Condensed Matter Physics-
We develop novel instruments to study interesting phenomena in superconductivity, nanostructures and magnetism. To accomplish this, we design and build unique scanning probe microscopes (STM, AFM, and MFM, many at low temperatures) and we use them to probe thin films we make by co-evaporation. We also pattern samples with a variety of lithographies, ranging from optical (one micron), to electron beam (50 nm), and down to STM (9 nm so far). All this supports a wide variety of projects:
Surface studies of cleaved YBa2Cu3O7-x -
We discovered that the CuO chains in this compound have a charge modulation [PRL 69, 2967 (1992); PRL 73, 1154 (1994); PRL 75, 1387 (1995)] that was not predicted by theorists. Our observations have been confirmed other groups using neutron scattering and NMR. We are now adding a magnetic field to search for superconducting vortices.
Colossal Magnetoresistance (CMR)-
We make thin films of CMR materials, such as LaxCa1-xMnO3, by co-evaporation of the pure elements in a low pressure of oxygen. We have studied the magnetic and electronic properties of these films. We were the first to obtain images of magnetic domains in these materials, by using our homemade low temperature Magnetic Force Microscope [Science 276, 2006 (June 27, 1997)].
Nanostructures-
We developed a new technique for making metal lines as narrow as 9 nm by using an STM to break down organometallic gases.[APL 51, 247 (1987)] That was the "easy" part. We have also managed a much more difficult experiment: to connect these tiny wires to external leads for measurements of resistance vs. temperature. So far the smallest wire measured in a "four-point probe" configuration is 60 nm wide. Such small wires show quantum effects at temperatures below 50K. This project is also relevant to the fabrication of nanoscale electronic devices. We are now synthesizing carbon nanotubes an using them as STM tips for this project.
Mesoscopic waveguides and cavities in 2DEGs-
This is a new project in collaboration with Prof. Linda Reichl's theory group. We will be starting with a two-dimensional electron gas (2DEG) grown in a GaAs/AlGaAs heterostructure by Prof. Ben Streetman's group. We will use our electron-beam lithography setup to pattern metal electrodes with the shape of waveguides and cavities, all in the order of 100 nm in size. We will then cool the samples in our dilution refrigerator down to 25mK and we will measure the conductance of these structures in magnetic fields up to 8 Tesla. The theory predicts many interesting features in the conductance as a function of voltage and magnetic field.
