The Experts below are selected from a list of 52929 Experts worldwide ranked by ideXlab platform
Yong Baek Kim - One of the best experts on this subject based on the ideXlab platform.
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Sign Structure of thermal hall conductivity and topological magnons for in plane field polarized kitaev magnets
Physical Review Letters, 2021Co-Authors: Li Ern Chern, E Zhang, Yong Baek KimAbstract:The appearance of half-quantized thermal Hall conductivity in $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ in the presence of in-plane magnetic fields has been taken as a strong evidence for the Kitaev spin liquid. Apart from the quantization, the observed Sign Structure of the thermal Hall conductivity is also consistent with predictions from the exact solution of the Kitaev honeycomb model. Namely, the thermal Hall conductivity changes Sign when the field direction is reversed with respect to the heat current, which is perpendicular to one of the three nearest neighbor bonds on the honeycomb lattice. On the other hand, the thermal Hall conductivity is almost zero when the field is applied along the bond direction. Here, we theoretically demonstrate that such a peculiar Sign Structure of the thermal Hall conductivity is a generic property of the polarized state in the presence of in-plane magnetic fields. In this case, the thermal Hall effect arises from topological magnons with finite Chern numbers, and the Sign Structure follows from the symmetries of the momentum space Berry curvature. Using a realistic spin model with bond-dependent interactions, we show that the thermal Hall conductivity can have a magnitude comparable to that observed in the experiments. Hence, the Sign Structure alone cannot make a strong case for the Kitaev spin liquid. The quantization at very low temperatures, however, will be a decisive test as the magnon contribution vanishes in the zero temperature limit.
Matthew P A Fisher - One of the best experts on this subject based on the ideXlab platform.
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entanglement and the Sign Structure of quantum states
Physical Review A, 2015Co-Authors: Tarun Grover, Matthew P A FisherAbstract:Many-body quantum eigenstates of generic Hamiltonians at finite-energy density typically satisfy the ``volume law'' of entanglement entropy: the von Neumann entanglement entropy and the Renyi entropies for a subregion scale in proportion to its volume. Here we provide a connection between the volume law and the Sign Structure of eigenstates. In particular, we ask the following question: Can a positive wave function support a volume law entanglement? Remarkably, we find that a typical random positive wave function exhibits a constant law for Renyi entanglement entropies ${S}_{n}$ for $ng1$, despite arbitrary large-amplitude fluctuations. We also provide evidence that the modulus of the finite-energy density eigenstates of generic local Hamiltonians shows similar behavior.
Li Ern Chern - One of the best experts on this subject based on the ideXlab platform.
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Sign Structure of thermal hall conductivity and topological magnons for in plane field polarized kitaev magnets
Physical Review Letters, 2021Co-Authors: Li Ern Chern, E Zhang, Yong Baek KimAbstract:The appearance of half-quantized thermal Hall conductivity in $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ in the presence of in-plane magnetic fields has been taken as a strong evidence for the Kitaev spin liquid. Apart from the quantization, the observed Sign Structure of the thermal Hall conductivity is also consistent with predictions from the exact solution of the Kitaev honeycomb model. Namely, the thermal Hall conductivity changes Sign when the field direction is reversed with respect to the heat current, which is perpendicular to one of the three nearest neighbor bonds on the honeycomb lattice. On the other hand, the thermal Hall conductivity is almost zero when the field is applied along the bond direction. Here, we theoretically demonstrate that such a peculiar Sign Structure of the thermal Hall conductivity is a generic property of the polarized state in the presence of in-plane magnetic fields. In this case, the thermal Hall effect arises from topological magnons with finite Chern numbers, and the Sign Structure follows from the symmetries of the momentum space Berry curvature. Using a realistic spin model with bond-dependent interactions, we show that the thermal Hall conductivity can have a magnitude comparable to that observed in the experiments. Hence, the Sign Structure alone cannot make a strong case for the Kitaev spin liquid. The quantization at very low temperatures, however, will be a decisive test as the magnon contribution vanishes in the zero temperature limit.
Kun Chen - One of the best experts on this subject based on the ideXlab platform.
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fermionic Sign Structure of high order feynman diagrams in a many fermion system
Physical Review B, 2021Co-Authors: Baozong Wang, Pengcheng Hou, Youjin Deng, Kristjan Haule, Kun ChenAbstract:The Sign cancellation between scattering amplitudes makes fermions different from bosons. We systematically investigate Feynman diagrams' fermionic Sign Structure in a representative many-fermion system---a uniform Fermi gas with Yukawa interaction. We analyze the role of the crossing symmetry and the global gauge symmetry in the fermionic Sign cancellation. The symmetry arguments are then used to identify the Sign-canceled groups of diagrams. Sign-Structure analysis has two applications. Numerically, it leads to a cluster diagrammatic Monte Carlo algorithm for fast diagram evaluations. This algorithm is about ${10}^{5}$ times faster than the conventional approaches in the sixth order. Analytically, our analysis systematically reveals the relevant diagrams that dominate the dynamics.
Zhengyu Weng - One of the best experts on this subject based on the ideXlab platform.
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critical role of the Sign Structure in the doped mott insulator luther emery versus fermi liquid like state in quasi one dimensional ladders
Physical Review B, 2020Co-Authors: Hongchen Jiang, Shuai Chen, Zhengyu WengAbstract:The mechanism of superconductivity in a purely interacting electron system has been one of the most challenging issues in condensed matter physics. In the BCS theory, the Landau's Fermi liquid is the ground state of weakly interacting fermions dictated by the fermion Sign Structure, and the superconducting instability only occurs when an additional pairing force is added. By contrast, as shown by density matrix renormalization group calculation, a quasi-one-dimensional superconducting state (specifically a Luther-Emery state) is an intrinsic ground state of the $t\ensuremath{-}J$ two-leg ladder and four-leg cylinder at finite doping. Such a Luther-Emery state with pairing can be directly turned into a Fermi-gas-like normal state without pairing by merely switching off the phase-string Signs hidden in the model via two schemes, which reduce the Sign Structure to the trivial fermion Signs associated with doped holes. It thus demonstrates a new pairing paradigm in a model-doped Mott insulator as due to the generic phase-string Sign Structure. Finally, as an example, the latter is explicitly shown to lead to a ``stringlike'' pairing force after adiabatically connecting to a strong anisotropic limit of the model.
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exact Sign Structure of the t j chain and the single hole ground state
Nuclear Physics, 2016Co-Authors: Zheng Zhu, Qingrui Wang, D N Sheng, Zhengyu WengAbstract:Abstract Injecting a single hole into a one-dimensional Heisenberg spin chain is probably the simplest case of doping a Mott insulator. The motion of such a single hole will generally induce a many-body phase shift, which can be identified by an exact Sign Structure of the model known as the phase string. We show that the Sign Structure is nontrivial even in this simplest problem, which is responsible for the essential properties of Mott physics. We find that the characteristic momentum Structure, the Luttinger liquid behavior, and the quantum phase interference of the hole under a periodic boundary condition can all be attributed to it. We use the density matrix renormalization group (DMRG) numerical simulation to make a comparative study of the t – J chain and a model in which the Sign Structure is switched off. We further show that the key DMRG results can be reproduced by a variational wave function with incorporating the correct Sign Structure. Physical implications of the Sign Structure for doped Mott insulators in general are also discussed.
