visual
visual

세미나

  • HOME
  • >
  • 소식
  • >
  • 세미나

KAIST Physics Distinguished Lecture

2015.07.14 10:44

admin 조회 수:2547

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
219 2024-01-16 16:00  E6-2, #2502  [High Energy Theory Seminar] Towards quantum black hole microstates
218 2024-03-27 16:00  E6-2, #2502  [High Energy Theory Seminar] The Callan Rubakov Effect
217 2024-05-14 16:00  E6-2, #2502  [High Energy Theory Seminar] Minimal Production of Prompt Gravitational Waves during Reheating.
216 2024-05-29 16:00  E6-2, #2502  [High Energy Theory Seminar] Amplitudes Meet Cosmology: From Inflation to the Large-Scale Structure
215 2023-06-01 16:00  E6-2, #5301  Hall viscosity and topological phenomena
214 2023-11-22 10:00  E6-2, #5301 & zoom  [High Energy Theory Seminar] Exact Quantum Algorithms to Recognize Quantum Phases of Matter
213 2015-10-23 15:00  E6-2, #5318  Development of a Rogowski Coil as a new beam position monitor
212 2015-11-06 16:30  E6-2, #5318  Topological Dirac line nodes in centrosymmetric semimetals
211 2020-02-12 13:00  E6-2, #5318  From inflation to new weak-scale file
210 2015-07-16 16:00  E6-2, 1318  Next-generation ultrafast laser technology for nonlinear optics and strong-field physics
» 2015-07-16 16:00  E6-2, 1501  KAIST Physics Distinguished Lecture
208 2016-03-11 13:30  E6-2, 1501 외  Physics Seminar Serises : 2016 Spring file
207 2019-07-03 15:00  E6-2, 2501  Many-body quantum electrodynamis (QED) with atoms and photons: A new platform for quantum optics" file
206 2018-06-14 10:00  E6-2, 2nd fl. #2502  Phonons and polariton-like particles in trapped ions for quantum computation and quantum simulation file
205 2015-10-15 10:00  E6-2, 5th fl. #5318  Development of Large-Bore, High Field Magnets at the NHMFL
204 2015-10-16 15:00  E6-2, 5th fl. #5318  High Magnetic Fields to Probe the sub-eV range of Particle/Astroparticle Physics - From the OSQAR experiments at CERN up to new perspectives at LNCMI-Grenoble
203 2017-12-15 09:20  E6-2, Lecture Room #1323  Workshop on Magnetism in Unconventional Superconductors 개최 file
202 2016-04-06 15:30  E6-2, RM #1323  Superconducting Quantum Interference Devices for Precision Detection
201 2024-04-11 16:00  E6-2, Rm#1323  Theoretical Studies of the Electric Field Induced Thermal Hall Effect in the Quantum Dimer Magnets XCuCl3 (X = Tl, K)
200 2023-12-08 10:30  E6-2, Rm#2502  Novel transport phenomena in insulators