The preparation and definition of large (3 - 5 mm edge length) single crystals of ScN, GdN, TbN, HoN, YbN and CeN is described. The Hall effect and the electrical conductivity are found to be metallic. The optical ref...The preparation and definition of large (3 - 5 mm edge length) single crystals of ScN, GdN, TbN, HoN, YbN and CeN is described. The Hall effect and the electrical conductivity are found to be metallic. The optical reflectivity between 30 meV (sometimes 1 meV) and 13 eV has been measured and the dielectric functions have been obtained. A plasma edge in the infrared confirms the metallic character. In GdN, a shift of this plasma edge with temperature through the magnetic ordering temperature has been observed as a new effect. GdN is in low magnetic fields antiferromagnetic, but becomes ferromagnetic in larger fields. The band structure is discussed. The magnetic exchange interactions have been derived. HoN in the relevant crystal directions has a spontaneous magnetic moment, but no saturation in fields up to 10 T. CeN is intermediate valent and exhibits a Pauli paramagnetism. The specific heat is measured down to 0.3 K and an enhanced?γ value is observed.展开更多
In this publication details of the calculation of heat conductivity and thermal diffusivity, compressibility, sound velocity and exciton-polaron dispersion of TmSe0.45Te0.55 will be shown. The properties of excitons, ...In this publication details of the calculation of heat conductivity and thermal diffusivity, compressibility, sound velocity and exciton-polaron dispersion of TmSe0.45Te0.55 will be shown. The properties of excitons, coupling to phonons, producing thus polarons, but also blocking the phonons as running waves lead to an exciton condensation or exciton liquid. Surprisingly this exciton liquid is contained in a macroscopic crystal, a solid nevertheless, which becomes extremely hard due to the exciton liquid and finally exhibits a strange type of superfluid in a two fluid model, where the superfluid phase increases more and more below about 20 K until the whole exciton liquid becomes a superfluid at zero temperature. Never else a superfluid phase has been observed at such high temperatures.展开更多
Unlike the classical phase transition driven by thermal fluctuations,the quantum phase transition arises at zero temperature when the system is tuned by a non-thermal parameter[1].For a continuous quantum phase transi...Unlike the classical phase transition driven by thermal fluctuations,the quantum phase transition arises at zero temperature when the system is tuned by a non-thermal parameter[1].For a continuous quantum phase transition,novel physics with higher symmetry may emerge at the quantum critical point(QCP).展开更多
Developing a bright,deterministic source of entangled photon pairs has been an outstanding scientific and technological challenge.Semiconductor quantum dots are a promising candidate for this task.A new device combini...Developing a bright,deterministic source of entangled photon pairs has been an outstanding scientific and technological challenge.Semiconductor quantum dots are a promising candidate for this task.A new device combining a circular Bragg resonator and a piezoelectric actuator achieves high brightness and entanglement fidelity simultaneously,overcoming previous limitations.This breakthrough enhances quantum dot applications in entanglement-based quantum communication protocols.展开更多
The REAl(Si,Ge)(RE=rare earth)family,known to break both the inversion-and time-reversal symmetries,represents one of the most suitable platforms for investigating the interplay between correlated-electron phenomena a...The REAl(Si,Ge)(RE=rare earth)family,known to break both the inversion-and time-reversal symmetries,represents one of the most suitable platforms for investigating the interplay between correlated-electron phenomena and topologically nontrivial bands.Here,we report on systematic magnetic,transport,and muon-spin rotation and relaxation(μSR)measurements on(Nd,Sm)AlGe single crystals,which exhibit antiferromagnetic(AFM)transitions at T_(N)=6.1 and 5.9 K,respectively.In addition,NdAlGe undergoes also an incommensurate-to-commensurate ferrimagnetic transition at 4.5 K.Weak transverse-fieldμSR measurements confirm the AFM transitions,featuring a~90%magnetic volume fraction.Zero-field(ZF)μSR measurements reveal a more disordered internal field distribution in NdAlGe than in SmAlGe,reflected in a larger transverse muon-spin relaxation rateλTat T<<T_(N).This may be due to the complex magnetic structure of NdAlGe,which undergoes a series of metamagnetic transitions