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Search Results: 1 - 10 of 14104 matches for " Andrea Cavalleri "
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Theory of nonlinear phononics for coherent light-control of solids
Alaska Subedi,Andrea Cavalleri,Antoine Georges
Physics , 2013, DOI: 10.1103/PhysRevB.89.220301
Abstract: We present a microscopic theory for ultrafast control of solids with high-intensity terahertz frequency optical pulses. When resonant with selected infrared-active vibrations, these pulses transiently modify the crystal structure and lead to new collective electronic properties. The theory predicts the dynamical path taken by the crystal lattice using first-principles calculations of the energy surface and classical equations of motion, as well as symmetry considerations. Two classes of dynamics are identified. In the perturbative regime, displacements along the normal mode coordinate of symmetry-preserving Raman active modes can be achieved by cubic anharmonicities. This explains the light-induced insulator-to-metal transition reported experimentally in manganites. We predict a regime in which ultrafast instabilities that break crystal symmetry can be induced. This nonperturbative effect involves a quartic anharmonic coupling and occurs above a critical threshold, below which the nonlinear dynamics of the driven mode displays softening and dynamical stabilization.
Proposed cavity Josephson plasmonics with complex-oxide heterostructures
Yannis Laplace,Stephanie Fernandez-Pena,Stefano Gariglio,Jean-Marc Triscone,Andrea Cavalleri
Physics , 2015,
Abstract: We discuss how complex-oxide heterostructures that include high-Tc superconducting cuprates can be used to realize an array of sub-millimeter cavities that support Josephson plasmon polaritons. These cavities have several attractive features for new types of light matter interaction studies and we show that they promote "ultrastrong" coupling between THz frequency radiation and Josephson plasmons. Cavity electrodynamics of Josephson plasmons allows to manipulate the superconducting order-parameter phase coherence. As an example, we discuss how it can be used to cool superconducting phase fluctuations with light.
Nonlinear phononics: A new ultrafast route to lattice control
Michael F?rst,Cristian Manzoni,Stefan Kaiser,Yasuhide Tomioka,Yoshinori Tokura,Roberto Merlin,Andrea Cavalleri
Physics , 2011, DOI: 10.1038/nphys2055
Abstract: To date, two types of coupling between electromagnetic radiation and a crystal lattice have been identified experimentally. One is direct, for infrared (IR)-active vibrations that carry an electric dipole. The second is indirect, it occurs through intermediate excitation of the electronic system via electron-phonon coupling, as in stimulated Raman scattering. Nearly 40 years ago, proposals were made of a third path, referred to as ionic Raman scattering (IRS). It was posited that excitation of an IR-active phonon could serve as the intermediate state for a Raman scattering process relying on lattice anharmonicity as opposed to electron phonon interaction. In this paper, we report an experimental demonstration of ionic Raman scattering and show that this mechanism is relevant to optical control in solids. The key insight is that a rectified phonon field can exert a directional force onto the crystal, inducing an abrupt displacement of the atoms from the equilibrium positions that could not be achieved through excitation of an IR-active vibration alone, for which the force is oscillatory. IRS opens up a new direction for the coherent control of solids in their electronic ground state, different from approaches that rely on electronic excitations.
Gabriele de Rosa (1917-2009), in memoriam
Cesare Cavalleri
Anuario de Historia de la Iglesia , 2011,
Polaronic conductivity in the photoinduced phase of 1T-TaS2
Nicky Dean,Jesse Petersen,Daniele Fausti,Ra'anan I. Tobey,Stefan Kaiser,Lev Gasparov,Helmuth Berger,Andrea Cavalleri
Physics , 2010, DOI: 10.1103/PhysRevLett.106.016401
Abstract: The transient optical conductivity of photoexcited 1T-TaS2 is determined over a three-order-of-magnitude frequency range. Prompt collapse and recovery of the Mott gap is observed. However, we find important differences between this transient metallic state and that seen across the thermally-driven insulator-metal transition. Suppressed low-frequency conductivity, Fano phonon lineshapes, and a mid-infrared absorption band point to polaronic transport. This is explained by noting that the photo-induced metallic state of 1T-TaS2 is one in which the Mott gap is melted but the lattice retains its low-temperature symmetry, a regime only accessible by photo-doping.
Ultrafast insulator-to-metal phase transition as a switch to measure the spectrogram of a supercontinuum light pulse
Federico Cilento,Claudio Giannetti,Gabriele Ferrini,Stefano Dal Conte,Tommaso Sala,Giacomo Coslovich,Matteo Rini,Andrea Cavalleri,Fulvio Parmigiani
Physics , 2009, DOI: 10.1063/1.3291105
Abstract: In this letter we demonstrate the possibility to determine the temporal and spectral structure (spectrogram) of a complex light pulse exploiting the ultrafast switching character of a non-thermal photo-induced phase transition. As a proof, we use a VO2 multi-film, undergoing an ultrafast insulator-to-metal phase transition when excited by femtosecond near-infrared laser pulses. The abrupt variation of the multi-film optical properties, over a broad infrared/visible frequency range, is exploited to determine, in-situ and in a simple way, the spectrogram of a supercontinuum pulse produced by a photonic crystal fiber. The determination of the structure of the pulse is mandatory to develop new pump-probe experiments with frequency resolution over a broad spectral range (700-1100 nm).
