The magnetic properties and Kondo effect in Ce3TiBi5 with a quasi-one-dimensional structure were investigated using in situ high-pressure resistivity measurements up to 48 GPa.At ambient pressure,Ce_(3)TiBi_(5) underg...The magnetic properties and Kondo effect in Ce3TiBi5 with a quasi-one-dimensional structure were investigated using in situ high-pressure resistivity measurements up to 48 GPa.At ambient pressure,Ce_(3)TiBi_(5) undergoes an antiferromagnetic(AFM)transition at T_(N)∼5 K.Under high pressures within 8.9 GPa,we find that Kondo scattering contributes differently to the high-temperature resistance,R(T),depending on the applied current direction,demonstrating a significantly anisotropic Kondo effect.The complete P–T phase diagram has been constructed,in which the pressure dependence of T_(N) exhibits a dome-like shape.The AFM order remains robust under pressure,even when the coherence temperature T^(*) far exceeds 300 K.We attribute the observed anisotropic Kondo effect and the robust AFM to the underlying anisotropy in electronic hybridization under high pressure.展开更多
Vanadium-based transition metal chalcogenides VmXn(X=S,Se,Te)with their distinctive quantum effects,tunable magnetism,spin-orbit coupling,and high carrier mobility are a valuable platform to explore the interplay betw...Vanadium-based transition metal chalcogenides VmXn(X=S,Se,Te)with their distinctive quantum effects,tunable magnetism,spin-orbit coupling,and high carrier mobility are a valuable platform to explore the interplay between magnetism and electronic correlations,especially with tunable structural phases and magnetic properties through stoichiometric variations,making them ideal candidates for advanced device applications.Here,we report the synthesis of high-quality V_(5+x)S_(8)single crystals with different concentrations of self-intercalated vanadium.V_(5+x)S_(8)crystals show an antiferromagnetic behavior and a spin-flop-like transition below TN of 30.6 K.The high-quality V_(5+x)S_(8)single crystals exhibit a large negative magnetoresistance of 12.3%at 2 K.Interestingly,V_(5+x)S_(8)crystals show an obvious low-temperature resistance upturn that gradually levels off with the increasing magnetic field,attributed to the Kondo effect arising from the interaction between conduction electrons and embedded vanadium magnetic impurities.With increasing V doping,the antiferromagnetic interactions intensify,weakening the coupling between the local moments and conduction electrons,which in turn lowers the Kondo temperature(TK).Furthermore,the anomalous Hall effect is observed in V5.73S8,with an anomalous Hall conductivity(AHC)of 50.46 W^(-1)·cm^(-1)and anomalous Hall angle of 0.73%at 2 K.Our findings offer valuable insights into the mechanisms of the Kondo effect and anomalous Hall effect in self-intercalated transition metal chalcogenides with complex magnetism and electronic correlation effects.展开更多
The exploration and synthesis of new materials are important for materials science and condensed matter physics.Here, we report the crystal structure, magnetic properties, and electrical transport properties of the si...The exploration and synthesis of new materials are important for materials science and condensed matter physics.Here, we report the crystal structure, magnetic properties, and electrical transport properties of the single crystals of Nd_(5)ScSb_(12), which is a quasi-one-dimensional new compound. Nd_(5)ScSb_(12) exhibits antiferromagnetic transition in both directions perpendicular and parallel to the long axis. Moreover, the magnetic field-dependent magnetization reveals two metamagnetic transitions. The electrical transport properties have been measured on the same sample but with different measurement lengths between the electrodes of the voltage. The resistivity exhibits the metallic behavior. At low temperatures, the Kondo effect and negative transverse magnetoresistance(MR)(B⊥I) have been observed. Interestingly, the measurement length has a significant impact on the Kondo effect and negative MR, providing an intuitive new approach to regulate the Kondo effect. As the measurement length increases, the Kondo effect and negative MR become more pronounced. This not only indicates that the interaction between magnetic impurities and conduction electrons dominates the electrical transport of Nd_(5)ScSb_(12) at low temperatures, but also confirms that the negative MR originates from the suppression of the Kondo effect.展开更多
We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper. We obtain the conductance for the system of a quantum dot...We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper. We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases. The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case. It increases as the external magnetic field increases, We obtain the relation between the coupling coefficient and conductance. If the interaction is big enough to prevent conduction electrons from tunnelling through the dot, the dispersion effect is dominant in this case. In the Kondo temperature regime, we obtain the conductivity of a quantum dot system with Kondo correlation.展开更多
The nonequilibrium Kondo effect is studied in a molecule quantum dot coupled asymmetrically to two ferromagnetic electrodes by employing the nonequilibrium Green function technique. The current-induced deformation of ...The nonequilibrium Kondo effect is studied in a molecule quantum dot coupled asymmetrically to two ferromagnetic electrodes by employing the nonequilibrium Green function technique. The current-induced deformation of the molecule is taken into account, modeled as interactions with a phonon system, and phonon-assisted Kondo satellites arise on both sides of the usual main Kondo peak. In the antiparallel electrode configuration, the Kondo satellites can be split only for the asymmetric dot-lead couplings, distinguished from the parallel configuration where splitting also exists, even though it is for symmetric case. We also analyze how to compensate the splitting and restore the suppressed zero-bias Kondo resonance. It is shown that one can change the TMR ratio significantly from a negative dip to a positive peak only by slightly modulating a local external magnetic field, whose value is greatly dependent on the electron-phonon coupling strength.展开更多
