A central result in superconductivity is that flat bands, though dispersionless, can still host a
nonzero superfluid weight due to quantum geometry. We show that the derivation of the …

The geometry of quantum states is well established as a basis for understanding the
response of electronic systems to static electromagnetic fields, as exemplified by the theory …

We study the low-frequency properties of the bulk photovoltaic effect in topological
semimetals. The bulk photovoltaic effect is a nonlinear optical effect that generates dc …

Nonlinear responses are actively studied as probes of topology and band geometric
properties of solids. Here, we show that second harmonic generation serves as a probe of …

Photocurrent in quantum materials is often collected at global contacts far away from the
initial photoexcitation. This collection process is highly nonlocal. It involves an intricate …

Emergent axion electrodynamics in magneto-electric media is expected to provide novel
ways to detect and control material properties with electromagnetic fields. However, despite …

The quantum metric is a central quantity of band theory but has so far not been related to
many response coefficients due to its nonclassical origin. However, within a newly …

The eigenvalues of a parameter-dependent Hamiltonian matrix form a band structure in
parameter space. In such N-band systems, the quantum geometric tensor (QGT), consisting …

Electron–phonon coupling is crucial for the existence of various phases of matter, in
particular superconductivity and density waves. Here, we devise a theory that incorporates …

The magnetic skyrmion crystal is a periodic array of a swirling topological spin texture. Since
it is regarded as an interference pattern by multiple helical spin density waves, the texture …