2015 BFY II Abstract Detail Page
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||W12 - Quantized Conductance: A Contemporary Physics Experiment on the Wave-Particle Duality of Electrons
||This workshop will show a simple and inexpensive experiment demonstrating the emergence of quantum mechanical behavior with atomic-scale confinement. It links the quantum conductance (QC) to the wave-particle duality and demonstrates that confinement/boundary conditions give rise to quantization. The quantized conductance in stretched gold wires offers a unique approach to demonstrate quantum mechanical behavior: It is based on transport (i.e. current-voltage) measurements. Furthermore, the users see all components of the setup with their un-assisted eyes and the setup is manually controlled to break the gold wire and reconnect it. As the wire gets so thin that its diameter is comparable to the de Broglie wavelength of the current-carrying electrons, the conductance becomes clearly quantized.
The experimental setup includes a 'macroscopic' gold wire connected in series to a 1.5V-battery and a resistor, making a simple voltage divider. A weak point is made on the wire using a blade, then the gold wire is gradually stretched utilizing a simple micrometer and a bending mechanism that offers a huge motion reduction down to the sub-atomic scale. As the wire is stretched, the weak point gets narrower, making a constriction. The electrical conductance across the constriction rises smoothly but eventually becomes quantized when its width gets to the atomic limit (becoming comparable to the de Broglie wavelength of the electrons). The simple voltage divider circuit reads the voltage across the 'break junction' via LabView. Just before the wire breaks, the lateral confinement of the conduction electrons causes the step-wise change in resistance, or conductance.
The workshop will start by inspecting the setup, the electric circuit and the bending beam that carries the gold wire. After discussing the different components briefly, we will discuss the simple LabVIEW program used to collect and graph the data. Each user will then run the experiment, where they will manually move the micrometer to observe the breaking and reconnection of the wire (where the voltage across the wire will jump between 0V and 1.5V). The user will then 'zoom-in" into the parts of the data showing the quantized steps and will briefly analyze to see that the conductance is an integer number times two fundamental constants of nature: electron charge and Plank constant. Sample (i.e. gold wire on bending beam) preparation will also be demonstrated.
|Workshop Doc 1:
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