We investigate the effect of the mechanical motion of a quantum dot on the transport properties of a quantum dot shuttle, Employing the equation of motion method for the nonequilibrium Green＇s function, we show that ...We investigate the effect of the mechanical motion of a quantum dot on the transport properties of a quantum dot shuttle, Employing the equation of motion method for the nonequilibrium Green＇s function, we show that the oscillation of the dot, i.e., the time-dependent coupling between the dot＇s electron and the reservoirs, can destroy the Kondo effect. With the increase in the oscillation frequency of the dot, the density of states of the quantum dot shuttle changes from the Kondo-like to a Coulomb-blockade pattern. Increasing the coupling between the dot and the electrodes may partly recover the Kondo peak in the spectrum of the density of states. Understanding of the effect of mechanical motion on the transport properties of an electron shuttle is important for the future application of nanoelectromechanical devices.展开更多
Using an equation-of-motion technique, we theoretically study the Fano-Kondo effect in the T-shaped double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. We calculate the density of state...Using an equation-of-motion technique, we theoretically study the Fano-Kondo effect in the T-shaped double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. We calculate the density of states in this system with both parallel and antiparaIlel lead-polarization alignments, and our results reveal that the interdot coupling, the spin-polarized strength and the energy level of the side coupled quantum dot greatly influence the density of states of the central quantum dot. This system is a possible candidate for spin valve transistors and may have potential applications in the spintronics.展开更多
The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn＋2 ion（S=5/2） are investigated by the non-equilibrium Green function method.We consider a minimal m...The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn＋2 ion（S=5/2） are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with（2S＋1） sublevels.In the sequential tunneling regime,the differential conductance exhibits（2S＋1） possible peaks,corresponding to resonance tunneling via（2S＋1） sublevels.At low temperature,Kondo physics dominates transport and（2S＋1） Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.展开更多
We theoretically investigate a device consisting of two quantum dots （QDs） side-coupled to a quantum wire which has many physical ingredients of an artificial heavy fermion system. An extra parameter, the distance L...We theoretically investigate a device consisting of two quantum dots （QDs） side-coupled to a quantum wire which has many physical ingredients of an artificial heavy fermion system. An extra parameter, the distance L between the two QDs, is introduced and it plays an important role on the competition of the Kondo temperature and magnetic coupling. Three different phases are found： antiferromagnetic phase, Kondo phase with spin S = 1/2, and Kondo phase with S = 1, depending on the distance L, the magnetic properties are qualitatively different for different phases： conductance tends to the unitary value 2e2 /h; for the S ： the distance. coupling, and the Kondo temperature. Quantum transport for the S = 1 Kondo and the antiferromagnetic phases, the 1/2 Kondo phase the conductance is strongly dependent onthe distance.展开更多
We presented results of electrical resistivity, magnetoresistivity and Seebek effect measurements done in the paramagnetic state of an antiferromagnetically ordering intermetalfic compound Trains. It was found that th...We presented results of electrical resistivity, magnetoresistivity and Seebek effect measurements done in the paramagnetic state of an antiferromagnetically ordering intermetalfic compound Trains. It was found that the magnetic part of the electrical resistivity showed maximum at 18 K and the lgT dependence in temperature range 20〈T〈100 K. The magnetoresistivity was negative. The txansversal magnetoresistivity fulfilled the single-ion Kondo scaling for temperatures 2〈（T＋0.5 K）〈28 K. Thermcelectricpower displayed a sharp minimum at 10 K. Electrical properties indicated that Tmln3 is likely a dense Kondo system.展开更多
We study the thermoelectric transport of a series-coupled double quantum dots(SDQDs)system,based on the hierarchical equations of motion approach.The thermocurrent as a function of the energy level of QDs gives rise t...We study the thermoelectric transport of a series-coupled double quantum dots(SDQDs)system,based on the hierarchical equations of motion approach.The thermocurrent as a function of the energy level of QDs gives rise to a sign-changing phenomenon.The temperature difference between the two leads can enhance the thermocurrent.Moreover,the sign changing also generates in thermocurrent as a function of temperature due to the transition from the many-body Kondo resonant tunneling process to the single electron process of the SDQDs system.The inter-dot coupling strength between two QDs not only affects the value of the thermocurrent but also influences the characteristic temperature at which the sign changing of thermocurrent emerges.In a weak coupling regime,the thermocurrent firstly is enhanced by inter-dot coupling strength due to the‘t-enhanced Kondo effect'and then decreases with inter-dot coupling strength due to the effective antiferromagnetic interaction between the two QDs.In the middle coupling regime,the forming coherence bonding and antibonding orbitals channels and the residual Kondo effect co-dominate the transport process.The thermocurrent firstly decreases,then increases,and finally decreases with temperature.However,the thermocurrent shows a transition from increasing to decreasing behavior with temperature in the strong coupling regime.Although the inter-dot coupling strength t has a complex impact on the SDQDs system,the characteristic temperature k_BT_c,at which a sign changing appears,indicates a quantitative relationship with the value of the inter-dot coupling strength t by an identical amount of the Kondo correlation being partially destroyed.展开更多
