Quantum Matters GradTalks

Tuesday, January 14, 2020 3:30 pm - 3:30 pm EST

Naman Gupta, Masters student with Prof. David Hawthorn

Introduction to the physics of high-Tc superconductivity

Superconductivity was discovered in 1911 in elemental metals by K. Onnes. Until the 1980s, physicists believed that the Bardeen–Cooper–Schrieffer (BCS) theory — which describes most of the physics of conventional superconductivity — barred superconductivity at temperatures greater than 30 K. In 1986, physicists G. Bednorz and A. Müller at the IBM Laboratory in Zurich reported that they have created a material (a Lanthanum based cuprate) that became superconducting at 35 K. Shortly after, other research groups found similar materials that became superconducting at around 90 K. Currently, the highest transition temperature known is around 140 K at ambient pressure.

In this meetup, I will give a brief introduction to the standing problem of high-Tc superconductivity (which is not described by the BCS theory) and briefly talk about different competing phases and orders observed on the cuprate phase diagram. Furthermore, I will introduce one of the experimental techniques to probe such orders, called Resonant X-Ray Scattering (REXS), if time permits.


1. From quantum matter to high-temperature superconductivity in copper oxides: https://www.nature.com/articles/nature14165

Tianze Zou, Masters student with Prof. Jan Kycia

Noise sources in low-level voltage measurements

When measuring voltage from the sample during an experiment, the noise is mixed in the detected signal. Understand the sources and magnitude of noise can help to explain the results from a low-level voltage measurement. The first part of the talk is a checklist of different types of noise, especially in the Hall voltage measurement of thermoelectric materials. The second part is to use the Agilent 34420A nano voltmeter as an example to talk about the specifications section of a voltmeter and its input noise.

1. Agilent technologies. Agilent 34420A nano volt/micro Ohm meter user guide. 2003
2. Keithley Instruments. Low-level measurements: precision DC current,  voltage, and resistance measurements. 4th edition, 1993.

These seminars consist of two 20 minute talks, with 10 minutes for questions and discussion.

We try to keep these talks general and for a broader audience with a basic understanding of condensed matter and quantum mechanics. It’s a monthly meetup by and for graduate students and post-docs; to talk about their research, learn new topics and share interesting ideas. If you have any questions or suggestions, feel free to contact us at qmgradtalks@gmail.com