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Ultrafast generation of hidden phases via energy-tuned electronic photoexcitation in magnetite
Authors:
B. Truc,
P. Usai,
F. Pennacchio,
G. Berruto,
R. Claude,
I. Madan,
V. Sala,
T. LaGrange,
G. M. Vanacore,
S. Benhabib,
F. Carbone
Abstract:
Metal-insulator transitions (MIT) occurring in non-adiabatic conditions can evolve through high-energy intermediate states that are difficult to observe and control via static methods. By monitoring the out-of-equilibrium structural dynamics of a magnetite (Fe3O4) crystal via ultrafast electron diffraction, we show that MITs can evolve through different pathways by properly selecting the electroni…
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Metal-insulator transitions (MIT) occurring in non-adiabatic conditions can evolve through high-energy intermediate states that are difficult to observe and control via static methods. By monitoring the out-of-equilibrium structural dynamics of a magnetite (Fe3O4) crystal via ultrafast electron diffraction, we show that MITs can evolve through different pathways by properly selecting the electronic excitation with light. Near-infrared (800 nm) photons inducing d-d electronic transitions is found to favor the destruction of the long-range zigzag network of the trimerons and to generate a phase separation between cubic-metallic and monoclinic-insulating regions. Instead, visible light (400 nm) further promotes the long-range order of the trimerons by stabilizing the charge density wave fluctuations through the excitation of the oxygen 2p to iron 3d charge transfer and, thus, fosters a reinforcement of the monoclinic insulating phase. Our experiments demonstrate that tailored light pulses can drive strongly correlated materials into different hidden phases, influencing the lifetime and emergent properties of the intermediate states.
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Submitted 30 September, 2022;
originally announced October 2022.
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Stochastic precession of the polarization in a polariton laser
Authors:
Vera Giulia Sala,
Félix Marsault,
Michiel Wouters,
Elisabeth Galopin,
Isabelle Sagnes,
Aristide Lemaître,
Jacqueline Bloch,
Alberto Amo
Abstract:
Microcavity polaritons in the lasing regime undergo a spontaneous symmetry breaking transition resulting in coherent emission with a well defined polarization. The order parameter is thus a vector describing both the laser global phase and polarization. Using an ultrafast single-shot detection technique we show that polariton lasing in GaAs-based microcavities presents a high degree of second orde…
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Microcavity polaritons in the lasing regime undergo a spontaneous symmetry breaking transition resulting in coherent emission with a well defined polarization. The order parameter is thus a vector describing both the laser global phase and polarization. Using an ultrafast single-shot detection technique we show that polariton lasing in GaAs-based microcavities presents a high degree of second order coherence ($g^{(2)}(τ=0) \approx 1$) above threshold, and that the initial polarization is stochastic, taking any possible direction in the Poincaré sphere (linear, elliptical or circular). Once the polarization direction is established, subsequent oscillations of the emission probability witness the presence of an intrinsic polarization splitting. Our results show the negligible role of polariton interactions in the total emission statistics and in the establishment of the initial polarization.
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Submitted 23 March, 2016; v1 submitted 10 December, 2015;
originally announced December 2015.
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Resonant optical control of the structural distortions that drive ultrafast demagnetization in Cr$_2$O$_3$
Authors:
Vera G. Sala,
Stefano Dal Conte,
Timothy A. Miller,
Daniele Viola,
Elenora Luppi,
Valérie Véniard,
Giulio Cerullo,
Simon Wall
Abstract:
We study how the color and polarization of ultrashort pulses of visible light can be used to control the demagnetization processes of the antiferromagnetic insulator Cr$_2$O$_3$. We utilize time-resolved second harmonic generation (SHG) to probe how changes in the magnetic and structural state evolve in time. We show that, varying the pump photon-energy to excite either localized transitions withi…
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We study how the color and polarization of ultrashort pulses of visible light can be used to control the demagnetization processes of the antiferromagnetic insulator Cr$_2$O$_3$. We utilize time-resolved second harmonic generation (SHG) to probe how changes in the magnetic and structural state evolve in time. We show that, varying the pump photon-energy to excite either localized transitions within the Cr or charge transfer states, leads to markedly different dynamics. Through a full polarization analysis of the SHG signal, symmetry considerations and density functional theory calculations, we show that, in the non-equilibrium state, SHG is sensitive to {\em both} lattice displacements and changes to the magnetic order, which allows us to conclude that different excited states couple to phonon modes of different symmetries. Furthermore, the spin-scattering rate depends on the induced distortion, enabling us to control the timescale for the demagnetization process. Our results suggest that selective photoexcitation of antiferromagnetic insulators allows fast and efficient manipulation of their magnetic state.