Magnetic frustrations can enhance quantum fluctuations in spin systems and lead to exotic topological insulating states.When coupled to mobile electrons,they may give rise to unusual non-Fermi liquid or metallic spin ...Magnetic frustrations can enhance quantum fluctuations in spin systems and lead to exotic topological insulating states.When coupled to mobile electrons,they may give rise to unusual non-Fermi liquid or metallic spin liquid states whose nature has not been well explored.Here,we propose a spin current Kondo mechanism underlying a series of non-Fermi liquid phases on the border of Kondo and magnetic phases in a frustrated three-impurity Kondo model.This mechanism is confirmed by renormalization group analysis and describes movable Kondo singlets called"holons"induced by an effective coupling between the spin current of conduction electrons and the vector chirality of localized spins.Similar mechanisms may widely exist in all frustrated Kondo systems and be detected through spin current noise measurements.展开更多
Herein, we show that a self-assembled phase of potassium(K)-doped single-layer para-sexiphenyl(PSP) film on a gold substrate is an excellent platform for studying the two-impurity Kondo model. On K-doped PSP molecules...Herein, we show that a self-assembled phase of potassium(K)-doped single-layer para-sexiphenyl(PSP) film on a gold substrate is an excellent platform for studying the two-impurity Kondo model. On K-doped PSP molecules well separated from others, we observe a Kondo resonance peak close to EFwith a Kondo temperature of 30 K. The Kondo resonance peak splits when another K-doped PSP molecule is present in the vicinity, and the splitting gradually increases with the decrease in intermolecular distance without signs of phase transition. Our data demonstrate how a Kondo singlet state gradually evolves into an antiferromagnetic singlet state due to the competition between Kondo screening and antiferromagnetic Ruderman-Kittel-Kasuya-Yosida coupling,as described in the two-impurity Kondo model. Intriguingly, the antiferromagnetic singlet is quickly destroyed on increasing temperature and transforms back to a Kondo singlet below the Kondo temperature. Our data provide a comprehensive picture and quantitative constraints on related theories and calculations of the two-impurity Kondo model.展开更多
Using angle-resolved photoemission spectroscopy(ARPES) and low-energy electron diffraction(LEED), together with densityfunctional theory(DFT) calculation, we report the formation of charge density wave(CDW) and its in...Using angle-resolved photoemission spectroscopy(ARPES) and low-energy electron diffraction(LEED), together with densityfunctional theory(DFT) calculation, we report the formation of charge density wave(CDW) and its interplay with the Kondo effect and topological states in CeSbTe. The observed Fermi surface(FS) exhibits parallel segments that can be well connected by the observed CDWordering vector, indicating that the CDWorder is driven by the electron-phonon coupling(EPC) as a result of the nested FS. The CDW gap is large(~0.3 eV) and momentum-dependent, which naturally explains the robust CDWorder up to high temperatures. The gap opening leads to a reduced density of states(DOS) near the Fermi level(EF), which correspondingly suppresses the many-body Kondo effect, leading to very localized 4 f electrons at 20 K and above. The topological Dirac cone at the X point is found to remain gapless inside the CDW phase. Our results provide evidence for the competition between CDWand the Kondo effect in a Kondo lattice system. The robust CDWorder in CeSbTe and related compounds provide an opportunity to search for the long-sought-after axionic insulator.展开更多
In a large number of rare-earth and actinide systems,Kondo effect tends to suppress magnetic orders by making the spin singlet between localized and conduction electron spins.In the presence of orbital degrees of free...In a large number of rare-earth and actinide systems,Kondo effect tends to suppress magnetic orders by making the spin singlet between localized and conduction electron spins.In the presence of orbital degrees of freedom,however,there emerge exotic electronic orders induced by Kondo effect.The orbital Kondo effect can collectively make diagonal and off-diagonal(superconducting) orders.With the particle-hole symmetry in conduction bands,these orders are all degenerate,forming a macroscopic SO(5) multiplet.This paper discusses recent theoretical development on these electronic orders which are relevant to Pr^(3+) and U^(4+) systems with even number of f electrons per site.In the superconducting order,each conduction–electron pair is coupled with local degrees of freedom,forming a composite entity with a staggered spatial pattern.The quasi-particle spectrum is best interpreted as virtual hybridization with resonant states at the Fermi level.Possible order parameter for URu_2Si_2 in the hidden order state is discussed in the context of composite orders.Briefly discussed are related issues such as homogeneous odd-frequency pairing and SO(5) theory for hightemperature superconductors.展开更多
