visual
visual

세미나

  • HOME
  • >
  • 소식
  • >
  • 세미나

KAIST Physics Distinguished Lecture

2015.07.14 10:44

admin 조회 수:1493

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)

번호 일시 장소 연사 제목
공지 2019/09/18 - 12/5  Seminar Room #1323  Prof. David Schuster and etc.  Fall 2019: Physics Seminar Serises
공지 2019/09/02 - 12/09  Seminar Room 1501  이호성 박사 (한국표준과학연구원) and etc.  Fall 2019: Physics Colloquium
133 Sep. 29th(Thu), 4PM  E6-2 #1323 (1st floor)  Dr. Sangyoon Han, Department of Physics, KAIST  Large-scale Silicon Photonic MEMS Switches
132 Sep. 02(Fri) 4:00 PM  E6-2(1st fl) #1323  Dr. Yong-Joo Doh, Department of Physics and Photon Science, GIST  Quantum Electrical Transport in Topological Insulator Nanowires
131 Sep. 02(Fri) 2:30 PM  E6-2(1st fl.), #1323  Dr. Yong-Hyun Kim,Graduate School of Nanoscience and Technology, KAIST  Nanoscale Thermal Physics: Seebeck Effect and Nanoscale Friction
130 Jun 28, 14:00  E6-2, #1322  Dr. Bongjae Kim, Dr. Sooran Kim, Dr. Jeongwoon Hwang  1st Research-exchange meeting of computational material physics file
129 2015/11/10, 4PM  E6-2, #1323  Dr. Woosuk Bang (Physics division, Los Alamos National Laboratory)  Rapid heating of matter using high power lasers
128 2015/11/19, 4PM  E6-2, #1323  Dr. Daesu Lee (University of Wisconsin-Madison)  Emergent Collective Phenomena and Functions at Reduced Dimensions
127 2015/12/09, 2PM  E6-2, #1323  Arjun G. Yodh (University of Pennsylvania)  SWELLABLE COLLOIDAL PARTICLES ARE SWELL
126 2015/12/02, 4PM  E6-2, #1323  Dr. Dae-Jeong Kim (Dept. of Physics and Astronomy, University of California, Irvine)  Samarium Hexaboride: Is it a Topological insulator?
125 2015/12/03, 4PM  E6-2, #1323  Dr. Sang-Yun Lee (3rd institute of Physics, University of Stuttgart, Germany)  Hybrid solid state spin qubits in wide bandgap semiconductors
124 2015/11/24, 4PM  E6-2, #1323  Dr. Kab-Jin Kim (Institute for Chemical Research, Kyoto University, Japan)  Topology-based understanding of spin dynamics in inhomogeneously magnetized systems
123 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
122 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
121 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
120 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
119 2015/12/11, 3:45PM  E6-2, #1323  Dr. Ji Hun Sim (POSTECH)  Dynamical mean field theory studies on heavy fermion system
118 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
117 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
116 2016/09/29-12/13  E6-2, #1323  Sangyoon Han 외  2016 Fall, Physics Seminar Serises file
115 Jun 24 (Mon) 11:00  E6-2, #1323  Dr. Henning Schomerus  Topological photonic anomalies file
114 July 25(Thur.),4:00PM  E6-2, #1323  Prof.Bohm-Jung Yang  Band topology of twisted bilayer graphene file