Post on 20-Mar-2018
Ultrafast Structural and Electronic Dynamics of theMetallic Phase in a Layered Manganite
Luca Piazza
Laboratory for Ultrafast Microscopy and Electron Scattering
Ecole Polytechnique Federale de Lausanne — Switzerland
LUMES
December 10, 2013 — FEIS 2013 — Key West
The manganites
Manganese compounds AMnO3 (A=La, Ca,Ba, Sr, Pb, Nd, Pr)
known since 50 years, present colossalmagnetoresistance
layered material
rich phase-space
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 3 / 12
The manganites
Manganese compounds AMnO3 (A=La, Ca,Ba, Sr, Pb, Nd, Pr)
known since 50 years, present colossalmagnetoresistance
layered material
rich phase-space
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 3 / 12
The manganites
Manganese compounds AMnO3 (A=La, Ca,Ba, Sr, Pb, Nd, Pr)
known since 50 years, present colossalmagnetoresistance
layered material
rich phase-space
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 3 / 12
The manganites
Manganese compounds AMnO3 (A=La, Ca,Ba, Sr, Pb, Nd, Pr)
known since 50 years, present colossalmagnetoresistance
layered material
rich phase-space
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 3 / 12
The manganites
Manganese compounds AMnO3 (A=La, Ca,Ba, Sr, Pb, Nd, Pr)
known since 50 years, present colossalmagnetoresistance
layered material
rich phase-space
Strongly correlated electron systems
- Spin - Charge
- Orbital - Crystal field
- Chemical doping - Magnetic field
- Temperature - Pressure
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 3 / 12
The manganites
Manganese compounds AMnO3 (A=La, Ca,Ba, Sr, Pb, Nd, Pr)
known since 50 years, present colossalmagnetoresistance
layered material
rich phase-space
Strongly correlated electron systems
- Spin - Charge
- Orbital - Crystal field
- Chemical doping - Magnetic field
- Temperature - Pressure
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 3 / 12
How to measure the energy gap?
Optical absorption spectroscopy in diamond envil cells
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 4 / 12
How to measure the energy gap?
Optical absorption spectroscopy in diamond envil cells Limitations:
for energy gaps of ∼0.1eV we needwavelengths of ∼10µm
pressure limited to ∼102GPa
it’s necessary a big sample (mm3)
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 4 / 12
The fs -TEM approach
Stimulate a pressure wave with a laserpulse:
not isotropic, we can choose whichaxis of the sample to analyze
no intensity restrictions
dimension of the monocrystal notcritical, we can work on flakes torule out border effects inpolycrystals
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 5 / 12
The fs -TEM approach
Stimulate a pressure wave with a laserpulse:
not isotropic, we can choose whichaxis of the sample to analyze
no intensity restrictions
dimension of the monocrystal notcritical, we can work on flakes torule out border effects inpolycrystals
Measure the system with fs-TEM:
have access to atatic andtime-dependent diffraction andelectron energy loss spectroscopy
straightforward observation of bothstructural and electronic propertiesof the same µ-size sample
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 5 / 12
PrSr0.2Ca1.8Mn2O7
Crystal structure
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 6 / 12
PrSr0.2Ca1.8Mn2O7
Crystal structurePhase diagram
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 6 / 12
PrSr0.2Ca1.8Mn2O7
Charge and orbital ordering Phase diagram
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 6 / 12
PrSr0.2Ca1.8Mn2O7
Charge and orbital ordering Mixed valence state
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 6 / 12
Diffraction - temperature dependence
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 7 / 12
Diffraction - time dependence
system in the metallic phase
decrease of the intensity of Braggpeak due to Debye-Waller effect
drum-like oscillation of the flake
termal expansion of the sample
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 8 / 12
EELS - time dependence
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 9 / 12
DFT simulations
Differential EELS spectra
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 10 / 12
DFT simulations
Differential EELS spectra - Oxygen K-edge and energy bandgap
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 11 / 12
Conclusions
we cannot directly observe the evolution of the energygap due to insufficient energy resolution
the DFT model reproduces correctly the static energy lossspectrum of the system
dynamic informations from time-resolved diffraction permitto extend the simulation in the time domain
we can indirectly obtain informations about cryticalproperties not easily accessible (energy gap)
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 12 / 12
Conclusions
we cannot directly observe the evolution of the energy gapdue to insufficient energy resolution
the DFT model reproduces correctly the static energyloss spectrum of the system
dynamic informations from time-resolved diffraction permitto extend the simulation in the time domain
we can indirectly obtain informations about cryticalproperties not easily accessible (energy gap)
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 12 / 12
Conclusions
we cannot directly observe the evolution of the energy gapdue to insufficient energy resolution
the DFT model reproduces correctly the static energy lossspectrum of the system
dynamic informations from time-resolved diffractionpermit to extend the simulation in the time domain
we can indirectly obtain informations about cryticalproperties not easily accessible (energy gap)
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 12 / 12
Conclusions
we cannot directly observe the evolution of the energy gapdue to insufficient energy resolution
the DFT model reproduces correctly the static energy lossspectrum of the system
dynamic informations from time-resolved diffraction permitto extend the simulation in the time domain
we can indirectly obtain informations about cryticalproperties not easily accessible (energy gap)
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 12 / 12
Conclusions
we cannot directly observe the evolution of the energy gapdue to insufficient energy resolution
the DFT model reproduces correctly the static energy lossspectrum of the system
dynamic informations from time-resolved diffraction permitto extend the simulation in the time domain
we can indirectly obtain informations about cryticalproperties not easily accessible (energy gap)
Thank you for your attention!
Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 12 / 12