物理工学コースからのおしらせ

物理工学ユニットでは、以下のように談話会を 対面形式で開催させて頂きます。

日時：　2025年9月11日（木）10：30 -
場所：　総合研究棟　W202室

講演者：Dr. Marvin A. Weiss (University of Konstanz, Germany)
演題：Ultrafast Spin Fluctuations in the Antiferromagnet Sm_0.3Er_0.7FeO₃ Revealed by Femtosecond Noise Correlation Spectroscopy

概要：
Although often regarded as detrimental, fluctuations can carry valuable information about the fundamental properties and dynamics of the materials in which they arise. In magnetic systems, random thermal fluctuations of collective spin waves - known as magnons - naturally occur and can influence a multitude of different physical phenomena.
Directly accessing these fluctuations is essential for understanding such fundamental processes, and in the case of antiferromagnets, for advancing the design of nextgeneration spintronic devices. However, detecting intrinsic spin fluctuations in antiferromagnets remains challenging due to their extremely small amplitude and ultrafast dynamics.
In this talk, I will introduce two-color femtosecond noise correlation spectroscopy (FemNoC), a technique designed to overcome this limitation. FemNoC uses pairs of ultrashort laser pulses at two wavelengths, separated by a variable time delay Δt, to detect subtle fluctuations in light polarization caused by transient spin noise. By crosscorrelating the polarimetric signals of individual laser pulses, the method can directly resolve ultrafast, stochastic spin fluctuations with femtosecond precision.
Applying FemNoC to the antiferromagnet Sm_0.3Er_0.7FeO₃ near its spin-reorientation transition - where the spin lattice rotates by 90° - revealed two key findings: 1. a pronounced enhancement of quasi-ferromagnetic spin-wave fluctuations near the transition, and 2. the first observation of ultrafast stochastic spin switching (random telegraph noise, RTN) on picosecond timescales, representing the fastest RTN process recorded to date.

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世話人：片山郁文