visual
visual

세미나

  • HOME
  • >
  • 소식
  • >
  • 세미나

KAIST Physics Distinguished Lecture

2015.07.14 10:44

admin 조회 수:2498

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
166 2019-08-16 14:00  E6 Room(#1323)  Multiferroic and Magnetoelectric Effects by Tailoring Interfacial Chemistry and Physics in Correlated Oxides file
165 2019-08-14 16:00  Rm. 1323, E6  Quantum Optics, at the heart of quantum metrology and quantum information file
164 2023-08-29 16:00  E6-2, #2502  [High Energy Theory Seminar] Towards string loop corrections in Calabi-Yau orientifold compactifications.
163 2019-08-27 16:00  Rm. 1323, E6  Critical current properties of Fe-based superconductors file
162 2018-08-01 11:00  양분순 빌딩 (E16-1) 207호  Future of AI: Is the brain a computer? file
161 2022-08-18 10:00  E6-1 #1323  Disorder-driven phase transition in the second-order non-Hermitian skin effect
160 2022-08-17 11:00  E6-6 #118호  Robust Hamiltonian Engineering of Large Quantum Systems (큰 양자시스템의 견고한 해밀토니안 엔지니어링)
159 2022-08-12 10:00  E6-1 #1323  Twisted Bilayer Magnets file
158 2022-08-12 10:00  E6-1 #1323  Twisted Bilayer Magnets file
157 2022-08-09 14:00  KI building (E4), Lecture Room Red (B501)  Quantum biology in fluorescent protein: a new model system to study quantum effects in biology file
156 2022-08-08 14:00  E6-2 #2502  Classical Shadow Tomography for Analog Quantum Simulators
155 2016-08-04 14:30  KAIST Natural Science Building (E6-5), EDU 3.0 Room(1st fl.)  Relational Logic (with applications to Quantum Mechanics, String Theory, Cosmology, Neutrino Oscillations, Statistical Mechanics)
154 2017-08-31 14:00  #5318(E6-2. 5th fl.)  “Berry phase and nonlinear response: photocurrent in noncentrosymmetric insulators and Weyl semimetals” file
153 2022-08-01 10:00  E6 #1501 & Zoom  [Update 세미나 영상] James Webb Space Telescope & OTE Commissioning
152 2020-08-17 20:00  Zoom webinar  Using magnetic tunnel junctions to compute like the brain file
151 2017-08-16 16:00  #1322 (E6-2. 1st fl.)  Phonon-driven spin-Floquet valleytro-magnetism file
150 2020-08-25 20:00  Zoom webinar  KAIST Global Forum for Spin and Beyond (Second Forum) file
149 2023-08-24 11:00  E6, Rm#1323  Advancing magnonic metamaterials: spin waves in nanomagnetic arrays
148 2023-08-23 16:00  E6-2, #1322  [High Energy Theory Seminar] A spacetime tensor network for AdS3/CFT2
147 2023-02-20 16:00  Room 1323, KAIST Natural Sciences Lecture Hall(E6)  Physics of ferromagnet/superconductor junctions