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Time Resolved ARPES

Angle-resolved photoelectron spectroscopy (ARPES) is a powerful experimental technique capable to unveil the electronic structure of solids. 
The technique is based on the photoelectric effect, consisting in the emission of electrons from the solid upon absorption of a photon. Modern two-dimensional electron analyzers provide access to both the energy and momentum distribution of the electrons in solids, thus allowing to image the material band structure.

 



The use of ultra-short laser pulses, with time duration of 100 fs has recently opened the possibility to investigate the temporal evolution of the low energy excitations in solids, via time-resolved ARPES (tr-ARPES). This technique relies on the use of two laser pulses, in a stroboscopic configuration: the first beam, with high intensity, excites the electronic properties out-of-equilibrium (pump). Instead, the second beam, with a suitable energy for photoemitting electrons, probes the band structure (probe). The relative arrival of the two pulses can be controlled, thus filming the evolution of the electronic properties before and after the optical excitation.

Tr-ARPES provides access to the characteristic relaxation times with energy and momentum resolution, in order to disentangle in the time domain scattering processes that at equilibrium compete on the same energy scales.

The T-ReX laboratory is equipped with a state-of-the art Specs Phoibos 225 hemispherical analyzer. The sample under scrutiny is mounted on a six degrees of freedom precision manipulator with He- cryostat, allowing for minimum sample temperature of ~ 30 K. 
Atomically clean sample surfaces can be obtained via sputtering-annealing cycles (for metallic single crystals) or by in-situ cleave
Sample alignment and surface quality are routinely verified by means of low energy electron diffraction (LEED) technique.Equilibrium ARPES experiments can be performed with a conventional discharge He plasma lamp.
All the main parameters are summarized in the tble below.
 

MAIN CHAMBER

PREP CHAMBER

LASER SOURCES

Phoibos 225 hemispherical Analyser
(Ang Res 0.2º, En. Res. 20 meV)
4 Axis Manipulator FHG at 6.2 eV (up to 700 kHz)
Six Axis Cryo- Manipulator
(T>20K)

Annealing (T<800ºC)

Cooling LN2

9.3 eV in Xe (up to 250 kHz)
Base Pressure: 5E-11 mbar Base Pressure:  < 1E-10 mbar HHG (>50 kHz)
LEED LEED - RGA TR-OPTICS on same crystal
Discharge Lamp: He (21.2 eV, 40.8 eV) Cleaving Tools 2 PPE
Electron Gun Sputtering (Ion Gun) Polarization Control
  Fast Entry Lock and sample parking Garage
(30 min for loading)
OPA pumping up to mid-IR
  Possibility to Install Evaporators  

For further information you can contact:
Federico Cilento
Michele Zacchigna
Ultima modifica il Giovedì, 21 Aprile 2016 13:14