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- Creator:
- Sheng, Donna, Balents, Leon, Starykh, Oleg A., Yang, Kun, and Gong, Shoushu
- Description:
- We study the ground-state phase diagram of the quantum spin-1/2 Heisenberg model on the kagome lattice with first- (J1<0), second- (J2<0), and third-neighbor interactions (Jd>0) by means of analytical low-energy field theory and numerical density-matrix renormalization group (DMRG) studies. The results offer a consistent picture of the Jd-dominant regime in terms of three sets of spin chains weakly coupled by the ferromagnetic interchain interactions J1,2. When either J1 or J2 is much stronger than the other one, the model is found to support one of two cuboctohedral phases, cuboc1, and cuboc2. These cuboc states host noncoplanar long-ranged magnetic order and possess finite scalar spin chirality. However, in the compensated regime J1≃J2, a valence bond crystal phase emerges between the two cuboc phases. We find excellent agreement between an analytical theory based on coupled spin chains and unbiased DMRG calculations, including at a very detailed level of comparison of the structure of the valence bond crystal state. To our knowledge, this is the first such comprehensive understanding of a highly frustrated two-dimensional quantum antiferromagnet. We find no evidence of either the one-dimensional gapless spin liquid or the chiral spin liquids, which were previously suggested by parton mean-field theories.
- Resource Type:
- Article
- Identifier:
- 1098-0121
- Campus Tesim:
- Northridge
- Creator:
- Wen, Xiao-Gang, Gu, Zheng-Cheng, Sheng, Donna, Jiang, Hong-Chen, and Balents, Leon
- Description:
- The emergence of superconductivity in doped Mott insulators has been debated for decades. In this paper, we report the theoretical discovery of a time-reversal symmetry breaking superconducting ground state in the doped Mott insulator (described by the well known t-J model) on honeycomb lattice, based on a recently developed variational method: the Grassmann tensor product state approach. As a benchmark, we use exact diagonalization and density-matrix renormalization methods to check our results on small clusters. We find systematic consistency for the ground-state energy as well as other physical quantities, such as the staggered magnetization. At low doping, the superconductivity coexists with antiferromagnetic ordering.
- Resource Type:
- Article
- Identifier:
- 1098-0121
- Campus Tesim:
- Northridge
- Creator:
- Zhu, Wei, Sheng, Donna, Gong, Shoushu, and Balents, Leon
- Description:
- We study the quantum phase diagram of the spin-1/2 Heisenberg model on the kagome lattice with first-, ´ second-, and third-neighbor interactions J1, J2, and J3 by means of density matrix renormalization group. For small J2 and J3, this model sustains a time-reversal invariant quantum spin liquid phase. With increasing J2 and J3, we find in addition a q = (0, 0) Neel phase, a chiral spin liquid phase, a valence-bond crystal phase, and ´ a complex non-coplanar magnetically ordered state with spins forming the vertices of a cuboctahedron known as a cuboc1 phase. Both the chiral spin liquid and cuboc1 phase break time reversal symmetry in the sense of spontaneous scalar spin chirality. We show that the chiralities in the chiral spin liquid and cuboc1 are distinct, and that these two states are separated by a strong first order phase transition. The transitions from the chiral spin liquid to both the q = (0, 0) phase and to time-reversal symmetric spin liquid, however, are consistent with continuous quantum phase transitions.
- Resource Type:
- Article
- Identifier:
- http://arxiv.org/pdf/1412.1571, 1098-0121
- Campus Tesim:
- Northridge
- Creator:
- Ishizuka, Hiroaki, Iaconis, Jason, Sheng, Donna, and Balents, Leon
- Description:
- We show that the interplay of a high-density two-dimensional electron gas and localized electrons in a neighboring Mott insulator leads to kinetic magnetism unique to the Mott and band insulator interface. Our study is based upon a bilayer Hubbard model at U=∞ with a potential difference between the two layers. We combine analytic results with DMRG simulations to show that magnetism, and especially ferromagnetism, is greatly enhanced relative to the proximity of the two subsystems. The results are potentially relevant to recent experiments, suggesting magnetism in RTiO3/SrTiO3 heterostructures.
