基于超快电子自旋动力学的太赫兹辐射研究进展
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摘要
回顾了近年来利用超快自旋动力学过程产生太赫兹(THz)辐射的研究进展。介绍了基于逆自旋霍尔效应和逆Rashba-Edelstein效应的瞬态自旋流-电荷流转换,指出铁磁/非磁性异质结构已被用于设计低成本、高效率的THz辐射源。通过优化膜厚、生长条件、衬底和结构,可进一步提高基于自旋电子学的THz发射器的效率和带宽。简述了THz发射光谱在研究超快自旋泽贝克效应形成动力学中的应用。
Recent research progress of terahertz(THz) radiation generation based on the ultrafast spin dynamics is reviewed. The transient spin-charge conversion based on the inverse spin Hall effect and the Rashba-Edelstein effect is introduced, and it is pointed out that the ferromagnetic/non-magnetic heterostructure has been used to design a low-cost and high-efficiency THz radiation source. The efficiency and bandwidth of a spintronics-based THz emitter can be improved by optimizing layer thickness, growth conditions, substrates, and construction. The applications of the THz emission spectrum are outlined in the study of the ultrafast formation dynamics of the spin Seebeck effect.
Recent research progress of terahertz(THz) radiation generation based on the ultrafast spin dynamics is reviewed. The transient spin-charge conversion based on the inverse spin Hall effect and the Rashba-Edelstein effect is introduced, and it is pointed out that the ferromagnetic/non-magnetic heterostructure has been used to design a low-cost and high-efficiency THz radiation source. The efficiency and bandwidth of a spintronics-based THz emitter can be improved by optimizing layer thickness, growth conditions, substrates, and construction. The applications of the THz emission spectrum are outlined in the study of the ultrafast formation dynamics of the spin Seebeck effect.
引文
[1] Vahaplar K,Kalashnikova A M,Kimel A V,et al.Ultrafast path for optical magnetization reversal via a strongly nonequilibrium state[J].Physical Review Letters,2009,103(11):117201.
[2] Kimel A V,Kirilyuk A,Usachev P A,et al.Ultrafast non-thermal control of magnetization by instantaneous photomagnetic pulses[J].Nature,2005,435(7042):655-657.
[3] Bigot J Y,Vomir M,Beaurepaire E.Coherent ultrafast magnetism induced by femtosecond laser pulses[J].Nature Physics,2009,5(7):515-520.
[4] Kirilyuk A,Kimel A V,Rasing T.Ultrafast optical manipulation of magnetic order[J].Reviews of Modern Physics,2010,82(3):2731-2784.
[5] Beaurepaire E,Merle J C,Daunois A,et al.Ultrafast spin dynamics in ferromagnetic nickel[J].Physical Review Letters,1996,76(22):4250-4253.
[6] Koopmans B,Malinowski G,Dalla Longa F,et al.Explaining the paradoxical diversity of ultrafast laser-induced demagnetization[J].Nature Materials,2010,9(3):259-265.
[7] Koopmans B,van Kampen M,Kohlhepp J T,et al.Ultrafast magneto-optics in nickel:magnetism or optics?[J].Physical Review Letters,2000,85(4):844-847.
[8] Stanciu C D,Hansteen F,Kimel A V,et al.All-optical magnetic recording with circularly polarized light[J].Physical Review Letters,2007,99(4):047601.
[9] Radu I,Vahaplar K,Stamm C,et al.Transient ferromagnetic-like state mediating ultrafast reversal of antiferromagnetically coupled spins[J].Nature,2011,472(7342):205-208.
[10] Zhang G P,Hübner W,Lefkidis G,et al.Paradigm of the time-resolved magneto-optical Kerr effect for femtosecond magnetism[J].Nature Physics,2009,5(7):499-502.
[11] Beaurepaire E,Turner G M,Harrel S M,et al.Coherent terahertz emission from ferromagnetic films excited by femtosecond laser pulses[J].Applied Physics Letters,2004,84(18):3465-3467.
[12] Kampfrath T,Battiato M,Maldonado P,et al.Terahertz spin current pulses controlled by magnetic heterostructures[J].Nature Nanotechnology,2013,8(4):256-260.
[13] Awari N,Kovalev S,Fowley C,et al.Narrow-band tunable terahertz emission from ferrimagnetic Mn3-xGa thin films[J].Applied Physics Letters,2016,109(3):032403.
[14] Huisman T J,Mikhaylovskiy R V,Tsukamoto A,et al.Simultaneous measurements of terahertz emission and magneto-optical Kerr effect for resolving ultrafast laser-induced demagnetization dynamics[J].Physical Review B,2015,92(10):104419.
