We demonstrate highly efficient avalanche multiphoton luminescence (MPL) from ordered-arrayed gold nanowires (NWs) with low time-average excitation intensity, Iexc (5.0-9.1 kW/cm2). The intensity of avalanche MPL, IMPL, is about 10(4) times larger than that of three-photon luminescence, the slope partial differential log IMPL/ partial differential log Iexc of avalanche MPL reaches as high as 18.3, and the corresponding polarization dependence of IMPL has a form of cos50 phip. The emission dynamics of avalanche MPL and three-photon luminescence are also studied comparatively. These observations indicate that the highly efficient avalanche MPL is attributed to the giant enhancement and coupling of longitudinal surface plasmon resonance of ordered-arrayed gold NWs.

As a charged spinning fermion drops into a charged rotating BTZ black hole, we investigate the laws of thermodynamics and weak cosmic censorship conjecture with and without pressure respectively. For the case without pressure, the first law, second law, as well as the weak cosmic censorship are found to be valid. While for the case with pressure, though the first law is still valid, the second law and the weak cosmic censorship conjecture are found to be violable, depending on the charge, angular momentum, AdS radius, and their variations. In addition, in both cases, the configurations of the extremal black holes are found to be stable since the final states of the extremal black holes are still extremal black holes. While for the near-extremal black holes, their configurations are not stable.

The ferrimagnetic spin-1/2 chain composed of alternating Ising and Heisenberg spins in an arbitrarily oriented magnetic field is exactly solved using the spin-rotation transformation and the transfer-matrix method. It is shown that the low-temperature magnetization process depends basically on a spatial orientation of the magnetic field. A sharp stepwise magnetization curve with a marked intermediate plateau, which emerges for the magnetic field applied along the easy-axis direction of the Ising spins, becomes smoother and the intermediate plateau shrinks if the external field is tilted from the easy-axis direction. The magnetization curve of a polycrystalline system is also calculated by performing powder averaging of the derived magnetization formula. The proposed spin-chain model brings an insight into high-field magnetization data of 3d-4f bimetallic polymeric compound Dy(NO 3 )(DMSO) 2 Cu(opba)(DMSO) 2 , which provides an interesting experimental realization of the ferrimagnetic chain composed of two different but regularly alternating spin-1/2 magnetic ions Dy 3+ and Cu 2+ that are reasonably approximated by the notion of Ising and Heisenberg spins, respectively.

Abstract:We explore orbital dynamics in the spin liquid candidate Ba 3 CuSb 2 O 9 using multi-frequency electron spin resonance. We prepared two high quality single crystals. The crystal with a slight copper deficiency shows a structural phase transition at around 200 K due to the cooperative Jahn-Teller effect, accompanied with orbital ordering. In contrast, the crystal with almost perfect stoichiometry shows no orbital ordering down to the lowest temperature of 1.5 K. Dramatic change in the g-factor anisotropy as a function of frequency and temperature demonstrates orbital quantum fluctuations at a nearly constant time scale of ~ 100 ps below 20 K, evidencing the emergence of an orbital liquid state in this quantum spin liquid compound.

