The Experts below are selected from a list of 8223 Experts worldwide ranked by ideXlab platform
Atac Imamoglu - One of the best experts on this subject based on the ideXlab platform.
-
Non-hygrogenic excitonic spectra of transition metal dichalcogenides: The role of quantum geometry of Bloch Bands
Conference on Lasers and Electro-Optics, 2016Co-Authors: Ajit Srivastava, Atac ImamogluAbstract:We investigate the role of Bloch-Band geometry in determining exciton spectra. We find that Berry-phase leads to a splitting of 2p states while the quantum geometric tensor leads to a Lamb-like shift. Our calculations are experimentally relevant for excitons in transition metal dichalcogenides.
-
signatures of Bloch Band geometry on excitons nonhydrogenic spectra in transition metal dichalcogenides
Physical Review Letters, 2015Co-Authors: Ajit Srivastava, Atac ImamogluAbstract:The geometry of electronic Bands in a solid can drastically alter single-particle charge and spin transport. We show here that collective optical excitations arising from Coulomb interactions also exhibit unique signatures of Berry curvature and quantum geometric tensor. A nonzero Berry curvature mixes and lifts the degeneracy of $l\ensuremath{\ne}0$ states, leading to a time-reversal-symmetric analog of the orbital Zeeman effect. The quantum geometric tensor, on the other hand, leads to $l$-dependent shifts of exciton states that is analogous to the Lamb shift. Our results provide an explanation for the nonhydrogenic exciton spectrum recently calculated for transition-metal dichalcogenides. Numerically, we find a Berry curvature induced splitting of $\ensuremath{\sim}10\text{ }\text{ }\mathrm{meV}$ between the $2{p}_{x}\ifmmode\pm\else\textpm\fi{}i2{p}_{y}$ states of ${\mathrm{WSe}}_{2}$.
-
signatures of Bloch Band geometry on excitons non hydrogenic spectra in transition metal dichalcogenides
arXiv: Mesoscale and Nanoscale Physics, 2015Co-Authors: Ajit Srivastava, Atac ImamogluAbstract:The geometry of electronic Bands in a solid can drastically alter single-particle charge and spin transport. We show here that collective optical excitations arising from Coulomb interactions also exhibit unique signatures of Berry curvature and quantum geometric tensor. A non-zero Berry curvature mixes and lifts the degeneracy of $l \neq 0$ states, leading to a time-reversal-symmetric analog of the orbital Zeeman effect. The quantum geometric tensor, on the other hand, leads to $l$-dependent shifts of exciton states that is analogous to the Lamb shift. Our results provide an explanation of the non-hydrogenic exciton spectrum recently calculated for transition metal dichalcogenides. Numerically, we find a Berry curvature induced splitting of $\sim 10$ meV between the $2p_x \pm i2p_y$ states of WSe$_2$.
Qian Niu - One of the best experts on this subject based on the ideXlab platform.
-
valley dependent optoelectronics from inversion symmetry breaking
Physical Review B, 2008Co-Authors: Wang Yao, Di Xiao, Qian NiuAbstract:Inversion symmetry breaking allows contrasted circular dichroism in different $k$-space regions, which takes the extreme form of optical selection rules for interBand transitions at high symmetry points. In materials where Band edges occur at noncentral valleys, this enables valley-dependent interplay of electrons with light of different circular polarizations, in analogy to spin dependent optical activities in semiconductors. This discovery is in perfect harmony with the previous finding of valley contrasted Bloch Band features of orbital magnetic moment and Berry curvatures from inversion symmetry breaking [D. Xiao, W. Yao, and Q. Niu, Phys. Rev. Lett. 99, 236809 (2007)]. A universal connection is revealed between the $k$-resolved optical oscillator strength of interBand transitions, the orbital magnetic moment and the Berry curvatures, which also provides a principle for optical measurement of orbital magnetization and intrinsic anomalous Hall conductivity in ferromagnetic systems. The general physics is demonstrated in graphene where inversion symmetry breaking leads to valley contrasted optical selection rule for interBand transitions. We discuss graphene based valley optoelectronics applications where light polarization information can be interconverted with electronic information.
