FY2018 Annual Report

Electronic and Quantum Magnetism Unit
Associate Professor Yejun Feng

Abstract

This is the second year of the Electronic and Quantum Magnetism Unit at OIST.

1. Staff & Students

Anjana Krishnadas, Graduate Student
Dr. Semyon Chervinskii, Postdoc Researcher
Dr. Oleksandr Smorodin, Postdoc Researcher
Dr. Volodymyr Monarkha, Technical Staff
Scott Cooper, Technical Staff
Yukiko Murabayashi, Administrative Assistant
Xing Zhu, rotation graduate student
Reo Shinagawa, intern undergraduate
Christina Nguyen, intern undergraduate

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 the x-rays from synchrotron radiation souces such as the Advanced Photon Source to explore magnetism evolution under GPa pressure. In this year, we focused on the study of all-in-all-out antiferromagnetic order in Sm₂Ir₂O₇. At the end of fiscal year, we established a collaboration on Eu₂Ir₂O₇.
Collaborators:
- Dr. Yishu Wang, Institute for Quantum Matter, Johns Hopkins University
- Professor Thomas Rosenbaum, Caltech
- Professor Andrew Boothroyd, University of Oxford
- Professor Satoru Nakatsuji, University of Tokyo

2.2 Planar Hall effects in ferromagnets

This is an expansion of our interest in galvanomagnetic behavior.
Collaborators:
- Dr. Yishu Wang, Institute for Quantum Matter, Johns Hopkins University
- Professor Patrick Lee, MIT
- Professor Thomas Rosenbaum, Caltech

2.3 Linear magnetoresistance in charge and spin density wave materials

Our continued interest in magnetoresistance.
Collaborators:
- Professor Peter Littlewood, University of Chicago
- Professor Thomas Rosenbaum, Caltech
- Dr. Yishu Wang, Institute for Quantum Matter, Johns Hopkins University
- Professor Yoshichika Onuki, University of the Ryukyus
- Professor Riki Kobayashi, University of the Ryukyus

3. Activities and Findings

3.1 X-ray magnetic diffraction under high pressure

We focused mostly on Sm₂Ir₂O₇ this year with its all-in-all-out antiferromagnetism under pressure. We finished the x-ray magnetic diffraction exploration in Feb. 2019.

3.2 Optical Raman scattering under high pressure

Our new postdoc Dr. Semyon Chervinskii is setting up the optical Raman spectroscopy to explore lattice and spin dynamics under high pressure and low temperature.

3.3 Synchrotron-based Mossbauer effect under high pressure

We explore the opportunity in Mossbauer technique to explore magnetic quantum phase transition in heavy fermion magnets. OIST graduate student Anjana Krishnadas is leading the effort.

3.4 Magnetic susceptibility measurements under pressure and sub-Kelvin temperature

During this year, Drs. Monarkha, and Smorodin, with the assistance of Scott Cooper, searched for unusual superconducting states in correlated electron systems under high pressure.

4. Publications

4.1 Journals

Yishu Wang, T. F. Rosenbaum, A. Palmer, Y. Ren, J.-W. Kim, D. Mandrus, Yejun Feng, Strongly-coupled quantum critical point in an all-in-all-out antiferromagnet. Nature Communications 9, 2953 (2018).

4.2 Books and other one-time publications

Nothing to report

4.3 Oral and Poster Presentations

Invited talks by the PI:

Institute for Quantum Matter, Johns Hopkins University, Quantum phase transitions from mean-field to strongly-coupling nature. Baltimore, MD, Oct. 26, 2018.

Contributed talks with the PI listed:

Yishu Wang et al., H06.00008 : Linear magnetoresistance in the all-in-all-out antiferromagnet Cd₂Os₂O₇. APS March Meeting, Boston, MA, USA, March 5, 2019.
Stephen Armstrong et al., R06.00003 : Hall Coefficient of Pure Chromium at Finite Temperatures and High Pressures. APS March Meeting, Boston, MA, USA, March 7, 2019.
Anjana Krishnadas et al., V07.00005 : Synchrotron-Mossbauer study of the pressure-driven magnetic evolution in EuGa₄. APS March Meeting, Boston, MA, USA, March 7, 2019.