Electronic and Quantum Magnetism Unit (Yejun Feng)

FY2017 Annual Report

Electronic and Quantum Magnetism Unit
Associate Professor Yejun Feng

Abstract

This is the first year of the Electronic and Quantum Magnetism Unit at OIST. The first half of the year was spent on lab renovation and hiring. In the second half of the year, equipments were gradually installed.

1. Staff and Students

Dr. Volodymyr Monarkha, Postdoc Researcher
Dr. Oleksandr Smorodin, Postdoc Researcher
Scott Cooper, Technical Staff
Yukiko Murabayashi, Administrative Assistant
Dr. Moovendaran Kalimuthu, Technical Staff (left)
Yuta Ito, rotation graduate student

2. Collaborations

2.1 Synchrotron x-ray magnetic diffraction under high pressure

This is a long term research interest of mine, that we mainly use x-rays from synchrotron radiation sources such as the Advanced Photon Source to explore magnetism evolution under GPa pressure. In this year, we were specifically interested in the all-in-all-out antiferromagnetic order in pyrochlore structured Cd₂Os₂O₇. We also explored collaborations on other all-in-all-out systems in the iridate family, and established a collaboration on Sm₂Ir₂O₇ by the end of fiscal year.
Collaborators:
- Professor Thomas Rosenbaum, Caltech
- Professor David Mandrus, University of Tennesses - Knoxville
- Professor Andrew Boothroyd, University of Oxford

2.2 Linear magnetoresistance in charge and spin density wave materials

In sevearl charge and spin density wave materials, we explored magnetoresistance at the low field limit with an unusal linear functional form.
Collaborators:
- Professor Peter Littlewood, University of Chicago
- Professor Thomas Rosenbaum, Caltech
- Professor Yoshichika Onuki, University of the Ryukyus
- Professor Riki Kobayashi, University of the Ryukyus
- Dr. Jiaqiang Yan, Oak Ridge National Laboratory
- Dr. Alexey Suslov, National High Magnetic Field Laboratory, Florida State University

3. Activities and Findings

3.1 Low-temperature galvanomagnetic measurements

Using a 14-T Physical Property Measurement System (PPMS) from Quantum Design, we explored fine details of electrical transport behavior in many charge and spin density wave materials.

3.2 Magnetic susceptibility measurements under pressure and sub-Kelvin temperature

During this year, Dr. Monarkha, with the assistance of Scott Cooper, developed an audio-frequency wave ac magnetic susceptivility measurement system in the cryogen-free dilution refrigerator. This paves the way to search for unusual superconducting states in correlated electron systems under high pressure.

3.3 Setting up optical probes

Starting from the second half of the year, we started to set up the optical measurement systems. Three optical tables and a triple-stage grating spectrometer were delivered before the end of fiscal year.

3.4 X-ray magnetic diffraction under high pressure

The pressure evolution of the all-in-all-out antiferromagnetic order in Cd₂Os₂O₇ was explored by x-ray diffraction techniques. We finished the study in August 2017.

4. Publications

4.1 Journals

Yejun Feng, Yishu Wang, A. Palmer, Ling Li, D. M. Silevitch, S. Calder, T. F. Rosenbaum, Multiple Superconducting States Induced by Pressure in Mo₃Sb₇, Phys. Rev. B. 95, 125102 (2017).

4.2 Books and other one-time publications

Nothing to report

4.3 Oral and Poster Presentations

Invited talks by the PI:

The Advanced Photon Source, Argonne National Laboratory, Resonant X-ray magnetic diffraction probe of a strongly-coupled quantum phase transition in three dimension, Argonne, IL, USA, Dec. 8, 2017.
Department of Physics, University of California – Los Angeles, Itinerant density wave instability at continuous thermal and quantum phase transitions, Los Angeles, CA, USA, March 22^nd, 2017.
The 37^th REIMEI workshop on Correlated Quantum Matters and Spintronics, High-pressure x-ray diffraction probes of antiferromagnetic quantum phase transitions, Tokai, Ibaraki, Japan, Jan. 14^th, 2017.

Contributed talks with the PI listed:

Yishu Wang et al., R44.00003: Strongly-coupled quantum critical point in the all-in-all-out antiferromagnet Cd₂Os₂O₇. APS March Meeting, Los Angeles, CA, USA, March 8, 2018.