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Submitted 20 July, 2016; v1 submitted 30 September, 2015;
originally announced September 2015.
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Engineering spin-orbit coupling for photons and polaritons in microstructures
Authors:
V. G. Sala,
D. D. Solnyshkov,
I. Carusotto,
T. Jacqmin,
A. Lemaître,
H. Terças,
A. Nalitov,
M. Abbarchi,
E. Galopin,
I. Sagnes,
J. Bloch,
G. Malpuech,
A. Amo
Abstract:
One of the most fundamental properties of electromagnetism and special relativity is the coupling between the spin of an electron and its orbital motion. This is at the origin of the fine structure in atoms, the spin Hall effect in semiconductors, and underlies many intriguing properties of topological insulators, in particular their chiral edge states. Configurations where neutral particles exper…
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One of the most fundamental properties of electromagnetism and special relativity is the coupling between the spin of an electron and its orbital motion. This is at the origin of the fine structure in atoms, the spin Hall effect in semiconductors, and underlies many intriguing properties of topological insulators, in particular their chiral edge states. Configurations where neutral particles experience an effective spin-orbit coupling have been recently proposed and realized using ultracold atoms and photons. Here we use coupled micropillars etched out of a semiconductor microcavity to engineer a spin-orbit Hamiltonian for photons and polaritons in a microstructure. The coupling between the spin and orbital momentum arises from the polarisation dependent confinement and tunnelling of photons between micropillars arranged in the form of a hexagonal photonic molecule. Dramatic consequences of the spin-orbit coupling are experimentally observed in these structures in the wavefunction of polariton condensates, whose helical shape is directly visible in the spatially resolved polarisation patterns of the emitted light. The strong optical nonlinearity of polariton systems suggests exciting perspectives for using quantum fluids of polaritons11 for quantum simulation of the interplay between interactions and spin-orbit coupling.
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Submitted 18 June, 2014;
originally announced June 2014.
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Macroscopic quantum self-trapping and Josephson oscillations of exciton-polaritons
Authors:
M. Abbarchi,
A. Amo,
V. G. Sala,
D. D. Solnyshkov,
H. Flayac,
L. Ferrier,
I. Sagnes,
E. Galopin,
A. Lemaitre,
G. Malpuech,
J. Bloch
Abstract:
A textbook example of quantum mechanical effects is the coupling of two states through a tunnel barrier. In the case of macroscopic quantum states subject to interactions, the tunnel coupling gives rise to Josephson phenomena including Rabi oscillations, the a.c. and d.c. effects, or macroscopic self-trapping depending on whether tunnelling or interactions dominate. Non-linear Josephson physics, o…
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A textbook example of quantum mechanical effects is the coupling of two states through a tunnel barrier. In the case of macroscopic quantum states subject to interactions, the tunnel coupling gives rise to Josephson phenomena including Rabi oscillations, the a.c. and d.c. effects, or macroscopic self-trapping depending on whether tunnelling or interactions dominate. Non-linear Josephson physics, observed in superfluid helium and atomic condensates, has remained inaccessible in photonic systems due to the required effective photon-photon interactions. We report on the observation of non-linear Josephson oscillations of two coupled polariton condensates confined in a photonic molecule etched in a semiconductor microcavity. By varying both the distance between the micropillars forming the molecule and the condensate density in each micropillar, we control the ratio of coupling to interaction energy. At low densities we observe coherent oscillations of particles tunnelling between the two micropillars. At high densities, interactions quench the transfer of particles inducing the macroscopic self-trapping of the condensate in one of the micropillars. The finite lifetime of polaritons results in a dynamical transition from self-trapping to oscillations with pi phase. Our results open the way to the experimental study of highly non-linear regimes in photonic systems, such as chaos or symmetry-breaking bifurcations.