[15] Venkatesh M,Ramakanth S,Chaudhary A K,et al.Study of terahertz emission from nickel (Ni) films of different thicknesses using ultrafast laser pulses[J].Optical Materials Express,2016,6(7):2342-2350.
[16] Kinoshita Y,Kida N,Sotome M,et al.Terahertz radiation by subpicosecond magnetization modulation in the ferrimagnet LiFe5O8[J].ACS Photonics,2016,3(7):1170-1175.
[17] Hilton D J,Averitt R D,Meserole C A,et al.Terahertz emission via ultrashort-pulse excitation of magnetic metal films[J].Optics Letters,2004,29(15):1805-1807.
[18] Shen J,Zhang H W,Li Y X.Terahertz emission of ferromagnetic Ni-Fe thin films excited by ultrafast laser pulses[J].Chinese Physics Letters,2012,29(6):067502.
[19] Kumar N,Hendrikx R W A,Adam A J L,et al.Thickness dependent terahertz emission from cobalt thin films[J].Optics Express,2015,23(11):14252-14262.
[20] Seifert T,Martens U,Günther S,et al.Terahertz spin currents and inverse spin hall effect in thin-film heterostructures containing complex magnetic compounds[J].SPIN,2017,7(3):1740010.
[21] K?mmerer S,Thomas A,Hütten A,et al.Co2MnSi Heusler alloy as magnetic electrodes in magnetic tunnel junctions[J].Applied Physics Letters,2004,85(1):79-81.
[22] Zhang S N,Jin Z M,Liu X M,et al.Photoinduced terahertz radiation and negative conductivity dynamics in Heusler alloy Co2MnSn film[J].Optics Letters,2017,42(16):3080-3083.
[23] Battiato M,Carva K,Oppeneer P M.Superdiffusive spin transport as a mechanism of ultrafast demagnetization[J].Physical Review Letters,2010,105(2):027203.
[24] Eschenlohr A,Battiato M,Maldonado P,et al.Ultrafast spin transport as key to femtosecond demagnetization[J].Nature Materials,2013,12(4):332-336.
[25] Zhang S N,Jin Z M,Zhu Z D,et al.Bursts of efficient terahertz radiation with saturation effect from metal-based ferromagnetic heterostructures[J].Journal of Physics D:Applied Physics,2018,51(3):034001.
[26] Huisman T J,Rasing T.THz emission spectroscopy for THz spintronics[J].Journal of the Physical Society of Japan,2017,86(1):011009.
[27] Walowski J,Münzenberg M.Perspective:ultrafast magnetism and THz spintronics[J].Journal of Applied Physics,2016,120(14):140901.
[28] Seifert T,Jaiswal S,Martens U,et al.Efficient metallic spintronic emitters of ultrabroadband terahertz radiation[J].Nature Photonics,2016,10(7):483-488.
[29] Tanaka T,Kontani H,Naito M,et al.Intrinsic spin Hall effect and orbital Hall effect in 4d and 5d transition metals[J].Physical Review B,2008,77(16):165117.
[30] Torosyan G,Keller S,Scheuer L,et al.Optimized spintronic terahertz emitters based on epitaxial grown Fe/Pt layer structures[J].Scientific Reports,2018,8:1311.
[31] Ferguson B,Zhang X C.Materials for terahertz science and technology[J].Nature Materials,2002,1(1):26-33.
[32] Reimann K.Table-top sources of ultrashort THz pulses[J].Reports on Progress in Physics,2007,70(10):1597-1632.
[33] Leitenstorfer A,Hunsche S,Shah J,et al.Detectors and sources for ultrabroadband electro-optic sampling:experiment and theory[J].Applied Physics Letters,1999,74(11):1516-1518.
[34] D′Angelo F,Mics Z,Bonn M,et al.Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics[J].Optics Express,2014,22(10):12475-12485.
[35] Seifert T,Jaiswal S,Sajadi M,et al.Ultrabroadband single-cycle terahertz pulses with peak fields of 300 kV·cm-1 from a metallic spintronic emitter[J].Applied Physics Letters,2017,110(25):252402.
[36] Sajadi M,Wolf M,Kampfrath T.Terahertz-field-induced optical birefringence in common window and substrate materials[J].Optics Express,2015,23(22):28985-28992.
[37] Schneider A.Beam-size effects in electro-optic sampling of terahertz pulses[J].Optics Letters,2009,34(7):1054-1056.
[38] Wu Y,Elyasi M,Qiu X P,et al.High-performance THz emitters based on Ferromagnetic/Nonmagnetic heterostructures[J].Advanced Materials,2017,29(4):1603031.
