Phonons#
In this example coherent acoustic phonon dynamics are calculated according to the results of the heat simulations.
Setup#
Do all necessary imports and settings.
import udkm1Dsim as ud
u = ud.u # import the pint unit registry from udkm1Dsim
import scipy.constants as constants
import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline
u.setup_matplotlib() # use matplotlib with pint units
Structure#
Refer to the structure-example for more details.
O = ud.Atom('O')
Ti = ud.Atom('Ti')
Sr = ud.Atom('Sr')
Ru = ud.Atom('Ru')
Pb = ud.Atom('Pb')
Zr = ud.Atom('Zr')
# c-axis lattice constants of the two layers
c_STO_sub = 3.905*u.angstrom
c_SRO = 3.94897*u.angstrom
# sound velocities [nm/ps] of the two layers
sv_SRO = 6.312*u.nm/u.ps
sv_STO = 7.800*u.nm/u.ps
# SRO layer
prop_SRO = {}
prop_SRO['a_axis'] = c_STO_sub # aAxis
prop_SRO['b_axis'] = c_STO_sub # bAxis
prop_SRO['deb_Wal_Fac'] = 0 # Debye-Waller factor
prop_SRO['sound_vel'] = sv_SRO # sound velocity
prop_SRO['opt_ref_index'] = 2.44+4.32j
prop_SRO['therm_cond'] = 5.72*u.W/(u.m *u.K) # heat conductivity
prop_SRO['lin_therm_exp'] = 1.03e-5 # linear thermal expansion
prop_SRO['heat_capacity'] = '455.2 + 0.112*T - 2.1935e6/T**2' # [J/kg K]
SRO = ud.UnitCell('SRO', 'Strontium Ruthenate', c_SRO, **prop_SRO)
SRO.add_atom(O, 0)
SRO.add_atom(Sr, 0)
SRO.add_atom(O, 0.5)
SRO.add_atom(O, 0.5)
SRO.add_atom(Ru, 0.5)
# STO substrate
prop_STO_sub = {}
prop_STO_sub['a_axis'] = c_STO_sub # aAxis
prop_STO_sub['b_axis'] = c_STO_sub # bAxis
prop_STO_sub['deb_Wal_Fac'] = 0 # Debye-Waller factor
prop_STO_sub['sound_vel'] = sv_STO # sound velocity
prop_STO_sub['opt_ref_index'] = 2.1+0j
prop_STO_sub['therm_cond'] = 12*u.W/(u.m *u.K) # heat conductivity
prop_STO_sub['lin_therm_exp'] = 1e-5 # linear thermal expansion
prop_STO_sub['heat_capacity'] = '733.73 + 0.0248*T - 6.531e6/T**2' # [J/kg K]
STO_sub = ud.UnitCell('STOsub', 'Strontium Titanate Substrate',
c_STO_sub, **prop_STO_sub)
STO_sub.add_atom(O, 0)
STO_sub.add_atom(Sr, 0)
STO_sub.add_atom(O, 0.5)
STO_sub.add_atom(O, 0.5)
STO_sub.add_atom(Ti, 0.5)
S = ud.Structure('Single Layer')
S.add_sub_structure(SRO, 100) # add 100 layers of SRO to sample
S.add_sub_structure(STO_sub, 2000) # add 1000 layers of STO substrate
Heat#
Refer to the heat-example for more details.
h = ud.Heat(S, True)
h.save_data = False
h.disp_messages = True
h.excitation = {'fluence': [5]*u.mJ/u.cm**2,
'delay_pump': [0]*u.ps,
'pulse_width': [0]*u.ps,
'multilayer_absorption': True,
'wavelength': 800*u.nm,
'theta': 45*u.deg}
# temporal and spatial grid
delays = np.r_[-10:90:0.1]*u.ps
_, _, distances = S.get_distances_of_layers()
temp_map, delta_temp_map = h.get_temp_map(delays, 300*u.K)
Surface incidence fluence scaled by factor 0.7071 due to incidence angle theta=45.00 deg
Absorption profile is calculated by multilayer formalism.
Total reflectivity of 56.1 % and transmission of 5.7 %.
Elapsed time for _temperature_after_delta_excitation_: 0.014078 s
Elapsed time for _temp_map_: 0.087904 s
plt.figure(figsize=[6, 8])
plt.subplot(2, 1, 1)
plt.plot(distances.to('nm').magnitude, temp_map[101, :])
plt.xlim([0, distances.to('nm').magnitude[-1]])
plt.xlabel('Distance (nm)')
plt.ylabel('Temperature (K)')
plt.title('Temperature Profile')
plt.subplot(2, 1, 2)
plt.pcolormesh(distances.to('nm').magnitude, delays.to('ps').magnitude, temp_map, shading='auto')
plt.colorbar()
plt.xlabel('Distance (nm)')
plt.ylabel('Delay (ps)')
plt.title('Temperature Map')
plt.tight_layout()
plt.show()
Analytical Phonons#
The PhononAna class requires a Structure object and a boolean force_recalc in order overwrite previous simulation results.
These results are saved in the cache_dir when save_data is enabled.