in an external magnetic field,while SmAlGe shows only a robust AFM order.In NdAlGe,the topological Hall effect(THE)appears between the first and the second metamagnetic transitions for H‖c,while it is absent in SmAlGe.Such THE in NdAlGe is most likely attributed to the field-induced topological spin textures.The longitudinal muon-spin relaxation rateλL,diverges near the AFM order,followed by a clear drop at T<T_N.In the magnetically ordered state,spin fluctuations are significantly stronger in NdAlGe than in SmAlGe.In general,our longitudinal-fieldμSR data indicate vigorous spin fluctuations in NdAlGe,thus providing valuable insights into the origin of THE and of the possible topological spin textures in REAl(Si,Ge)Weyl semimetals.展开更多
Measured and calculated results are presented for the emission properties of a new class of emitters operating in the cavity quantum electrodynamics regime.The structures are based on high-finesse GaAs/AlAs micropilla...Measured and calculated results are presented for the emission properties of a new class of emitters operating in the cavity quantum electrodynamics regime.The structures are based on high-finesse GaAs/AlAs micropillar cavities,each with an active medium consisting of a layer of InGaAs quantum dots(QDs)and the distinguishing feature of having a substantial fraction of spontaneous emission channeled into one cavity mode(highβ-factor).This paper demonstrates that the usual criterion for lasing with a conventional(lowβ-factor)cavity,that is,a sharp non-linearity in the input–output curve accompanied by noticeable linewidth narrowing,has to be reinforced by the equal-time second-order photon autocorrelation function to confirm lasing.The paper also shows that the equal-time second-order photon autocorrelation function is useful for recognizing superradiance,a manifestation of the correlations possible in high-βmicrocavities operating with QDs.In terms of consolidating the collected data and identifying the physics underlying laser action,both theory and experiment suggest a sole dependence on intracavity photon number.Evidence for this assertion comes from all our measured and calculated data on emission coherence and fluctuation,for devices ranging from light-emitting diodes(LEDs)and cavity-enhanced LEDs to lasers,lying on the same two curves:one for linewidth narrowing versus intracavity photon number and the other for g(2)(0)versus intracavity photon number.展开更多
The discovery of superconductivity in Sr/Ca-doped infinite-layer nickelates Nd(La)NiO_(2)thin films inspired extensive experimental and theoretical research.However,research on the possibilities of enhanced critical t...The discovery of superconductivity in Sr/Ca-doped infinite-layer nickelates Nd(La)NiO_(2)thin films inspired extensive experimental and theoretical research.However,research on the possibilities of enhanced critical temperature by interface heterostructure is still lacking.Due to the similarities of the crystal structure and band structure of infinite-layer nickelate La NiO_(2)and cuprate CaCuO_(2),we investigate the crystal,electronic and magnetic properties of La NiO_(2):CaCuO_(2)heterostructure using density functional theory and dynamical mean-field theory.Our theoretical results demonstrate that,even a very weak inter-layer z-direction bond is formed,an intrinsic charge transfer between Cu-3d_(x^(2)-y^(2))and Ni-3d_((x^(2)-y^(2)))orbitals is obtained.The weak interlayer hopping between Cu and Ni leaves a parallel band contributed by Ni/Cu-3d_((x^(2)-y^(2)))orbitals near the Fermi energy.Such an infinite-layer heterostructure with negligible interlayer interaction and robust charge transfer opens a new way for interface engineering and nickelate superconductors.展开更多
Two-level emitters are the main building blocks of photonic quantum technologies and are model systems for the exploration of quantum optics in the solid state.Most interesting is the strict resonant excitation of suc...Two-level emitters are the main building blocks of photonic quantum technologies and are model systems for the exploration of quantum optics in the solid state.Most interesting is the strict resonant excitation of such emitters to control their occupation coherently and to generate close to ideal quantum light,which is of utmost importance for applications in photonic quantum technology.To date,the approaches and experiments in this field have been performed exclusively using bulky lasers,which hinders the application of resonantly driven two-level emitters in compact photonic quantum systems.Here we address this issue and present a concept for a