We theoretically investigate the Kondo effect of a quantum dot embedded in a mesoscopic Aharonov-Bohm （AIR） ring in the presence of the spin flip processes by means of the one-impurity Anderson Hamiltonian. Based on...We theoretically investigate the Kondo effect of a quantum dot embedded in a mesoscopic Aharonov-Bohm （AIR） ring in the presence of the spin flip processes by means of the one-impurity Anderson Hamiltonian. Based on the slave-boson mean-field theory, we find that in this system the persistent current （PC） sensitively depends on the parity and size of the AB ring and can be tuned by the spin-flip scattering （R）. In the small AB ring, the PC is suppressed due to the enhancing R weakening the Kondo resonance. On the contrary, in the large AB ring, with R increasing, the peak of PC firstly moves up to max-peak and then down. Especially, the PC phase shift of π appears suddenly with the proper value of R, implying the existence of the anomalous Kondo effect in this system. Thus this system may be a carldidate for quantum switch.展开更多
Quantum critical phenomena in the quasi-one-dimensional limit remain an open issue.We report the uniaxial stress effect on the quasi-one-dimensional Kondo lattice CeCo_(2)Ga_(8) by electric transport and AC heat capac...Quantum critical phenomena in the quasi-one-dimensional limit remain an open issue.We report the uniaxial stress effect on the quasi-one-dimensional Kondo lattice CeCo_(2)Ga_(8) by electric transport and AC heat capacity measurements.CeCo_(2)Ga_(8) is speculated to sit in close vicinity but on the quantum-disordered side of a quantum critical point.Upon compressing the c axis,parallel to the Ce-Ce chain,the onset of coherent Kondo effect is enhanced.In contrast,the electronic specific heat diverges more rapidly at low temperature when the intra-chain distance is elongated by compressions along a or b axis.These results suggest that a tensile intra-chain strain(ε_(c)>0)pushes CeCo_(2)Ga_(8) closer to the quantum critical point,while a compressive intra-chain strain(ε_(c)<0)likely causes departure.Our work provides a rare paradigm of manipulation near a quantum critical point in a quasi-1D Kondo lattice by uniaxial stress,and paves the way for further investigations on the unique feature of quantum criticality in the quasi-1D limit.展开更多
In the present paper, we study the effect of van Hove singularities of conduction electron on the transport of a single quantum dot system in the Kondo regime. By using both the equation-of-motion and the noncrossing ...In the present paper, we study the effect of van Hove singularities of conduction electron on the transport of a single quantum dot system in the Kondo regime. By using both the equation-of-motion and the noncrossing approximation techniques, we show that the corrections caused by these singularities are actually minor. It can be explained by observing that the singularities in the equations, which determine the electronic DOS on the dot, are integrable. Furthermore, we find that, although each line width function is divergent at van Hove singular points, the total divergence is canceled out in the final formula to calculate the current through the system. Therefore, as far as the qualitative properties of the system is concerned, these singularities can be ignored and the wide-band approximation can be safely used in calculation.展开更多
Motivated by recent theoretical and experimental advances in quantum simulations using alkaline earth(AE)atoms,we put forward a proposal to detect the Kondo physics in a cold atomic system.It has been demonstrated tha...Motivated by recent theoretical and experimental advances in quantum simulations using alkaline earth(AE)atoms,we put forward a proposal to detect the Kondo physics in a cold atomic system.It has been demonstrated that the intrinsic spin-exchange interaction in AE atoms can be significantly enhanced near a confinement-induced resonance(CIR),which facilitates the simulation of Kondo physics.Since the Kondo effect appears only for antiferromagnetic coupling,we find that the conductivity of such system exhibits an asymmetry across a resonance of spin-exchange interaction.The asymmetric conductivity can serve as the smoking gun evidence for Kondo physics in the cold atom context.When an extra magnetic field ramps up,the spin-exchange process near Fermi surface is suppressed by Zee-man energy and the conductivity becomes more and more symmetric.Our results can be verified in the current experimental setup.展开更多
Dirac node-line(DNL) materials constitute a distinct category of topological semimetals, defined by the linear crossing of valence and conduction bands along one-dimensional lines within the Brillouin zone(BZ), resemb...Dirac node-line(DNL) materials constitute a distinct category of topological semimetals, defined by the linear crossing of valence and conduction bands along one-dimensional lines within the Brillouin zone(BZ), resembling the behavior of Dirac fermions. However, spin–orbit coupling(SOC) and electronic interactions can typically alter these intersections and break the DNLs. In mostly reported cases, DNLs are classified as non-interacting types, which highlights the significant research value in searching for robust interacting DNLs in practical materials. Here, by employing first-principles calculations that combine density functional theory(DFT) with dynamical mean-field theory(DMFT), and leveraging symmetry-based indicator theory, we identify CeAgSb_(2) as a Dirac semimetal. Our investigation reveals that robust Dirac nodal lines(DNLs)in this Kondo system are driven by Kondo interactions and nonsymmorphic lattice symmetries. Furthermore, our results demonstrate that the properties of these DNLs are substantially modulated by Kondo behavior across varying temperature regimes. The interacting DNLs in CeAgSb_(2) represents a rare example of Dirac semimetal under electronic correlations, and the peculiar variation of Dirac fermions with temperature provides theoretical reference for future experimental explorations of novel electronic-correlation effects in topological materials.展开更多