-
attractive electron electron interaction induced by geometric phase in a Bloch Band
arXiv: Superconductivity, 2006Co-Authors: Junren Shi, Qian NiuAbstract:We investigate electron pairing in the presence of the Berry curvature field that ubiquitously exists in ferromagnetic metals with spin-orbit coupling. We show that a sufficiently strong Berry curvature field on the Fermi surface can transform a repulsive interaction between electrons into an attractive one in the p-wave channel. We also reveal a topological possibility for turning an attractive s-wave interaction into one in the p-wave channel, even if the Berry curvature field only exists inside the Fermi surface (circle). We speculate that these novel mechanism might be relevant to the recently discovered ferromagnetic superconductors such as UGe$_{2}$ and URhGe.
-
Bloch waves and Bloch Bands of Bose-Einstein condensates in optical lattices
Physical Review A, 2002Co-Authors: Roberto B. Diener, Qian NiuAbstract:Bloch waves and Bloch Bands of Bose-Einstein condensates in optical lattices are studied. We provide further evidence for the loop structure in the Bloch Band, and compute the critical values of the mean-field interaction strength for the Landau instability and the dynamical instability.
-
Dynamical Bloch Band Suppression in an Optical Lattice
Physical Review Letters, 1998Co-Authors: Kirk W. Madison, Qian Niu, Martin C. Fischer, Roberto B. Diener, Mark G. RaizenAbstract:Dynamical Bloch Band suppression is observed for the first time, using cold sodium atoms in a far detuned standing wave of light. This system has well-defined Bloch Bands as its energy spectrum, which are modified dynamically by imposing a strong phase modulation of the standing wave. The atoms are prepared in the lowest Band, and the spectrum is mapped out by introducing a weak spectroscopic probe that drives transitions between the modified Bands. Dynamical suppression of the Bands is observed at a critical value of the modulation strength, and is well supported by a full quantum mechanical analysis that goes beyond the single-Band and tight-binding approximations.
-
Centralized distribution of adiabatic current in a split Bloch Band.
Physical review. B Condensed matter, 1992Co-Authors: Chiu Liu, Qian NiuAbstract:It is known that for a filled Bloch Band, the particle transport in a cycle induced by a slow change of the periodic potential is quantized as integers. In this paper, we consider the case where a Bloch Band is split by an extra static potential into a number of miniBands. We study how the number of particle transports is distributed among the miniBands, and when the distribution is concentrated at a few central miniBands. Particular attention is given to situations where the splitting potential has a long spatial period and is random within a unit cell
Stefano Longhi - One of the best experts on this subject based on the ideXlab platform.
-
Ultrafast and anharmonic Rabi oscillations between non-Bloch Bands
Communications Physics, 2020Co-Authors: Ching Hua Lee, Stefano LonghiAbstract:Bloch Band theory and bulk-boundary correspondence in non-Hermitian systems are attracting great attention in different areas of science. InterBand transitions and Rabi flopping induced by emission or absorption of field quanta are fundamental and well-understood processes in Hermitian systems. However, they are challenged in a non-Hermitian system, where Band theory is affected by system boundaries. Here we consider Rabi oscillations in non-Hermitian lattices exhibiting unbalanced non-Hermitian skin effect, and unveil an unprecedented scenario of Rabi flopping. The effective dipole moment of the transition - usually considered a bulk property - is however strongly dependent on boundary conditions. Rabi oscillations become anharmonic and transitions cease to be vertical in the energy-momentum plane in systems with open boundaries. Remaining stable even in the presence of complex energies, Rabi oscillations provide a vivid illustration of how competition between non-Hermitian, non-local and Floquet effects can result in significant enhancements of physically measurable quantities. The bulk boundary effects of non-hermitian systems are a burgeoning area of interest with the potential to unveil new and interesting physics. Here, the authors investigate how the non-Hermitian skin effect can drastically affect the emission and absorption quanta and Rabi oscillations in a driven non-Hermitian two-level lattice, which is sustainable even the system possess gain or loss.
-
Non-Bloch-Band Collapse and Chiral Zener Tunneling.
Physical review letters, 2020Co-Authors: Stefano LonghiAbstract:Non-Bloch-Band theory describes bulk energy spectra and topological invariants in non-Hermitian crystals with open boundaries, where the bulk eigenstates are squeezed toward the edges (skin effect). However, the interplay of non-Bloch-Band theory, skin effect, and coherent Bloch dynamics is so far unexplored. In two-Band non-Hermitian lattices, it is shown here that collapse of non-Bloch Bands and skin modes deeply changes the Bloch dynamics under an external force. In particular, for resonance forcing non-Bloch-Band collapse results in Wannier-Stark ladder coalescence and chiral Zener tunneling between the two dispersive Bloch Bands.
