Latest Papers in Condensed Matter Physics

Mesoscale And Nanoscale Physics

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Plasmon-Assisted Suppression of Surface Trap States and Enhanced Band-Edge Emission in a Bare CdTe Quantum Dot (1903.03572v1)

Assegid M. Flatae, Francesco Tantussi, Gabriele C. Messina, Francesco De Angelis, Mario Agio

2019-03-08

Colloidal quantum dots have emerged as a versatile photoluminescent and optoelectronic material. Issues like fluorescence intermittency, non-radiative Auger recombination and surface traps are commonly addressed by growing a wide-bandgap shell around the quantum dot. However, the shell isolates the excitonic wave function and reduces its interaction with nanoscale optical fields, which are instrumental for applications such as charge transport in photovoltaics and lasers. Furthermore, the shell causes a longer emission lifetime, which limits their use for high-speed nanoscale optoelectronics and as photoluminescence probes. Here, we demonstrate a high degree of control on the photophysics of a bare core CdTe quantum dot solely by plasmon-coupling, showing that more than 99% of the surface defect-state emission from a trap-rich quantum dot can be quenched. Moreover, the band-edge state excitonic and biexcitonic radiative recombination rates are enhanced by 676 and 293-fold, respectively. The larger photon emission rate improves the quantum efficiency of the excitonic transition by more than a factor of 3, while the increase of the radiative decay rate of the biexciton prevents Auger non-radiative decay channels, leading to a 10-fold enhancement in the quantum efficiency. Plasmonic coupling represents an effective approach for controlling the quantum dot optical properties, with implications for developing nanoscale thresholdless lasers, light emitting devices and single-photon sources.

Nanoantenna Enhanced Terahertz Interaction of Biomolecules (1903.03415v1)

Subham Adak, Laxmi Narayan Tripathi

2019-03-08

Terahertz time-domain spectroscopy (THz-TDS) is a non-invasive, non-contact and label-free technique for biological and chemical sensing as THz-spectra is less energetic and lies in the characteristic vibration frequency regime of proteins and DNA molecules. However, THz-TDS is less sensitive for detection of micro-organisms of size equal to or less than (where, is wavelength of incident THz wave) and, molecules in extremely low concentrated solutions (like, a few femtomolar). After successful high-throughput fabrication of nanostructures, nanoantennas and metamaterials were found to be indispensable in enhancing the sensitivity of conventional THz-TDS. These nanostructures lead to strong THz field enhancement which when in resonance with absorption spectrum of absorptive molecules, causing significant changes in the magnitude of the transmission spectrum, therefore, enhancing the sensitivity and allowing detection of molecules and biomaterials in extremely low concentrated solutions. Hereby, we review the recent developments in ultra-sensitive and selective nanogap biosensors. We have also provided an in-depth review of various high-throughput nanofabrication techniques. We also discussed the physics behind the field enhancements in sub-skin depth as well as sub-nanometer sized nanogaps. We introduce finite-difference time-domain (FDTD) and molecular dynamics (MD) simulations tools to study THz biomolecular interactions. Finally, we provide a comprehensive account of nanoantenna enhanced sensing of viruses (like, H1N1) and biomolecules such as artificial sweeteners which are addictive and carcinogenic.

Optical conductivity of black phosphorus with a tunable electronic structure (1811.07529v2)

Jiho Jang, Seongjin Ahn, Hongki Min

2018-11-19

Black phosphorus (BP) is a two-dimensional layered material composed of phosphorus atoms. Recently, it was demonstrated that external perturbations such as an electric field close the band gap in few-layer BP, and can even induce a band inversion, resulting in an insulator phase with a finite energy gap or a Dirac semimetal phase characterized by two separate Dirac nodes. At the transition between the two phases, a semi-Dirac state appears in which energy disperses linearly along one direction and quadratically along the other. In this work, we study the optical conductivity of few-layer BP using a lattice model and the corresponding continuum model, incorporating the effects of an external electric field and finite temperature. We find that the low-frequency optical conductivity scales a power law that differs depending on the phase, which can be utilized as an experimental signature of few-layer BP in different phases. We also systematically analyze the evolution of the material parameters as the electric field increases, and the consequence on the power-law behavior of the optical conductivity.

Quantised conductance of one-dimensional strongly-correlated electrons in an oxide heterostructure (1903.03476v1)

H. Hou, Y. Kozuka, Jun-Wei Liao, L. W. Smith, D. Kos, J. P. Griffiths, J. Falson, A. Tsukazaki, M. Kawasaki, C. J. B. Ford

2019-03-08

Oxide heterostructures are versatile platforms with which to research and create novel functional nanostructures. We successfully develop one-dimensional (1D) quantum-wire devices using quantum point contacts on MgZnO/ZnO heterostructures and observe ballistic electron transport with conductance quantised in units of 2e^{2}/h. Using DC-bias and in-plane field measurements, we find that the g-factor is enhanced to around 6.8, more than three times the value in bulk ZnO. We show that the effective mass m^{*} increases as the electron density decreases, resulting from the strong electron-electron interactions. In this strongly interacting 1D system we study features matching the 0.7 conductance anomalies up to the fifth subband. This paper demonstrates that high-mobility oxide heterostructures such as this can provide good alternatives to conventional III-V semiconductors in spintronics and quantum computing as they do not have their unavoidable dephasing from nuclear spins. This paves a way for the development of qubits benefiting from the low defects of an undoped heterostructure together with the long spin lifetimes achievable in silicon.

Exceptional point enhances sensitivity of optomechanical mass sensors (1903.02542v2)

P. Djorwé, Y. Pennec, B. Djafari-Rouhani

2019-03-06

We propose an efficient optomechanical mass sensor operating at exceptional points (EPs), non-hermitian degeneracies where eigenvalues of a system and their corresponding eigenvectors simultaneously coalesce. The benchmark system consists of two optomechanical cavities (OMCs) that are mechanically coupled, where we engineer mechanical gain (loss) by driving the cavity with a blue (red) detuned laser. The system features EP at the gain and loss balance, where any perturbation induces a frequency splitting that scales as the square-root of the perturbation strength, resulting in a giant sensitivity factor enhancement compared to the conventional optomechanical sensors. For non-degenerated mechanical resonators, quadratic optomechanical coupling is used to tune the mismatch frequency in order to get closer to the EP, extending the efficiency of our sensing scheme to mismatched resonators. This work paves the way towards new levels of sensitivity for optomechanical sensors, which could find applications in many other fields including nanoparticles detection, precision measurement, and quantum metrology.

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