[39] Sasaki Y,Suzuki K Z,Mizukami S.Annealing effect on laser pulse-induced THz wave emission in Ta/CoFeB/MgO films[J].Applied Physics Letters,2017,111(10):102401.
[40] Papaioannou E T,Torosyan G,Keller S,et al.Efficient terahertz generation using Fe/Pt spintronic emitters pumped at different wavelengths[J].IEEE Transactions on Magnetics,2018,54:9100205.
[41] Chen M,Mishra R,Wu Y,et al.Terahertz emission from compensated magnetic heterostructures[J].Advanced Optical Materials,2018,6(17):1800430.
[42] Schneider R,Fix M,Heming R,et al.Magnetic-field-dependent THz emission of spintronic TbFe/Pt layers[J].ACS Photonics,2018,5(10):3936-3942.
[43] Feng Z,Yu R,Zhou Y,et al.Highly efficient spintronic terahertz emitter enabled by metal-dielectric photonic crystal[J].Advanced Optical Materials,2018,6(23):1800965.
[44] Seifert S,Tran M,Gueckstock O,et al.Terahertz spectroscopy for all-optical spintronic characterization of the spin-Hall-effect metals Pt,W and Cu80Ir20[J].Journal of Physics D:Applied Physics,2018,51(36):364003.
[45] Yang D W,Liang J H,Zhou C,et al.Powerful and tunable THz emitters based on the Fe/Pt magnetic heterostructure[J].Advanced Optical Materials,2016,4(12):1944-1949.
[46] Luo L,Chatzakis I,Wang J G,et al.Broadband terahertz generation from metamaterials[J].Nature Communications,2014,5:3055.
[47] Edelstein V M.Spin polarization of conduction electrons induced by electric current in two-dimensional asymmetric electron systems[J].Solid State Communications,1990,73(3):233-235.
[48] Culcer D,Winkler R.Publisher′s note:generation of spin currents and spin densities in systems with reduced symmetry[J].Physical Review Letters,2007,99(23):239902.
[49] Sánchez J C R,Vila L,Desfonds G,et al.Spin-to-charge conversion using Rashba coupling at the interface between non-magnetic materials[J].Nature Communications,2013,4:2944.
[50] Jungfleisch M B,Zhang Q,Zhang W,et al.Control of terahertz emission by ultrafast spin-charge current conversion at Rashba interfaces[J].Physical Review Letters,2018,120(20):207207.
[51] Zhou C,Liu Y,Wang Z,et al.Broadband terahertz generation via the interface inverse rashba-edelstein effect[J].Physical Review Letters,2018,121(8):086801.
[52] Uchida K,Xiao J,Adachi H,et al.Spin Seebeck insulator[J].Nature Materials,2010,9(11):894-897.
[53] Agrawal M,Vasyuchka V I,Serga A A,et al.Role of bulk-magnon transport in the temporal evolution of the longitudinal spin-Seebeck effect[J].Physical Review B,2014,89(22):224414.
[54] Xiao J,Bauer G E W,Uchida K C,et al.Theory of magnon-driven spin Seebeck effect[J].Physical Review B,2010,81(21):214418.
[55] Seifert T S,Jaiswal S,Barker J,et al.Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy[J].Nature Communications,2018,9:2899.
[2] Kimel A V,Kirilyuk A,Usachev P A,et al.Ultrafast non-thermal control of magnetization by instantaneous photomagnetic pulses[J].Nature,2005,435(7042):655-657.
[3] Bigot J Y,Vomir M,Beaurepaire E.Coherent ultrafast magnetism induced by femtosecond laser pulses[J].Nature Physics,2009,5(7):515-520.
[4] Kirilyuk A,Kimel A V,Rasing T.Ultrafast optical manipulation of magnetic order[J].Reviews of Modern Physics,2010,82(3):2731-2784.
[5] Beaurepaire E,Merle J C,Daunois A,et al.Ultrafast spin dynamics in ferromagnetic nickel[J].Physical Review Letters,1996,76(22):4250-4253.
[6] Koopmans B,Malinowski G,Dalla Longa F,et al.Explaining the paradoxical diversity of ultrafast laser-induced demagnetization[J].Nature Materials,2010,9(3):259-265.
[7] Koopmans B,van Kampen M,Kohlhepp J T,et al.Ultrafast magneto-optics in nickel:magnetism or optics?[J].Physical Review Letters,2000,85(4):844-847.
[8] Stanciu C D,Hansteen F,Kimel A V,et al.All-optical magnetic recording with circularly polarized light[J].Physical Review Letters,2007,99(4):047601.
