Photoconductive emitters for terahertz generation hold promise for highly efficient down-conversion of optical photons because it is not constrained by the Manley-Rowe relation.Existing terahertz photoconductive devic...Photoconductive emitters for terahertz generation hold promise for highly efficient down-conversion of optical photons because it is not constrained by the Manley-Rowe relation.Existing terahertz photoconductive devices,however,faces limits in efficiency due to the semiconductor properties of commonly used GaAs materials.Here,we demonstrate that large bandgap semiconductor GaN,characterized by its high breakdown electric field,facilitates the highly efficient generation of terahertz waves in a coplanar stripline waveguide.Towards this goal,we investigated the excitonic contribution to the electro-optic response of GaN under static electric field both through experiments and first-principles calculations,revealing a robust excitonic Stark shift.Using this electro-optic effect,we developed a novel ultraviolet pump-probe spectroscopy for in-situ characterization of the terahertz electric field strength generated by the GaN photoconductive emitter.Our findings show that terahertz power scales quadratically with optical excitation power and applied electric field over a broad parameter range.We achieved an optical-to-terahertz conversion efficiency approaching 100%within the 0.03–1 THz bandwidth at the highest bias field(116 kV/cm)in our experiment.Further optimization of GaN-based terahertz generation devices could achieve even greater optical-toterahertz conversion efficiencies.展开更多
Classical Monte Carlo simulation of the Heisenberg model poorly describes many thermodynamic phenomena due to its neglect of the quantum nature of spins.Alternatively,we discuss how to semiclassically approach the qua...Classical Monte Carlo simulation of the Heisenberg model poorly describes many thermodynamic phenomena due to its neglect of the quantum nature of spins.Alternatively,we discuss how to semiclassically approach the quantum problem and demonstrate a simple method for introducing a locally approximate form of spin quantization.While the procedure underestimates magnetic short-range order,our results suggest a simple correction for recovering realistic spin–spin correlations above the critical temperature.Moreover,ensemble fluctuations are found to provide reasonably accurate thermodynamics,largely reproducing quantum mechanically calculated heat capacities and experimental magnetometry for ferromagnetic Fe and antiferromagnetic RbMnF3.Extensions of the method are proposed to address remaining inaccuracies.展开更多
基金supported by the National Science Foundation under the award number 2414287 and the theoretical work on pump-probe spectroscopy and calculations of the GaN excitonic electro-optic effect were supporte by the National Science Foundation under grant DMR-2325410The Center for Computational Study of Excited-State Phenomena in Energy Materials(C2SEPEM)at Lawrence Berkeley National Laboratory,supported by the US Department of Energy,Office of Science,Basic Energy Sciences,Materials Sciences and Engineering Division under contract no.DE-AC02-05CH11231,as part of the Computational Materials Sciences Program provided advanced codes for excited state computations+3 种基金The first-principles calculations were performed using computation resources at the National Energy Research Scientific Computing Center(NERSC)The U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division under Contract No.DE-AC02-05-CH11231(van der Waals heterostructure program KCFW16)supported the device fabricationThe waveguide simulations were performed at the Molecular Graphics and Computation Facility(MGCF)at UC Berkeley and the MGCF is in part supported by NIH S10OD034382S.D.C.acknowledges support from the Kavli ENSI Heising-Simons Junior Fellowship.
文摘Photoconductive emitters for terahertz generation hold promise for highly efficient down-conversion of optical photons because it is not constrained by the Manley-Rowe relation.Existing terahertz photoconductive devices,however,faces limits in efficiency due to the semiconductor properties of commonly used GaAs materials.Here,we demonstrate that large bandgap semiconductor GaN,characterized by its high breakdown electric field,facilitates the highly efficient generation of terahertz waves in a coplanar stripline waveguide.Towards this goal,we investigated the excitonic contribution to the electro-optic response of GaN under static electric field both through experiments and first-principles calculations,revealing a robust excitonic Stark shift.Using this electro-optic effect,we developed a novel ultraviolet pump-probe spectroscopy for in-situ characterization of the terahertz electric field strength generated by the GaN photoconductive emitter.Our findings show that terahertz power scales quadratically with optical excitation power and applied electric field over a broad parameter range.We achieved an optical-to-terahertz conversion efficiency approaching 100%within the 0.03–1 THz bandwidth at the highest bias field(116 kV/cm)in our experiment.Further optimization of GaN-based terahertz generation devices could achieve even greater optical-toterahertz conversion efficiencies.
基金F.W.was supported by the U.S.Department of Defense through the National Defense Science and Engineering Graduate Fellowship ProgramM.A.and L.-W.W.were supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division,under Contract No.DE-AC02-05-CH11231(Materials Project program KC23MP and Non-Equilibrium Magnetic Materials program MSMAG,respectively)Computational resources were provided by award BES-ERCAP0021088 of the National Energy Research Scientific Computing Center(NERSC),a U.S.Department of Energy Office of Science User Facility at Lawrence Berkeley National Laboratory,operated under the same contract.
文摘Classical Monte Carlo simulation of the Heisenberg model poorly describes many thermodynamic phenomena due to its neglect of the quantum nature of spins.Alternatively,we discuss how to semiclassically approach the quantum problem and demonstrate a simple method for introducing a locally approximate form of spin quantization.While the procedure underestimates magnetic short-range order,our results suggest a simple correction for recovering realistic spin–spin correlations above the critical temperature.Moreover,ensemble fluctuations are found to provide reasonably accurate thermodynamics,largely reproducing quantum mechanically calculated heat capacities and experimental magnetometry for ferromagnetic Fe and antiferromagnetic RbMnF3.Extensions of the method are proposed to address remaining inaccuracies.
