Quantum interference effect serves as a critical strategy for addressing incorrect energy level alignment between frontier molecular orbitals and electrodes in molecular junctions. Weak-coupling structures offer an ef...Quantum interference effect serves as a critical strategy for addressing incorrect energy level alignment between frontier molecular orbitals and electrodes in molecular junctions. Weak-coupling structures offer an effective approach to suppress phonon thermal conductance. The thermoelectric properties of pure C_(3)N_(4) nanoribbon devices and C_(3)N_(4)-C_(20) molecular junctions are systematically investigated based on density functional theory(DFT) combined with nonequilibrium Green's function(NEGF) formalism. The results show that pure C_(3)N_(4) nanoribbon devices have superior charge transport capabilities and excellent Seebeck coefficients. A remarkable thermoelectric figure of merit(ZT = 0.98)is achieved near 0.09 e V. The pronounced scattering effect induced by embedding a C_(20) molecule in the center of the C_(3)N_(4) nanoribbon significantly suppresses phonon transport. A maximum ZT value of 1.68 is observed at 0.987 e V. The electron mobility of C_(3)N_(4)-C_(20)-par is effectively increased due to quantum interference effect which greatly improves the alignment between the C_(20) molecule's frontier orbital energy level and C_(3)N_(4) electrodes. The C_(3)N_(4)-C_(20)-van der Waals(vd W) molecular junction allows very few phonons to pass through the C_(20) molecule from the left electrode to the right electrode. As a result, the C_(3)N_(4)-C_(20)-vd W junction achieves an excellent ZT value of 3.82 near the Femi level.展开更多
Inspired by a recent experiment[Phys.Rev.Lett.122253201(2019)]that an unprecedented quantum interference was observed in the way of stimulated Raman adiabatic passage(STIRAP)due to the coexisting resonant-and detuned-...Inspired by a recent experiment[Phys.Rev.Lett.122253201(2019)]that an unprecedented quantum interference was observed in the way of stimulated Raman adiabatic passage(STIRAP)due to the coexisting resonant-and detuned-STIRAPs,we comprehensively study this effect.Our results uncover the scheme robustness towards any external-field fluctuations coming from laser intensity noise and imperfect resonance condition,as well as the persistence of high-contrast interference pattern even when more nearby excited levels are involved.We verify that an auxiliary dynamical phase accumulated in hold time caused by the presence of the quasi-dark state in detuned-STIRAP can sensitively manipulate the visibility and frequency of the interference pattern,representing a new hallmark to measure the hyperfine energy accurately.The robust stability of the scheme comes from the intrinsic superiority embedded in the STIRAP mechanism that preserves the coherence of population transfer,which promises a remarkable performance of quantum interference in a practical implementation.展开更多
MoS_(2) monolayer, as a highly promising two-dimensional semiconducting material for electronic and optoelectronic applications, exhibits deep-ultraviolet(DUV) laser-induced anomalous lattice dynamics as revealed by R...MoS_(2) monolayer, as a highly promising two-dimensional semiconducting material for electronic and optoelectronic applications, exhibits deep-ultraviolet(DUV) laser-induced anomalous lattice dynamics as revealed by Raman spectroscopy. Remarkably, not only the Raman intensity of many second-order Raman peaks but also the intensity ratio between the first-order modes E′and A′_1 exhibits a non-monotonic behavior that depends on laser energy. Moreover, there are significant inconsistencies in the literature regarding the assignments of these second-order Raman modes. In this work, we perform a thorough exploration of the anomalous lattice dynamics and conduct a renewed assignment of the numerous double resonant Raman modes of MoS_(2) monolayer. At three laser energies(E_L= 2.33, 3.50, and 4.66 e V) spanning from the visible to the ultraviolet and further into the DUV region, the calculated double-resonance Raman spectra correlate reasonably well with the experimental ones in terms of both peak positions and relative intensities. We confirm that the P_1 peak at ~450 cm^(-1) represents the second-order longitudinal acoustic(2LA) overtone mode. Each of the P_i(i = 1, 2,..., 7) peaks has multiple contributions from two phonons with distinct q wavevectors. Our calculations further reveal that the DUV laser-induced anomalous lattice dynamics stems from the quantum interference effect among different Raman scattering channels.展开更多