With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include Bose−Einstein condensation of cold atoms, superconductivity, quantum Hall state of electron systems, and quantum spin liquid state in the frustrated magnets. Moreover, recent studies have clarified the possibility of another exotic quantum liquid state based on the spin-orbital entanglement in FeSc 2 S 4 . To confirm this exotic ground state, experiments based on single-crystalline samples are essential. However, no such single-crystal study has been reported to date. Here, we report, to our knowledge, the first single-crystal study on the spin-orbital liquid candidate, 6H-Ba 3 CuSb 2 O 9 , and we have confirmed the absence of an orbital frozen state. In strongly correlated electron systems, orbital ordering usually appears at high temperatures in a process accompanied by a lattice deformation, called a static Jahn−Teller distortion. By combining synchrotron X-ray diffraction, electron spin resonance, Raman spectroscopy, and ultrasound measurements, we find that the static Jahn−Teller distortion is absent in the present material, which indicates that orbital ordering is suppressed down to the lowest temperatures measured. We discuss how such an unusual feature is realized with the help of spin degree of freedom, leading to a spin-orbital entangled quantum liquid state.Q uantum spin liquids have been widely recognized as a new state of matter, as an increasing number of candidates with quantum spin S = 1/2 have been found recently (1-4), a long time after the first proposal was made for the resonating valence-bond state (5). On the other hand, quantum liquids based on another electronic degree of freedom, orbital, have been theoretically proposed (6). However, this type of liquid state has never been experimentally confirmed because the energy of orbital correlation is normally one order of magnitude stronger than spin exchange coupling, leading to an orbital ordering at a significantly high temperature accompanied by a cooperative Jahn-Teller (JT) distortion. Nevertheless, if we can bring down the orbital energy to the same scale as for the spin coupling, it may lead to a novel spin-orbital entangled state, a "quantum spin-orbital liquid." A possible spin-orbital entangled liquid state with dimer correlations has been theoretically discussed on a triangular lattice with singly occupied but triply degenerate t 2g orbitals (7). In comparison with the t 2g orbitals' case, the experimental realization of such a quantum spin-orbital liquid state in the e g orbital system has been even more challenging (8), because e g orbitals more strongly couple to the JT modes.Perovskite-type 6H-Ba 3 CuSb 2 O 9 is a good candidate material for the spin-orbital liquid state that has been ...

After studying the energy-momentum relation of charged particles' Hamilton-Jacobi equations, we discuss the laws of thermodynamics and the weak cosmic censorship conjecture in torus-like black holes. We find that both the first law of thermodynamic as well as the weak cosmic censorship conjecture are valid in both the normal phase space and extended phase space. However, the second law of thermodynamics is only valid in the normal phase space. Our results show that the first law and weak cosmic censorship conjecture do not depend on the phase spaces while the second law depends. What's more, we find that the shift of the metric function that determines the event horizon take the same form in different phase spaces, indicating that the weak cosmic censorship conjecture is independent of the phase space.

The relative probability of two- and three-photon absorption in Au nanoparticles was adjusted by tuning the surface-plasmon-resonance (SPR) wavelength and the excitation intensity. Consequently, highly efficient three-photon luminescence from Au nanoparticles with strong SPR enhancement was observed. The decay rate and polarization of two- and three-photon luminescence from Au nanoparticles were comparatively studied. Furthermore, the multiphoton luminescence from Au nanoparticles was used to investigate the resonant energy transfer from CdSe semiconductor quantum dots.

The relaxation dynamics of hot electrons and the third-order optical nonlinearity in gold nanorods (GNRs) with different aspect ratios were investigated with the help of femtosecond optical Kerr (OKE) technique. Relaxation process on the time scale of picosecond (ps) was obtained at the longitudinal surface plasmon resonant (SPR) wavelength. As the aspect ratio (AR) of the GNRs varied from 4.2 ± 0.3 to 3.3 ± 0.3, the SPR wavelength changed accordingly from 808 to 750 nm, but the corresponding relaxation time and the third-order optical susceptibility did not change much. However, as the pump power increased from 150 mW to 400 mW, the relaxation time of the nanorod with AR = 4.2 ± 0.3 increased by 50% from 1.20 ± 0.01 ps to 1.84 ± 0.04 ps, indicating that the pump power is an important factor that affects the response time of the nanostructures. Comparative studies between Au nanorods, Au nanobipyramids, and Au triangular prisms measured under the same setup demonstrated that excitation conditions (excitation wavelength or pump power) and structure shapes were key factors to modulate the relaxation time of hot electrons. These results are important for the control and modulation of the response time in metallic nanostructures, which is essential for their applications in photovoltaic, photocatalytic, and ultrafast optic devices.