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Register a new userRoom temperature manipulation of long lifetime spins in metallic-like carbon nanospheres
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The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin-lattice (T1) and spin-spin (T2) relaxation times of electrons. Minimising the effects of spin-orbit coupling and the local magnetic contributions of neighbouring atoms on T1 and T2 at room temperature remain substantial challenges to practical spintronics. Here, we report a record-high conduction electron T1=T2 of 175 ns at 300 K in 37 nm +/- 7 nm carbon spheres, which exceeds by far the highest values observed for any conducting solid state material of comparable size. The long T1=T2 is due to quantum confinement effects, to the intrinsically weak spin-orbit coupling of carbon, and to the protecting nature of the outer shells of the inner spins from the influences of environmental disturbances. Following the observation of spin polarization by electron spin resonance, we controlled the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observed coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temperature.
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Unexpected ferromagnetism has been observed in carbon doped ZnO films grown by pulsed laser deposition [Phys. Rev. Lett. 99, 127201 (2007)]. In this letter, we introduce carbon into ZnO films by ion implantation. Room temperature ferromagnetism has been observed. Our analysis demonstrates that (1) C-doped ferromagnetic ZnO can be achieved by an alternative method, i.e. ion implantation, and (2) the chemical involvement of carbon in the ferromagnetism is indirectly proven.
Multiwalled carbon nanotubes are shown to be ballistic conductors at room temperature, with mean free paths of the order of tens of microns. These experiments follow and extend the original experiments by Frank et al (Science, 280 1744 1998) including in-situ electron microscopy experiments and a detailed analysis of the length dependence of the resistance. The per unit length resistance r < 100 Ohm/micron, indicating free paths l > 65 microns, unambiguously demonstrate ballistic conduction at room temperature up to macroscopic distances. The nanotube-metal contact resistances are in the range 0.1-1 kOhm micron. Contact scattering can explain why the measured conductances are about half the expected theoretical value of 2 G0 . For V>0.1V the conductance rises linearly (dG/dV~0.3 G0 /V) reflecting the linear increase in the density-of-states in a metallic nanotube above the energy gap. Increased resistances (r =2- 10 k Ohm/micron) and anomalous I-V dependences result from impurities and surfactants on the tubes.Evidence is presented that ballistic transport occurs in undoped and undamaged tubed for which the top layer is metallic and the next layer is semiconducting. The diffusive properties of lithographically contacted multiwalled nanotubes most likely result from purification and other processing steps that damage and dope the nanotubes thereby making them structurally and electronically different than the pristine nanotubes investigated here.
We propose a method for nano-scale characterization of long range magnetic order in diluted magnetic systems to clarify the origins of the room temperature ferromagnetism. The GaN:Mn thin films are grown by metal-organic chemical vapor deposition with the concentration of Ga-substitutional Mn up to 3.8%. Atomic force microscope (AFM) and magnetic force microscope (MFM) characterizations are performed on etched artificial microstructures and natural dislocation pits. Numerical simulations and theoretical analysis on the AFM and MFM data have confirmed the formation of long range magnetic order and ruled out the possibility that nano-clusters contributed to the ferromagnetism. We suggest that delocalized electrons might play a role in the establishment of this long range magnetic order.
Perovskites have been the focus of attention due to their multitude of outstanding optoelectronic properties and structural versatility. Two-dimensional halide perovskite such as (C_6H_5C_2H_4NH_3)_2PbI_4, or simply PEPI, forms natural multiple quantum wells with enhanced light-matter interactions, making them attractive systems for further investigation. This work reports tunable splitting of exciton modes in PEPI resulting from strong light-matter interactions, manifested as multiple dips (modes) in the reflection spectra. While the origin of the redder mode is well understood, that for the bluer dip at room temperature is still lacking. Here, it is revealed that the presence of the multiple modes originates from an indirect coupling between excitons in different quantum wells. The long-range characteristic of the mediated coupling between excitons in distant quantum wells is also demonstrated in a structure design along with its tunability. Moreover, a device architecture involving an end silver layer enhances the two excitonic modes and provides further tunability. Importantly, this work will motivate the possibility of coupling of the excitonic modes with a confined light mode in a microcavity to produce multiple exciton-polariton modes.
Room temperature strong coupling of WS_2 monolayer exciton transitions to metallic Fabry-Perot and plasmonic optical cavities is demonstrated. A Rabi splitting of 101 meV is observed for the Fabry-Perot cavity, more than double those reported to date in other 2D materials. The enhanced magnitude and visibility of WS_2 monolayer strong coupling is attributed to the larger absorption coefficient, the narrower linewidth of the A exciton transition, and greater spin-orbit coupling. For WS_2 coupled to plasmonic arrays, the Rabi splitting still reaches 60 meV despite the less favorable coupling conditions, and displays interesting photoluminescence features. The unambiguous signature of WS_2 monolayer strong coupling in easily fabricated metallic resonators at room temperature suggests many possibilities for combining light-matter hybridization with spin and valleytronics.
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