Photon-drag photovoltaic effects and quantum geometric nature (2502.21002v1)

Abstract: The bulk photovoltaic effect (BPVE) generates a direct current photocurrent under uniform irradiation and is a nonlinear optical effect traditionally studied in non-centrosymmetric materials. The two main origins of BPVE are the shift and injection currents, arising from transitions in electron position and electron velocity during optical excitation, respectively. Recently, it was proposed that photon-drag effects could unlock BPVE in centrosymmetric materials. However, experimental progress remains limited. In this work, we provide a comprehensive theoretical analysis of photon-drag effects inducing BPVE (photon-drag BPVE). Notably, we find that photon-drag BPVE can be directly linked to quantum geometric tensors. Additionally, we propose that photon-drag shift currents can be fully isolated from other current contributions in non-magnetic centrosymmetric materials. We apply our theory explicitly to the 2D topological insulator $1T'$-WTe$_2$. Furthermore, we investigate photon-drag BPVE in a centrosymmetric magnetic Weyl semimetal, where we demonstrate that linearly polarized light generates photon-drag shift currents.

Analysis of Photon-Drag Photovoltaic Effects and Their Quantum Geometric Nature

The paper by Xie and Nagaosa offers a comprehensive theoretical exploration of the photon-drag bulk photovoltaic effect (BPVE) and explores its connection with quantum geometric tensors. The notion of BPVE, known for generating direct current (DC) under uniform light irradiation without heterostructures, has been traditionally linked to non-centrosymmetric materials, driven primarily by the shift and injection currents. However, this paper introduces the photon-drag effect as a mechanism to activate BPVE in centrosymmetric materials, thus broadening the scope of materials available for photovoltaic applications.

Theoretical and Numerical Framework

The authors employ a density matrix formalism to derive the various contributions to the photon-drag-induced photocurrents, distinguishing among the shift, injection, and Fermi surface currents. Through meticulous expansion at small photon momentum, they establish a direct relationship to quantum geometric tensors. This formulation makes a significant leap by encompassing centrosymmetric, and even magnetic materials, into the purview of BPVE by highlighting the role of photon momentum in facilitating non-vertical electronic transitions.

Crucial to this discussion is the connection with quantum geometric concepts. The paper delineates the involvement of quantum geometric components like the quantum metric and Berry curvature dipole in photon-drag-induced photocurrents. Intriguingly, they find that in nonmagnetic centrosymmetric materials, photon-drag shift currents are discernible by their unique polarization dependence, which follows a sinusoidal pattern—$C\sin(2\alpha)$—distinct from other current contributions.

Applications to Prototypical Systems

The application of this theoretical formulation to specific materials reveals unique insights. For example, they apply their theory to the 2D topological insulator $1T'$-WTe$_2$, a material known for its prominent particle-hole asymmetry and topological surface states. The paper predicts finite photocurrent contributions under photon drag, confirming the theoretical prediction with computational results showcasing distinct polarization dependencies that could be experimentally verified.

In exploring another dimension, the authors consider centrosymmetric magnetic Weyl semimetals, demonstrating that linear photon-drag shift currents can emerge under linearly polarized light. This is significant given the interest in such materials for their exotic electronic properties, including chiral anomalies and surface Fermi arcs, which enrich the topological landscape of photovoltaic responses.

Implications and Future Directions

This work carries implications for photovoltaic technology innovation, particularly in developing efficient photo-responsive materials that do not rely on structural asymmetry. The link to quantum geometry not only deepens the theoretical understanding but also motivates the integration of these geometric concepts into the design of novel materials for energy applications.

Theoretically, this paper suggests pathways for enhancing photon-drag BPVE, such as exploiting materials with significant quantum geometric tensors or enhancing photon momentum through polaritons. Experimentally, this sets a fertile ground for probing these effects in both traditional non-centrosymmetric materials and the broader class of centrosymmetric and topologically non-trivial materials.

Overall, Xie and Nagaosa's work fortifies the theoretical backbone for BPVE exploration through photon-drag effects and suggests a rich avenue for future research to experimentally harness these theoretical predictions in practical photovoltaic applications.