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Reza Mosalanejad Prof. Johan Chang
Overview
University of Zurich - Physics Institute 2/17
• Introduction
• TOF INS
• ISIS Facility
• Motivation
• Antiferromagnet Spectrum
• Discussion
• Summary & Conclusions
Introduction
University of Zurich - Physics Institute 4/17
Time of Flight spectroscopy
University of Zurich - Physics Institute 6/17
Rutherford Appleton Laboratory DIAMOND synchrotron
ISIS spallation neutron facility
PSI
SLS synchrotron
SINQ Swiss spallation neutron Source
Image of SINQ Swiss spallation neutron Source
Image of ISIS MAPS beamline
MAPS Neutron beam energy:
160, 240, 450 meV This energy range is called epithermal
University of Zurich - Physics Institute 8/19
Neutron has no electric charge Weak interaction with matter
Experiments need to be run for hours Multiple samples as the
target
Motivation
Motivation
University of Zurich - Physics Institute 10/19
Layered copper oxides + doping are HTS
These compounds are Mott-insulating
square-lattice antiferromagnets
Superconductivity related to magnetic order?
It is important to
investigate the magnetic interactions
But no theory for cuprate HTS Layered copper oxides:
YBCO, BSCCO, LCO, etc
Antiferromagnet Spectrum
University of Zurich - Physics Institute 12/19
Our starting point should be Hubbard model
, ,
Starting from the atomic limit for 2 atoms
Adding the perturbative hopping term t
MBZ LBZ
Heisenberg Model
2-magnon continuum
1-magnon (SW) dispersion
Calculations within SWT => SW excitations
University of Zurich - Physics Institute 14/19
Results from 3-4 days of measurement Measurement done with HET
beamline – no longer operational
Discussion
University of Zurich - Physics Institute 16/19
5 crystals were annealed in Ar at 1073 K for 48 h. Susceptibility measurements showed a Ne´el temperature of 320 K. INS data were corrected using the form factor
2-magnon scattering 4-magnon scattering
Higher magnon scatterings
Lines’ positions are well approximated by SWT But the line shape and intensity does not
Spinon continuum SW dispersion
(1- magnon)
Magnon dispersion within this model
Summary & Conclusions
• Magnetic interactions in layered copper oxides are of great importance
• Raman spectroscopy shows line shapes and high energy magnetic excitations not explained by SWT (e.g. up to 750 meV for )
• Optical absorption spectroscopy, and RIXS show high energy magnetic excitations not explained by SWT
• A q-dependent continuous spectrum is observed
• A dip in the intensity of the SW pole at (1/2,0) is observed
• Based on the total spectral weight measured, the total moment squared is , while the expectation is of the spectral intensity is missing
•
University of Zurich - Physics Institute 18/19
