SCANNING SET TRANSISTOR MICROSCOPE

研究了能量耗散对单个小约瑟夫森结中宏观量子隧穿的影响。我们成功地观察到了耗散相变。通过在小约瑟夫森结附近附加电阻来调节能量耗散。在这里，我们保持约瑟夫森的正常状态隧道电阻大于量子电阻，并改变附加电阻的电阻。在由镍铬合金制成的欧姆分流电阻器的情况下，当分流电阻Rs小于量子电阻Rq=h/4 e2时，呈现绝缘击穿电压的约瑟夫森结恢复超导性。另一方面，当Rs > Rq时，它是绝缘的。我们通过改变EJ/EC值确定了超导体-绝缘体转变的相图。并对隧道电阻的情况进行了研究。一个正常的小隧道结与一个小约瑟夫森结并联。欧姆分流电阻和隧道结具有不同类型的能量耗散，因为在前一种情况下电荷转移是连续的，而在后一种情况下是离散的。在理论预测中，S-I转变的相图在这两者之间是不同的。在初步实验中，隧道结的作用与欧姆分流电阻非常相似。

We studied the effect of energy dissipation on macroscopic quantum tunneling (MQT) in single small Josephson junction. We succeeded in observing dissipative phase transition. Energy dissipation was tuned by attaching a resistor at the very vicinity of small Josephson junction. Here we kept the normal state tunneling resistance of Josephson larger than the quantum resistance, and varied the resistance of the attached resistor. In case of Ohmic shunt resistor made of nickel chromium alloy, the Josephson junction that exhibits insulating behavor recovers superconductivity when the shunt resistance Rs was less than the quantum resistance Rq=h/4e2. On the other hand, when Rs > Rq, it was insulating. We determined the phase diagram for superconductor-insulator transition by varying EJ/EC values. The case of tunneling resistance was also studied. A normal small tunneling junction was connected to a small Josephson junction in parallel. The ohmic shunt resistor and the tunneling junction have different types of energy dissipation in that the charge transfer in the former case is continuous while in the latter discrete. In a theoretical prediction, the phase diagrams for the S-I transition are different between these two. In preliminary experiments, the tunneling junction acted quite similarly to the ohmic shunt resistance.