Krich, Jacob Jonathan

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Krich, Jacob Jonathan

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Krich

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Jacob Jonathan

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Krich, Jacob Jonathan

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A Witness for Coherent Electronic vs Vibronic-Only Oscillations in Ultrafast Spectroscopy
(American Institute of Physics, 2012) Yuen-Zhou, Joel; Krich, Jacob Jonathan; Aspuru-Guzik, Alan
We report a conceptually straightforward witness that distinguishes coherent electronic oscillations from their vibronic-only counterparts in nonlinear optical spectra of molecular aggregates. Coherent oscillations as a function of waiting time in broadband pump/broadband probe spectra correspond to coherent electronic oscillations in the singly excited manifold. Oscillations in individual peaks of 2D electronic spectra do not necessarily yield this conclusion. Our witness is simpler to implement than quantum process tomography and potentially resolves a long-standing controversy on the character of oscillations in ultrafast spectra of photosynthetic light harvesting systems.
Picosecond carrier recombination dynamics in chalcogen-hyperdoped silicon
(AIP Publishing, 2014) Sher, Meng-Ju; Simmons, Christie B.; Krich, Jacob Jonathan; Akey, Austin; Winkler, Mark T.; Recht, Daniel; Buonassisi, Tonio; Aziz, Michael; Lindenberg, Aaron M.
Intermediate-band materials have the potential to be highly efficient solar cells and can be fabricate by incorporating ultrahigh concentrations of deep-level dopants. Direct measurements of the ultrafast carrier recombination processes under supersaturated dopant concentrations have not been previously conducted. Here, we use optical-pump/terahertz-probe measurements to study carrier recombination dynamics of chalcogen-hyperdoped silicon with sub-picosecond resolution. The recombination dynamics is described by two exponential decay time scales: a fast decay time scale ranges between 1 and 200ps followed by a slow decay on the order of 1 ns. In contrast to the prior theoretical predictions, we find that the carrier lifetime decreases with increasing dopant concentration up to and above the insulator-to-metal transition. Evaluating the material’s figure of merit reveals an optimum doping concentration for maximizing performance.
Quantum state and process tomography of energy transfer systems via ultrafast spectroscopy
(Proceedings of the National Academy of Sciences, 2011) Yuen-Zhou, Joel; Krich, Jacob Jonathan; Mohseni, Masoud; Aspuru-Guzik, Alan
The description of excited state dynamics in energy transfer systems constitutes a theoretical and experimental challenge in modern chemical physics. A spectroscopic protocol that systematically characterizes both coherent and dissipative processes of the probed chromophores is desired. Here, we show that a set of two-color photon-echo experiments performs quantum state tomography (QST) of the one-exciton manifold of a dimer by reconstructing its density matrix in real time. This possibility in turn allows for a complete description of excited state dynamics via quantum process tomography (QPT). Simulations of a noisy QPT experiment for an inhomogeneously broadened ensemble of model excitonic dimers show that the protocol distills rich information about dissipative excitonic dynamics, which appears nontrivially hidden in the signal monitored in single realizations of four-wave mixing experiments.
Deactivation of metastable single-crystal silicon hyperdoped with sulfur
(AIP Publishing, 2013) Simmons, C. B.; Akey, Austin; Krich, Jacob Jonathan; Sullivan, Joseph T.; Recht, Daniel; Aziz, Michael; Buonassisi, Tonio
Silicon supersaturated with sulfur by ion implantation and pulsed laser melting exhibits broadband optical absorption of photons with energies less than silicon's band gap. However, this metastable, hyperdoped material loses its ability to absorb sub-band gap light after subsequent thermal treatment. We explore this deactivation process through optical absorption and electronic transport measurements of sulfur-hyperdoped silicon subject to anneals at a range of durations and temperatures. The deactivation process is well described by the Johnson-Mehl-Avrami-Kolmogorov framework for the diffusion-mediated transformation of a metastable supersaturated solid solution, and we find that this transformation is characterized by an apparent activation energy of \(E_A=1.7 ± 0.1 eV\). Using this activation energy, the evolution of the optical and electronic properties for all anneal duration-temperature combinations collapse onto distinct curves as a function of the extent of reaction. We provide a mechanistic interpretation of this deactivation based on short-range thermally activated atomic movements of the dopants to form sulfur complexes.
