News

A new step in understanding the metal-insulator transition of nickelates

A new step in understanding the metal-insulator transition of nickelates - 30/08/2020

Research in materials physics is one of the cornerstones of our company's technological development. Just as a better understanding of the mode of action of COVID-19 appears to us today to be an indispensable prerequisite for the development of effective treatments and vaccines, an understanding at the atomic scale of the phenomena originating at the heart of materials is an indispensable step for their subsequent use in innovative and practical devices. It is in this context that Yajun Zhang, Alain Mercy and Philippe Ghosez, from the Department of Theoretical Physics of Materials of the CESAM research unit (University of Liège), have just made an important discovery [1] : read more here !

[1] Length-scales of interfacial coupling between metal-insulator phases in oxides. C. Dominguez, A.B. Georgescu, B. Mundet, Y. Zhang, J. Fowlie, A. Mercy, S. Catalano, T. Duncan, T.L. Alexander, Ph. Ghosez, A. Georges, A. Millis, M. Gibert and J.-M. Triscone, Nature Materials (2020). https://doi.org/10.1038/s41563-020-0757-x

Quantum confinement at polar oxide interfaces

Quantum confinement at polar oxide interfaces - 02/08/2018

Polar discontinuities occurring at interfaces between two materials constitute both a challenge and an opportunity in the study and application of a variety of devices. In order to cure the large electric field occurring in such struc- tures, a reconfiguration of the charge landscape sets in at the interface via chemical modifications, adsorbates, or charge transfer. In the latter case, one may expect a local electronic doping of one material: one example is the two-dimensional electron liquid (2DEL) appearing in SrTiO3 once covered by
a polar LaAlO3 layer. Here, it is shown that tuning the formal polarization of
a (La,Al)1-x(Sr,Ti)xO3 (LASTO:x) overlayer modifies the quantum confinement
of the 2DEL in SrTiO3 and its electronic band structure. The analysis of the behavior in magnetic field of superconducting field-effect devices reveals, in agreement with ab initio calculations and self-consistent Poisson–Schrödinger modeling, that quantum confinement and energy splitting between electronic bands of different symmetries strongly depend on the interface total charge densities. These results strongly support the polar discontinuity mechanisms with a full charge transfer to explain the origin of the 2DEL at the celebrated LaAlO3/SrTiO3 interface and demonstrate an effective tool for tailoring the electronic structure at oxide interfaces. Learn more here !

Probing Quantum Confinement and electronic structure at polar oxide interfaces, D. Li, S. Lemal, S. Gariglio, Z. Wu, A. Fête, M. Boselli, Ph. Ghosez and J.-M. Triscone, Advanced Science 5, 1800242 (2018)

Conductors or insulators ?

Conductors or insulators ? - 06/12/2017

Microscopic origin of the intriguing behaviour of nickelates. Depending on whether or not they conduct electricity, materials are typically classified as either conductors or insulators. But is it that simple? Can the same material eventually change its behaviour depending on the environment in which it is placed? This is the case of some compounds such as nickelates, a series of complex oxides of perovskite structure. Depending on the temperature, these materials can change from electrical conductors to insulators in an abrupt and reversible way, a transformation that is as unusual as it is intriguing.   Alain Mercy and Philippe Ghosez, in collaboration with researchers of CEA and LIST reveal the microscopic mechanism behind this change of state. Learn more here !   See also the advertisement on Daily Science !

Structurally triggered metal-insulator transition in rare-earth nickelates. A. Mercy, J. Bieder, J. Iñiguez and Ph. Ghosez, Nature Communications 8, 1677 (2017).