基金supported by the National Key Research and Development Program of Chinathe National Natural Science Foundation of China (Grant Nos.2024YFA1408000,12474097,and2023YFA1406001)+2 种基金the Guangdong Provincial Quantum Science Strategic Initiative (Grant No.GDZX2201001)the Center for Computational Science and Engineering at Southern University of Science and Technology,the Major Science and Technology Infrastructure Project of Material Genome Big-science Facilities Platform supported by Municipal Development and Reform Commission of Shenzhen(for J.L.Z.and Y.L.)the Chinese funding sources applied via HPSTAR。
文摘The magnetic properties and Kondo effect in Ce3TiBi5 with a quasi-one-dimensional structure were investigated using in situ high-pressure resistivity measurements up to 48 GPa.At ambient pressure,Ce_(3)TiBi_(5) undergoes an antiferromagnetic(AFM)transition at T_(N)∼5 K.Under high pressures within 8.9 GPa,we find that Kondo scattering contributes differently to the high-temperature resistance,R(T),depending on the applied current direction,demonstrating a significantly anisotropic Kondo effect.The complete P–T phase diagram has been constructed,in which the pressure dependence of T_(N) exhibits a dome-like shape.The AFM order remains robust under pressure,even when the coherence temperature T^(*) far exceeds 300 K.We attribute the observed anisotropic Kondo effect and the robust AFM to the underlying anisotropy in electronic hybridization under high pressure.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1204100)the National Natural Science Foundation of China(Grant Nos.62488201 and 1240041502)+2 种基金the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-003)the Chinese Academy of Sciences(Grant No.XDB33030100)the Innovation Program of Quantum Science and Technology(Grant No.2021ZD0302700).
文摘Vanadium-based transition metal chalcogenides VmXn(X=S,Se,Te)with their distinctive quantum effects,tunable magnetism,spin-orbit coupling,and high carrier mobility are a valuable platform to explore the interplay between magnetism and electronic correlations,especially with tunable structural phases and magnetic properties through stoichiometric variations,making them ideal candidates for advanced device applications.Here,we report the synthesis of high-quality V_(5+x)S_(8)single crystals with different concentrations of self-intercalated vanadium.V_(5+x)S_(8)crystals show an antiferromagnetic behavior and a spin-flop-like transition below TN of 30.6 K.The high-quality V_(5+x)S_(8)single crystals exhibit a large negative magnetoresistance of 12.3%at 2 K.Interestingly,V_(5+x)S_(8)crystals show an obvious low-temperature resistance upturn that gradually levels off with the increasing magnetic field,attributed to the Kondo effect arising from the interaction between conduction electrons and embedded vanadium magnetic impurities.With increasing V doping,the antiferromagnetic interactions intensify,weakening the coupling between the local moments and conduction electrons,which in turn lowers the Kondo temperature(TK).Furthermore,the anomalous Hall effect is observed in V5.73S8,with an anomalous Hall conductivity(AHC)of 50.46 W^(-1)·cm^(-1)and anomalous Hall angle of 0.73%at 2 K.Our findings offer valuable insights into the mechanisms of the Kondo effect and anomalous Hall effect in self-intercalated transition metal chalcogenides with complex magnetism and electronic correlation effects.
基金Project supported by the National Key Research and Development Program of China (Grant No. 2023YFA1406500)the National Natural Science Foundation of China (Grant Nos. 12474098, 12274388, 12174361, 12404043, and 12204004)the Natural Science Foundation of Anhui Province, China (Grant No. 2408085QA024)。
文摘The exploration and synthesis of new materials are important for materials science and condensed matter physics.Here, we report the crystal structure, magnetic properties, and electrical transport properties of the single crystals of Nd_(5)ScSb_(12), which is a quasi-one-dimensional new compound. Nd_(5)ScSb_(12) exhibits antiferromagnetic transition in both directions perpendicular and parallel to the long axis. Moreover, the magnetic field-dependent magnetization reveals two metamagnetic transitions. The electrical transport properties have been measured on the same sample but with different measurement lengths between the electrodes of the voltage. The resistivity exhibits the metallic behavior. At low temperatures, the Kondo effect and negative transverse magnetoresistance(MR)(B⊥I) have been observed. Interestingly, the measurement length has a significant impact on the Kondo effect and negative MR, providing an intuitive new approach to regulate the Kondo effect. As the measurement length increases, the Kondo effect and negative MR become more pronounced. This not only indicates that the interaction between magnetic impurities and conduction electrons dominates the electrical transport of Nd_(5)ScSb_(12) at low temperatures, but also confirms that the negative MR originates from the suppression of the Kondo effect.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10074029 and 60276005）, and by the State Key Development Program for Basic Research of China （Grant No G1999064509）.
文摘We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper. We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases. The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case. It increases as the external magnetic field increases, We obtain the relation between the coupling coefficient and conductance. If the interaction is big enough to prevent conduction electrons from tunnelling through the dot, the dispersion effect is dominant in this case. In the Kondo temperature regime, we obtain the conductivity of a quantum dot system with Kondo correlation.
