The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1–2.0 THz with the driving current in the Pt layer from 108 A/cm2 to 109 A/cm2. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.
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机译:相干太赫兹频率信号的紧凑且可调的室温源的发展将为众多新应用开辟道路。现有的基于超导体约瑟夫逊结(JJ),自由电子激光器和量子级联的太赫兹频率产生方法需要低温或低温和/或复杂的设置,从而阻止了这些设备的小型化和广泛使用。我们从理论上证明,重金属(Pt)和双轴反铁磁(AFM)电介质(NiO)的双层可以是相干THz信号的来源。由于存在弱的易平面AFM各向异性,自DC电流驱动的Pt层流出并沿硬AFM各向异性轴极化的自旋电流会激发AFM中磁化亚晶格的时间进动不均匀。随着Pt层中的驱动电流从10 8 sup> A / cm 2 sup>到10 9,AFM振荡频率在0.1–2.0 THz范围内变化 sup> A / cm 2 sup>。振幅超过1 TV / cm的AFM的THz频率信号通过Pt中的反自旋霍尔效应得到。室温AFM THz频率振荡器的操作类似于低温JJ振荡器,其易平面磁各向异性的能量起着约瑟夫森能量的作用。
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