Ultrafast Structural and Electronic Dynamics of the ...bt.pa.msu.edu/FEIS2013/talks/piazza.pdfrule out border e ects in polycrystals Luca Piazza (EPFL) Ultrafast Dynamics of a Layered

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

People

Luca Piazza (EPFL) Ultrafast Dynamics of a Layered Manganite 10.12.2013 2 / 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


The manganites



layered material

rich phase-space


The manganites



layered material

rich phase-space


The manganites



layered material

rich phase-space


The manganites



layered material

rich phase-space

Strongly correlated electron systems

- Spin - Charge

- Orbital - Crystal field

- Chemical doping - Magnetic field

- Temperature - Pressure


The manganites



layered material

rich phase-space

Strongly correlated electron systems

- Spin - Charge

- Orbital - Crystal field

- Chemical doping - Magnetic field

- Temperature - Pressure


How to measure the energy gap?

Optical absorption spectroscopy in diamond envil cells


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)


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


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


PrSr0.2Ca1.8Mn2O7

Crystal structure


PrSr0.2Ca1.8Mn2O7

Crystal structurePhase diagram


PrSr0.2Ca1.8Mn2O7

Charge and orbital ordering Phase diagram


PrSr0.2Ca1.8Mn2O7

Charge and orbital ordering Mixed valence state


Diffraction - temperature dependence


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


EELS - time dependence


DFT simulations

Differential EELS spectra


DFT simulations

Differential EELS spectra - Oxygen K-edge and energy bandgap


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)


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




Conclusions



dynamic informations from time-resolved diffractionpermit to extend the simulation in the time domain



Conclusions






Conclusions





Thank you for your attention!


Documents

Ultrafast Structural and Electronic Dynamics of the ...bt.pa.msu.edu/FEIS2013/talks/piazza.pdfrule out border e ects in polycrystals Luca Piazza (EPFL) Ultrafast Dynamics of a Layered