Enhancement of the Bulk Photovoltaic Effect in Topological Insulators

Abstract

We investigate the shift current bulk photovoltaic response of materials close to a band inversion topological phase transition. We find that the bulk photocurrent reverses direction across the band inversion transition, and that its magnitude is enhanced in the vicinity of the phase transition. These results are demonstrated with first principles DFT calculations of BiTeI and CsPbI3 under hydrostatic pressure, and explained with an analytical model, suggesting that this phenomenon remains robust across disparate material systems.The field of topological insulators [1,2] has proven to be a fruitful avenue of research in condensed matter physics in recent years. The symmetry protected surface states of topological insulators [3][4][5] give rise to novel and useful phenomena such as dissipationless transport [6,7]. Even though band topology is a ground state property, defined on the occupied valence bands of an insulator [8], the excited state properties should be affected by topological considerations as well. There is a growing body of research investigating the optical properties of topological insulators[9] using photoemission spectroscopy [3,4], Raman spectroscopy [10][11][12][13], nonlinear optics [14][15][16][17][18][19], and photocurrent generation [20][21][22].While the presence or absence of topological surface states has thus far being the main experimental route for detecting topological phase transitions, in this work we propose an optical, non-surface approach for detecting topological phase transitions in the bulk. This is a direct approach which does not rely on the quality or ease of detection of surface states. We consider the influence of band topology on the bulk photovoltaic effect (BPVE, also known as the photogalvanic effect) [23,24], which is the generation of photocurrents in the bulk of a singlephase material.The bulk photovoltaic effect is a second-order optical effect which gives current densities, J r = σ rst E s E t , as a quadratic function of the applied electric fields. This dictates that the BPVE can only be observed in materials with broken inversion symmetry. Measurements of appreciable BPVE have been reported for many ferroelectric materials [25][26][27][28]. In the prototypical ferroelectric BaTiO 3 , experiments [29,30] and first-principles calculations [31] show that the primary mechanism for BPVE is the shift current [32]. In this mechanism, carriers are excited into a current-carrying superposition of excited states. Due to its dominant effect in the bulk photovoltaic response, we will focus on the shift current in this paper.Because optical excitations probe both the valence and conduction band wavefunctions, we expect the band inversion process, which is the interchange of the conduction and valence band characters, to result in dramatic changes in the finite-frequency response functions of the system. We show that band inversion reverses the direction of the shift current. The magnitude of the shift cur- rent is enhanced in the vicinity of the band inversion transition....

Tunable Intrinsic Plasmons due to Band Inversion in Topological Materials

“…However, there has been little study of the effect of band inversion on the optical properties of topological materials [12]. Recently, the experimental observation of the quantum anomalous Hall (QAH) effect [13,14] has been reported in magnetically doped ultrathin films of topological insulators V-or Cr-doped (Bi, Sb) 2 Te 3 [15][16][17], in which its band topology can be tuned by external fields.…”

Search for Lorentz Violation Using Short-Range Tests of Gravity

“…Results, shown in Table I Results improve significantly on inclusion of data from the short-range experiment at the Huazhong University of Science and Technology, a torsion balance with planar test masses separated by ∼ 300 µm. 6 Terms in the Lorentz-violating torque for this experiment (the analog of Eq. (4)) are of order 10 nNm/m 2 , while measured torque Fourier components have errors ∼ 10 aNm.…”

“…Improvement in sensitivity by a factor of ∼10 3 would be expected; the resulting constraints on the (k eff ) are typically 10 −9 m 2 . 7 The (k eff ) are derived from the 336 coefficients (k (6) 1 ) and (k (6) 2 ) in the fully relativistic SME; the simultaneous constraints on (k eff ) translate into comparable constraints on 131 fundamental coefficients taken one at a time.…”

Spatio-temporal dynamics of shift current quantum pumping by femtosecond light pulse

“…However, photocurrent generated by BPVE in a closed circuit remains small compared to pn-junctions. This has ignited renewed experimental [4,[6][7][8][9][10][11] and theoretical [12][13][14][15][16][17][18] interest in BPVE with the ultimate goal [15] to optimize its power conversion efficiency.…”

“…The widely used [12][13][14][15][16][17] 'standard model' [25,26] for computing the magnitude of shift current is based on a perturbative expansion which yields its DC component…”