We have fabricated a two-dimensional array of Josephson junctions within 100 nm of a twodimensional electron gas (2DEG) in a GaAs ͞AlGaAs heterostructure. The screening provided by the 2DEG causes the array to show superconducting behavior despite a large junction resistance. Varying the resistance per square of the 2DEG changes the dissipation in the electrodynamic environment of the array independently of any other parameters in the system. As the resistance increases, the current-voltage characteristics of the array change from superconducting to insulating in character. [S0031-9007(97)02822-6] PACS numbers: 74.50. + r, 05.30. -d, 74.25.Fy, 74.40. + k A variety of diverse physical systems, including granular [1] or homogeneous [2] thin films, two-dimensional (2D) Josephson-junction arrays [3], and high temperature superconductors [4] undergo a superconductor-insulator (S-I) phase transition as a characteristic resistance of the system in its normal state increases through a critical value on the order of the resistance quantum R Q h͞4e 2 ഠ 6.45 kV. The transition is quantum mechanical in nature: the increasing normal state resistance is associated with an increase in quantum fluctuations of the superconducting phase. Eventually, these fluctuations destroy global phase coherence and lead to an insulating state. It has been suggested [5-8] that the S-I transition in these systems could be driven by changes in dissipation; however, there appears to be no unambiguous supporting evidence. In thin films disorder plays a strong role, and recent theoretical work treating these systems as charge-2e bosons moving in a random 2D potential [9] has been met with substantial experimental verification [2,10]. Furthermore, the physical origin of the dissipation is unclear. In the case of Josephson junction arrays, although quasiparticle tunneling [5] at energies large compared to the superconducting gap produces dissipation characterized by the normal state resistance R N , it is unlikely that the relevant energy scales are so large [3,11]. At lower energies, quasiparticle dissipation is negligible since the subgap resistance is much larger than R N . In high temperature superconductors, it has been proposed [8] that an interpenetrating fluid of normal electrons produces the dissipation. However, radiation damage inflicted to increase the normal state resistance probably also increases the disorder and reduces the density of superconducting electrons.In this Letter, we describe the unambiguous observation of a dissipation-driven S-I transition. The sample was a specially designed and fabricated 40 3 40 Josephson junction array for which we can continuously vary the dissipation associated with the local electrodynamic environment independently of any other relevant parameters. To provide the variable dissipation, we fabricated the array on a GaAs͞Al 0.3 Ga 0.7 As heterostructure in which a 2D electron gas (2DEG) is located approximately 100 nm from the surface (see Fig. 1). The heterostructure was grown on a GaAs substrate usi...

We have measured the current-voltage (I V) cha-racteristics of oneand two-dimensional arrays of normal metal islands linked by small tunnel junctions. The tunneling resistance is large compared to the resistance quantum, and a ground plane reduces the screening length to much less than the interisland spacing. At temperatures well below the island charging energy, we find a threshold voltage Vr below which little current flows. For V & VT, I scales as (V/Vr -I)» where g = 1.36~0. 1 (1D) and 1.80 +. 0.16 (2D). We interpret this behavior as a dynamic critical phenomenon.