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UMN Center for Quantum Materials scientists demonstrated the first molecular beam epitaxy (MBE) growth of YTiO3 films. Through a combined study of thin films and floating-zone grown bulk single crystals, a thermally-activated conduction mechanism involving positively charged carriers was revealed. Together with scientists at the University of Delaware, a combined theoretical and experimental investigation of the electronic structure and charge transport properties provided a definite answer to the governing mechanism for conduction in YTiO3 and related materials. The team has demonstrated that the charge transport in YTiO3 (a ferromagnetic Mott insulator) is due to small hole polaron migration and that the Mott-Hubbard gap of YTiO3 is ~ 1.5 eV.

The application of reversible, elastic uniaxial strain has recently emerged as a powerful means to study and manipulate quantum materials. The effects of uniaxial stress beyond the elastic regime, however, are not widely studied in single-crystalline materials, with notable exceptions in the field of geophysics. The resultant plastic deformation fundamentally differs from elastic strain, as it creates extended defects – dislocations – and induces their self-organization into structures spanning many length scales. The local atomic arrangement near dislocation cores is very different from bulk, significantly modifying nearby electronic properties. Such effects are expected to be amplified when dislocations assemble into larger structures. More information

This work reported on the first detailed, systematic study of low temperature electronic specific heat in doped SrTiO3. This was done over a wide doping range, in Nb-doped single crystals. The electronic specific heat was shown to be typical of a Fermi liquid, using both experimental and theoretical approaches. More information

Strontium titanate, or SrTiO3, is the most widely studied perovskite oxide, a family of materials of vital importance in basic science and energy technologies. It was discovered over 50 years ago that SrTiO3 undergoes a phase transition at 105 K reffered to as an “antiferrodistortive” transition. What is so important about this structural change in SrTiO3 is that it has become a model for similar transitions in a large number of compounds, occurring via a mechanism known as mode softening. Although this mechanism has been understood for some time, some aspects of the transition remain mysterious. More information

Superconductivity – the quantum state in which a metal loses all electrical resistance and exhibits magnetic flux expulsion (the Meissner-Ochsenfeld effect) – is one of the major research topics in condensed matter physics. Here a team of scientists at University of Minnesota’s Center for Quantum Materials uncovered a remarkable universal feature shared by these distinct materials. The discovery was enabled by the development of a novel nonlinear magnetic response technique, an extremely sensitive probe of magnetism. More information

Many complex compounds that contain oxygen and copper – known as cuprates – become superconducting at temperatures much higher than most other materials. It is still not understood why this is the case and if these compounds can be tweaked to further increase the superconducting transition temperatures. In this respect, an outstanding open question is the nature of the superconducting precursor regime at temperatures above the bulk transition. In this regime, the materials are not fully-developed superconductors, but traces of superconductivity are still observable. In order to address these long-standing issues, a team of scientists from the University of Minnesota, Vienna University of Technology, Austria, and University of Zagreb, Croatia, developed a new approaches to detect the elusive superconducting precursor. They employ the fact that superconductivity is easily influenced by an external magnetic or electric field, and measured the resulting nontrivial response with several distinct experimental setups in a number of representative cuprates. More information

Unraveling the connection between superconductivity, patterns of charge and magnetic organization, and partial energy gaps (“pseudogaps”) in the cuprates is a major thrust in quantum materials research. With the aim to understand the dynamic charge and magnetic correlations and their connection to the mechanism of pairing in these high-temperature superconductors, a collaboration led by scientists form University of Minnesota’s Center for Quantum Materials studied a model cuprate compound via state-of-the-art resonant inelastic X-ray scattering (RIXS). The experiment had nearly unprecedented energy resolution and it primarily focused on the charge degrees of freedom. The scientists uncovered two unexpectedly large charge fluctuation scales and were able to connect these findings to a range of prior observations for the cuprates regarding the pseudogap phenomenon and superconducting pairing. More information

The cuprates – complex oxides of copper – are remarkable compounds that lose electrical resistance at record temperatures. Understanding the physics behind this high-temperature superconductivity would be of enormous fundamental and practical importance. Yet after more than three decades of truly remarkable research activity, the salient features of both the ‘normal’ state (above the superconducting transition temperature) and the superconductivity itself remain debated. In this work, a team of scientists from the University of Minnesota, Vienna University of Technology, Austria, and University of Zagreb, Croatia have developed a simple yet powerful phenomenological model that resolves several of the major open questions. More information

The cuprate superconductors exhibit remarkably-high superconducting transition temperatures (Tc) and remain the source of unsolved fundamental problems in quantum materials research after decades of intense study. In particular, the pseudogap phase, observed above Tc at low and intermediate doping, has been associated with a range of experimental signatures, but still no theoretical model that fully describes these results has been developed. More information