Parametric Amplification of a Terahertz Quantum Plasma Wave
Srivats Rajasekaran,Eliza Casandruc,Yannis Laplace,Daniele Nicoletti,Genda D. Gu,Stephen R. Clark,Dieter Jaksch,Andrea Cavalleri
Physics , 2015,
Abstract: Many applications in photonics require all-optical manipulation of plasma waves, which can concentrate electromagnetic energy on sub-wavelength length scales. This is difficult in metallic plasmas because of their small optical nonlinearities. Some layered superconductors support weakly damped plasma waves, involving oscillatory tunneling of the superfluid between capacitively coupled planes. Such Josephson plasma waves (JPWs) are also highly nonlinear, and exhibit striking phenomena like cooperative emission of coherent terahertz radiation, superconductor-metal oscillations and soliton formation. We show here that terahertz JPWs in cuprate superconductors can be parametrically amplified through the cubic tunneling nonlinearity. Parametric amplification is sensitive to the relative phase between pump and seed waves and may be optimized to achieve squeezing of the order parameter phase fluctuations or single terahertz-photon devices.
Population Inversion in Monolayer and Bilayer Graphene
Isabella Gierz,Matteo Mitrano,Jesse C. Petersen,Cephise Cacho,I. C. Edmond Turcu,Emma Springate,Alexander St?hr,Axel K?hler,Ulrich Starke,Andrea Cavalleri
Physics , 2014, DOI: 10.1088/0953-8984/27/16/164204
Abstract: The recent demonstration of saturable absorption and negative optical conductivity in the Terahertz range in graphene has opened up new opportunities for optoelectronic applications based on this and other low dimensional materials. Recently, population inversion across the Dirac point has been observed directly by time- and angle-resolved photoemission spectroscopy (tr-ARPES), revealing a relaxation time of only ~ 130 femtoseconds. This severely limits the applicability of single layer graphene to, for example, Terahertz light amplification. Here we use tr-ARPES to demonstrate long-lived population inversion in bilayer graphene. The effect is attributed to the small band gap found in this compound. We propose a microscopic model for these observations and speculate that an enhancement of both the pump photon energy and the pump fluence may further increase this lifetime.
Snapshots of non-equilibrium Dirac carrier distributions in graphene
Isabella Gierz,Jesse C. Petersen,Matteo Mitrano,Cephise Cacho,Edmond Turcu,Emma Springate,Alexander St?hr,Axel K?hler,Ulrich Starke,Andrea Cavalleri
Physics , 2013, DOI: 10.1038/nmat3757
Abstract: The optical properties of graphene are made unique by the linear band structure and the vanishing density of states at the Dirac point. It has been proposed that even in the absence of a semiconducting bandgap, a relaxation bottleneck at the Dirac point may allow for population inversion and lasing at arbitrarily long wavelengths. Furthermore, efficient carrier multiplication by impact ionization has been discussed in the context of light harvesting applications. However, all these effects are difficult to test quantitatively by measuring the transient optical properties alone, as these only indirectly reflect the energy and momentum dependent carrier distributions. Here, we use time- and angle-resolved photoemission spectroscopy with femtosecond extreme ultra-violet (EUV) pulses at 31.5 eV photon energy to directly probe the non-equilibrium response of Dirac electrons near the K-point of the Brillouin zone. In lightly hole-doped epitaxial graphene samples, we explore excitation in the mid- and near-infrared, both below and above the minimum photon energy for direct interband transitions. While excitation in the mid-infrared results only in heating of the equilibrium carrier distribution, interband excitations give rise to population inversion, suggesting that terahertz lasing may be possible. However, in neither excitation regime do we find indication for carrier multiplication, questioning the applicability of graphene for light harvesting. Time-resolved photoemission spectroscopy in the EUV emerges as the technique of choice to assess the suitability of new materials for optoelectronics, providing quantitatively accurate measurements of non-equilibrium carriers at all energies and wavevectors.
Momentum-dependent snapshots of a melting charge density wave
Jesse C. Petersen,Stefan Kaiser,Nicky Dean,Alberto Simoncig,Haiyun Liu,Adrian L. Cavalieri,Cephise Cacho,I. C. Edmond Turcu,Emma Springate,Fabio Frassetto,Luca Poletto,Sarnjeet S. Dhesi,Helmuth Berger,Andrea Cavalleri
Physics , 2010, DOI: 10.1103/PhysRevLett.107.177402
Abstract: Charge density waves (CDWs) underpin the electronic properties of many complex materials. Near-equilibrium CDW order is linearly coupled to a periodic, atomic-structural distortion, and the dynamics is understood in terms of amplitude and phase modes. However, at the shortest timescales lattice and charge order may become de-coupled, highlighting the electronic nature of this many-body broken symmetry ground state. Using time and angle resolved photoemission spectroscopy with sub-30-fs XUV pulses, we have mapped the time- and momentum-dependent electronic structure in photo-stimulated 1T-TaS2, a prototypical two-dimensional charge density wave compound. We find that CDW order, observed as a splitting of the uppermost electronic bands at the Brillouin zone boundary, melts well before relaxation of the underlying structural distortion. Decoupled charge and lattice modulations challenge the view of Fermi Surface nesting as a driving force for charge density wave formation in 1T-TaS2.
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