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일시: 8월 5일(금) 오전 10:30 ~ 12:00

장소: 31동 2층 물리학과 라운지세미나실

연사: 김  세  권 박사님 (UCLA)

Title: Phase Slips in Superfluid Spin Transport in Magnetic Wires

○ Abstract:

In this talk, we will discuss two types of mechanisms responsible for intrinsic resistance in superfluid spin transport in easy-plane magnetic wires: thermally-activated and quantum phase slips. First, we theoretically study thermally-activated phase slips within the stochastic Landau-Lifshitz-Gilbert phenomenology, which runs parallel to the Langer-Ambegaokar-McCumber-Halperin theory for thermal resistances in superconducting wires [1]. To that end, we start by obtaining the exact solutions for free-energy minima and saddle points. We provide an analytical expression for the phase-slip rate in the zero spin-current limit, which involves detailed analysis of spin fluctuations at extrema of the free energy. 

Secondly, we theoretically investigate effects of quantum fluctuations on superfluid spin transport through easy-plane quantum antiferromagnetic spin chains in the large-spin limit [2]. Quantum fluctuations result in the decaying spin supercurrent by unwinding the magnetic order parameter within the easy plane, which is referred to as phase slips. We show that the topological term in the nonlinear sigma model for the spin chains qualitatively differentiates decaying rate of the spin supercurrent between integer and half-odd-integer spin chains. We propose an experimental setup for a magnetoelectric circuit, in which both phase slips can be inferred by measuring nonlocal magnetoresistance.

[1] S. K. Kim, S. Takei, and Y. Tserkovnyak, Phys. Rev. B \textbf{93}, 020402(R) (2016)

[2] S. K. Kim and Y. Tserkovnyak, Phys. Rev. Lett. \textbf{116}, 127201 (2016)

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