@article{19828,
  abstract     = {We describe an optical method to directly measure the position-dependent thermal diffusivity of reflective single crystal samples across a broad range of temperatures for condensed matter physics research. Two laser beams are used, one as a source to locally modulate the sample temperature, and the other as a probe of sample reflectivity, which is a function of the modulated temperature. Thermal diffusivity is obtained from the phase delay between source and probe signals. We combine this technique with a microscope setup in an optical cryostat, in which the sample is placed on a three-axis piezo-stage, allowing for spatially resolved measurements. Furthermore, we demonstrate experimentally and mathematically that isotropic in-plane diffusivity can be obtained when overlapping the two laser beams instead of separating them in the traditional way, which further enhances the spatial resolution to a micron scale, especially valuable when studying inhomogeneous or multidomain samples. We discuss in detail the experimental conditions under which this technique is valuable and demonstrate its performance on two stoichiometric bilayer ruthenates: Sr3Ru2O7 and Ca3Ru2O7. The spatial resolution allowed us to study the diffusivity in single domains of the latter, and we uncovered a temperature-dependent in-plane diffusivity anisotropy. Finally, we used the enhanced spatial resolution enabled by overlapping the two beams to measure the temperature-dependent diffusivity of Ti-doped Ca3Ru2O7, which exhibits a metal–insulator transition. We observed large variations of transition temperature over the same sample, originating from doping inhomogeneity and pointing to the power of spatially resolved techniques in accessing inherent properties.},
  author       = {Sun, F. and Mishra, S. and McGuinness, P. H. and Filipiak, Z. H. and Marković, I. and Sokolov, D. A. and Kikugawa, N. and Orenstein, J. W. and Hartnoll, S. A. and Mackenzie, A. P. and Sunko, Veronika},
  issn         = {1089-7623},
  journal      = {Review of Scientific Instruments},
  number       = {4},
  publisher    = {AIP Publishing},
  title        = {{A spatially resolved optical method to measure thermal diffusivity}},
  doi          = {10.1063/5.0098800},
  volume       = {94},
  year         = {2023},
}

@article{5816,
  abstract     = {Solid-state qubit manipulation and read-out fidelities are reaching fault-tolerance, but quantum error correction requires millions of physical qubits and therefore a scalable quantum computer architecture. To solve signal-line bandwidth and fan-out problems, microwave sources required for qubit manipulation might be embedded close to the qubit chip, typically operating at temperatures below 4 K. Here, we perform the first low temperature measurements of a 130 nm BiCMOS based SiGe voltage controlled oscillator at cryogenic temperature. We determined the frequency and output power dependence on temperature and magnetic field up to 5 T and measured the temperature influence on its noise performance. The device maintains its full functionality from 300 K to 4 K. The carrier frequency at 4 K increases by 3% with respect to the carrier frequency at 300 K, and the output power at 4 K increases by 10 dB relative to the output power at 300 K. The frequency tuning range of approximately 20% remains unchanged between 300 K and 4 K. In an in-plane magnetic field of 5 T, the carrier frequency shifts by only 0.02% compared to the frequency at zero magnetic field.},
  author       = {Hollmann, Arne and Jirovec, Daniel and Kucharski, Maciej and Kissinger, Dietmar and Fischer, Gunter and Schreiber, Lars R.},
  issn         = {0034-6748},
  journal      = {Review of Scientific Instruments},
  number       = {11},
  publisher    = {AIP Publishing},
  title        = {{30 GHz-voltage controlled oscillator operating at 4 K}},
  doi          = {10.1063/1.5038258},
  volume       = {89},
  year         = {2018},
}