visual
visual

세미나

  • HOME
  • >
  • 소식
  • >
  • 세미나

KAIST Physics Distinguished Lecture

2015.07.14 10:44

admin 조회 수:2355

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
공지 2022-11-25 11:00  E6-2 #1323  [Update 세미나영상](응집물리 세미나) DMFT+ NRG: From models to real materials, from local to nonlocal correlations
100 2020-09-22 09:30  Zoom webinar  Physics and applications of soliton microcombs(Quantum- & Nano-Photonics) file
99 2017-11-08 13:00  #5318 (E6-2. 5th fl.)  “Emergent exotic quasiparticles in quantum spin liquids” file
98 2017-09-13 16:00  #1323 (E6-2. 1st fl.)  An Introduction to Quantum Spin Liquids file
97 2017-09-12 16:00  #1323 (E6-2. 1st fl.)  Exact Solution for the Interacting Kitaev Chain at Symmetric Point file
96 2018-05-17 13:30  E6-2. 1st fl. #1323  Quantum Spin Liquid in Kitaev Materials file
95 2015-10-23 10:30  E6, #1501  How to write a good scientific paper[Open lecture series]
94 2020-12-23 10:00  Online  Online workshop for Quantitative Phase Imaging file
93 2017-04-06 16:00  IBS CAPP seminar room, Creation Hall (3F), KAIST Munji Campus  For whom the Belle tolls
92 2016-11-01 14:30  Seminar Room #1323(E6-2)  Search for dark sector particles in the B-factory experiments
91 2015-10-16 16:00  E6-2. 2nd fl. #2501  Fluctuations of entropy production in partially masked electric circuits
90 2019-07-25 16:00  E6-2, #1323  Band topology of twisted bilayer graphene file
89 2019-09-18 16:00  #1323, E6-2  Exploring Synthetic Quantum Matter in Superconducting Circuits file
88 2017-04-27 16:00  Seminar Room(#1323, E6-2)  반도체 양자점을 이용한 단광자 광원
87 2022-04-15 11:00  Online seminar  (응집물리 세미나) First-principles studies of polar oxides and their applications file
86 2017-11-28 16:00  #1323 (E6-2. 1st fl.)  Physics after the lab and the desk: Your work in PRL file
» 2015-07-16 16:00  E6-2, 1501  KAIST Physics Distinguished Lecture
84 2021-11-02 16:00  자연과학동(E6-2) #1323  Metrology of Band Topology via Resonant Inelastic X-ray Scattering file
83 2023-01-11 11:00  E6-2 #1323  Directly proving magnetoelastic coupling in a soft ferromagnet using Lorentz 4D-STEM file
82 2016-09-29 16:00  E6-2, #1323  2016 Fall, Physics Seminar Serises file
81 2022-12-13 11:00  E6-2 #1322  Art of thin film engineering toward topological quantum computation file