compact resonantly driven single-photon source by performing quantum-optical spectroscopy of a two-level system using a compact high-βmicrolaser as the excitation source.The two-level system is based on a semiconductor quantum dot(QD),which is excited resonantly by a fiber-coupled electrically driven micropillar laser.We dress the excitonic state of the QD under continuous wave excitation,and trigger the emission of single photons with strong multi-photon suppression(ge2Te0T?0:02)and high photon indistinguishability(V=57±9%)via pulsed resonant excitation at 156 MHz.These results clearly demonstrate the high potential of our resonant excitation scheme,which can pave the way for compact electrically driven quantum light sources with excellent quantum properties to enable the implementation of advanced quantum communication protocols.展开更多
Torque measurements were performed on single crystal samples of Ca0.73La0.27(Fe0.96Co0.04)As2 in both the normal and superconducting states.Contributions to the torque signal from the paramagnetism and the vortex latt...Torque measurements were performed on single crystal samples of Ca0.73La0.27(Fe0.96Co0.04)As2 in both the normal and superconducting states.Contributions to the torque signal from the paramagnetism and the vortex lattice were identified.The superconducting anisotropy parameterγwas determined from the reversible part of the vortex contribution based on Kogan's model.It is found thatγ≈7.5 at t=T/Tc=0.85,which is smaller than the result of CaFe0.88Co0.12AsFγ≈15 at t=0.83,but larger than the result of 11 and 122 families,whereγstays in the range of 2-3.The moderate anisotropy of this 112 iron-based superconductor fills the gap between 11,122 families and 1111 families.In addition,we found that theγshows a temperature dependent behavior,i.e.,decreasing with increasing temperature.The fact thatγis not a constant point towards a multiband scenario in this compound.展开更多
Ⅲ-nitride quantum dots(QDs)are a promising system actively studied for their ability to maintain single photon emission up to room temperature.Here,we report on the evolution of the emission properties of self-assemb...Ⅲ-nitride quantum dots(QDs)are a promising system actively studied for their ability to maintain single photon emission up to room temperature.Here,we report on the evolution of the emission properties of self-assembled GaN/AlN QDs for temperatures ranging from 5 to 300 K.We carefully track the photoluminescence of a single QD and measure an optimum single photon purity of g^((2))(0)=0.05±0.02 at 5 K and 0.17±0.08 at 300 K.We complement this study with temperature dependent time-resolved photoluminescence measurements(TRPL)performed on a QD ensemble to further investigate the exciton recombination dynamics of such polar zero-dimensional nanostructures.By comparing our results to past reports,we emphasize the complexity of recombination processes in this system.Instead of the more conventional mono-exponential decay typical of exciton recombination,TRPL transients display a bi-exponential feature with short-and long-lived components that persist in the low excitation regime.From the temperature insensitivity of the long-lived excitonic component,we first discard the interplay of dark-to-bright state refilling in the exciton recombination process.Besides,this temperature-invariance also highlights the absence of nonradiative exciton recombinations,a likely direct consequence of the strong carrier confinement observed in GaN/AlN QDs up to 300 K.Overall,our results support the viability of these dots as a potential single-photon source for quantum applications at room temperature.展开更多
文摘The preparation and definition of large (3 - 5 mm edge length) single crystals of ScN, GdN, TbN, HoN, YbN and CeN is described. The Hall effect and the electrical conductivity are found to be metallic. The optical reflectivity between 30 meV (sometimes 1 meV) and 13 eV has been measured and the dielectric functions have been obtained. A plasma edge in the infrared confirms the metallic character. In GdN, a shift of this plasma edge with temperature through the magnetic ordering temperature has been observed as a new effect. GdN is in low magnetic fields antiferromagnetic, but becomes ferromagnetic in larger fields. The band structure is discussed. The magnetic exchange interactions have been derived. HoN in the relevant crystal directions has a spontaneous magnetic moment, but no saturation in fields up to 10 T. CeN is intermediate valent and exhibits a Pauli paramagnetism. The specific heat is measured down to 0.3 K and an enhanced?γ value is observed.