基金Project supported by the National Natural Science Foundation of China (Grant No 10974058)the Shanghai Natural Science Foundation of China (Grant No 09ZR1421400)+1 种基金Science and Technology Program of Shanghai Maritime University (Grant No2008475)Postdoctoral Science Foundation of Jiangsu Province of China (Grant No 0802008C)
文摘The nonequilibrium Kondo effect is studied in a molecule quantum dot coupled asymmetrically to two ferromagnetic electrodes by employing the nonequilibrium Green function technique. The current-induced deformation of the molecule is taken into account, modeled as interactions with a phonon system, and phonon-assisted Kondo satellites arise on both sides of the usual main Kondo peak. In the antiparallel electrode configuration, the Kondo satellites can be split only for the asymmetric dot-lead couplings, distinguished from the parallel configuration where splitting also exists, even though it is for symmetric case. We also analyze how to compensate the splitting and restore the suppressed zero-bias Kondo resonance. It is shown that one can change the TMR ratio significantly from a negative dip to a positive peak only by slightly modulating a local external magnetic field, whose value is greatly dependent on the electron-phonon coupling strength.
基金Project supported by the National Natural Science Foundation of China(Grant No.11204016)
文摘We investigate the effect of the mechanical motion of a quantum dot on the transport properties of a quantum dot shuttle, Employing the equation of motion method for the nonequilibrium Green＇s function, we show that the oscillation of the dot, i.e., the time-dependent coupling between the dot＇s electron and the reservoirs, can destroy the Kondo effect. With the increase in the oscillation frequency of the dot, the density of states of the quantum dot shuttle changes from the Kondo-like to a Coulomb-blockade pattern. Increasing the coupling between the dot and the electrodes may partly recover the Kondo peak in the spectrum of the density of states. Understanding of the effect of mechanical motion on the transport properties of an electron shuttle is important for the future application of nanoelectromechanical devices.
基金supported by the Scientific Research Funds of Education Department of Sichuan Province (Grant No 2006A069)the Major Basic Research Project of Sichuan Province (Grant No 2006J13-155)the Scientific Research Innovation for Postgraduates of Sichuan Normal University
文摘Using an equation-of-motion technique, we theoretically study the Fano-Kondo effect in the T-shaped double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. We calculate the density of states in this system with both parallel and antiparaIlel lead-polarization alignments, and our results reveal that the interdot coupling, the spin-polarized strength and the energy level of the side coupled quantum dot greatly influence the density of states of the central quantum dot. This system is a possible candidate for spin valve transistors and may have potential applications in the spintronics.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10974124 and 11004124)the Natural Science Foundation of Shanxi Province of China (Grant No. 2009011001-1)
文摘The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn＋2 ion（S=5/2） are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with（2S＋1） sublevels.In the sequential tunneling regime,the differential conductance exhibits（2S＋1） possible peaks,corresponding to resonance tunneling via（2S＋1） sublevels.At low temperature,Kondo physics dominates transport and（2S＋1） Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.
基金supported by National Science Foundation of China under Grant Nos.10974236 and 11074174
文摘We theoretically investigate a device consisting of two quantum dots （QDs） side-coupled to a quantum wire which has many physical ingredients of an artificial heavy fermion system. An extra parameter, the distance L between the two QDs, is introduced and it plays an important role on the competition of the Kondo temperature and magnetic coupling. Three different phases are found： antiferromagnetic phase, Kondo phase with spin S = 1/2, and Kondo phase with S = 1, depending on the distance L, the magnetic properties are qualitatively different for different phases： conductance tends to the unitary value 2e2 /h; for the S ： the distance. coupling, and the Kondo temperature. Quantum transport for the S = 1 Kondo and the antiferromagnetic phases, the 1/2 Kondo phase the conductance is strongly dependent onthe distance.
文摘We presented results of electrical resistivity, magnetoresistivity and Seebek effect measurements done in the paramagnetic state of an antiferromagnetically ordering intermetalfic compound Trains. It was found that the magnetic part of the electrical resistivity showed maximum at 18 K and the lgT dependence in temperature range 20〈T〈100 K. The magnetoresistivity was negative. The txansversal magnetoresistivity fulfilled the single-ion Kondo scaling for temperatures 2〈（T＋0.5 K）〈28 K. Thermcelectricpower displayed a sharp minimum at 10 K. Electrical properties indicated that Tmln3 is likely a dense Kondo system.
