Presentation on theme: "1-Dimensional Aluminum Superconducting Nanowires Albert M. Chang, Duke University, DMR 0701948 Superconductivity (SC) in ultra-narrow metallic wires is."— Presentation transcript:
1-Dimensional Aluminum Superconducting Nanowires Albert M. Chang, Duke University, DMR Superconductivity (SC) in ultra-narrow metallic wires is exciting from both fundamental and applications- technology perspectives. When the width and height of a nanowire approach 30 atoms in each direction, one enters the 1-dimensional limit. Our goals are to determine to what degree SC can survive at such reduced dimensions, and whether new behaviors can arise, such as the recently proposed "voltage Josephson" effect, based on which a new standard for the electrical current as well as a novel SC nanowire qubits for quantum computation can be constructed. As a important step, we have investigated the relationship between the voltage and the current in aluminum nanowires. When the electrical current is increased beyond a critical value, Ic, the wire switches from a SC state with minimal resistance to a resistive state. Upon repeated measurements, Ic varies slightly, and is characterized by an average (Ic_ave), and a width of the distribution of Ic values, (Ic_sd). These quantities can provide hints about the mechanism, which causes the SC to weaken, leading to the new regime of behavior. Top panel--A transmission electron microscope (TEM) picture of a 8 nm x 8 nm x 20 m aluminum nanowire. Bottom-- Ic_ave and Ic_sd in a 10 m long Al nanowire. As the temperature approaches absolute zero, Ic_sd, appears to extrapolate to a finite value, green curve region (1). This may be an indication that macroscopic quantum tunneling of the SC phase is taking place, and is the mechanism for the weakening of the SC. The macroscopic quantum tunneling of the SC phase is a critical ingredient of the novel, “voltage Josephson" effect. SC-pads denotes connection of the wire to SC electrical measurement leads.
1-Dimensional Aluminum Superconducting Nanowires Albert M. Chang, Duke University, DMR P.I. A.M. Chang was on a year-long sabbatical abroad in AY Thus, he was not able to actively engage in outreach. However, as an indication of the type of effort he had put forth in the past (AY ) while funded by this grant, in the left panel, a copy of the from physics teacher, Mr. Green (a senior member close to retirement) at Jordan High School in Durham, NC, following Dr. Chang’s visit to his Advanced Placement Physics class in May, 2008, is reproduced. Going forward, P.I. A.M. Chang plans to expand his effort, to include high schools without AP physics, to introduce science to minority students. Date: Sun, 8 Jun :37: From: David Green To: Subject: Talk/Demo at Jordan HS Parts/Attachments: 1 OK ~27 lines Text 2 Shown ~32 lines Text Dr. Chang, I spoke with Bill McNairy at church today and he asked me how your presentation went. My first comment was fantastic! then I remembered that I not formally thanked you for your efforts. I do apologize to you for this late thank you note but I will admit that the press of end of school work floored me. First I want you to know that my kids really liked what you did. It let directly into my last two days of class where I used magnetism to measure the mass of the electron (using an ancient tuning eye inside a solenoid). It was very obvious that the kids appreciated your work since just two days ago they gave me a new basketball to replace the one we tore up using the liquid N2. They even signed it for me!! I am very interested in having you come again next year - hopefully more than once. You did a wonderful job and were very able to work with HS aged kids! Thanks so very much! David Green Jordan HS Durham, NC June 8, 2008