magnon excitations.

 

 

 

 

Changhee Sohn (UNIST): Honeycomb heterostructure for Kitaev quantum spin liquid

Kitaev quantum spin liquid (QSL) has attracted great attention because of its new physics beyond the classical Landau-Ginzberg-Wilson paradigm but also because of its relevance to topological quantum computation. However, realizing and utilizing Kitaev QSL in honeycomb lattices remain at a very early stage. The one of the major bottlenecks is the incompetence of synthesizing honeycomb heterostructures, as precise control of spin Hamiltonian is required for materializing Kitaev QSL. In this talk, we show our recent attempt utilizing heterostructure approaches to realize this exotic quntum phase. Successful synthesis of stoichiometric, single-phase, and epitaxial Na3Co2SbO6 and Cu3Co2SbO6 thin film will be presented. Spectroscopy and magnetic susceptibility measurement shows evidence of Kitaev physics in these Co honeycomb heterostructures.

 

 

 

Minsoo Kim (KHU): Electron quantum transport in graphene and its twisted superlattices

Twisted heterostructure of graphene multilayers provides a facile route for the study of topological properties and highly correlated phenomena. At very small twist angles of ~0.1°, twisted graphene exhibits a strain-accompanied lattice reconstruction resulting in submicron-size triangular domains with the standard, Bernal stacking. The domain boundary remains conductive due to a triangular network of topological one-dimensional states. First, I will present the electron quantum transport through this helical network and giant Aharonov-Bohm oscillations that reach in amplitude up to 50 % of resistivity and persist to temperatures above 100 K. On the other hand, the broken crystal symmetry in twisted monolayer-bilayer graphene allows higher control over the band structure. Here, I will describe the electron quantum transport characteristics of correlated insulating states at the twisted angle of ~1.2°. At half-filling, where two-electrons are filled per Moiré unit cell, the correlated insulating state exhibits the spin-polarized nature. I will also discuss a critical-current behavior in non-linear current-voltage characteristics in graphene and its superlattices, resembling those of superconductors. The criticality develops upon the velocity of electron flow reaching the Fermi velocity, where the carrier distribution is shifted far from its equilibrium.

 

 

 

 

Jaeyoon Choi (KAIST): Classifying coarsening dynamics in a quenched ferromagnetic condensate far from equilibrium

Understanding and classifying out-of-equilibrium dynamics in a closed quantum many-body system have been outstanding problems in modern physics. In this talk, we will introduce our experimental platform of strongly ferromagnetic spin-1 condensate [1] and recent experimental results on the universal coarsening dynamics after a quantum quench. Initially prepared polar condensate is quenched to easy-axis ferromagnetic phase by microwave dressing [2]. Right after the quench, we observe the emission of spin 1/-1 pairs due to dynamical instability [2]. After a long time, they form micro domains, which are coarse to form a larger domain as time evolves. We analyze spin correlation functions at various evolution times, which collapsed onto a single function after rescaling the domain length. The results are compared with numerical simulations, where the dynamics belong to the binary fluid universality class with its dynamical critical exponent z=3/2 [3].

[1] S.-J. Huh, K. Kim, K. Kwon, and J.-y. Choi, Phys. Rev. Research 2, 033471 (2020).

[2] K. Kim, J. Hur, S.-J. Huh, S. Choi, and J.-y. Choi, Phys. Rev. Lett 127, 043401 (2021).

[3] L. A. Williamson and P. B. Blakie, Phys. Rev. Lett. 116, 025301 (2016).

 

 

 

 

Hyukjoon Kwon (KIAS): Revealing quantum correlation functions without measurement back-action

 

 

 

 

Kwon Park (KIAS): Visualizing the Fractional Topological Order: From Fractional Chern Insulators to the Tao-Thouless State

 

 

 

 

Hyun-Yong Lee (KU): Variational Tensor Network Operator

 

 

 

 

Je-Geun Park (SNU): Spin dynamics and thermal Hall effect of Spin-orbit entangled Co compounds

 

 

 

 

 

Kwang-Yong Choi (SKKU): Kondo screening in a Majorana metal

Kondo impurities provide a nontrivial probe to unravel the underlying gauge and topological character of a quantum spin liquid. In the S=1/2 Kitaev model on the honeycomb lattice, Kondo impurities embedded in the spin-liquid host can be screened by binding them to gauge fluxes. Here, we report experimental signatures of metallic-like Kondo screening at intermediate temperatures in the Kitaev honeycomb material α-RuCl3 with dilute Cr (S=3/2) impurities. The linear temperature dependence of the magnetic specific heat shows the metallic transport of Majorana fermions. The static magnetic susceptibility, the muon Knight shift, and the muon spin-relaxation rate feature logarithmic divergence, a hallmark of the Kondo effect. This observation opens up new avenues for exploring uncharted Kondo physics in insulating quantum magnets.

 

 

 

 

 

Aaram Kim (DGIST): Vertex-based diagrammatic solver for quantum impurity models

 

 

 

 

 

Bohm Jung Yang (SNU): Correlated normal state fermiology and topological superconductivity in UTe2