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Liu, M. K.; Pardo, Brian; Zhang, J.; Qazilbash, M. M.; Yun, Sun Jin; Fei, Zhe; Shin, Jun‐Hwan; Kim, Hyun-Tak; Basov, D. N.; Averitt, R. D.

doi:10.1103/physrevlett.107.066403

Cited by 59 publications

(43 citation statements)

References 34 publications

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“…Similar, or even more efficient ways to control J ex under nonequilibrium conditions might be found by extending our work to more complex multi-band systems such as the prototype Mott-insulator V 2 O 3 [34] and to materials with different exchange mechanisms.…”

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confidence: 56%

Ultrafast Quenching of the Exchange Interaction in a Mott Insulator

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Eckstein

2014

Phys. Rev. Lett.

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We investigate how fast and how effective photocarrier excitation can modify the exchange interaction Jex in the prototype Mott-Hubbard insulator. We demonstrate an ultrafast quenching of Jex both by evaluating exchange integrals from a time-dependent response formalism, and by explicitly simulating laser-induced spin precession in an antiferromagnet that is canted by an external magnetic field. In both cases, the electron dynamics is obtained from nonequilibrium dynamical mean-field theory. We find that the modified Jex emerges already within a few electron hopping times after the pulse, with a reduction that is comparable to the effect of chemical doping. PACS numbers: 75.78.Jp,71.10.Fd Magnetic long-range order and the dynamics of spins in magnetic materials are governed by the exchange interaction J ex , the strongest force of magnetism. Because J ex emerges from the Pauli principle and the electrostatic Coulomb repulsion between electrons, it is sensitive to purely nonmagnetic perturbations. This fact implies intriguing and largely unexplored possibilities for the ultrafast control of magnetism by femtosecond laser pulses, which is currently a very active research area [1]. In principle, laser-excitation can effect J ex by modulating the electronic structure (electron hopping, Coulomb repulsion) and by creating a nonequilibrium distribution of photoexcited carriers (photodoping). A modification of J ex has been discussed within the context of experiments on manganites [2-4], magnetic semi-conductors [5], and, using static field gradients, ultracold atoms in optical lattices [6,7]. While it might play a role as well in metallic ferromagnets [8][9][10][11], ultrafast demagnetization [12] and laser-induced magnetization reversal [13][14][15] seem at least partly understood in terms of a given time-independent J ex . Clearly, more theoretical work is needed to understand how effective a modification of J ex under nonequilibrium conditions can be, and how fast J ex can be modified. The latter touches the fundamental question for the time scale at which the description of spin dynamics in terms of a J ex emerges from the full electronic dynamics, before which J ex is not a valid concept at all. Although this question has not been directly addressed in the experiments mentioned above, an investigation of this ultimate limit of spin dynamics is in range using today's femtosecond laser technology.In general, the exchange interaction arises from a lowenergy description of the electronic states in terms of magnetic degrees of freedom. Recently, Secchi et al. defined the nonequilibrium exchange interaction via an effective action that governs the spin dynamics out of equilibrium, leading to an expression in terms of nonequilibrium electronic Green's functions [16]. Here, we apply this framework to the paradigm single-band Mott-Hubbard insulator at half-filling, for which the concept of exchange interaction in equilibrium is very well understood. To directly assess the nonequilibrium electron dynamics and evaluate th...

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confidence: 56%

Ultrafast Quenching of the Exchange Interaction in a Mott Insulator

Mentink

Eckstein

2014

Phys. Rev. Lett.

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“…Indeed, tr-ARPES provides a direct probe of the transient electronic structure 66,67,120,153 , tabletop and accelerator-based X-ray free-electron lasers readily capture momentary crystal arrangements 118,154 , nonlinear optical methods can directly interrogate the symmetries of quantum phases and their host lattices 30,[155][156][157][158] , while optical and soft X-ray techniques document electronic excitations, in some cases with elemental and orbital specificity 159 . Importantly, mesoscopic phenomena that are prevalent in quantum materials lead to new time and energy scales, as documented in various ultrafast studies 110,160 . Modern scanning optical probe tools are set to dramatically advance our understanding of mesoscopic dynamics, visualizing local transient phenomena at nano-and mesoscales [161][162][163] .…”

