Difference: QuantizedConductance (7 vs. 8)

Revision 82019-01-08 - JinHe

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META TOPICPARENT	name="PHY4821L"

Lab Assignment: Quantized Conductance Lab

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In this lab, you will explore the phenomena of quantized conductance in a gold nanocontact repeated created at room temperature. From the experiment, you will understand the importance of quantum mechanics at the nanoscale. You will also learn the typical electrical characterization techniques in condensed matter Physics and nano science fields.

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Quantum mechanics states that electrons behave like waves. Howver, in macroscopic systems, we rarely observe their wavelike properties. For example, the electron transport in bulk metal can be well-expalined by the classical Drude's model

. As the system becomes smaller and the temperature goes down, Drude’s model no longer explains the electronic transport. the wave properties of electroan appear.

In this lab, you will explore the phenomena of quantized conductance in a gold quantum point contact repeatedly created at room temperature. From the experiment, you will understand the importance of quantum mechanics at the nanoscale. You will also learn the typical electrical characterization techniques in condensed matter Physics and nano science fields.

Theory

Please read the references(see the three attachments at the bottom of this page) to understand the quantized conductance through classical Physics (Drude model) and Quantum Physics.

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Quantum conductance can also refer to Wikipedia: https://en.wikipedia.org/wiki/Conductance_quantum

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Quantum conductance, denoted by the symbol G_0, is the quantized unit of electrical conductance. It is defined by the elementary charge e and Planck constant h as G0=2e^2/h=7.7480917310(18)×10⁻⁵ S≈1/13 kΩ

More information can refer to Wikipedia: https://en.wikipedia.org/wiki/Conductance_quantum

You should also read refs about quantum tunneling. Quantum tunneling happens when the two metal electrodes are in a distance of a few nanometers. You will observe the quantum tunneling current right after the breakage of the gold point contact. Based on quantum tunnleing, Scanning Tunneling Microscope (STM) was invented and STM can help us to see individual atoms at real space.

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You can also read refs about quantum tunneling.

Setup and calibration

Before the experiment, you need to understand the theory and principle of the experiment.

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6. Develop understanding of quantum mechanics

Part A: Data Collection

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Observe quantum steps in the current vs distance (I-d) curve. You should be able to see at least one conductance (conductance=current/voltage) step at G0=2e^2/h=77.5 microsiemen (uS) or R0=1/G0=12.9 kohm, There are typically more than 1 steps, appearing at 1G0, 2G0, 3G0...

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Observe quantum steps in the current vs distance (I-d) curve. You should be able to see at least one conductance (conductance=current/voltage) step at G0=2e^2/h≈77.5 microsiemen (uS) or R0=1/G0=12.9 kΩ, There are typically more than 1 steps, appearing at 1G0, 2G0, ...

Learn how to optimize the experimental conditions, i.e., tip approach and withdraw speed of the tip, applied bias, environment (in air and in solution).

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Build histograms from 50, 100 and 200 I-d curves at 0.1V bias. Compare the shape of peaks.

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Build histograms from 50, 100 and 200 I-d curves at 0.1V bias. Compare the shape of peaks and understand how the statistics play the role.

Collect about 200 withdraw conductance curves (more is better) at different biases, 0.05V, 0.1V, 0.2V.

Part B: Data Analysis

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Electrical and Mechanical noise reduction setup

Write Up

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You need to explain the experiment principle and theory.

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You need to explain the experiment principle and theory, quantum conductance, quantum tunneling.

The experimental setup: Simple diagram of electrical circuit of electrical measurement. How the gold point contact was repeatedly formed, the Piezoelectric effect. The precise control of distance by Piezo actuator.

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