• HOME
  • >
  • 소식
  • >
  • 세미나

KAIST Physics Distinguished Lecture

2015.07.14 10:44

admin 조회 수:2371

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 2023-02-27 12:00  E6-1 #1501  2023 봄학기 콜로키움 전체 일정
공지 2023-03-16 16:00  E6-2 #1323  2023 봄학기 광학분야 및 응집물리 특별세미나 전체 일정
379 2020-12-10 13:55  Zoom  Consistency of Boltzmann equation and light dark matter from inflaton decay
378 2016-09-05 16:00  Natual Scien Bldg.(E6)m #1501  Physics Colloquium : 2016 Fall file
377 2021-01-28 15:00  Zoom  Topological Transport of Deconfined Hedgehogs in Magnets file
376 2018-12-26 16:00  E6-1. 3rd fl. #3434  Informal Workshop on Topology and Correlation file
375 2021-06-22 17:00  Zoom webinar  Spintronics meets Quantum Materials file
374 2021-06-08 10:00  Zoom webinar  Photonic crystal devices for sensing file
373 2020-09-14 17:30  Zoom webinar  KAIST Global Forum for Spin and Beyond (Third Forum) file
372 2022-11-03 13:00  E6-2 #1323  [High-Energy Theory Seminar] Supersymmetric observables via Fermi-gas method
371 2019-07-08 14:00  E6, #1322  Ultrabroadband squeezed pulses and their relation to relativity file
370 2023-02-20 17:00  KI building (E4), Lecture Room Red (B501)  (Optics Seminar) Neural Holography for Next generation Virtual and Augmented Reality Displays file
369 2022-06-23 11:00  E6 Room(#1322)  JILA’s search for the electron’s Electric Dipole Moment (eEDM) to probe physics beyond the standard model file
368 2022-01-11 15:00  E6 #1501  Ultrafast optical studies on CDW collective modes of the Weyl-CDW (TaSe4)2I file
367 2020-02-20 16:00  #1323, E6-2  Unconventional superconductivity in the locally non-centrosymmetric heavy-fermion CeRh2As2 file
366 2022-12-13 11:00  E6-2 #1322  Art of thin film engineering toward topological quantum computation file
365 2016-09-29 16:00  E6-2, #1323  2016 Fall, Physics Seminar Serises file
364 2023-01-11 11:00  E6-2 #1323  Directly proving magnetoelastic coupling in a soft ferromagnet using Lorentz 4D-STEM file
363 2021-11-02 16:00  자연과학동(E6-2) #1323  Metrology of Band Topology via Resonant Inelastic X-ray Scattering file
» 2015-07-16 16:00  E6-2, 1501  KAIST Physics Distinguished Lecture
361 2017-11-28 16:00  #1323 (E6-2. 1st fl.)  Physics after the lab and the desk: Your work in PRL file
360 2022-04-15 11:00  Online seminar  (응집물리 세미나) First-principles studies of polar oxides and their applications file