Section: Looking Into the Futurementioning

confidence: 99%

Towards properties on demand in quantum materials

2017

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Q uantum materials are on the ascent. This term embodies a vast portfolio of compounds and phenomena where ramifications of quantum mechanics are demonstrably real. Quantum materials are in the vanguard of contemporary physics in part because these systems afford an exceptional venue to uncover the many roles of symmetry, topology, dimensionality and strong correlations in macroscopic observables. Here we set out to explore the ways and means of creating new states of matter in quantum materials and manipulating their phases via external stimuli. Practical control of these properties is a precondition for exploiting quantum advantages in new photonic, electronic and energy technologies, a task of significant societal impact 1 . We will primarily focus on the following classes of quantum materials: transition metal oxides, Fe-and Cu-based high-T c superconductors, van der Waals semiconductors, topological insulators and Weyl semimetals, and, finally, graphene.The properties of quantum materials are anomalously sensitive to external stimuli. In these systems, interactions associated with spin, charge, lattice and orbital degrees of freedom are commonly on par with the electronic kinetic energy. A rather fragile balance between coexisting and competing ground states can be readily shifted via external stimuli, leading to a raft of quantum phases and transitions between them 2,3 . Furthermore, certain classes of driven quantum states (Fig. 1a and Box 1) are explicit products of coherent interaction between light and matter 4-6 . Alternatively, the properties of quantum materials can be pre-programmed by directly manipulating the electronic wavefunction and the attendant Berry phase that give rise to the anomalous velocity of electrons in a solid [7][8][9] . These complementary avenues of controls mean that investigations no longer need to be reduced to merely observing (in contrast, for example, to astrophysics). Instead, it is now feasible to attain, in a predictable fashion, 'properties on demand' by steering a quantum material towards a desirable ground, metastable or transient state. The past decade has witnessed an explosion in the field of quantum materials, headlined by the predictions and discoveries of novel Landau-symmetry-broken phases in correlated electron systems, topological phases in systems with strong spin-orbit coupling, and ultra-manipulable materials platforms based on two-dimensional van der Waals crystals. Discovering pathways to experimentally realize quantum phases of matter and exert control over their properties is a central goal of modern condensed-matter physics, which holds promise for a new generation of electronic/photonic devices with currently inaccessible and likely unimaginable functionalities. In this Review, we describe emerging strategies for selectively perturbing microscopic interaction parameters, which can be used to transform materials into a desired quantum state. Particular emphasis will be placed on recent successes to tailor electronic interaction parameters through th...

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“…Nonequilibrium dynamics following the photoexcitation can lead to surprisingly fast transitions between competing phases leading to, for example, quenching of the magnetic order 1 , insulator-to-metal transitions [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] , unexpected phases 17,18 , and melting of charge-density waves or stripes [19][20][21] . The theoretical understanding of these fascinating effects has not kept pace with the experimental advances and is often limited to phenemenological Landau-type models 20 , exact diagonalizations of small systems 22,23 or three-temperature models 1,11,21 .…”

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Ultrafast photoinduced insulator-to-metal transitions in vanadium dioxide

Veenendaal

2013

Phys. Rev. B

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An explanation is given for the ultrafast insulator-to-metal transition in VO2 following photoexcitation. The photoinduced orbital imbalance induces a coherent motion of the V-V dimers affecting the electronic structure. After the closing of the gap, Boltzmann scattering equilibrates the electron densities. If the electron density exceeds a critical value, a phase transition occurs to the metallic state. The model explains several key features, such as a structural bottleneck, coherent structural motion combined with phase shifts in the oscillation, the absence of ultrafast metal-to-insulator transitions, and the need for a critical fluency.

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Photoinduced Phase Transitions by Time-Resolved Far-Infrared Spectroscopy inV2O3

Cited by 59 publications

References 34 publications

Ultrafast Quenching of the Exchange Interaction in a Mott Insulator

Ultrafast Quenching of the Exchange Interaction in a Mott Insulator

Towards properties on demand in quantum materials

Ultrafast photoinduced insulator-to-metal transitions in vanadium dioxide

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