Femtosecond switching of magnetism via strongly correlated spin–charge quantum excitations

Abstract

The technological demand to push the gigahertz (10(9) hertz) switching speed limit of today's magnetic memory and logic devices into the terahertz (10(12) hertz) regime underlies the entire field of spin-electronics and integrated multi-functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation. By analogy to femtosecond chemistry and photosynthetic dynamics--in which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states--femtosecond-laser-excited coherence between electronic states can switch magnetic order by 'suddenly' breaking the delicate balance between competing phases of correlated materials: for example, manganites exhibiting colossal magneto-resistance suitable for applications. Here we show femtosecond (10(-15) seconds) photo-induced switching from antiferromagnetic to ferromagnetic ordering in Pr0.7Ca0.3MnO3, by observing the establishment (within about 120 femtoseconds) of a huge temperature-dependent magnetization with photo-excitation threshold behaviour absent in the optical reflectivity. The development of ferromagnetic correlations during the femtosecond laser pulse reveals an initial quantum coherent regime of magnetism, distinguished from the picosecond (10(-12) seconds) lattice-heating regime characterized by phase separation without threshold behaviour. Our simulations reproduce the nonlinear femtosecond spin generation and underpin fast quantum spin-flip fluctuations correlated with coherent superpositions of electronic states to initiate local ferromagnetic correlations. These results merge two fields, femtosecond magnetism in metals and band insulators, and non-equilibrium phase transitions of strongly correlated electrons, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders.

Laser-induced white-light emission from graphene ceramics–opening a band gap in graphene

“…26 However, the first reports of CW-excited hot luminescence were published by Chen et al, 27 who were studying inelastic light scattering in highly doped graphene; WL emission from cold samples has never previously been reported. It is also worth noting that photoinduced phase transitions involving switching between anti-ferromagnetic and magnetic states induced by femtosecond pulses via strongly correlated spin-charge quantum excitation have also been demonstrated by Li et al 28 in non-carbonaceous compounds (Pr 0.7 Ca 0.3 MnO 3 ).…”

Ultrafast probes of nonequilibrium hole spin relaxation in the ferromagnetic semiconductor GaMnAs

“…Spin exchange, fluctuation and relaxation play important roles in various collective behaviors emerging in advanced materials with scientific interest and technological potential, such as carrier-mediated ferromagnetism in semiconductors, colossal magnetoresistance in manganites, and electronic nematicity in iron pnictide superconductors [1][2][3] . These processes develop on ultrafast time scales and can be driven and probed by ultrashort laser pulses interacting with magnetic materials.…”

Polaronic Transport Induced by Competing Interfacial Magnetic Order in aLa0.7Ca0.3MnO3/BiFe

“…In fact, the interfacial spin-spin interaction J FM-AFMðGÞ could enable the use of effective "AFM staggered fields" to control FM spins in an alternating arrangement, which cannot be done using an applied magnetic (B) field. Furthermore, relatively little effort has been made to explain the E-field switchable magnetotransport in the manganite layer, which is arguably of equal importance.One can shed light on these issues using ultrafast optical spectroscopy (UOS), which has been demonstrated to be a sensitive probe of the charge, spin, and orbital order in colossal magnetoresistive manganites [17][18][19][20][21][22][23]. In particular, much insight into the physics of these systems has been * ymsheu@lanl.gov † rpprasan@lanl.gov…”

“…One can shed light on these issues using ultrafast optical spectroscopy (UOS), which has been demonstrated to be a sensitive probe of the charge, spin, and orbital order in colossal magnetoresistive manganites [17][18][19][20][21][22][23]. In particular, much insight into the physics of these systems has been * ymsheu@lanl.gov † rpprasan@lanl.gov…”

“…One can shed light on these issues using ultrafast optical spectroscopy (UOS), which has been demonstrated to be a sensitive probe of the charge, spin, and orbital order in colossal magnetoresistive manganites [17][18][19][20][21][22][23]. In particular, much insight into the physics of these systems has been obtained from probing large photoinduced changes in the optical conductivity between low and high frequencies [known as dynamical spectral weight transfer (DSWT)] [17][18][19][20]24], which are strongly coupled to the magnetotransport properties [25].…”