Physicists measure quantum geometry of electrons in crystalline materials for the first time

Amazing stuff! 

The global Covid-19 pandemic may have helped to bring this research about and facilitated a necessary "close cooperation between theorists and experimentalists".

"MIT physicists and colleagues have for the first time measured the geometry, or shape, of electrons in solids at the quantum level. Scientists have long known how to measure the energies and velocities of electrons in crystalline materials, but until now, those systems’ quantum geometry could only be inferred theoretically, or sometimes not at all. ...

The work could be applied to “any kind of quantum material, not just the one we worked with,” ...

a technique called angle-resolved photoemission spectroscopy, or ARPES ..."

From the abstract:

"Understanding the geometric properties of quantum states and their implications in fundamental physical phenomena is a core aspect of contemporary physics. The quantum geometric tensor (QGT) is a central physical object in this regard, encoding complete information about the geometry of the quantum state. The imaginary part of the QGT is the well-known Berry curvature, which plays an integral role in the topological magnetoelectric and optoelectronic phenomena. The real part of the QGT is the quantum metric, whose importance has come to prominence recently, giving rise to a new set of quantum geometric phenomena such as anomalous Landau levels, flat band superfluidity, excitonic Lamb shifts and nonlinear Hall effect.

Despite the central importance of the QGT, its experimental measurements have been restricted only to artificial two-level systems. Here, we develop a framework to measure the QGT in crystalline solids using polarization-, spin- and angle-resolved photoemission spectroscopy. Using this framework, we demonstrate the effective reconstruction of the QGT in the kagome metal CoSn, which hosts topological flat bands. Establishing this momentum- and energy-resolved spectroscopic probe of the QGT is poised to significantly advance our understanding of quantum geometric responses in a wide range of crystalline systems."

Physicists measure quantum geometry for the first time | MIT News | Massachusetts Institute of Technology "The work opens new avenues for understanding and manipulating electrons in materials."

Measurements of the quantum geometric tensor in solids (no public access)

Measurements of the quantum geometric tensor in solids (preprint, open access)