125 research outputs found
Ultrafast Angle-Resolved Photoemission Spectroscopy of Quantum Materials
Techniques in time- and angle-resolved photoemission spectroscopy have
facilitated a number of recent advances in the study of quantum materials. We
review developments in this field related to the study of incoherent
nonequilibrium electron dynamics, the analysis of interactions between
electrons and collective excitations, the exploration of dressed-state physics,
and the illumination of unoccupied band structure. Future prospects are also
discussed.Comment: 7 pages, 6 figure
Multidimensional Coherent Spectroscopy of Semiconductors
Optical multidimensional coherent spectroscopy (MDCS) is a nonlinear spectroscopy technique where a material is excited by a series of laser pulses to produce a spectrum as a function of multiple frequencies. The technique’s ability to elucidate excited‐state structure and interactions has made MDCS a valuable tool in the study of excitons in semiconductors. This review introduces the method and describes progress it has fostered establishing a better understanding of dephasing rates, coherent coupling mechanisms, and many‐body interactions pertaining to optically generated electronic excitations in a variety of semiconductor material systems. Emphasis is placed on nanostructured gallium arsenide quantum wells and quantum dots, on quantum dots in other III–V and II–VI semiconductors, and on atomically thin transition metal dichalcogenides. Recent technical advances and potential future directions in the field are also discussed.Optical multidimensional coherent spectroscopy (MDCS) is a nonlinear spectroscopy technique where a material is excited by a series of laser pulses to produce a spectrum as a function of multiple frequencies. This review introduces the method and describes progress it has fostered establishing a better understanding of excitons and excitonic interactions in semiconductors.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146919/1/lpor201800171.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146919/2/lpor201800171_am.pd
Stimulated emission of Cooper pairs in a high-temperature cuprate superconductor
The concept of stimulated emission of bosons has played an important role in
modern science and technology, and constitutes the working principle for
lasers. In a stimulated emission process, an incoming photon enhances the
probability that an excited atomic state will transition to a lower energy
state and generate a second photon of the same energy. It is expected, but not
experimentally shown, that stimulated emission contributes significantly to the
zero resistance current in a superconductor by enhancing the probability that
scattered Cooper pairs will return to the macroscopically occupied condensate
instead of entering any other state. Here, we use time- and angle-resolved
photoemission spectroscopy to study the initial rise of the non-equilibrium
quasiparticle population in a BiSrCaCuO cuprate
superconductor induced by an ultrashort laser pulse. Our finding reveals
significantly slower buildup of quasiparticles in the superconducting state
than in the normal state. The slower buildup only occurs when the pump pulse is
too weak to deplete the superconducting condensate, and for cuts inside the
Fermi arc region. We propose this is a manifestation of stimulated
recombination of broken Cooper pairs, and signals an important momentum space
dichotomy in the formation of Cooper pairs inside and outside the Fermi arc
region.Comment: 16 pages, 4 figure
The Excitation Ladder of Cavity Polaritons
Multidimensional coherent spectroscopy directly unravels multiply excited
states that overlap in a linear spectrum. We report multidimensional coherent
optical photocurrent spectroscopy in a semiconductor polariton diode and
explore the excitation ladder of cavity polaritons. We measure doubly and
triply avoided crossings for pairs and triplets of exciton-polaritons,
demonstrating the strong coupling between light and dressed doublet and triplet
semiconductor excitations. These results demonstrate that multiply excited
excitonic states strongly coupled to a microcavity can be described as two
coupled quantum-anharmonic ladders
Excitation Ladder of Cavity Polaritons
Multidimensional coherent spectroscopy directly unravels multiply excited states that overlap in a linear spectrum. We report multidimensional coherent optical photocurrent spectroscopy in a semiconductor polariton diode and explore the excitation ladder of cavity polaritons. We measure doubly and triply avoided crossings for pairs and triplets of exciton polaritons, demonstrating the strong coupling between light and dressed doublet and triplet semiconductor excitations. These results demonstrate that multiply excited excitonic states strongly coupled to a microcavity can be described as two coupled quantum-anharmonic ladders
Hidden Silicon-Vacancy Centers in Diamond
We characterize a high-density sample of negatively charged silicon-vacancy
(SiV) centers in diamond using collinear optical multidimensional coherent
spectroscopy. By comparing the results of complementary signal detection
schemes, we identify a hidden population of \ce{SiV^-} centers that is not
typically observed in photoluminescence, and which exhibits significant
spectral inhomogeneity and extended electronic times. The phenomenon is
likely caused by strain, indicating a potential mechanism for controlling
electric coherence in color-center-based quantum devices
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