Bolometric response of superconducting microbridges and single-walled carbon nanotubes

This thesis is an experimental study of the electrothermal properties of two types of microstructures, the superconducting microbridge and the single-walled carbon nanotube. A device that uses a temperature-dependent resistance to detect power is known as a bolometer. When biased on its superconducting transition, the strongly temperature-dependent resistance of a superconducting microbridge can be used to make an extremely sensitive power detector. We have developed two different types of superconducting bolometers for applications in terahertz spectroscopy.;The first type of superconducting bolometer consists of a thin film niobium microbridge with a superconducting critical temperature of approximately 6 K. The device is made much smaller than the detection wavelength (∼0.1-1 mm) to increase the sensitivity, and efficient coupling is achieved by integrating the microbridge in a planar terahertz antenna. The response time is set by electron-phonon coupling, which can be faster than one nanosecond. This detector has been developed for applications in time-resolved terahertz spectroscopy, in which one uses a terahertz signal to probe the state of a dynamic system on nanosecond to microsecond timescales.;The second type of superconducting bolometer consists of a thin film superconducting titanium nanobridge with a superconducting critical temperature of 0.3 K. This device is designed to achieve extremely high sensitivity and is predicted to be capable of detecting individual terahertz photons (energy ∼1-10 meV). To test these devices, we have developed a new experimental technique in which the energy of a single terahertz photon is simulated by the absorbed energy of a short microwave pulse. We find that, consistent with theoretical predictions, this device achieves sufficient energy resolution to detect single terahertz photons.;Finally, we discuss how the experimental techniques that we have developed to characterize superconducting bolometric detectors can also be used to study the physics of a different system, the single-walled carbon nanotube. Measurements of the bolometric response enable us to study the inelastic scattering processes in the nanotube. In particular, we are able to determine the thermal conductance for cooling of the nanotube electron system as a function of both the temperature of the electron system and the nanotube length.