visual
visual

세미나

  • HOME
  • >
  • 소식
  • >
  • 세미나

KAIST Physics Distinguished Lecture

2015.07.14 10:44

admin 조회 수:2495

날짜 2015-07-16 16:00 
일시 2015/07/16-07/17 
장소 E6-2, 1501 
연사 Sang-Wook Cheong (Rutgers Univ.) 

[Lecture1] Multiferroic vortices: why & how do they form?

 

2015/7/16 (THU) 4PM, Lecture Hall, College of Natural Sciences (1501, E6-2) /자연과학대학 공동강의실

Sang-Wook Cheong

Director, Rutgers Center for Emergent Materials, Rutgers University

 

 

Hexagonal REMnO3 (RE= rare earths) with RE=Ho-Lu, Y, and Sc, is an improper ferroelectric where the size mismatch between RE and Mn induces a trimerization-type structural phase transition, and this structural transition leads to three structural domains, each of which can support two directions of ferroelectric polarization. Six different types of domains in h-REMnO3 meet in cloverleaf arrangements that cycle through all possible configurations, Occurring in pairs, the cloverleafs can be viewed as vortices and antivortices, in which the cycle of domain configurations is reversed. Vortices and antivortices are topological defects: even in a strong electric field they won’t annihilate. These ferroelectric vortices/antivortices are found to be associated with intriguing collective magnetism at domain walls, reflecting the multiferroic nature of vortices.

 

The formation of these multiferroic vortices turns out to be analogous to the formation of cosmic strings right after big bag and also the unbinding of vortex loops in superfluid transition. We will discuss the exact nature of this proliferation process of multiferroic vortices.

 

 

[Lecture2] Hybrid Improper Ferroelectrics: Z4xZ2 domains with Z3 vortices

 

2015/7/17 (FRI) 11AM, Lecture Hall, College of Natural Sciences (1501, E6-2) / 자연과학대학 공동강의실

Sang-Wook Cheong

Director, Rutgers Center for Emergent Materials, Rutgers University

 

 

Utilizing trilinear coupling of two types of octahedron rotations, hybrid improper ferroelectricity has been theoretically predicted in double layered compounds such as (Ca,Sr,Ba)3(Mn,Ti,Sn,Zr,Ge)2O7. On the other hand, there exists little theoretical prediction on practical properties of the potentially-ferroelectric compounds such as ferroelectric transition temperature, switchability of polarization, and chemical phase stability. We have attempted to fabricate single crystals of some of these compounds, and examined the physical properties of the crystals with the aim of discovering new bulk ferroelectrics with switchable polarization at room temperature. We will discuss the results of our comprehensive experimental investigation.

Ordering of charge/spin/orbital degrees of freedom in complex materials accompanies domains and domain walls associated with the directional variants (Zm) and also antiphases (Zn). In hybrid improper ferroelectric (Ca,Sr,Ba)3(Mn,Ti,Sn,Zr,Ge)2O7, four directional variants with different polarization directions can exist, and each polarization domain has two degenerate antiphases. It turns out that the hybrid improper ferroelectrics tend to exhibit a Z4xZ2 domain structure with Z3 vortices. This can be compared with the Z2xZ3 domain structure with Z6 vortices in hexagonal REMnO3.

 

 

Host: Department of Physics, KAIST
Contact: Prof. Chan-Ho Yang (Ext.2513)

번호 날짜 장소 제목
76 2022-06-03 09:30  Online seminar  (Quantum-&Nano-Photonics Webinar) Seeing glass in a new light: reimagine chalcogenide photonics file
75 2022-06-10 11:00  Online seminar  Record-quality two-dimensional electron systems file
74 2022-03-18 11:00  Online seminar  (응집물리 세미나) Illuminating exotic states of matter: Raman spectroscopy as an experimental tool to characterize quantum spin liquids file
73 2021-05-14 14:30  Online seminar  Electrically tunable spin valve effect in vertical van-der-Waals magnetic tunnel junctions file
72 2021-07-29 14:00  Online seminar  Gravitationally Induced Dark Sector and Inflationary Dynamics file
71 2021-01-28 18:00  Online Seminar  Quantum metamaterials: concept, theory, prototypes and possible applications file
70 2021-06-11 14:30  Online seminar  Engineering sound waves and vibrations in multi-mode nanomechanical systems file
69 2021-06-11 16:00  Online seminar  Pseudogap in surface-doped black phosphorus file
68 2021-05-14 16:00  Online seminar  Spatial and temporal separation of environmental dephasing sources from solid-state quantum emitters file
67 2021-03-25 16:00  Online Seminar (Zoom)  Search for dark matter axion with Rydberg atoms file
66 2020-11-17 12:00  Online(Zoom)  Quantum- & Nano-Photonics" 세미나 시리즈 file
65 2021-04-02 14:30  Online(Zoom)  Quantum computing and entanglement generation using trapped ions and photons
64 2021-04-02 16:00  Online(Zoom)  Van der Waals heterostructures for orbital gating-based phototransistors and electronic spectroscopy
63 2020-11-26 16:00  Online(Zoom)  2020 가을학기 광학분야 특별세미나(Light Engineering Beyond the Diffraction Limit)
62 2019-06-12 15:00  Rm# 1323, E6-2  The relation between free and interacting fermionic SPT phases file
61 2019-08-19 10:00  Rm. 1322, E6-2  Tutorials on Multimode Quantum Optics in the Continuous Variable Regime file
60 2019-07-16 16:00  Rm. 1323 (E6-2)  2019 Physics Distinguished Lecture file
59 2019-08-14 16:00  Rm. 1323, E6  Quantum Optics, at the heart of quantum metrology and quantum information file
58 2019-08-27 16:00  Rm. 1323, E6  Critical current properties of Fe-based superconductors file
57 2019-03-21 16:00  RM. 1323, E6-2  Spring 2019: Physics Seminar Serises file