Xian-geng Zhao - One of the best experts on this subject based on the ideXlab platform.
-
Rabi oscillations between dissipative Bloch Bands
Physica E: Low-dimensional Systems and Nanostructures, 2001Co-Authors: Duan Suqing, Wei Zhang, Xian-geng ZhaoAbstract:Abstract Within a two-Band tight-binding model driven by DC–AC electric fields, we investigate the dynamics of electrons with Markoffian dephasing. We find that Rabi oscillations between the Bloch Bands under the resonant condition may be destroyed by scattering from lattice imperfections. Through a perturbative calculation, we also obtain the effective decay time for the approach to equal Bloch Band populations under conditions of small interBand coupling and in the long-time limit. The decay rate shows characteristic sharp peaks at values of the parameters that give a signature of Rabi oscillations, and quasienergy spectra display avoided crossings at the same time.
-
The suppression of a Bloch Band in a driving laser field
Journal of Physics: Condensed Matter, 1994Co-Authors: Xian-geng ZhaoAbstract:The dynamic effect of Bloch electrons in a spatial periodic system under the influence of a driving laser field is studied within the single-Band approximation. A quasienergy Band is obtained exactly for the case of long-range intersite interactions. It is found that the quasienergy Band will be suppressed heavily by the laser field if the ratio of the Bloch frequency to the laser frequency is a root of the ordinary Bessel function of order zero. If only the nearest-neighbour intersite interaction is involved, the Band suppression will turn into the Band collapse proposed very recently. However, a numerical calculation of the Band width shows that in comparison with the nearest-neighbour intersite interaction, the contribution of other intersite interactions to the quasienergy is not negligible. This may imply that the experimental observation of the dynamic effect will be that of Band suppression rather than Band collapse.
Ajit Srivastava - One of the best experts on this subject based on the ideXlab platform.
-
Non-hygrogenic excitonic spectra of transition metal dichalcogenides: The role of quantum geometry of Bloch Bands
Conference on Lasers and Electro-Optics, 2016Co-Authors: Ajit Srivastava, Atac ImamogluAbstract:We investigate the role of Bloch-Band geometry in determining exciton spectra. We find that Berry-phase leads to a splitting of 2p states while the quantum geometric tensor leads to a Lamb-like shift. Our calculations are experimentally relevant for excitons in transition metal dichalcogenides.
-
signatures of Bloch Band geometry on excitons nonhydrogenic spectra in transition metal dichalcogenides
Physical Review Letters, 2015Co-Authors: Ajit Srivastava, Atac ImamogluAbstract:The geometry of electronic Bands in a solid can drastically alter single-particle charge and spin transport. We show here that collective optical excitations arising from Coulomb interactions also exhibit unique signatures of Berry curvature and quantum geometric tensor. A nonzero Berry curvature mixes and lifts the degeneracy of $l\ensuremath{\ne}0$ states, leading to a time-reversal-symmetric analog of the orbital Zeeman effect. The quantum geometric tensor, on the other hand, leads to $l$-dependent shifts of exciton states that is analogous to the Lamb shift. Our results provide an explanation for the nonhydrogenic exciton spectrum recently calculated for transition-metal dichalcogenides. Numerically, we find a Berry curvature induced splitting of $\ensuremath{\sim}10\text{ }\text{ }\mathrm{meV}$ between the $2{p}_{x}\ifmmode\pm\else\textpm\fi{}i2{p}_{y}$ states of ${\mathrm{WSe}}_{2}$.
-
signatures of Bloch Band geometry on excitons non hydrogenic spectra in transition metal dichalcogenides
arXiv: Mesoscale and Nanoscale Physics, 2015Co-Authors: Ajit Srivastava, Atac ImamogluAbstract:The geometry of electronic Bands in a solid can drastically alter single-particle charge and spin transport. We show here that collective optical excitations arising from Coulomb interactions also exhibit unique signatures of Berry curvature and quantum geometric tensor. A non-zero Berry curvature mixes and lifts the degeneracy of $l \neq 0$ states, leading to a time-reversal-symmetric analog of the orbital Zeeman effect. The quantum geometric tensor, on the other hand, leads to $l$-dependent shifts of exciton states that is analogous to the Lamb shift. Our results provide an explanation of the non-hydrogenic exciton spectrum recently calculated for transition metal dichalcogenides. Numerically, we find a Berry curvature induced splitting of $\sim 10$ meV between the $2p_x \pm i2p_y$ states of WSe$_2$.