- Resource Type:
- Article
- Identifier:
- 1098-0121
- Campus Tesim:
- Northridge
- Creator:
- Sheng, Donna and Balents, Leon
- Description:
- Based on exact numerical calculations, we show that the generalized kagome spin model in the easy-axis limit exhibits a spin liquid, topologically degenerate ground state over a broad range of phase space, including a point at which the model is equivalent to a Heisenberg model with purely two-spin exchange interactions. We further present an explicit calculation of the gap (and dispersion) of “vison” excitations, and exponentially decaying spin and vison two-point correlators. These are hallmarks of deconfined, fractionalized, and gapped spinons. The nature of the phase transition from the spin-liquid state to a magnetic ordered state tuned by a negative four-spin “potential” term is also discussed in light of the low energy spectrum. These results greatly expand the range and the theoretical view of the spin-liquid phase in the vicinity of the Rokhsar and Kivelson exactly soluble point.
- Resource Type:
- Article
- Identifier:
- 0031-9007
- Campus Tesim:
- Northridge
- Creator:
- Burkov, A.A., Melko, R.G., Paramekanti, A., Sheng, Donna, and Balents, Leon
- Description:
- We study the interplay of Mott localization, geometric frustration, and superfluidity for hard-core bosons with nearest-neighbor repulsion on the triangular lattice. For this model at half filling, we demonstrate that superfluidity survives for arbitrarily large repulsion, and that diagonal solid order emerges in the strongly correlated regime from an order-by-disorder mechanism. This is thus an unusual example of a stable supersolid phase of hard-core lattice bosons at a commensurate filling.
- Resource Type:
- Article
- Identifier:
- 0031-9007
- Campus Tesim:
- Northridge
- Creator:
- Wang, Ziqiang, Sheng, Donna, and Balents, Leon
- Description:
- We present a phase diagram for a double quantum well bilayer electron gas in the quantum Hall regime at a total filling factor ν=1, based on exact numerical calculations of the topological Chern number matrix and the (interlayer) superfluid density. We find three phases: a quantized Hall state with pseudospin superfluidity, a quantized Hall state with pseudospin “gauge-glass” order, and a decoupled composite Fermi liquid. Comparison with experiments provides a consistent explanation of the observed quantum Hall plateau, Hall drag plateau, and vanishing Hall drag resistance, as well as the zero-bias conductance peak effect, and suggests some interesting points to pursue experimentally.
- Resource Type:
- Article
- Identifier:
- 0031-9007
- Campus Tesim:
- Northridge
- Creator:
- Sheng, L., Haldane, F.D.M., Sheng, Donna, and Balents, Leon
- Description:
- We study the competition between the long-range Coulomb interaction, disorder scattering, and lattice effects in the integer quantum Hall effect (IQHE) in graphene. By direct transport calculations, both ν=1 and ν=3 IQHE states are revealed in the lowest two Dirac Landau levels. However, the critical disorder strength above which the ν=3 IQHE is destroyed is much smaller than that for the ν=1 IQHE, which may explain the absence of a ν=3 plateau in recent experiments. While the excitation spectrum in the IQHE phase is gapless within numerical finite-size analysis, we do find and determine a mobility gap, which characterizes the energy scale of the stability of the IQHE. Furthermore, we demonstrate that the ν=1 IQHE state is a Dirac valley and sublattice polarized Ising pseudospin ferromagnet, while the ν=3 state is an xy plane polarized pseudospin ferromagnet.
- Resource Type:
- Article
- Identifier:
- 0031-9007
- Campus Tesim:
- Northridge
- Creator:
- Jiang, H.C., Weng, Z.Y., Sheng, Donna, Balents, Leon, and Weng, M.Q.
- Description:
- We numerically demonstrate that a supersolid phase exists in a frustrated hard-core boson system on a triangular lattice over a wide range of interaction strength. In the infinite repulsion Ising limit, we establish a mapping to the same problem with unfrustrated hopping, which connects the supersolid to the known results in that case. The weak superfluidity can be destroyed or strongly enhanced by a next-nearest-neighbor hopping term, which provides valuable information for experimental realization of a supersolid phase on optical lattice. A phase diagram for the frustrated anisotropic Heisenberg model on triangular lattice is also established.
- Resource Type:
- Article
- Identifier:
- 1098-0121
- Campus Tesim:
- Northridge