We theoretically present the results for a scanning tunneling transport between a metallic tip and a Kondo lattice.We calculate the density of states(DOS)and the tunneling current and differential conductance(DC)under...We theoretically present the results for a scanning tunneling transport between a metallic tip and a Kondo lattice.We calculate the density of states(DOS)and the tunneling current and differential conductance(DC)under different conduction-fermion band hybridization and temperature in the Kondo lattice.It is found that the hybridization strength and temperature give asymmetric coherent peaks in the DOS separated by the Fermi energy.The corresponding current and DC intensity depend on the temperature and quantum interference effect among the c-electron and f-electron states in the Kondo lattice.展开更多
The ballistic thermoelectric properties in bended graphene nanoribbons（GNRs） are systematically investigated by using atomistic simulation of electron and phonon transport. We find that the electron resonant tunneli...The ballistic thermoelectric properties in bended graphene nanoribbons（GNRs） are systematically investigated by using atomistic simulation of electron and phonon transport. We find that the electron resonant tunneling effect occurs in the metallic–semiconducting linked ZZ-GNRs（the bended GNRs with zigzag edge leads）. The electron-wave quantum interference effect occurs in the metallic–metallic linked AA-GNRs（the bended GNRs with armchair edge leads）.These different physical mechanisms lead to the large Seebeck coefficient S and high electron conductance in bended ZZGNRs/AA-GNRs. Combined with the reduced lattice thermal conduction, the significant enhancement of the figure of merit ZT is predicted. Moreover, we find that the ZTmax（the maximum peak of ZT） is sensitive to the structural parameters. It can be conveniently tuned by changing the interbend length of bended GNRs. The magnitude of ZT ranges from the 0.15 to 0.72. Geometry-controlled ballistic thermoelectric effect offers an effective way to design thermoelectric devices such as thermocouples based on graphene.展开更多
The tunneling behavior of the Néel vector out of metastable easy directions or between degenerate easy directions is studied for a small single\|domain antiferromagnetic particle at low temperature. The quantum t...The tunneling behavior of the Néel vector out of metastable easy directions or between degenerate easy directions is studied for a small single\|domain antiferromagnetic particle at low temperature. The quantum tunneling rates for these processes are evaluated for two examples of macroscopic quantum tunneling and one example of macroscopic quantum coherence. The calculations are performed by using the two sublattice model and the instanton method in the spin coherent state path integral. Quantum interference or the spin parity effect is also discussed for each case.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 12164046)。
文摘Quantum interference effect serves as a critical strategy for addressing incorrect energy level alignment between frontier molecular orbitals and electrodes in molecular junctions. Weak-coupling structures offer an effective approach to suppress phonon thermal conductance. The thermoelectric properties of pure C_(3)N_(4) nanoribbon devices and C_(3)N_(4)-C_(20) molecular junctions are systematically investigated based on density functional theory(DFT) combined with nonequilibrium Green's function(NEGF) formalism. The results show that pure C_(3)N_(4) nanoribbon devices have superior charge transport capabilities and excellent Seebeck coefficients. A remarkable thermoelectric figure of merit(ZT = 0.98)is achieved near 0.09 e V. The pronounced scattering effect induced by embedding a C_(20) molecule in the center of the C_(3)N_(4) nanoribbon significantly suppresses phonon transport. A maximum ZT value of 1.68 is observed at 0.987 e V. The electron mobility of C_(3)N_(4)-C_(20)-par is effectively increased due to quantum interference effect which greatly improves the alignment between the C_(20) molecule's frontier orbital energy level and C_(3)N_(4) electrodes. The C_(3)N_(4)-C_(20)-van der Waals(vd W) molecular junction allows very few phonons to pass through the C_(20) molecule from the left electrode to the right electrode. As a result, the C_(3)N_(4)-C_(20)-vd W junction achieves an excellent ZT value of 3.82 near the Femi level.
基金the National Natural Science Foundation of China(Grant Nos.11474094 and 11104076)the Science and Technology Commission of Shanghai Municipality,China(Grant No.18ZR1412800).