Practical witness for electronic coherences
(AIP Publishing, 2014) Johnson, Allan S.; Yuen-Zhou, Joel; Aspuru-Guzik, Alan; Krich, Jacob Jonathan
The origin of the coherences in two-dimensional spectroscopy of photosynthetic complexes remains disputed. Recently, it has been shown that in the ultrashort-pulse limit, oscillations in a frequency-integrated pump-probe signal correspond exclusively to electronic coherences, and thus such experiments can be used to form a test for electronic vs. vibrational oscillations in such systems. Here, we demonstrate a method for practically implementing such a test, whereby pump-probe signals are taken at several different pulse durations and used to extrapolate to the ultrashort-pulse limit. We present analytic and numerical results determining requirements for pulse durations and the optimal choice of pulse central frequency, which can be determined from an absorption spectrum. Our results suggest that for numerous systems, the required experiment could be implemented by many ultrafast spectroscopy laboratories using pulses of tens of femtoseconds in duration. Such experiments could resolve the standing debate over the nature of coherences in photosynthetic complexes.
Scaling and Localization Lengths of a Topologically Disordered System
(American Physical Society, 2011) Krich, Jacob Jonathan; Aspuru-Guzik, Alan
We consider a noninteracting disordered system designed to model particle diffusion, relaxation in glasses, and impurity bands of semiconductors. Disorder originates in the random spatial distribution of sites. We find strong numerical evidence that this model displays the same universal behavior as the standard Anderson model. We use finite-size scaling to find the localization length as a function of energy and density, including localized states away from the delocalization transition. Results at many energies all fit onto the same universal scaling curve.
Nonradiative Lifetimes in Intermediate Band Materials - Absence of Lifetime Recovery
(American Physical Society, 2012) Krich, Jacob Jonathan; Halperin, Bertrand; Aspuru-Guzik, Alan
Intermediate band photovoltaics hold the promise of being highly efficient and cost effective photovoltaic cells. Intermediate states in the band gap, however, are known to facilitate nonradiative recombination. Much effort has been dedicated to producing metallic intermediate bands in hopes of producing lifetime recovery - an increase in carrier lifetime as doping levels increase. We show that lifetime recovery induced by the insulator-to-metal transition will not occur, because the metallic extended states will be localised by phonons during the recombination process. Only trivial forms of lifetime recovery, e.g., from an overall shift in intermediate levels, are possible. Future work in intermediate band photovoltaics must focus on optimizing subgap optical absorption and minimizing recombination, but not via lifetime recovery.
Dynamic Nuclear Polarization in Double Quantum Dots
(American Physical Society, 2010) Gullans, Michael John; Krich, Jacob Jonathan; Taylor, Jacob; Bluhm, Hendrik; Halperin, Bertrand; Marcus, C; Stopa, Michael P; Yacoby, Amir; Lukin, Mikhail
We theoretically investigate the controlled dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. Three regimes of long-term dynamics are identiﬁed, including the buildup of a large difference in the Overhauser ﬁelds across the dots, the saturation of the nuclear polarization process associated with formation of so-called ‘‘dark states’’, and the elimination of the difference ﬁeld. We show that in the case of unequal dots, buildup of difference ﬁelds generally accompanies the nuclear polarization process, whereas for nearly identical dots, buildup of difference ﬁelds competes with polarization saturation in dark states. The elimination of the difference ﬁeld does not, in general, correspond to a stable steady state of the polarization process.
Spin Polarized Current Generation from Quantum Dots without Magnetic Fields
(American Physical Society, 2008) Krich, Jacob Jonathan; Halperin, Bertrand
An unpolarized charge current passing through a chaotic quantum dot with spin-orbit coupling can produce a spin-polarized exit current without magnetic fields or ferromagnets. We use random matrix theory to estimate the typical spin polarization as a function of the number of channels in each lead in the limit of large spin-orbit coupling. We find rms spin polarizations up to 45% with one input channel and two output channels. Finite temperature and dephasing both suppress the effect, and we include dephasing effects using a variation of the third lead model. If there is only one channel in the output lead, no spin polarization can be produced, but we show that dephasing lifts this restriction.