I. J. Maasilta

Observation of disorder-induced weakening of electron-phonon interaction in thin noble-metal films

We have used symmetric normal metal-insulator-superconductor (NIS) tunnel junction pairs, known as SINIS structures, for ultrasensitive thermometry in the temperature range 50 - 700 mK. By Joule heating the electron gas and measuring the electron temperature, we show that the electron-phonon (e-p) scattering rate in the simplest noble metal disordered thin films (Cu,Au) follows a

Heat under the microscope

T^4

Influence of phonon dimensionality on electron energy relaxation.

temperature dependence, leading to a stronger decoupling of the electron gas from the lattice at the lowest temperatures. This power law is indicative e-p coupling mediated by vibrating disorder, in contrast to the previously observed

Complex impedance, responsivity and noise of transition-edge sensors: Analytical solutions for two- and three-block thermal models

T^3

Infrared Pulsed Laser Deposition of Niobium Nitride Thin Films

and

Ray optics behavior of flux avalanche propagation in superconducting films

T^2

Microwave nanobolometer based on proximity Josephson junctions

laws.

Nanosecond voltage pulses from dendritic flux avalanches in superconducting NbN films

Recent advances in computational and spectroscopic tools offer new insights into the nature of thermal conduction at ever-finer length scales and ways to control it.

Normal metal-superconductor decoupling as a source of thermal fluctuation noise in transition-edge sensors

We studied experimentally the role of phonon dimensionality on electron-phonon (e-p) interaction in thin copper wires evaporated either on suspended silicon nitride membranes or on bulk substrates, at sub-Kelvin temperatures. The power emitted from electrons to phonons was measured using sensitive normal metal-insulator-superconductor tunnel junction thermometers. Membrane thicknesses ranging from 30 to 750 nm were used to clearly see the onset of the effects of two-dimensional (2D) phonon system. We observed for the first time that a 2D phonon spectrum clearly changes the temperature dependence and strength of the e-p scattering rate, with the interaction becoming stronger at the lowest temperatures below approximately 0.5 K for the 30 nm membranes.

Sub-micron normal-metal/insulator/superconductor tunnel junction thermometer and cooler using Nb

The responsivity and noise of a voltage-biased superconducting transition-edge sensor depends strongly on the details of its thermal model, and the simplest theory for TES response assumes a single heat capacity connected to the heat bath. Here, analytical results are derived and discussed for the complex impedance, the responsivity and the noise of a transition-edge sensor, when the thermal model is not simple but consists of either two or three connected heat capacities. The implications of the differences of the models are discussed, as well.