文摘In this publication details of the calculation of heat conductivity and thermal diffusivity, compressibility, sound velocity and exciton-polaron dispersion of TmSe0.45Te0.55 will be shown. The properties of excitons, coupling to phonons, producing thus polarons, but also blocking the phonons as running waves lead to an exciton condensation or exciton liquid. Surprisingly this exciton liquid is contained in a macroscopic crystal, a solid nevertheless, which becomes extremely hard due to the exciton liquid and finally exhibits a strange type of superfluid in a two fluid model, where the superfluid phase increases more and more below about 20 K until the whole exciton liquid becomes a superfluid at zero temperature. Never else a superfluid phase has been observed at such high temperatures.
基金supported by the National Natural Science Foundation of China(U2032213(J.M.),12274288(X.W.and J.W.))the Innovation Program for Quantum Science and Technology(2021ZD0301900(X.W.and J.W.),2022YFA1402702(J.M.))+1 种基金the Natural Science Foundation of Shanghai(20ZR1428400),Shanghai Pujiang Program(20PJ1408100(X.W.and J.W.))Grants-in-Aid for Scientific Research(25220803 and 24244059)from MEXT.
文摘Unlike the classical phase transition driven by thermal fluctuations,the quantum phase transition arises at zero temperature when the system is tuned by a non-thermal parameter[1].For a continuous quantum phase transition,novel physics with higher symmetry may emerge at the quantum critical point(QCP).
基金funding support from the European Research Council(ERC starting grant“QD-NOMS”,ERC consolidator grant“MiNet”).
文摘Developing a bright,deterministic source of entangled photon pairs has been an outstanding scientific and technological challenge.Semiconductor quantum dots are a promising candidate for this task.A new device combining a circular Bragg resonator and a piezoelectric actuator achieves high brightness and entanglement fidelity simultaneously,overcoming previous limitations.This breakthrough enhances quantum dot applications in entanglement-based quantum communication protocols.
基金supported by the Natural Science Foundation of Shanghai(Grant Nos.21ZR1420500,and 21JC1402300)the Natural Science Foundation of Chongqing(Grant No.CSTB-2022NSCQ-MSX1678)+3 种基金the National Natural Science Foundation of China(Grant Nos.12374105,and 12350710785)the Fundamental Research Funds for the Central Universitiesthe Schweizerische Nationalfonds zur F?rderung der Wissenschaftlichen Forschung(SNF)(Grant Nos.200021169455,and 200021188706)support from Paul Scherrer Institute Research Grant(Grant No.202101346)。
文摘The REAl(Si,Ge)(RE=rare earth)family,known to break both the inversion-and time-reversal symmetries,represents one of the most suitable platforms for investigating the interplay between correlated-electron phenomena and topologically nontrivial bands.Here,we report on systematic magnetic,transport,and muon-spin rotation and relaxation(μSR)measurements on(Nd,Sm)AlGe single crystals,which exhibit antiferromagnetic(AFM)transitions at T_(N)=6.1 and 5.9 K,respectively.In addition,NdAlGe undergoes also an incommensurate-to-commensurate ferrimagnetic transition at 4.5 K.Weak transverse-fieldμSR measurements confirm the AFM transitions,featuring a~90%magnetic volume fraction.Zero-field(ZF)μSR measurements reveal a more disordered internal field distribution in NdAlGe than in SmAlGe,reflected in a larger transverse muon-spin relaxation rateλTat T<<T_(N).This may be due to the complex magnetic structure of NdAlGe,which undergoes a series of metamagnetic transitions in an external magnetic field,while SmAlGe shows only a robust AFM order.In NdAlGe,the topological Hall effect(THE)appears between the first and the second metamagnetic transitions for H‖c,while it is absent in SmAlGe.Such THE in NdAlGe is most likely attributed to the field-induced topological spin textures.The longitudinal muon-spin relaxation rateλL,diverges near the AFM order,followed by a clear drop at T<T_N.In the magnetically ordered state,spin fluctuations are significantly stronger in NdAlGe than in SmAlGe.In general,our longitudinal-fieldμSR data indicate vigorous spin fluctuations in NdAlGe,thus providing valuable insights into the origin of THE and of the possible topological spin textures in REAl(Si,Ge)Weyl semimetals.