基金the support of NSFC(Grants No.11804245,No.11747098,No.12247101,&No.12047501)the Fund from the Ministry of Science and Technology of China(Grant No.2022YFA1402704)。
文摘We study the thermoelectric transport of a series-coupled double quantum dots(SDQDs)system,based on the hierarchical equations of motion approach.The thermocurrent as a function of the energy level of QDs gives rise to a sign-changing phenomenon.The temperature difference between the two leads can enhance the thermocurrent.Moreover,the sign changing also generates in thermocurrent as a function of temperature due to the transition from the many-body Kondo resonant tunneling process to the single electron process of the SDQDs system.The inter-dot coupling strength between two QDs not only affects the value of the thermocurrent but also influences the characteristic temperature at which the sign changing of thermocurrent emerges.In a weak coupling regime,the thermocurrent firstly is enhanced by inter-dot coupling strength due to the‘t-enhanced Kondo effect'and then decreases with inter-dot coupling strength due to the effective antiferromagnetic interaction between the two QDs.In the middle coupling regime,the forming coherence bonding and antibonding orbitals channels and the residual Kondo effect co-dominate the transport process.The thermocurrent firstly decreases,then increases,and finally decreases with temperature.However,the thermocurrent shows a transition from increasing to decreasing behavior with temperature in the strong coupling regime.Although the inter-dot coupling strength t has a complex impact on the SDQDs system,the characteristic temperature k_BT_c,at which a sign changing appears,indicates a quantitative relationship with the value of the inter-dot coupling strength t by an identical amount of the Kondo correlation being partially destroyed.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFA0303103)the National Natural Science Foundation of China(Grant Nos.12174429,11774401,11974397)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB33010100)the Youth Innovation Promotion Association of Chinese Academy of Sciences。
文摘Magnetic frustrations can enhance quantum fluctuations in spin systems and lead to exotic topological insulating states.When coupled to mobile electrons,they may give rise to unusual non-Fermi liquid or metallic spin liquid states whose nature has not been well explored.Here,we propose a spin current Kondo mechanism underlying a series of non-Fermi liquid phases on the border of Kondo and magnetic phases in a frustrated three-impurity Kondo model.This mechanism is confirmed by renormalization group analysis and describes movable Kondo singlets called"holons"induced by an effective coupling between the spin current of conduction electrons and the vector chirality of localized spins.Similar mechanisms may widely exist in all frustrated Kondo systems and be detected through spin current noise measurements.
基金supported by the National Key R&D Program of China(Grant Nos.2017YFA0303004,and 2017YFA0303104)the National Natural Science Foundation of China(Grant No.11774060)+2 种基金the Science Challenge Project(Grant No.TZ2016004)the Shanghai Education Development Foundation and Shanghai Municipal Education Commission(Chenguang Program)the Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01)。
文摘Herein, we show that a self-assembled phase of potassium(K)-doped single-layer para-sexiphenyl(PSP) film on a gold substrate is an excellent platform for studying the two-impurity Kondo model. On K-doped PSP molecules well separated from others, we observe a Kondo resonance peak close to EFwith a Kondo temperature of 30 K. The Kondo resonance peak splits when another K-doped PSP molecule is present in the vicinity, and the splitting gradually increases with the decrease in intermolecular distance without signs of phase transition. Our data demonstrate how a Kondo singlet state gradually evolves into an antiferromagnetic singlet state due to the competition between Kondo screening and antiferromagnetic Ruderman-Kittel-Kasuya-Yosida coupling,as described in the two-impurity Kondo model. Intriguingly, the antiferromagnetic singlet is quickly destroyed on increasing temperature and transforms back to a Kondo singlet below the Kondo temperature. Our data provide a comprehensive picture and quantitative constraints on related theories and calculations of the two-impurity Kondo model.
基金supported by the National Key R&D Program of the Ministry of Science and Technology of China (Grant Nos. 2016YFA0300203, and 2017YFA0303100)the National Science Foundation of China (Grant Nos. 11674280, and 11774305)+1 种基金the Science Challenge Program of ChinaPart of this research used Beam line 03U of the Shanghai Synchrotron Radiation Facility, which was supported by ME2 Project (Grant No. 11227902) from the National Natural Science Foundation of China。
文摘Using angle-resolved photoemission spectroscopy(ARPES) and low-energy electron diffraction(LEED), together with densityfunctional theory(DFT) calculation, we report the formation of charge density wave(CDW) and its interplay with the Kondo effect and topological states in CeSbTe. The observed Fermi surface(FS) exhibits parallel segments that can be well connected by the observed CDWordering vector, indicating that the CDWorder is driven by the electron-phonon coupling(EPC) as a result of the nested FS. The CDW gap is large(~0.3 eV) and momentum-dependent, which naturally explains the robust CDWorder up to high temperatures. The gap opening leads to a reduced density of states(DOS) near the Fermi level(EF), which correspondingly suppresses the many-body Kondo effect, leading to very localized 4 f electrons at 20 K and above. The topological Dirac cone at the X point is found to remain gapless inside the CDW phase. Our results provide evidence for the competition between CDWand the Kondo effect in a Kondo lattice system. The robust CDWorder in CeSbTe and related compounds provide an opportunity to search for the long-sought-after axionic insulator.
基金supported by KAKENHI of Japan Society for the Promotion of Science (JP24340072 and JP16K05464)
文摘In a large number of rare-earth and actinide systems,Kondo effect tends to suppress magnetic orders by making the spin singlet between localized and conduction electron spins.In the presence of orbital degrees of freedom,however,there emerge exotic electronic orders induced by Kondo effect.The orbital Kondo effect can collectively make diagonal and off-diagonal(superconducting) orders.With the particle-hole symmetry in conduction bands,these orders are all degenerate,forming a macroscopic SO(5) multiplet.This paper discusses recent theoretical development on these electronic orders which are relevant to Pr^(3+) and U^(4+) systems with even number of f electrons per site.In the superconducting order,each conduction–electron pair is coupled with local degrees of freedom,forming a composite entity with a staggered spatial pattern.The quasi-particle spectrum is best interpreted as virtual hybridization with resonant states at the Fermi level.Possible order parameter for URu_2Si_2 in the hidden order state is discussed in the context of composite orders.Briefly discussed are related issues such as homogeneous odd-frequency pairing and SO(5) theory for hightemperature superconductors.
