Physics 838 Seminar
10.15.2018 4:00 pm - 5:00 pm
John S. Toll Rm 1201


Speaker 1: Mark Zic

Title: Enhancement of Superconductivity in Unconventional Superconductors by Gamma Irradiation

Abstract: Irradiation is intuitively thought to cause disorder in superconducting systems, especially through magnetic impurities. Gamma irradiation, although a charge neutral process, can introduce magnetic impurities in a lattice through vacancies and pair production. Surprisingly, we observe an enhancement of superconductivity rather than a degradation. This talk will show results from irradiated YPtBi, (Ba,K)Fe2As2, and CeCoIn5 crystals that have received doses from a Co60 source up to 60 MRad. Electrical resistance data will be displayed and an emphasis will be made on the profile of the superconducting transition for each compound. Types of irradiation and their processes will also be discussed.
Speaker 2: Wen-Chen Lin

Title: Development of a radio frequency oscillator technique utilizing a tunnel diode: precise magnetic susceptibility measurements

Abstract: Measurement techniques utilizing the radio frequency (rf) have been successfully employed to investigate the magnetic and superconducting properties of a solid state, which offers high sensitivity and stability. A tunnel diode oscillator (TDO), an LC tank circuit powered by a tunnel diode, is among the most precise and versatile probes. We have been developing a precise ac magnetometer based on TDO operating at 20 MHz in Physical Properties Measurement System (PPMS). Our TDO circuit configuration can be used in a wide temperature range between 2 K and 400 K and in high magnetic fields up to 14 T. We apply this TDO setup to study the magnetic property of antiferromagnetic CeAlGe and ferromagnetic CeAlSi. Recently, the former has been attracting much attention since it was theoretically identified as a Weyl semimetal [1]. In this talk, we will present detail studies of temperature-and field-dependent ac magnetic susceptibility in both compounds after introducing the working principle of our TDO setup in PPMS.

[1] Guoqing Chang et al., PHYSICAL REVIEW B 97, 041104(R) (2018)