基金the European Research Council under the Seventh Framework ERC Grant Agreement No.615613 of the European Unionthe German Research Foundation via the projects RE2974/5-1,Ka23187-1 and JA 619/10-3+3 种基金the US Department of Energy under Contract No.DE-AC04-94AL85000the Technical University Berlin for hospitality and the German Research Foundation via collaborative research center 787 for travel supportsupport from the German Science Foundation(DFG)support from the German Federal Ministry of Education and Research(BMBF).
文摘Measured and calculated results are presented for the emission properties of a new class of emitters operating in the cavity quantum electrodynamics regime.The structures are based on high-finesse GaAs/AlAs micropillar cavities,each with an active medium consisting of a layer of InGaAs quantum dots(QDs)and the distinguishing feature of having a substantial fraction of spontaneous emission channeled into one cavity mode(highβ-factor).This paper demonstrates that the usual criterion for lasing with a conventional(lowβ-factor)cavity,that is,a sharp non-linearity in the input–output curve accompanied by noticeable linewidth narrowing,has to be reinforced by the equal-time second-order photon autocorrelation function to confirm lasing.The paper also shows that the equal-time second-order photon autocorrelation function is useful for recognizing superradiance,a manifestation of the correlations possible in high-βmicrocavities operating with QDs.In terms of consolidating the collected data and identifying the physics underlying laser action,both theory and experiment suggest a sole dependence on intracavity photon number.Evidence for this assertion comes from all our measured and calculated data on emission coherence and fluctuation,for devices ranging from light-emitting diodes(LEDs)and cavity-enhanced LEDs to lasers,lying on the same two curves:one for linewidth narrowing versus intracavity photon number and the other for g(2)(0)versus intracavity photon number.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2021YFA0718900and 2022YFA1403000)the Key Research Program of Frontier Sciences of CAS(Grant No.ZDBS-LY-SLH008)+2 种基金the National Natural Science Foundation of China(Grant Nos.11974365,12004400,and 51931011)the Science Center of the National Natural Science Foundation of China(Grant No.52088101)the K.C.Wong Education Foundation(Grant No.GJTD-2020-11)。
文摘The discovery of superconductivity in Sr/Ca-doped infinite-layer nickelates Nd(La)NiO_(2)thin films inspired extensive experimental and theoretical research.However,research on the possibilities of enhanced critical temperature by interface heterostructure is still lacking.Due to the similarities of the crystal structure and band structure of infinite-layer nickelate La NiO_(2)and cuprate CaCuO_(2),we investigate the crystal,electronic and magnetic properties of La NiO_(2):CaCuO_(2)heterostructure using density functional theory and dynamical mean-field theory.Our theoretical results demonstrate that,even a very weak inter-layer z-direction bond is formed,an intrinsic charge transfer between Cu-3d_(x^(2)-y^(2))and Ni-3d_((x^(2)-y^(2)))orbitals is obtained.The weak interlayer hopping between Cu and Ni leaves a parallel band contributed by Ni/Cu-3d_((x^(2)-y^(2)))orbitals near the Fermi energy.Such an infinite-layer heterostructure with negligible interlayer interaction and robust charge transfer opens a new way for interface engineering and nickelate superconductors.
