arXiv subjects

Abolhassan Vaezi

Publications and source records attributed to Abolhassan Vaezi.

42 records · Page 3Linked to original sources

arXiv2011

Phase diagram of the strongly correlated Kane-Mele-Hubbard model

We explore the phase diagram of the strongly correlated Hubbard model with intrinsic spin orbit coupling on the honeycomb lattice. We obtain the low energy effective model describing the spin degree of freedom. We study the resulting model within the Schwinger boson and Schwinger fermion approaches. The Schwinger boson approach gives the boundary between the spin liquid phase and the magnetically ordered phases, Neel order and incommensurate Neel order. We find that increasing the strength of the spin orbit coupling, narrows the width of the spin liquid region. The Schwinger fermion approach sheds further light on the nature of the spin liquid phase. We obtain three different candidates for the spin liquid phase within the mean field approximation which are gapless spin liquid, topological Mott insulator, and the chiral spin liquid phases. We argue that the gauge fluctuations and the instanton effect may suppress the first two spin liquids, while the chiral spin liquid is stable against gauge fluctuations due to its nontrivial topology.

cond-mat.str-el↗

arXiv2011

Fractional quantum Hall effect at zero magnetic field

In this letter, we discuss the recently proposed fractional quantum Hall effect in the absence of Landau levels. It is shown that the parton construction can explain all properties of 1/3 state, including the effective charge of quasi-particles, their statistics and the many-body ground-state degeneracy. The low energy description of these states has been discussed. We also generalize our model to construct the hierarchical quantum Hall states at filling fractions other than $1/m$.

cond-mat.str-el↗

arXiv2011

Gauge theory of the Hubbard model on honeycomb lattice and its instanton effect

In this paper we investigate possible spin disordered phase in the Hubbard model on the honeycomb lattice. Using a slave-particle theory that include the charge fluctuations, we find a meanfield spin disordered phase in a range of on-site repulsion $U$. The spin disordered state is described by gapped fermions coupled to compact U(1) gauge field. We study the confinement/deconfinement problem of the U(1) gauge theory due to the instantons proliferation. We calculate all allowed instanton terms and compute their quantum numbers. It is shown that the meanfield spin disordered phase is unstable. The instantons proliferation induce a translation symmetry breaking.

cond-mat.str-el↗

arXiv2010

Self-consistent calculation of the single particle scattering rate in high $Tc$ cuprates

The linear temperature dependence of the resistivity above the optimal doping is a longstanding problem in the field of high temperature superconductivity in cuprates. In this paper, we investigate the effect of gauge fluctuations on the momentum relaxation time and the transport scattering rate within the slave boson method. We use a more general slave treatment to resolve the ambiguity of decomposing the Heisenberg exchange term. We conclude that this term should be decomposed only in the Cooper channel. This results in the spinon mass inversely proportional to the doping. It is showed that solving the equation for the transport scattering rate self-consistently, we find a crossover temperature above which we obtain the linear temperature dependence of the electrical resistivity as well as the single particle scattering rate. It is also shown that this linear temperature dependence of the scattering rate in the pseudogap region explains the existence of the Fermi arcs with a length that linearly varies with temperature.

cond-mat.str-el↗

arXiv2010

Phase diagram of the Hubbard model on honeycomb lattice

In this paper we generalized the slave-particle technique to study the phase diagram of the Hubbard model on honeycomb lattice which may contain charge fluctuations. For large $U$, we have antiferromagnetic order phase. As we decrease $U$ below $U_{c2}\simeq 3t$, the system undergoes a first order phase transition into a gapped spin rotation invariant phase. Under a semiclassical approximation of the slave-particle approach, we find that such phase breaks the translation symmetry, the parity and the lattice rotation symmetry. However, beyond the semiclassical approximation, a $Z_2$ spin liquid that does not break any lattice symmetry is also possible.

cond-mat.str-el↗

arXiv2010

Isotope effect on Tc and the superfluid density of high-temperature superconductors

In this paper, I study the oxygen isotope effect (OIE) in cuprates. I introduce a simple model that can explain experiments both qualitatively and quantitatively. In this theory, isotope substitution only affects the superfluid density, but not the pseudo-gap. Within the spin-charge separation picture, I argue that the spinon-phonon interaction is in the adiabatic limit, and therefore within the Migdal-Eliashberg theory, there is no isotope effect in the spinon mass renormalization. On the other hand, I show that the holon-phonon interaction is in the non-adiabatic limit. Therefore, the small polaron picture is applicable and there is a large mass enhancement in an isotope-dependent way. Our theory explains why upon $^{16}$O/$^{18}$O substitution, the superconducting transition temperature changes only in underdoped cuprates, while there is no considerable OIE at the optimal doped as well as the overdoped cuprates. Additionally, in contrast to the conventional superconductors, we obtain OIE on the superfluid density for whole superconducting region in agreement with the experimental observations.

cond-mat.supr-con↗