Cross-Correlated Interface Research Unit

Principal Investigator

PI Name Pu Yu
Degree Ph.D.
Title Unit Leader
Brief Resume
2011Ph.D. in Physics, University of California, Berkeley, USA
2012Postdoctoral Researcher, Correlated Electron Research Group, RIKEN, Japan
2012Assistant Professor, Tsinghua University, Beijing, China
2014Unit Leader, Cross-Correlated Interface Research Unit, Cross-Divisional Materials Research Program, RIKEN Center for Emergent Matter Science (-present)
2017Associate Professor, Tsinghua University, Beijing, China (-present)


Our research unit is dedicated to exploring the emergent phenomena at complex oxide and other cross-correlated heterostructures and interfaces. In particular, we are interested about quantum manipulation of ferroelectric and ferromagnetic properties by means of heteroepitaxy, artificial design of novel multiferroic materials with strong magnetoelectric coupling and emergent phenomena (with a strong focus on the spin and charge degrees of freedom) at complex oxide interfaces and their cross correlations to other correlated material systems. Our goal is to reveal the underlying mechanisms of these heretofore-unexplored functionalities, and transfer them into novel device concepts for applications.

Research Fields

Condensed Matter Physics, Materials Sciences


Interface electronic structure
Magnetoelectric effect
Thin films and interfaces


Electric-field control of tri-state phase transformation with selective dual-ion switch

Electric-field control of phase transformation with ion transfer is of great interest in materials science with enormous and important practical applications, such as batteries, smart windows, fuel cells, etc. Although increasing the number of the transport ion species and the corresponding controllable crystalline phases can greatly enrich the material functionalities, studies have so far targeted mainly on the evolution of only single ionic species (e.g. O2-, H+ or Li+, etc.). In this work, we report the reversible and nonvolatile electric-field control of dual-ion (O2- and H+) phase transformation associated with the discovery of the exotic tri-state electrochromic and magnetoelectric effects. With the independently controllable O2- and H+ ion insertion and extraction, we realize the reversible phase transformation among three phases – the perovskite SrCoO3-δ, brownmillerite SrCoO2.5 and a hitherto-unexplored SrCoO2.5H. By utilizing their distinct optical absorption, we demonstrate a selective manipulation of the optical-spectral transparency among the visible-light and infrared regions, revealing a fascinating dual-band electrochromic effect with promising applications in smart windows. Moreover, the starkly different magnetic and electric properties of SrCoO2.5H (ferromagnetic insulator) as compared with SrCoO3-δ (ferromagnetic metal) and SrCoO2.5 (antiferromagnetic insulator) reveal an intriguing concept of tri-state magnetoelectric coupling with the deterministic electric-field control of three different magnetic ground states. These findings open up new opportunities for the electric-field control of multi-state phase transformation with novel crystalline structures and rich functionalities.

Schematic illustration of the reversible phase transformation through the electric-field selectively controlled dual-ion (O2- and H+) switch.


Pu Yu

Unit Leader R