Transitions between 2D superfluids and insulators is the focus of many experiments, ranging from cold atoms in optical lattices
[3] to thin films of superconductors and helium.
Two-dimensional Superconductors
One of the debated problems in condensed matter physics is the nature of the phase transition separating the superconducting state from metallic or
insulating phases in low-dimensional materials. The focus of most recent investigations has been to understand the transitions in these systems that occur
not as a result of typical thermal fluctuations but that occur strictly at zero temperature via quantum fluctuations. These so-called quantum phase
transitions are tuned by varying parameters such as charge density or magnetic field, and can occur in a wide variety of material systems.
The main focus of our investigations is to study the magnetic-field tuned superconductor-metal or superconductor-insulator transition in two-dimensional
superconductors. [1] These systems provide a model situation to study the nature of quantum transitions;
however, experiments over the past two decades have failed to provide a generally accepted perspective for these transitions. The impasse is partly because
the majority of experiments carried out on these systems have been performed using conventional electrical transport measurements, which are unable to
distinguish among a variety of proposed theoretical pictures.
Among the outstanding puzzles is the apparent observation of a "metallic" state, which occurs when there is a substantial number of cooper pairs
in the sample and also in the presence of a magnetic field which induces vortices [2]. Our current
investigations are focused to develop new experimental techniques that can probe more directly the superconducting state and track its destruction more
precisely when a magnetic field is applied
[1] “Superconductor-Insulator Transition in a-MoGe Thin Films,” Ali Yazdani, and A. Kapitulnik, Physical Review Letters 74, 3037–3040, (1995).(PDF FORMAT)
[2] “Observation of Quantum Dissipation in the Vortex State of Highly Disordered Two-Dimensional Superconductors,” D. Ephron, A. Yazdani, A. Kapitulnik, and M. R. Beasley, Physical Review Letters 76, 1529–1532, (1996). (PDF FORMAT)
[3] “Bose-Einstein condensation: Breaking up a superfluid,” H. Stoof, Nature 415, 25-26, (2002). (PDF FORMAT)
