KAIST Physics Distinguished Lecture
2015.07.14 10:44
장소 | E6-2, 1501 |
---|---|
일시 | 2015/07/16-07/17 |
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)
댓글 0
번호 | 일시 | 장소 | 연사 | 제목 |
---|---|---|---|---|
185 | 2015/11/23, 1:30PM | E6-2, #1323 | Dr. Michael Park (Stanford University) | What's Beyond the Standard Model? Lessons from Run I and what might come in Run II |
184 | 2015/11/28, 10AM | E6-2, #1323 | Dr. Suyong Jung (Korea Research Institute of Standards and Science) | Electron Tunneling Spectroscopy of Single and Bilayer Graphene with Hexagonal Boron Nitride as Tunneling Barrier |
183 | 2015/12/01, 4PM | E6-2, #1323 | Dr. Yeong Kwan Kim(Lawrence Berkeley National Laboratory, USA) | Introducing extra dimensions to spectroscopic studies of advanced quantum materials |
182 | 2015/12/11, 1:30PM | E6-2, #1323 | Dr. KwangYong Choi (Chung-Ang University) | Quantum spin liquid in the 1/3 depleted triangular lattice Ba3(Ru1-xIrx)Ti2O9 |
181 | 2015/12/11, 3:45PM | E6-2, #1323 | Dr. Ji Hun Sim (POSTECH) | Dynamical mean field theory studies on heavy fermion system |
180 | 2016/1/11, 4PM | E6-2, #1323 | Dr. B.J.Kim (Max Planck Institute for Solid State Research) | Mott Physics in the Strong Spin-Orbit Coupling Regime |
179 | 2016/1/26, 2PM | E6-2, #1323 | Dr. Sergei V. Kalinin (Center for Nanophase Materials Sciences, Oak Ridge National Laboratory) | Electrochemistry on Nano- and Atomic Levels: Scanning Probe Microscopy Meets Deep Data |
178 | 2016/09/29-12/13 | E6-2, #1323 | Sangyoon Han 외 |
2016 Fall, Physics Seminar Serises
![]() |
177 | Jun 24 (Mon) 11:00 | E6-2, #1323 | Dr. Henning Schomerus |
Topological photonic anomalies
![]() |
176 | July 25(Thur.),4:00PM | E6-2, #1323 | Prof.Bohm-Jung Yang |
Band topology of twisted bilayer graphene
![]() |
175 | July 31(Wed.)/ 16:00 | E6-2, #1323 | Dr. Ivan Borzenets |
Features of ballistic superconducting graphene
![]() |
174 | 2015/08/03,10:30AM | E6-2, #1323 (Seminar Room) | Dr. Jonghee Yoo (Fermi National Accelerator Laboratory, USA ) | Axion Search |
173 | 2015/10/23, 3PM | E6-2, #5318 | Dr. Helmut Soltner (Forschungszentrum Juelich) | Development of a Rogowski Coil as a new beam position monitor |
172 | 2015/11/06, 4:30 PM | E6-2, #5318 | Dr. Youngkuk Kim (University of Pennsylvania) | Topological Dirac line nodes in centrosymmetric semimetals |
171 | February 12(Web.) | E6-2, #5318 | Prof. Kunio Kaneta |
From inflation to new weak-scale
![]() |
170 | 2015/07/16, 4PM | E6-2, 1318 | Dr. Kyunghan Hong(MIT) | Next-generation ultrafast laser technology for nonlinear optics and strong-field physics |
» | 2015/07/16-07/17 | E6-2, 1501 | Sang-Wook Cheong (Rutgers Univ.) | KAIST Physics Distinguished Lecture |
168 | 2016/03/11-06/09 | E6-2, 1501 외 | 박권(KAIS) 외 |
Physics Seminar Serises : 2016 Spring
![]() |
167 | Jul 3rd, 2019 (Wed) | E6-2, 2501 | Kyung Soo Choi |
Many-body quantum electrodynamis (QED) with atoms and photons: A new platform for quantum optics"
![]() |
166 | June 14 (THU), 10:00 AM | E6-2, 2nd fl. #2502 | Prof. Kenji Toyoda |
Phonons and polariton-like particles in trapped ions for quantum computation and quantum simulation
![]() |