Bulletin of the American Physical Society
15th Annual Meeting of the Northwest Section of the APS
Volume 59, Number 6
Thursday–Saturday, May 1–3, 2014; Seattle, Washington
Session G6: Condensed Matter II |
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Chair: Kai-Mei Fu, University of Washington Room: Alder Commons 104 |
Saturday, May 3, 2014 4:00PM - 4:30PM |
G6.00001: Optoelectronics of Two-Dimensional Transition Metal Dichalcogenides Invited Speaker: Xiaodong Xu Monolayer transition metal dichalcogenides (TMDs) are a new class of 2D semiconductors with the band edge at the corners of the hexagonal Brillouin zone. There has been rapid progress in demonstrating the interesting 2D excitonic properties of TMDs, such as tunable exciton charging effects, large exciton and trion binding energies, and valley exciton polarization and coherence. In this talk, I will discuss the role of excitons in solid--state light emitting devices made from monolayer TMDs, as well as intralayer and interlayer excitonic properties in both TMD bilayers and heterostructure devices. The results are relevant for energy-efficient optoelectronics based on 2D layered materials. [Preview Abstract] |
Saturday, May 3, 2014 4:30PM - 4:42PM |
G6.00002: High Resolution Nonlinear Spectroscopy of 2D Excitons in Monolayer MoSe$_{2}$ John Schaibley, Todd Karin, Hongyi Yu, Jason Ross, Pasqual Rivera, Aaron Jones, Marie Scott, Jiaqiang Yan, David Mandrus, Wang Yao, Kai-Mei Fu, Xiaodong Xu Monolayer transition metal dichalcogenides (mTMDs), such as MoSe$_{2}$, have emerged as the first truly 2D semiconductors, exhibiting a wide range of novel electro-optical phenomena which arise from the material's graphene-like honeycomb lattice. The optical response of mTMDs is dominated by strongly bound excitons which are localized in momentum space to two sets of inequivalent valleys ($+$K, -K) at the edge of the Brillouin zone. We report the first high resolution nonlinear spectroscopy measurements on monolayer MoSe$_{2}$. Differential reflection measurements reveal that the degenerate nonlinear optical response agrees with the previously reported photoluminescence and reflectivity measurements, showing a broadened linewidth on order of 5 meV. Non-degenerate spectral holeburning measurements reveal narrow optical resonances approximately 1000 times narrower (order of 2 micro eV), indicating that excitons in mTMDs are dominantly inhomogenously broadened and exhibit an intrinsic lifetime on the order of 1 ns, over an order of magnitude longer than all previously reported lifetimes obtained through time domain techniques. Polarization dependent spectral holeburning measurements probe valley dependent processes such as the intervalley relaxation rates. [Preview Abstract] |
Saturday, May 3, 2014 4:42PM - 4:54PM |
G6.00003: Vapor-Solid Growth of WSe$_{2}$ Monolayers and Lateral Heterostructures Genevieve Clark, Pasqual Rivera, Sanfeng Wu, Chunming Hwang, Grant Aivazian, David Cobden, Xiaodong Xu Monolayer transition metal dichalcogenides (TMDCs) are atomically thin direct-gap semiconductors that show a variety of novel electronic and optical properties such as valley-polarization of Bloch electrons, due to their symmetry and two-dimensional nature. Heterostructures and devices combining various TMDCs via vertical or lateral stacking have shown further promise for applications in nanoelectronics and nano-optics, however the need for exfoliated samples limits the investigation of such materials and devices. Here, we present the synthesis of WSe$_{2}$ monolayers and lateral WSe$_{2}$-MoSe$_{2}$ heterostructures on insulating substrates using a catalyst-free physical vapor deposition method. Monolayers and heterostructures up to 15 microns in size show high optical quality, demonstrated by a high degree of valley-polarization observed via low temperature polarization-resolved photoluminescence measurements. [Preview Abstract] |
Saturday, May 3, 2014 4:54PM - 5:06PM |
