[Monthly Seminar] (March 8, 2024, 11:00~12:30) Youngwook Kim & Dongseok Suh
- 극한양자기능물질연구센터
- Hit334
- 2024-03-05
March 8, 2024, 11:00~12:30, Samsung Library 7F Creative Learning Room, SKKU
[Talk 1]
Proximity-Induced Symmetry Engineering in 2D Materials
Youngwook Kim (DGIST, Korea)
The quantum Hall effect, a prominent phenomenon in two-dimensional electron systems, emerges under the influence of a strong magnetic field and is renowned for its quantized Hall conductance and distinctive topological characteristics. In this study, we focus on the engineering of graphene systems through the stacking of diverse materials, including graphene itself, Kitaev quantum spin liquids, and two-dimensional antiferromagnetic substances, to observe novel quantum Hall states. Initially, we demonstrate transport results from graphene proximitized with RuCl3, which induces significant heavy hole doping in graphene, reflecting a robust interfacial interaction between graphene and RuCl3. Additionally, we disclose the detection of robust spin-associated quantum Hall states, which emerge from reduced interfacial interactions within similar heterostructures.
Contrary to the typical quantum Hall effect, which is observed in the linear response regime due to broken time-reversal symmetry from an external magnetic field or intrinsic magnetic orders as per Onsager’s reciprocal theorem, the nonlinear Hall effect—characterized by a Hall voltage that nonlinearly depends on perpendicular driving currents—stems from disrupted inversion symmetry and reduced crystal symmetries. This effect, deeply linked to the Berry curvature dipole moment, offers novel perspectives for exploring the topological properties of emergent quantum material phases. In our research, the nonlinear Hall effect is observed in graphene when symmetry is intentionally disrupted through proximity effects induced by molecular beam epitaxy-grown a-plane ZnO, a substance with inherent inversion symmetry breaking and a single mirror line along the crystal's a-axis. Our angle-resolved electrical measurements highlight that the second harmonic transverse Hall voltage reaches its maximum when the bias current aligns perpendicularly to the mirror axis and disappears when parallel.
[Talk 2]
Review of the recent reports combining graphene's quantum Hall effect and the Andreev reflection by the superconducting electrode
Dongseok Suh (Dept. of Physics, Ewha Womans University, Korea)
This short presentation introduces the recent literatures studying graphene in the quantum Hall regime interfaced with superconducting electrodes. The occurrence of Andreev reflection in this context brings forth fascinating physical behaviors due to the unique combination of edge transport in graphene within the quantum Hall state. Moreover, the interplay of counter-propagating charge states in this setup hints at connections to emergent Majorana physics. The presentation will focus on the experimental side of these studies and aims to foster discussions with the audience for further brain-storming idea.