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Submitted 21 December, 2012;
originally announced December 2012.
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All-optical control of the quantum flow of a polariton superfluid
Authors:
D. Sanvitto,
S. Pigeon,
A. Amo,
D. Ballarini,
M. De Giorgi,
I. Carusotto,
R. Hivet,
F. Pisanello,
V. G. Sala,
P. S. Soares-Guimaraes,
R. Houdré,
E. Giacobino,
C. Ciuti,
A. Bramati,
G. Gigli
Abstract:
While photons in vacuum are massless particles that do not interact with each other, significant photon-photon interactions appear in suitable nonlinear media, leading to novel hydrodynamic behaviors typical of quantum fluids. Here we show the formation of vortex-antivortex pairs in a Bose-Einstein condensate of exciton-polaritons -a coherent gas of strongly dressed photons- flowing at supersonic…
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While photons in vacuum are massless particles that do not interact with each other, significant photon-photon interactions appear in suitable nonlinear media, leading to novel hydrodynamic behaviors typical of quantum fluids. Here we show the formation of vortex-antivortex pairs in a Bose-Einstein condensate of exciton-polaritons -a coherent gas of strongly dressed photons- flowing at supersonic speed against an artificial potential barrier created and controlled by a light beam in a planar semiconductor microcavity. The observed hydrodynamical phenomenology is in agreement with original theoretical predictions based on the Gross-Pitaevskii equation, recently generalized to the polariton context. However, in contrast to this theoretical work, we show how the initial position and the subsequent trajectory of the vortices crucially depend on the strength and size of the artificial barrier. Additionally, we demonstrate how a suitably tailored optical beam can be used to permanently trap and store the vortices that are hydrodynamically created in the wake of a natural defect. These observations are borne out by time-dependent theoretical simulations.
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Submitted 24 March, 2011;
originally announced March 2011.
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Polariton superfluids reveal quantum hydrodynamic solitons
Authors:
A. Amo,
S. Pigeon,
D. Sanvitto,
V. G. Sala,
R. Hivet,
I. Carusotto,
F. Pisanello,
G. Lemenager,
R. Houdre,
E. Giacobino,
C. Ciuti,
A. Bramati
Abstract:
A quantum fluid passing an obstacle behaves differently from a classical one. When the flow is slow enough, the quantum gas enters a superfluid regime and neither whirlpools nor waves form around the obstacle. For higher flow velocities, it has been predicted that the perturbation induced by the defect gives rise to the turbulent emission of quantised vortices and to the nucleation of solitons. Us…
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A quantum fluid passing an obstacle behaves differently from a classical one. When the flow is slow enough, the quantum gas enters a superfluid regime and neither whirlpools nor waves form around the obstacle. For higher flow velocities, it has been predicted that the perturbation induced by the defect gives rise to the turbulent emission of quantised vortices and to the nucleation of solitons. Using an interacting Bose gas of exciton-polaritons in a semiconductor microcavity, we report the transition from superfluidity to the hydrodynamic formation of oblique dark solitons and vortex streets in the wake of a potential barrier. The direct observation of these topological excitations provides key information on the mechanisms of superflow and shows the potential of polariton condensates for quantum turbulence studies.
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Submitted 2 December, 2015; v1 submitted 13 January, 2011;
originally announced January 2011.