基金funding from the European Research Council(ERC)under the European Union’s Seventh Framework ERC Grant Agreement No.615613the German Research Foundation(DFG)via CRC 787 and Projects No.RE2974/5-1,RE2974/9-1,and SCHN1376/2-1+1 种基金the State of Bavaria,and the German Ministry of Education and Research(BMBF)the support of the DFG through the project B1 of the SFB 910.
文摘Two-level emitters are the main building blocks of photonic quantum technologies and are model systems for the exploration of quantum optics in the solid state.Most interesting is the strict resonant excitation of such emitters to control their occupation coherently and to generate close to ideal quantum light,which is of utmost importance for applications in photonic quantum technology.To date,the approaches and experiments in this field have been performed exclusively using bulky lasers,which hinders the application of resonantly driven two-level emitters in compact photonic quantum systems.Here we address this issue and present a concept for a compact resonantly driven single-photon source by performing quantum-optical spectroscopy of a two-level system using a compact high-βmicrolaser as the excitation source.The two-level system is based on a semiconductor quantum dot(QD),which is excited resonantly by a fiber-coupled electrically driven micropillar laser.We dress the excitonic state of the QD under continuous wave excitation,and trigger the emission of single photons with strong multi-photon suppression(ge2Te0T?0:02)and high photon indistinguishability(V=57±9%)via pulsed resonant excitation at 156 MHz.These results clearly demonstrate the high potential of our resonant excitation scheme,which can pave the way for compact electrically driven quantum light sources with excellent quantum properties to enable the implementation of advanced quantum communication protocols.
基金Project supported by NSAF,China(Grant No.U1530402)P.G.Li acknowledges the support of the National Natural Science Foundation of China(Grant No.51572241).
文摘Torque measurements were performed on single crystal samples of Ca0.73La0.27(Fe0.96Co0.04)As2 in both the normal and superconducting states.Contributions to the torque signal from the paramagnetism and the vortex lattice were identified.The superconducting anisotropy parameterγwas determined from the reversible part of the vortex contribution based on Kogan's model.It is found thatγ≈7.5 at t=T/Tc=0.85,which is smaller than the result of CaFe0.88Co0.12AsFγ≈15 at t=0.83,but larger than the result of 11 and 122 families,whereγstays in the range of 2-3.The moderate anisotropy of this 112 iron-based superconductor fills the gap between 11,122 families and 1111 families.In addition,we found that theγshows a temperature dependent behavior,i.e.,decreasing with increasing temperature.The fact thatγis not a constant point towards a multiband scenario in this compound.
基金supported by the Swiss National Science Foundation through Grants 200021E_15468 and 200020_162657by the Marie SklodowskaCurie action“PhotoHeatEffect”(Grant no.749565)withinEuropean Union’s Horizon 2020 research and innovation program.
文摘Ⅲ-nitride quantum dots(QDs)are a promising system actively studied for their ability to maintain single photon emission up to room temperature.Here,we report on the evolution of the emission properties of self-assembled GaN/AlN QDs for temperatures ranging from 5 to 300 K.We carefully track the photoluminescence of a single QD and measure an optimum single photon purity of g^((2))(0)=0.05±0.02 at 5 K and 0.17±0.08 at 300 K.We complement this study with temperature dependent time-resolved photoluminescence measurements(TRPL)performed on a QD ensemble to further investigate the exciton recombination dynamics of such polar zero-dimensional nanostructures.By comparing our results to past reports,we emphasize the complexity of recombination processes in this system.Instead of the more conventional mono-exponential decay typical of exciton recombination,TRPL transients display a bi-exponential feature with short-and long-lived components that persist in the low excitation regime.From the temperature insensitivity of the long-lived excitonic component,we first discard the interplay of dark-to-bright state refilling in the exciton recombination process.Besides,this temperature-invariance also highlights the absence of nonradiative exciton recombinations,a likely direct consequence of the strong carrier confinement observed in GaN/AlN QDs up to 300 K.Overall,our results support the viability of these dots as a potential single-photon source for quantum applications at room temperature.
