G. Coslovich - Academia.edu (original) (raw)

Papers by G. Coslovich

Ultrafast Phenomena and Nanophotonics XVII, 2013

ABSTRACT We present the first ultrafast mid-infrared study of charge and spin-ordered nickelates.... more ABSTRACT We present the first ultrafast mid-infrared study of charge and spin-ordered nickelates. A sub-picosecond modulation of the optical reflectivity is observed, indicating the filling and subsequent re-establishment of the pseudogap in the time-domain.

CLEO: 2013, 2013

ABSTRACT We study the low-energy conductivity dynamics after femtosecond perturbation of the stri... more ABSTRACT We study the low-energy conductivity dynamics after femtosecond perturbation of the stripe-ordered phase in a strongly-correlated nickelate. The experiments reveal ultrafast suppression and recovery of electron-phonon coupling that tracks the atomic-scale localization of correlated charges.

Physical Review Letters, 2013

A pairing gap and coherence are the two hallmarks of superconductivity. In a classical BCS superc... more A pairing gap and coherence are the two hallmarks of superconductivity. In a classical BCS superconductor they are established simultaneously at T c . In the cuprates, however, an energy gap (pseudogap) extends above T c [1, 2, 3,. The origin of this gap is one of the central issues in high temperature superconductivity. Recent experimental evidence demonstrates that the pseudogap and the superconducting gap are associated with different energy scales . It is however not clear whether they coexist independently or compete . In order to understand the physics of cuprates and improve their superconducting properties it is vital to determine whether the pseudogap is friend or foe of high temperature supercondctivity . Here we report evidence from angle resolved photoemission spectroscopy (ARPES) that the pseudogap and high temperature superconductivity represent two competing orders. We find that there is a direct correlation between a loss in the low energy spectral weight due to the pseudogap and a decrease of the coherent fraction of paired electrons. Therefore, the pseudogap competes with the superconductivity by depleting the spectral weight available for pairing in the region of momentum space where the superconducting gap is largest. This leads to a very unusual state in the underdoped cuprates, where only part of the Fermi surface develops coherence.

Physical Review B, 2009

We report the experimental evidence of an abrupt transition of the ultrafast electronic response ... more We report the experimental evidence of an abrupt transition of the ultrafast electronic response of underdoped superconducting Bi2Sr2CaCu2O8+delta , under the impulsive photoinjection of a high density of excitations, using ultrashort laser pulses and avoiding significant laser heating. The direct proof of this process is the discontinuity of the transient optical electronic response, observed at a critical fluence of Phith~=70muJ/cm2

Journal of Physics: Conference Series, 2013

In strongly correlated materials the electronic and optical properties are significantly affected... more In strongly correlated materials the electronic and optical properties are significantly affected by the coupling of fermionic quasiparticles to different degrees of freedom, such as lattice vibrations and bosonic excitations of electronic origin. Broadband ultrafast spectroscopy [1, 2] is emerging as the premier technique to unravel the subtle interplay between quasiparticles and electronic or phononic collective excitations, by their different characteristic timescales and spectral responses. By investigating the femtosecond dynamics of the optical properties of Bi2Sr2Ca0.92Y0.08Cu2O 8+δ (Y-Bi2212) crystals over the 0.5-2 eV energy range, we disentangle the electronic and phononic contributions to the generalized electron-boson Eliashberg function [3,, showing that the spectral distribution of the electronic excitations, such as spin fluctuations and current loops, and the strength of their interaction with quasiparticles can account for the high critical temperature of the superconducting phase transition . Finally, we discuss how the use of this technique can be extended to the underdoped region of the phase diagram of cuprates, in which a pseudogap in the quasiparticle density of states opens.

Photoinduced phase transitions from insulating to metallic states, accompanied by structural re-a... more Photoinduced phase transitions from insulating to metallic states, accompanied by structural re-arrangements, have been recently reported in complex transition-metal oxides. However, the optical control of a purely electronic phase transition, where the thermodynamic phase is determined by the distribution of excitations, has remained elusive. Here we report optical control of the electronic phase in an underdoped Bi2Sr2CaCu2O8+δ crystal through impulsive photoinjection of quasiparticles (QP) via ultrashort laser pulses, avoiding significant laser heating. An abrupt transition of the transient optical electronic response is observed at a critical fluence of Ipump≅70 μJ/cm 2 . We show that the measured dynamics is consistent with an inhomogenous first-order superconducting-to-normal state phase transition, triggered by a sudden shift of the chemical potential. The impulsive modification by ultrashort light pulses (∼100 fs) of electronic, magnetic and structural properties in complex materials, has recently opened the field of photo-induced phase-transitions (PIPT)(1). Previous studies have focused on the insulator-to-metal PIPT in perovskite manganites (2-4) or vanadium dioxide (5,6), in which the transformation of both the electronic and structural properties occurs at once. On the contrary no evidence of optical control of a purely electronic phase transition has been reported so far. The superconducting-to-normal state phase-transition (SNPT) is one of the most important examples of electronic phase transitions in solid-state systems. At zero temperature the BCS theory (7) explains the formation of the superconducting (SC) electronic phase in terms of the macroscopic condensation of the Cooper pairs, originated from the phonon-mediated coupling of two electrons. The excitation spectrum is characterized by the opening of the superconducting gap Δk, representing half the energy necessary to break a Cooper pair

Ultrafast Phenomena and Nanophotonics XVII, 2013

ABSTRACT We present the first ultrafast mid-infrared study of charge and spin-ordered nickelates.... more ABSTRACT We present the first ultrafast mid-infrared study of charge and spin-ordered nickelates. A sub-picosecond modulation of the optical reflectivity is observed, indicating the filling and subsequent re-establishment of the pseudogap in the time-domain.