[9] Radu I,Vahaplar K,Stamm C,et al.Transient ferromagnetic-like state mediating ultrafast reversal of antiferromagnetically coupled spins[J].Nature,2011,472(7342):205-208.
[10] Zhang G P,Hübner W,Lefkidis G,et al.Paradigm of the time-resolved magneto-optical Kerr effect for femtosecond magnetism[J].Nature Physics,2009,5(7):499-502.
[11] Beaurepaire E,Turner G M,Harrel S M,et al.Coherent terahertz emission from ferromagnetic films excited by femtosecond laser pulses[J].Applied Physics Letters,2004,84(18):3465-3467.
[12] Kampfrath T,Battiato M,Maldonado P,et al.Terahertz spin current pulses controlled by magnetic heterostructures[J].Nature Nanotechnology,2013,8(4):256-260.
[13] Awari N,Kovalev S,Fowley C,et al.Narrow-band tunable terahertz emission from ferrimagnetic Mn3-xGa thin films[J].Applied Physics Letters,2016,109(3):032403.
[14] Huisman T J,Mikhaylovskiy R V,Tsukamoto A,et al.Simultaneous measurements of terahertz emission and magneto-optical Kerr effect for resolving ultrafast laser-induced demagnetization dynamics[J].Physical Review B,2015,92(10):104419.
[15] Venkatesh M,Ramakanth S,Chaudhary A K,et al.Study of terahertz emission from nickel (Ni) films of different thicknesses using ultrafast laser pulses[J].Optical Materials Express,2016,6(7):2342-2350.
[16] Kinoshita Y,Kida N,Sotome M,et al.Terahertz radiation by subpicosecond magnetization modulation in the ferrimagnet LiFe5O8[J].ACS Photonics,2016,3(7):1170-1175.
[17] Hilton D J,Averitt R D,Meserole C A,et al.Terahertz emission via ultrashort-pulse excitation of magnetic metal films[J].Optics Letters,2004,29(15):1805-1807.
[18] Shen J,Zhang H W,Li Y X.Terahertz emission of ferromagnetic Ni-Fe thin films excited by ultrafast laser pulses[J].Chinese Physics Letters,2012,29(6):067502.
[19] Kumar N,Hendrikx R W A,Adam A J L,et al.Thickness dependent terahertz emission from cobalt thin films[J].Optics Express,2015,23(11):14252-14262.
[20] Seifert T,Martens U,Günther S,et al.Terahertz spin currents and inverse spin hall effect in thin-film heterostructures containing complex magnetic compounds[J].SPIN,2017,7(3):1740010.
[21] K?mmerer S,Thomas A,Hütten A,et al.Co2MnSi Heusler alloy as magnetic electrodes in magnetic tunnel junctions[J].Applied Physics Letters,2004,85(1):79-81.
[22] Zhang S N,Jin Z M,Liu X M,et al.Photoinduced terahertz radiation and negative conductivity dynamics in Heusler alloy Co2MnSn film[J].Optics Letters,2017,42(16):3080-3083.
[23] Battiato M,Carva K,Oppeneer P M.Superdiffusive spin transport as a mechanism of ultrafast demagnetization[J].Physical Review Letters,2010,105(2):027203.
[24] Eschenlohr A,Battiato M,Maldonado P,et al.Ultrafast spin transport as key to femtosecond demagnetization[J].Nature Materials,2013,12(4):332-336.
[25] Zhang S N,Jin Z M,Zhu Z D,et al.Bursts of efficient terahertz radiation with saturation effect from metal-based ferromagnetic heterostructures[J].Journal of Physics D:Applied Physics,2018,51(3):034001.
[26] Huisman T J,Rasing T.THz emission spectroscopy for THz spintronics[J].Journal of the Physical Society of Japan,2017,86(1):011009.
[27] Walowski J,Münzenberg M.Perspective:ultrafast magnetism and THz spintronics[J].Journal of Applied Physics,2016,120(14):140901.
[28] Seifert T,Jaiswal S,Martens U,et al.Efficient metallic spintronic emitters of ultrabroadband terahertz radiation[J].Nature Photonics,2016,10(7):483-488.
[29] Tanaka T,Kontani H,Naito M,et al.Intrinsic spin Hall effect and orbital Hall effect in 4d and 5d transition metals[J].Physical Review B,2008,77(16):165117.
[30] Torosyan G,Keller S,Scheuer L,et al.Optimized spintronic terahertz emitters based on epitaxial grown Fe/Pt layer structures[J].Scientific Reports,2018,8:1311.
