ABSTRACT
Comprehensive characterization of thermal properties in nanoscale heterostructures requires microscale thermally isolated platforms combined with sensitive thermometry in order to measure small heat accumulations. Amorphous SiNx membranes are often used for these measurements due to their low thermal conductivity and compatibility with standard fabrication techniques. The total thermal conductance of such SiNx membranes is typically microwatts per kelvin or higher. Here, we further reduce this thermal coupling to 120 nW/K by using a focused ion beam (FIB) to remove large portions of commercially available amorphous SiNx membranes, leaving a 100 µm × 100 µm square platform suspended by 10 µm wide by 325 µm long support legs. We demonstrate the capability of these platforms by measuring the heat capacity of a 6.2 ng Au sample and show that it matches well with established specific heat of bulk Au.
ABSTRACT
Using density matrix equations of motion, we predict a femtosecond collective spin tilt triggered by nonlinear, near-ultraviolet (approximately 3 eV), coherent photoexcitation of (Ga,Mn)As ferromagnetic semiconductors with linearly polarized light. This dynamics results from carrier coherences and nonthermal populations excited in the {111} equivalent directions of the Brillouin zone and triggers a subsequent uniform precession. We predict nonthermal magnetization control by tuning the laser frequency and polarization direction. Our mechanism explains recent ultrafast pump-probe experiments.
