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Register a new userCoherence Control of Directional Nonlinear Photocurrent in Spatially Symmetric Systems
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The interplay between crystal symmetry and its optical responses is at the heart of tremendous recent advances in light-matter interactions and applications. Nonlinear optical processes that produce electric currents, for example bulk photovoltaic (BPV) effect, require inversion symmetry broken materials, such as ferroelectrics. In the current work, we demonstrate that such BPV current could be generated in centrosymmetric materials with excitation of out-of-equilibrium coherent phonons. This is much different from the generally studied static or thermally excited states. We show that depending on the oscillating phase factor of the coherent phonon, uni-directional static electric current can be observed, in addition to some terahertz alternating currents. We also generalize the conventional injection charge current into angular momentum (spin and orbital) degrees of freedom, and demonstrate spin and orbital BPV photocurrents under coherent phonons. Our findings open the pathway to exploring the exotic phonon-photon-electron coherent interactions in quantum materials.
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There is growing interest in the photo-induced generation of rectified current, namely photocurrent phenomenon. While the response was attributed to noncentrosymmetric structures of crystals, the parity violation accompanied by the magnetic ordering, that is, magnetic parity violation, is recently attracting attention as a platform for a photocurrent generator. In this paper, we investigate the photocurrent response in the current-ordered phase, realizing the magnetic parity violation without the spin degree of freedom, although prior studies focused on the parity-violating spin structure. The loop-current order breaks the inversion symmetry while preserving the parity-time-reversal symmetry. With a model of Sr$_2$IrO$_4$, we demonstrate the linearly and circularly polarized light-induced photocurrent responses in the current-ordered state. Each photocurrent has a distinct tolerance of the scattering rate according to the mechanism for the photocurrent creation. The predicted photocurrent response is comparable to that in prototypical semiconductors. We propose a probe to detect the hidden-ordered phase in Sr$_2$IrO$_4$ by the photocurrent response.
Electric field enhanced electron spin coherence is characterized using time-resolved Faraday rotation spectroscopy in n-type ZnO epilayers grown by molecular beam epitaxy. An in-plane dc electric field E almost doubles the transverse spin lifetime at 20 K, without affecting the effective g-factor. This effect persists till high temperatures, but decreases with increasing carrier concentration. Comparisons of the variations in the spin lifetime, the carrier recombination lifetime and photoluminescence lifetimes indicate that the applied E enhances the radiative recombination rate. All observed effects are independent of crystal directionality and are performed at low magnetic fields (B < 0.2 T).
Methylammonium lead iodide (MAPI) is a benchmark hybrid organic perovskite material, which is used for the low-cost, printed solar cells with over 20 percent power conversion efficiency. Yet, the nature of light-matter interaction in MAPI as well as the exact physical mechanism behind device operation is currently debated. Here we report room temperature, ultrafast photocurrent and freespace terahertz (THz) emission generation from unbiased MAPI induced by 150 fs light pulses. Polarization dependence of the observed photoresponse is consistent with the Bulk Photovoltaic Effect (BPVE) caused by a combination of injection and shift currents. We believe that this observation of can shed light on low recombination, and long carrier diffusion lengths due to indirect bandgap. Moreover, ballistic by nature shift and injection BPVE photocurrents may enable third generation perovskite solar cells with efficiency that exceed the Shockley_Queisser limit. Our observations also open new venues for perovskite spintronics and tunable THz sources.
We propose a scheme to manipulate the spin coherence in vertically coupled GaAs double quantum dots. Up to {em ten} orders of magnitude variation of the spin relaxation and {em two} orders of magnitude variation of the spin dephasing can be achieved by a small gate voltage applied vertically on the double dot. Specially, large variation of spin relaxation still exists at 0 K. In the calculation, the equation-of-motion approach is applied to obtain the electron decoherence time and all the relevant spin decoherence mechanisms, such as the spin-orbit coupling together with the electron--bulk-phonon scattering, the direct spin-phonon coupling due to the phonon-induced strain, the hyperfine interaction and the second-order process of electron-phonon scattering combined with the hyperfine interaction, are included. The condition to obtain the large variations of spin coherence is also addressed.
Nonlinear interactions between phonon modes govern the behavior of vibrationally highly excited solids and molecules. Here, we demonstrate theoretically that optical cavities can be used to control the redistribution of energy from a highly excited coherent infrared-active phonon state into the other vibrational degrees of freedom of the system. The hybridization of the infrared-active phonon mode with the fundamental mode of the cavity induces a polaritonic splitting that we use to tune the nonlinear interactions with other vibrational modes in and out of resonance. We show that not only can the efficiency of the redistribution of energy be enhanced or decreased, but also the underlying scattering mechanisms may be changed. This work introduces the concept of cavity control to the field of nonlinear phononics, enabling nonequilibrium quantum optical engineering of new states of matter.
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