[31] Ferguson B,Zhang X C.Materials for terahertz science and technology[J].Nature Materials,2002,1(1):26-33.
[32] Reimann K.Table-top sources of ultrashort THz pulses[J].Reports on Progress in Physics,2007,70(10):1597-1632.
[33] Leitenstorfer A,Hunsche S,Shah J,et al.Detectors and sources for ultrabroadband electro-optic sampling:experiment and theory[J].Applied Physics Letters,1999,74(11):1516-1518.
[34] D′Angelo F,Mics Z,Bonn M,et al.Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics[J].Optics Express,2014,22(10):12475-12485.
[35] Seifert T,Jaiswal S,Sajadi M,et al.Ultrabroadband single-cycle terahertz pulses with peak fields of 300 kV·cm-1 from a metallic spintronic emitter[J].Applied Physics Letters,2017,110(25):252402.
[36] Sajadi M,Wolf M,Kampfrath T.Terahertz-field-induced optical birefringence in common window and substrate materials[J].Optics Express,2015,23(22):28985-28992.
[37] Schneider A.Beam-size effects in electro-optic sampling of terahertz pulses[J].Optics Letters,2009,34(7):1054-1056.
[38] Wu Y,Elyasi M,Qiu X P,et al.High-performance THz emitters based on Ferromagnetic/Nonmagnetic heterostructures[J].Advanced Materials,2017,29(4):1603031.
[39] Sasaki Y,Suzuki K Z,Mizukami S.Annealing effect on laser pulse-induced THz wave emission in Ta/CoFeB/MgO films[J].Applied Physics Letters,2017,111(10):102401.
[40] Papaioannou E T,Torosyan G,Keller S,et al.Efficient terahertz generation using Fe/Pt spintronic emitters pumped at different wavelengths[J].IEEE Transactions on Magnetics,2018,54:9100205.
[41] Chen M,Mishra R,Wu Y,et al.Terahertz emission from compensated magnetic heterostructures[J].Advanced Optical Materials,2018,6(17):1800430.
[42] Schneider R,Fix M,Heming R,et al.Magnetic-field-dependent THz emission of spintronic TbFe/Pt layers[J].ACS Photonics,2018,5(10):3936-3942.
[43] Feng Z,Yu R,Zhou Y,et al.Highly efficient spintronic terahertz emitter enabled by metal-dielectric photonic crystal[J].Advanced Optical Materials,2018,6(23):1800965.
[44] Seifert S,Tran M,Gueckstock O,et al.Terahertz spectroscopy for all-optical spintronic characterization of the spin-Hall-effect metals Pt,W and Cu80Ir20[J].Journal of Physics D:Applied Physics,2018,51(36):364003.
[45] Yang D W,Liang J H,Zhou C,et al.Powerful and tunable THz emitters based on the Fe/Pt magnetic heterostructure[J].Advanced Optical Materials,2016,4(12):1944-1949.
[46] Luo L,Chatzakis I,Wang J G,et al.Broadband terahertz generation from metamaterials[J].Nature Communications,2014,5:3055.
[47] Edelstein V M.Spin polarization of conduction electrons induced by electric current in two-dimensional asymmetric electron systems[J].Solid State Communications,1990,73(3):233-235.
[48] Culcer D,Winkler R.Publisher′s note:generation of spin currents and spin densities in systems with reduced symmetry[J].Physical Review Letters,2007,99(23):239902.
[49] Sánchez J C R,Vila L,Desfonds G,et al.Spin-to-charge conversion using Rashba coupling at the interface between non-magnetic materials[J].Nature Communications,2013,4:2944.
[50] Jungfleisch M B,Zhang Q,Zhang W,et al.Control of terahertz emission by ultrafast spin-charge current conversion at Rashba interfaces[J].Physical Review Letters,2018,120(20):207207.
[51] Zhou C,Liu Y,Wang Z,et al.Broadband terahertz generation via the interface inverse rashba-edelstein effect[J].Physical Review Letters,2018,121(8):086801.
[52] Uchida K,Xiao J,Adachi H,et al.Spin Seebeck insulator[J].Nature Materials,2010,9(11):894-897.
[53] Agrawal M,Vasyuchka V I,Serga A A,et al.Role of bulk-magnon transport in the temporal evolution of the longitudinal spin-Seebeck effect[J].Physical Review B,2014,89(22):224414.
[54] Xiao J,Bauer G E W,Uchida K C,et al.Theory of magnon-driven spin Seebeck effect[J].Physical Review B,2010,81(21):214418.
[55] Seifert T S,Jaiswal S,Barker J,et al.Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy[J].Nature Communications,2018,9:2899.