Printing simulation messages can be en-/disabled using disp_messages and progress bars can using the boolean switch progress_bar.
pana = ud.PhononAna(S, True)
pana.save_data = False
pana.disp_messages = True
strain_map, A, B = pana.get_strain_map(delays, temp_map, delta_temp_map)
Calculating linear thermal expansion ...
Calculating _eigen_values_ ...
Elapsed time for _eigen_values_: 5.798789 s
Calculating _strain_map_ ...
Elapsed time for _strain_map_: 22.619074 s
plt.figure(figsize=[6, 8])
plt.subplot(2, 1, 1)
plt.plot(distances.to('nm').magnitude, strain_map[130, :], label=np.round(delays[130]))
plt.plot(distances.to('nm').magnitude, strain_map[350, :], label=np.round(delays[350]))
plt.xlim([0, distances.to('nm').magnitude[-1]])
plt.xlabel('Distance (nm)')
plt.ylabel('Strain')
plt.legend()
plt.title('Analytical Strain Profile')
plt.subplot(2, 1, 2)
plt.pcolormesh(distances.to('nm').magnitude, delays.to('ps').magnitude,
strain_map, cmap='RdBu', vmin=-np.max(strain_map),
vmax=np.max(strain_map), shading='auto')
plt.colorbar()
plt.xlabel('Distance (nm)')
plt.ylabel('Delay (ps)')
plt.title('Analytical Strain Map')
plt.tight_layout()
plt.show()
Energy Spectrum#
The analytical phonon model easily allows for calculating the energy per eigenmode of the coherent acoustic phonon spectrum for every delay of the simulation.
omega, E = pana.get_energy_per_eigenmode(A, B)
Calculating _eigen_values_ ...
Elapsed time for _eigen_values_: 4.613268 s
plt.figure()
plt.plot(omega, E[-1, :])
plt.xlim(omega[0], omega[-1])
plt.xscale('log')
plt.xlabel('Frequency (Hz)')
plt.ylabel('Energy (J)')
plt.title('Analytical Energy Spectrum')
plt.show()
Numerical Phonons#
The PhononNum class requires a Structure object and a boolean force_recalc in order overwrite previous simulation results.
These results are saved in the cache_dir when save_data is enabled.
Printing simulation messages can be en-/disabled using disp_messages and progress bars can using the boolean switch progress_bar.
pnum = ud.PhononNum(S, True)
pnum.save_data = False
pnum.disp_messages = True
The actual calculation is done in one line:
strain_map = pnum.get_strain_map(delays, temp_map, delta_temp_map)
Calculating linear thermal expansion ...
Calculating coherent dynamics with ODE solver ...
Elapsed time for _strain_map_: 0.513159 s
plt.figure(figsize=[6, 8])
plt.subplot(2, 1, 1)
plt.plot(distances.to('nm').magnitude, strain_map[130, :], label=np.round(delays[130]))
plt.plot(distances.to('nm').magnitude, strain_map[350, :], label=np.round(delays[350]))
plt.xlim([0, distances.to('nm').magnitude[-1]])
plt.xlabel('Distance (nm)')
plt.ylabel('Strain')
plt.legend()
plt.title('Numerical Strain Profile')
plt.subplot(2, 1, 2)
plt.pcolormesh(distances.to('nm').magnitude, delays.to('ps').magnitude,
strain_map, cmap='RdBu', vmin=-np.max(strain_map),
vmax=np.max(strain_map), shading='auto')
plt.colorbar()
plt.xlabel('Distance (nm)')
plt.ylabel('Delay (ps)')
plt.title('Numerical Strain Map')
plt.tight_layout()
plt.show()
Anharmonic Phonon Propagation#
The numerical phonon dynamic calculations also allow for phonon damping and non-linear phonon propagation.
This can be achieved by setting the phonon_damping property and using the set_ho_spring_constants() method of the according layers.
STO_sub.phonon_damping = -1e10*u.kg/u.s
STO_sub.set_ho_spring_constants([-7e11])
Recalculate the coherent phonon dynamics:
strain_map = pnum.get_strain_map(delays, temp_map, delta_temp_map)
Calculating linear thermal expansion ...
Calculating coherent dynamics with ODE solver ...
Elapsed time for _strain_map_: 0.792851 s
plt.figure(figsize=[6, 8])
plt.subplot(2, 1, 1)
plt.plot(distances.to('nm').magnitude, strain_map[130, :], label=np.round(delays[130]))
plt.plot(distances.to('nm').magnitude, strain_map[350, :], label=np.round(delays[350]))
plt.plot(distances.to('nm').magnitude, strain_map[-1, :], label=np.round(delays[-1]))
plt.xlim([0, distances.to('nm').magnitude[-1]])
plt.xlabel('Distance (nm)')
plt.ylabel('Strain')
plt.legend()
plt.title('Anharmonic Strain Profile')
plt.subplot(2, 1, 2)
plt.pcolormesh(distances.to('nm').magnitude, delays.to('ps').magnitude,
strain_map, cmap='RdBu', vmin=-np.max(strain_map),
vmax=np.max(strain_map), shading='auto')
plt.colorbar()
plt.xlabel('Distance (nm)')
plt.ylabel('Delay (ps)')
plt.title('Anharmonic Strain Map')
plt.tight_layout()
plt.show()