文摘Inspired by a recent experiment[Phys.Rev.Lett.122253201(2019)]that an unprecedented quantum interference was observed in the way of stimulated Raman adiabatic passage(STIRAP)due to the coexisting resonant-and detuned-STIRAPs,we comprehensively study this effect.Our results uncover the scheme robustness towards any external-field fluctuations coming from laser intensity noise and imperfect resonance condition,as well as the persistence of high-contrast interference pattern even when more nearby excited levels are involved.We verify that an auxiliary dynamical phase accumulated in hold time caused by the presence of the quasi-dark state in detuned-STIRAP can sensitively manipulate the visibility and frequency of the interference pattern,representing a new hallmark to measure the hyperfine energy accurately.The robust stability of the scheme comes from the intrinsic superiority embedded in the STIRAP mechanism that preserves the coherence of population transfer,which promises a remarkable performance of quantum interference in a practical implementation.
基金Project supported by the Strategic Priority Research Program of CAS (Grant No. XDB0460000)the National Natural Science Foundation of China (Grant Nos. 12404213, 52031014, and 51702146)the National Key Research and Development Program of China (Grant No. 2022YFA1203900)。
文摘MoS_(2) monolayer, as a highly promising two-dimensional semiconducting material for electronic and optoelectronic applications, exhibits deep-ultraviolet(DUV) laser-induced anomalous lattice dynamics as revealed by Raman spectroscopy. Remarkably, not only the Raman intensity of many second-order Raman peaks but also the intensity ratio between the first-order modes E′and A′_1 exhibits a non-monotonic behavior that depends on laser energy. Moreover, there are significant inconsistencies in the literature regarding the assignments of these second-order Raman modes. In this work, we perform a thorough exploration of the anomalous lattice dynamics and conduct a renewed assignment of the numerous double resonant Raman modes of MoS_(2) monolayer. At three laser energies(E_L= 2.33, 3.50, and 4.66 e V) spanning from the visible to the ultraviolet and further into the DUV region, the calculated double-resonance Raman spectra correlate reasonably well with the experimental ones in terms of both peak positions and relative intensities. We confirm that the P_1 peak at ~450 cm^(-1) represents the second-order longitudinal acoustic(2LA) overtone mode. Each of the P_i(i = 1, 2,..., 7) peaks has multiple contributions from two phonons with distinct q wavevectors. Our calculations further reveal that the DUV laser-induced anomalous lattice dynamics stems from the quantum interference effect among different Raman scattering channels.
基金Supported by the National Natural Science Foundation of China under Grant No.11547203the Research Project of Education Department in Sichuan Province of China under Grant No.15ZB0457
文摘We theoretically present the results for a scanning tunneling transport between a metallic tip and a Kondo lattice.We calculate the density of states(DOS)and the tunneling current and differential conductance(DC)under different conduction-fermion band hybridization and temperature in the Kondo lattice.It is found that the hybridization strength and temperature give asymmetric coherent peaks in the DOS separated by the Fermi energy.The corresponding current and DC intensity depend on the temperature and quantum interference effect among the c-electron and f-electron states in the Kondo lattice.
基金Project supported by the National Natural Science Foundation of China(Grant No.61401153)the Natural Science Foundation of Hunan Province,China(Grant Nos.2015JJ2050 and 14JJ3126)
文摘The ballistic thermoelectric properties in bended graphene nanoribbons（GNRs） are systematically investigated by using atomistic simulation of electron and phonon transport. We find that the electron resonant tunneling effect occurs in the metallic–semiconducting linked ZZ-GNRs（the bended GNRs with zigzag edge leads）. The electron-wave quantum interference effect occurs in the metallic–metallic linked AA-GNRs（the bended GNRs with armchair edge leads）.These different physical mechanisms lead to the large Seebeck coefficient S and high electron conductance in bended ZZGNRs/AA-GNRs. Combined with the reduced lattice thermal conduction, the significant enhancement of the figure of merit ZT is predicted. Moreover, we find that the ZTmax（the maximum peak of ZT） is sensitive to the structural parameters. It can be conveniently tuned by changing the interbend length of bended GNRs. The magnitude of ZT ranges from the 0.15 to 0.72. Geometry-controlled ballistic thermoelectric effect offers an effective way to design thermoelectric devices such as thermocouples based on graphene.
文摘The tunneling behavior of the Néel vector out of metastable easy directions or between degenerate easy directions is studied for a small single\|domain antiferromagnetic particle at low temperature. The quantum tunneling rates for these processes are evaluated for two examples of macroscopic quantum tunneling and one example of macroscopic quantum coherence. The calculations are performed by using the two sublattice model and the instanton method in the spin coherent state path integral. Quantum interference or the spin parity effect is also discussed for each case.
