Nonlinear photoconductivities and quantum geometry of chiral multifold fermions
Journal
Physical Review B
Journal Volume
107
Journal Issue
15
Date Issued
2023-01-05
Author(s)
Abstract
Chiral multifold fermions are quasi-particles that appear only in chiral
crystals such as transition metal silicides in the cubic B20 structure (i.e.,
the CoSi family), and they may show exotic physical properties. Here we study
the injection and shift photoconductivities and also the related geometrical
quantities for several types of chiral multifold fermions, including spin-1/2
as well as pseudospin-1 and -3/2 fermions, dubbed as Kramers Weyl, triple point
and Rarita-Schwinger-Weyl (RSW) fermions, respectively. We utilize the minimal
symmorphic model to describe the triple point fermions (TPF). We also consider
the more realistic model Hamiltonian for the CoSi family including both linear
and quadratic terms. We find that circular injection currents are quantized as
a result of the Chern numbers carried by the multifold fermions within the
linear models. Surprisingly, we discover that in the TPF model, linear shift
conductivities are proportional to the pseudo spin-orbit coupling and
independent of photon frequency. In contrast, for the RSW and Kramer Weyl
fermions, the linear shift conductivity is linearly proportional to photon
frequency. The numerical results agree with the power-counting analysis for
quadratic Hamiltonians. The frequency independence of the linear shift
conductivity could be attributed to the strong resonant symplectic Christoffel
symbols of the flat bands. Moreover, the calculated symplectic Christoffel
symbols show significant peaks at the nodes, suggesting that the shift currents
are due to the strong geometrical response near the topological nodes.
Subjects
Physics - Mesoscopic Systems and Quantum Hall Effect; Physics - Mesoscopic Systems and Quantum Hall Effect
Type
journal article