Shift-current bulk photovoltaic effect influenced by quasiparticle and exciton

Abstract

We compute the shift current bulk photovoltaic effect (BPVE) in bulk BaTiO3 and twodimensional monochalcogenide SnSe considering quasi-particle corrections and exciton effects. We explore changes in shift current peak position and magnitude reduction due to band renormalization. For BaTiO3, we demonstrate that shift current is reduced near the band edge due to exciton effects. Comparison of these results with experiments on BaTiO3 indicate that mechanisms other than shift current may be contributing to BPVE. Additionally, we reveal that the shift current near the band gap shows only a small change due to excitons in two-dimensional SnSe, suggesting that the thin film geometry provides a feasible way to reduce the exciton effect on the shift current. These results suggest that many-body corrections are important for accurate assessments of bulk photovoltaic materials and to understand the mechanisms behind the BPVE.The bulk photovoltaic effect (BPVE), which has also been referred to as the "photogalvanic effect", is a resonant nonlinear process where photocurrent is generated in the bulk of materials [1,2]. The BPVE requires a lack of inversion symmetry, allowing an asymmetric photoexcitation of carriers [3][4][5]. Because the photovoltage is not limited by the band-gap energy, and a p-n junction or interface is not required, the BPVE in ferroelectrics has attracted a lot of attention [6][7][8]. Ferroelectric oxide materials including BaTiO 3 [9-11], LiNbO 3 [12,13] and BiFeO 3 [14-17] have been widely studied for their photovoltaic properties, with substantial effort devoted to understanding their origins. Deeper understanding of photovoltaic effects is crucial for the discovery and the design of new types of ferroelectric semiconductors, including organic and hybrid materials [18,19], topological materials [20], and layered two-dimensional materials [21] for BPVE applications. More than one mechanism could contribute to the DC photocurrent, including the shift current [2,22] and the ballistic current [23-25], with their relative magnitudes currently under debate. The shift current is the result of the movement of the center of charge during optical excitation, e.g., transitions from valence to conduction bands. In similar fashion, transitions from defect levels to conduction bands should give rise to shift currents as well. In this paper, we focus on the shift current, which has been a topic of current research, and show that many-body effects which are often neglected in its computation give rise to sizable corrections.Comparisons of the experimentally measured BPVE in ferroelectric BaTiO 3 [10, 11] and BiFeO 3 [26] with firstprinciples DFT calculations [17,27] suggests that shift current is responsible for a significant portion of the BPVE in ferroelectrics. However, these conclusions were drawn from calculations neglecting quasiparticle corrections and excitonic effects, and should be revised with these many-body effects taken into account. Similarly, * rappe@sas.upenn.edu many theoretical predictions of shif...

Giant topological longitudinal circular photo-galvanic effect in the chiral multifold semimetal CoSi

“…3 a for room temperature, showing a peak value of ~550 μ A/V 2 at 0.4 eV. The CPGE spectrum peak value is much larger than the photo-galvanic effect in any chiral crystals reported in the literature 33 , BaTiO 3 34 , single-layer monochalcogenides 34 , 35 , the colossal bulk-photovoltaic response in TaAs 36 and RhSi in the same space group 24 , 25 .

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Linear and nonlinear optical responses in the chiral multifold semimetal RhSi

“…Further decreasing the photon energy from 0.7 to 0.2 eV, the CPGE conductivity displays a sharp drop with a striking sign change at 0.4 eV, which was not seen before as the lowest photon energy measured in a previous study was around 0.5 eV 51 . Interestingly, the peak photoconductivity at 0.7 eV is much larger than the photogalvanic effect in BaTiO 3 65 , single-layer monochalcogenides 65,66 , and other chiral crystals 67 , and it is comparable to the colossal bulk-photovoltaic response in TaAs 22 . It is also one order of magnitude larger than the previous study on RhSi 51 probably due to a larger hot-carrier lifetime.…”

Phonon-Assisted Ballistic Current from First-Principles Calculations

“…With the rate and band velocities, current can be calculated according to the Boltzmann transport equation. We compare our results with theoretically calculated shift current and also with the experimentally measured photocurrent of BaTiO 3 [18,28]. We also explore the ballistic current in different crystal structures of this material, and we find that the magnitude of ballistic current can vary significantly.…”

“…To compare with experiment, we calculate the real photocurrent based on the Glass coefficient [18,46], by further computing the absorption coefficient with quasiparticle corrections. As pointed out by our previous work [18], the quasiparticle correction will significantly influence the absorption profile, but it will mainly blueshift the tensor within the frequency range of interest.…”