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Quantification of charge transport parameters with electronic Raman scattering
It is a technical challenge to independently measure charge transport parameters for both holes and electrons in a semimetal using electric transport experiments. We bypassed this problem with the electronic Raman scattering method that allows us to resolve the dynamics of both conduction holes and electrons in thin films of SrIrO3. The Raman responses of both holes and electrons display an electronic continuum which is well described by a marginal Fermi liquid model. Analyzing these Raman responses within a memory function formalism, we extracted their frequency-dependent scattering rate and mass enhancement, from which we determined their DC-mobilities and electrical resistivities. More details ...
Raman scattering as a probe for phonons and magnons in CrAs
CrAs exhibit a first-order magneto-structural transition at 265 K, below which the magnetic moments of Cr form an incommensurate helical magnetic structure. At the transition, the unit-cell volume abruptly expands by a massive 2 %. We detected phonons, magnons, and the signature of spin-phonon coupling in this compound using Raman scattering. More details ...
Momentum-resolved phonons with inelastic x-ray scattering
Raman scattering is a sensitive probe for the phonons that are close to the zone-center, i.e. the phonons that have vanishing crystal momentums. On contrary, inelastic x-ray scattering can map out the entire phonon branches in a Brillouin zone. We used this method at ESRF synchrotron facility to map out the phonon dispersions for two iridates Sr2IrO4 and Sr3Ir2O7. More details ...
Tweaking interaction between interfacial Cu and Mn moments in artificial heterostructures
YBa2Cu3O7 is a high-Tc superconductor, in which Cu ions do not form any magnetic order. However, if a strong ferromagnet, e.g. La2/3Ca1/3MnO3, is brought to the proximity of YBa2Cu3O7 in artificial heterostructures, then the Cu ions at the interfaces become magnetic. In particular, a pronounced antiferromagnetic coupling evolves between Cu and Mn ions at the interface. We specifically obtained that this antiferromagnetic coupling is extremely sensitive to the electric and magnetic properties of the magnetic layers. We can achieve ferromagnetic coupling between interfacial Cu and Mn ions if the magnetic layers become insulating but remain magnetic. We used pulsed laser deposition to grow these artificial heterostructures. We performed x-ray magnetic circular dichroism experiments at the Swiss Light Source to elucidate element-specific magnetism. More details ...
Charge carrier localization in extremely thin superconducting thin films
Superconductivity in Cu-based superconductors arises from an antiferromagnetic insulating state. For example, La2CuO4 is an antiferromagnetic insulator, whereas Sr-doped La1.85Sr0.15CuO4 is a high-Tc superconductor that does not have a long-range antiferromagnetic order. These apparent antagonistic order parameters motivated us to combine a very thin (1 unit cell thick) superconducting layer with the antiferromagnetic La2CuO4 in thin-film bilayers. We observed that the one-unit-cell thick La1.85Sr0.15CuO4 remains a superconductor as long as the capping La2CuO4 layer is very thin, about 2 unit cells thick. Remarkably, we observed a huge localization in electric resistance when the top La2CuO4 layer is about 7 unit-cells thick. We used pulsed laser deposition and in-situ RHEED to grow these ultrathin bilayers with controlled thickness. More details ...
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