visual
visual

세미나

  • HOME
  • >
  • 소식
  • >
  • 세미나

KAIST Physics Distinguished Lecture

2015.07.14 10:44

admin 조회 수:7925

날짜 2015-07-16 16:00 
연사  
장소 E6-2, 1501 

[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 연사 제목
공지 2025-02-24 16:00    2025년 봄학기 콜로키움 안내
공지 2025-02-27 16:00    2025년 봄 물리학과 특별세미나 (광학/응집물리 분야)
254 2022-04-25 16:00    Ultrafast electron beam, a tool to explore the nanoscopic world of materials(우리말강의)
253 2022-04-28 16:00    (광학분야 특별세미나)Adiabaticity and symmetry in optical waveguide design
252 2022-05-02 16:00    What can we learn from the history of science and technology?(우리말강의)
251 2022-05-09 16:00    Searching for new electronic properties in correlated material flatland
250 2022-05-10 16:00    (광학분야 특별세미나)Testing quantum thermodynamics using quantum optics
249 2022-05-11 16:00    Gravity as a phenomenon in quantum dynamics
248 2022-05-12 16:00    New frontiers of electroweak physics at the LHC
247 2022-05-13 14:30    Topological Superconducting Spintronics Towards Zero-Power Computing Technologies file
246 2022-05-13 16:00    High-fidelity iToffoli gate for fixed-frequency superconducting qubits file
245 2022-05-16 16:00    Design synthetic topological matter with atoms and lights
244 2022-05-18 16:00    Geometry, Algebra, and Quantum Field Theory
243 2022-05-19 15:00    (광학분야 특별세미나)Development of a multimodal optical system for improved disease diagnosis
242 2022-05-19 15:00    (광학분야 특별세미나)Development of a multimodal optical system for improved disease diagnosis
241 2022-05-19 16:00    Chasing Long Standing Neutrino Anomalies with MicroBooNE
240 2022-05-20 11:00    (응집물리 세미나) Exploration of new polymorphs in van der Waals crystals
239 2022-05-23 16:00    Novel electronic transport in topological van der Waals magnets
238 2022-05-25 14:00    Atomic-level insights into ferroelectric switching and preferred orientation of ultrathin hafnia file
237 2022-05-25 16:00    Uncovering New Lampposts for Dark Matter: Continuum or Conformal
236 2022-05-26 16:00    (광학분야 특별세미나)Topological photonic devices
235 2022-05-27 11:00    Current Status and Future Plans of ADMX file