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Using light to control the properties of quantum materials has become a central theme in modern condensed matter physics. This approach has enabled the discovery of a variety of light-induced phases, including superconductivity (Mitrano et al., Nature 530(7591):461–464, 2016), ferroelectricity (Nova et al., Science 364(6445):1075–1079, 2019; Li et al., Science 364(6445):1079–1082, 2019), magnetism (McLeod et al., Nature Mater. 19(4):397–404, 2020; Disa et al., Nature Phys. 16(9):937–941, 2020; Nature 617(7959):73–78, 2023), and charge density waves (Kogar et al., Nature Phys. 16(2):159–163, 2020). However, a key limitation of many of these photoinduced states is their transient nature, that they often return to equilibrium states almost immediately after the light source is turned off, posing challenges for practical applications. In this chapter, we explore a case where light can induce a new long-lived magnetic state. Specifically, we use intense terahertz (THz) pulses to generate a metastable magnetization in the van der Waals antiferromagnet FePS \({ }_3\) , with a lifetime exceeding 2.5 milliseconds, orders of magnitude longer than typical ultrafast processes. Remarkably, this metastable state becomes more stable as the system approaches the antiferromagnetic transition temperature. This behavior suggests that critical fluctuations, which become prominent near phase transitions, play a crucial role in sustaining the induced magnetization. To understand the microscopic mechanism, we combine first-principles calculations with classical Monte Carlo and spin dynamics simulations. Our analysis reveals that the excitation of a specific phonon mode alters the magnetic exchange couplings in a way that energetically favors a weakly magnetized ground state, particularly near the Néel temperature. Moreover, the presence of strong critical fluctuations near this transition point enhances both the magnitude and lifetime of the induced magnetic state. These findings demonstrate a non-thermal pathway for tuning magnetic order in layered materials using terahertz light. More broadly, they highlight the potential of targeting regions near critical points, where order parameter fluctuations are enhanced, to stabilize long-lived, hidden quantum states.

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THz Field-induced Metastable Magnetization Near Criticality in FePS \({ }_3\)

  • 章节

  • 发表日期：

    2025年

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  • Batyr Ilyas

摘要

Using light to control the properties of quantum materials has become a central theme in modern condensed matter physics. This approach has enabled the discovery of a variety of light-induced phases, including superconductivity (Mitrano et al., Nature 530(7591):461–464, 2016), ferroelectricity (Nova et al., Science 364(6445):1075–1079, 2019; Li et al., Science 364(6445):1079–1082, 2019), magnetism (McLeod et al., Nature Mater. 19(4):397–404, 2020; Disa et al., Nature Phys. 16(9):937–941, 2020; Nature 617(7959):73–78, 2023), and charge density waves (Kogar et al., Nature Phys. 16(2):159–163, 2020). However, a key limitation of many of these photoinduced states is their transient nature, that they often return to equilibrium states almost immediately after the light source is turned off, posing challenges for practical applications. In this chapter, we explore a case where light can induce a new long-lived magnetic state. Specifically, we use intense terahertz (THz) pulses to generate a metastable magnetization in the van der Waals antiferromagnet FePS \({ }_3\) , with a lifetime exceeding 2.5 milliseconds, orders of magnitude longer than typical ultrafast processes. Remarkably, this metastable state becomes more stable as the system approaches the antiferromagnetic transition temperature. This behavior suggests that critical fluctuations, which become prominent near phase transitions, play a crucial role in sustaining the induced magnetization. To understand the microscopic mechanism, we combine first-principles calculations with classical Monte Carlo and spin dynamics simulations. Our analysis reveals that the excitation of a specific phonon mode alters the magnetic exchange couplings in a way that energetically favors a weakly magnetized ground state, particularly near the Néel temperature. Moreover, the presence of strong critical fluctuations near this transition point enhances both the magnitude and lifetime of the induced magnetic state. These findings demonstrate a non-thermal pathway for tuning magnetic order in layered materials using terahertz light. More broadly, they highlight the potential of targeting regions near critical points, where order parameter fluctuations are enhanced, to stabilize long-lived, hidden quantum states.