CLEO: 2013, 2013

ABSTRACT We study the low-energy conductivity dynamics after femtosecond perturbation of the stri... more ABSTRACT We study the low-energy conductivity dynamics after femtosecond perturbation of the stripe-ordered phase in a strongly-correlated nickelate. The experiments reveal ultrafast suppression and recovery of electron-phonon coupling that tracks the atomic-scale localization of correlated charges.

Physical Review Letters, 2013

A pairing gap and coherence are the two hallmarks of superconductivity. In a classical BCS superc... more A pairing gap and coherence are the two hallmarks of superconductivity. In a classical BCS superconductor they are established simultaneously at T c . In the cuprates, however, an energy gap (pseudogap) extends above T c [1, 2, 3,. The origin of this gap is one of the central issues in high temperature superconductivity. Recent experimental evidence demonstrates that the pseudogap and the superconducting gap are associated with different energy scales . It is however not clear whether they coexist independently or compete . In order to understand the physics of cuprates and improve their superconducting properties it is vital to determine whether the pseudogap is friend or foe of high temperature supercondctivity . Here we report evidence from angle resolved photoemission spectroscopy (ARPES) that the pseudogap and high temperature superconductivity represent two competing orders. We find that there is a direct correlation between a loss in the low energy spectral weight due to the pseudogap and a decrease of the coherent fraction of paired electrons. Therefore, the pseudogap competes with the superconductivity by depleting the spectral weight available for pairing in the region of momentum space where the superconducting gap is largest. This leads to a very unusual state in the underdoped cuprates, where only part of the Fermi surface develops coherence.

Physical Review B, 2009

We report the experimental evidence of an abrupt transition of the ultrafast electronic response ... more We report the experimental evidence of an abrupt transition of the ultrafast electronic response of underdoped superconducting Bi2Sr2CaCu2O8+delta , under the impulsive photoinjection of a high density of excitations, using ultrashort laser pulses and avoiding significant laser heating. The direct proof of this process is the discontinuity of the transient optical electronic response, observed at a critical fluence of Phith~=70muJ/cm2

Journal of Physics: Conference Series, 2013

In strongly correlated materials the electronic and optical properties are significantly affected... more In strongly correlated materials the electronic and optical properties are significantly affected by the coupling of fermionic quasiparticles to different degrees of freedom, such as lattice vibrations and bosonic excitations of electronic origin. Broadband ultrafast spectroscopy [1, 2] is emerging as the premier technique to unravel the subtle interplay between quasiparticles and electronic or phononic collective excitations, by their different characteristic timescales and spectral responses. By investigating the femtosecond dynamics of the optical properties of Bi2Sr2Ca0.92Y0.08Cu2O 8+δ (Y-Bi2212) crystals over the 0.5-2 eV energy range, we disentangle the electronic and phononic contributions to the generalized electron-boson Eliashberg function [3,, showing that the spectral distribution of the electronic excitations, such as spin fluctuations and current loops, and the strength of their interaction with quasiparticles can account for the high critical temperature of the superconducting phase transition . Finally, we discuss how the use of this technique can be extended to the underdoped region of the phase diagram of cuprates, in which a pseudogap in the quasiparticle density of states opens.

Photoinduced phase transitions from insulating to metallic states, accompanied by structural re-a... more Photoinduced phase transitions from insulating to metallic states, accompanied by structural re-arrangements, have been recently reported in complex transition-metal oxides. However, the optical control of a purely electronic phase transition, where the thermodynamic phase is determined by the distribution of excitations, has remained elusive. Here we report optical control of the electronic phase in an underdoped Bi2Sr2CaCu2O8+δ crystal through impulsive photoinjection of quasiparticles (QP) via ultrashort laser pulses, avoiding significant laser heating. An abrupt transition of the transient optical electronic response is observed at a critical fluence of Ipump≅70 μJ/cm 2 . We show that the measured dynamics is consistent with an inhomogenous first-order superconducting-to-normal state phase transition, triggered by a sudden shift of the chemical potential. The impulsive modification by ultrashort light pulses (∼100 fs) of electronic, magnetic and structural properties in complex materials, has recently opened the field of photo-induced phase-transitions (PIPT)(1). Previous studies have focused on the insulator-to-metal PIPT in perovskite manganites (2-4) or vanadium dioxide (5,6), in which the transformation of both the electronic and structural properties occurs at once. On the contrary no evidence of optical control of a purely electronic phase transition has been reported so far. The superconducting-to-normal state phase-transition (SNPT) is one of the most important examples of electronic phase transitions in solid-state systems. At zero temperature the BCS theory (7) explains the formation of the superconducting (SC) electronic phase in terms of the macroscopic condensation of the Cooper pairs, originated from the phonon-mediated coupling of two electrons. The excitation spectrum is characterized by the opening of the superconducting gap Δk, representing half the energy necessary to break a Cooper pair