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
206 2018-02-12 15:00  #C303, (Creation Hall 3F, KAIST Munji Campus)  The recent result of XMASS Experiment
205 2017-02-01 14:00  #1323(E6-2. 1st fl.)  Quantum electron optics using flying electrons
204 2019-12-05 16:00  #1323, E6-2  Subwavelenth Photonic Devices: From Single Photon Sources to Solar Cell file
203 2019-12-03 16:00  #1323, E6-2  Toward Quantum Materials with Correlated Oxides file
202 2019-12-27 15:00  E6-2,#5318  The superconducting order parameter puzzle of Sr2RuO4 file
201 2020-12-02 10:00  Zoom  Recent progress in Axion Dark Matter eXperiment (ADMX) technology file
200 2019-12-18 16:00  #1323, E6-2  Road to Higher Tc Superconductivity file
199 2019-12-13 13:30  #1323, E6-2  Biophysics Mini-symposium at KAIST file
198 2019-12-13 13:00  #2501, E6-2  Computational Material Designs: Current Status and Future Directions file
197 2023-12-14 16:00  CAPP Seminar Room C303, Creation Hall, KAIST Munji Campus  Superconducting qubits for large-scale quantum computers file
196 2020-12-09 10:00  Zoom  Searching for the QCD axion with the ARIADNE experiment file
195 2020-12-23 10:00  Online  Online workshop for Quantitative Phase Imaging file
194 2020-12-10 13:55  Zoom  Consistency of Boltzmann equation and light dark matter from inflaton decay
193 2016-12-09 16:00  #1323(E6-2. 1st fl.  Shift Charge and Spin Photocurrents in Dirac Surface States of Topological Insulator
192 2016-12-09 13:30  #1323(E6-2. 1st fl.)  Entanglement area law in strongly-correlated systems
191 2022-12-09 11:00  E6-2 #1323  [Update 세미나영상](응집물리 세미나) Single-shot measurements of strongly-correlated artificial molecular levels in semiconductor quantum dots file
190 2016-12-8 16:00  #1323(E6-2. 1st fl.)  Dynamical Resonance between Two Optical Cavities via Optomechanical Oscillator
189 2022-12-07 16:00  E6-2 #1323  (광학분야 세미나) Non-Hermitian physics and non-Hermitian singularity
188 2018-12-07 16:00  E6-2. 1st fl. #1323  Novel probes of interacting electrons in 2D systems file
187 2018-12-07 14:30  E6-2. 1st fl. #1323  Spin generation from heat and light in metals file