基金Supported by Scientific Research Fund of Hunan Provincial Education Department under Grant No.09B079
文摘We theoretically investigate the Kondo effect of a quantum dot embedded in a mesoscopic Aharonov-Bohm （AIR） ring in the presence of the spin flip processes by means of the one-impurity Anderson Hamiltonian. Based on the slave-boson mean-field theory, we find that in this system the persistent current （PC） sensitively depends on the parity and size of the AB ring and can be tuned by the spin-flip scattering （R）. In the small AB ring, the PC is suppressed due to the enhancing R weakening the Kondo resonance. On the contrary, in the large AB ring, with R increasing, the peak of PC firstly moves up to max-peak and then down. Especially, the PC phase shift of π appears suddenly with the proper value of R, implying the existence of the anomalous Kondo effect in this system. Thus this system may be a carldidate for quantum switch.
文摘Quantum critical phenomena in the quasi-one-dimensional limit remain an open issue.We report the uniaxial stress effect on the quasi-one-dimensional Kondo lattice CeCo_(2)Ga_(8) by electric transport and AC heat capacity measurements.CeCo_(2)Ga_(8) is speculated to sit in close vicinity but on the quantum-disordered side of a quantum critical point.Upon compressing the c axis,parallel to the Ce-Ce chain,the onset of coherent Kondo effect is enhanced.In contrast,the electronic specific heat diverges more rapidly at low temperature when the intra-chain distance is elongated by compressions along a or b axis.These results suggest that a tensile intra-chain strain(ε_(c)>0)pushes CeCo_(2)Ga_(8) closer to the quantum critical point,while a compressive intra-chain strain(ε_(c)<0)likely causes departure.Our work provides a rare paradigm of manipulation near a quantum critical point in a quasi-1D Kondo lattice by uniaxial stress,and paves the way for further investigations on the unique feature of quantum criticality in the quasi-1D limit.
文摘In the present paper, we study the effect of van Hove singularities of conduction electron on the transport of a single quantum dot system in the Kondo regime. By using both the equation-of-motion and the noncrossing approximation techniques, we show that the corrections caused by these singularities are actually minor. It can be explained by observing that the singularities in the equations, which determine the electronic DOS on the dot, are integrable. Furthermore, we find that, although each line width function is divergent at van Hove singular points, the total divergence is canceled out in the final formula to calculate the current through the system. Therefore, as far as the qualitative properties of the system is concerned, these singularities can be ignored and the wide-band approximation can be safely used in calculation.
基金This work was supported by the National Key R&D Program of China under Grant No.2018YFA0307601the National Natural Science Foundation of China under Grant No.11804268.
文摘Motivated by recent theoretical and experimental advances in quantum simulations using alkaline earth(AE)atoms,we put forward a proposal to detect the Kondo physics in a cold atomic system.It has been demonstrated that the intrinsic spin-exchange interaction in AE atoms can be significantly enhanced near a confinement-induced resonance(CIR),which facilitates the simulation of Kondo physics.Since the Kondo effect appears only for antiferromagnetic coupling,we find that the conductivity of such system exhibits an asymmetry across a resonance of spin-exchange interaction.The asymmetric conductivity can serve as the smoking gun evidence for Kondo physics in the cold atom context.When an extra magnetic field ramps up,the spin-exchange process near Fermi surface is suppressed by Zee-man energy and the conductivity becomes more and more symmetric.Our results can be verified in the current experimental setup.
基金Project supported by the National Natural Science Foundation of China (Grant No. 12364023)the Natural Science Foundation of Guangxi Zhuang Autonomous Regin, China (Grant No. 2024GXNSFAA010273)。
文摘Dirac node-line(DNL) materials constitute a distinct category of topological semimetals, defined by the linear crossing of valence and conduction bands along one-dimensional lines within the Brillouin zone(BZ), resembling the behavior of Dirac fermions. However, spin–orbit coupling(SOC) and electronic interactions can typically alter these intersections and break the DNLs. In mostly reported cases, DNLs are classified as non-interacting types, which highlights the significant research value in searching for robust interacting DNLs in practical materials. Here, by employing first-principles calculations that combine density functional theory(DFT) with dynamical mean-field theory(DMFT), and leveraging symmetry-based indicator theory, we identify CeAgSb_(2) as a Dirac semimetal. Our investigation reveals that robust Dirac nodal lines(DNLs)in this Kondo system are driven by Kondo interactions and nonsymmorphic lattice symmetries. Furthermore, our results demonstrate that the properties of these DNLs are substantially modulated by Kondo behavior across varying temperature regimes. The interacting DNLs in CeAgSb_(2) represents a rare example of Dirac semimetal under electronic correlations, and the peculiar variation of Dirac fermions with temperature provides theoretical reference for future experimental explorations of novel electronic-correlation effects in topological materials.