G6.00004: Exciton and charge carrier dynamics in high-performance small-molecule bulk heterojunctions Keshab Paudel, Brian Johnson, Bradley Rose, Michael Haley, John Anthony, Oksana Ostroverkhova Organic donor-acceptor (D/A) bulk heterojunctions (BHJs) are of interest due to their applications in low-cost (opto)electronic devices relying on charge carrier photogeneration. However, understanding of charge photogeneration in small-molecule-based BHJs is lacking. We present studies of photoluminescence (PL) and transient photocurrent on spin-cast films of small-molecule D/A composites with a high-performance functionalized anthradithiophene derivative (ADT-TES-F) as the donor (D) and three different acceptor (A) molecules: (i) a functionalized pentacene derivative (Pn-TIPS-F8) (ii) an indenofluorene derivative (IF-Mes) and (iii) a fullerene derivative (PCBM). In each case, charge transfer from D to A was observed. In the D/A composites with Pn-TIPS-F8, it resulted in a formation of emissive charge transfer exciton, which did not significantly contribute to the photocurrent, so that the photocurrent decreased as the concentration of Pn-TIPS-F8 increased. The latter trend was also observed in films with IF-Mes acceptors. In contrast, in D/A composites with PCBM, the photocurrent increased by a factor of $\sim$ 7 at PCBM concentrations of 10 wt\%, as compared to that in the pristine ADT-TES-F donor film, due to efficient charge separation at the ADT-TES-F and PCBM interface. [Preview Abstract] |
Saturday, May 3, 2014 5:06PM - 5:18PM |
G6.00005: Hybrid GaP/diamond waveguide-integrated resonators for quantum information processing applications Nicole Thomas, Russell Barbour, Yuncheng Song, Minjoo Larry Lee, Kai-Mei C. Fu Nitrogen-vacancy (NV) centers are considered a promising qubit system for on-chip entanglement generation in future quantum information processing (QIP) platforms. Optical networks for creating entanglement between NV centers require efficient collection and enhancement of the NV emission, photon routing along the diamond surface and entanglement generation via measurement-based schemes. As a first building block for such a network, we present gallium phosphide (GaP) waveguide-integrated disk resonators on a diamond substrate, and demonstrate coupling between 1 $\mu $m diameter resonators and waveguides with loaded quality factors of 3,800. The devices were fabricated from single-crystalline GaP transferred onto the diamond using an epitaxial lift-off process. A hybrid GaP/diamond system is ideal in that the GaP device layer provides both a high-index material for efficient waveguiding and the potential for the integration of active optical switches due to its linear electro-optic properties. Our devices show quality factors and coupling characteristics that are extremely promising for a future integration with near-surface NV centers in diamond, with the efficiency of on-chip photon collection in bus waveguides being several magnitudes higher than in comparable platforms utilizing free-space collection. [Preview Abstract] |
Saturday, May 3, 2014 5:18PM - 5:30PM |
G6.00006: Applying Renormalization Group Theory to the Square Well Liquid Dan Roth, David Roundy We will present a study of the convergence properties of renormalization group theory (RGT) when applied to the square well (SW) liquid. RGT is a recursive process that allows us to make accurate predictions of propeties of a liquid near its critical point by accounting for the effects of fluctuations at multiple length scales. This can be computationally intensive, with the computing time scaling as an exponential of the longest length-scale fluctuations considered---that is, the recursion depth. I will present an overview of this method, a discussion of the computational difficulties and limitations that I have encountered, and some preliminary results comparing SW and SW+RGT. [Preview Abstract] |
Saturday, May 3, 2014 5:30PM - 5:42PM |
G6.00007: Softening the Hard-Sphere Fluid Eric Krebs, Samuel Loomis, Patrick Kreitzberg, David Roundy The hard-sphere fluid is a widely used reference fluid for theoretical frameworks for real fluids that, while well studied and understood, doesn't match particularly well with real physical fluids. For inhomogeneous hard-sphere fluids, Fundamental Measure Theory (FMT) is a standard classical density functional theory that predicts the hard-sphere free energy. A ``soft'' FMT (SFMT) was introduced by Schmidt [1] which is based on FMT and allows for penetrable spheres determined by a pair potential. We study a soft fluid with a simple potential describing slightly penetrating spheres at moderate temperatures based on SFMT. We compare the predicted equation of state against Monte-Carlo simulation for a homogeneous soft fluid and for soft spheres near a hard wall. \\[4pt] [1] Schmidt, M. Phys. Rev. E 62(4), 4976 (2000) [Preview Abstract] |
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