290S/290K Quantum Materials Seminar speakers Nathan Giles-Donovan and Yu-Ping Lin (both UC Berkeley) on Wednesday, September 14 at 2:00 pm in Physics South 402

Time/Venue Wednesday, September 14 at 2:00 pm PST in Physics South 402 (in person only)
Host Bob Birgeneau
Speaker  Nathan Giles-Donovan (Birgeneau Group)
Title Characterization of Coupled Orders in Multiferroic Dielectric Oxides
Abstract  In general, coupling and competition of different orders result in materials which exhibit many intriguing properties and can result in thought-provoking physics. Materials with coupled ferroic orders are central to developing transduction devices due to their ability to convert between different forms of energy. This is seen in both the case of piezoelectric/ferroelectrics which are used in ultrasonic applications and in multiferroics which have the potential to enable hybrid magnetoelectric devices independently controllable using magnetic and electric fields. However, due to this necessary and often complex interplay of orders, the microscopic mechanisms present in these materials are typically not well-understood. In this talk I will present some research highlights from a study into the fundamental behaviour of novel ferroelectric and multiferroic materials. Firstly, polarized neutrons were used to characterise the magnetic ground state of Cu3Nb2O8, addressing an issue in the literature regarding the ordering mechanism. Secondly, muon techniques were used to study the magnetic structure and composition of the relaxor Pb(Fe1/2Nb1/2)O3 which provided insight into the role of disorder and random fields.
Speaker  Yu-Ping Lin (CMT Group)
Title  Band geometry from position-momentum duality
Abstract  I propose a simple viewpoint of band geometry by analogizing to the free-particle theory. Specifically, I deduce that the quantum metric trace is a momentum-space “dual kinetic energy” under the Berry gauge field. This “position-momentum duality” allows us to borrow the knowledge of free-particle motion under the magnetic field. The possibility of “dual energy quantization” arises in the quantum metric trace. Although a simple quantization rule is generally unavailable due to the nonuniform Berry flux, a lowest-Landau-level interpretation applies to the lower bound by the Berry flux. I further present some examples of interesting quantization rules at the band crossings with approximate rotation symmetries.

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