University at Buffalo
132 Fronczak Hall
Buffalo, NY 14260
PH: (716) 645-2017, ext. 126
Web: http://enthalpy.physics.buffalo.edu
E: fmg@buffalo.edu
139 Fronczak Hall
Buffalo, NY 14260
PH: (716) 645-2017, ext. 132
Research
Measurement of the separation between two bonded wafers used for helium confinement as a function of position along the wafer surface. (a), (b), and (c) Cells designed for 2D, 1D, and 0D crossover, respectively. The wafers are separated with less than ~1% deviation from the average value.
- critical behavior at continuous phase transitions
- quantum fluids
- cryogenic techniques
- direct Si wafer bonding
- low temperature measurements
Most recent research is summarized in a paper to appear in Oct. 2008 in Reviews of Modern Physics, available at: http://enthalpy.physics.buffalo.edu/Papers/RevModPhys_80_001009-2.pdf The abstract follows.
Experimental results for confined 4He are reviewed that are relevant to correlation-length scaling near the superfluid transition. Data are discussed for which the uniform confinement represents dimensionality crossover from three dimensions (3D) to 2D, 1D, and 0D. In addition, data for the onset of superfluidity are discussed representing 2D to 1D crossover. Collectively, these data for the specific heat, superfluid density, and thermal conductivity yield, in some cases, excellent agreement with expectations of correlation-length scaling and, in others, surprising disagreement. This is especially true in the case of 3D to 2D crossover where data are most plentiful. Here there is a clear distinction between scaling when the confined helium is normal and the lack of scaling when helium becomes superfluid. By far the most problematic result is the lack of scaling for the superfluid density for 3D to 2D crossover and, to some extent, for 3D to 1D crossover. Connectivity and proximity effects can be identified with some data. These might explain some experimental results and present opportunities for further studies of weakly coupled superfluid regions. Measurements to test the universality of finite-size effects along the superfluid transition lines as a function of pressure and 3He concentration are also discussed. In the case of the specific heat, data indicate that the nonuniversal behavior of the critical exponent α, obtained from bulk measurements, is responsible for the observation of a distinct scaling locus for confined pure 4He versus that of the confined mixtures.
Two cryostats to work down to 1.5K and associated measuring instrumentation; Equipment for direct Si wafer bonding