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Fei Zhou

Publications and source records attributed to Fei Zhou.

176 records · Page 10Linked to original sources
arXiv2003

Spin Singlet Mott States and Evidence For Spin Singlet Quantum Condensates of Spin-One Bosons in Lattices

We have investigated spin singlet Mott states of spin-one bosons with antiferromagnetic interactions. These spin singlet states do not break rotational symmetry and exhibit remarkably different macroscopic properties compared with nematic Mott states of spin-one bosons. We demonstrate that the dynamics of spin singlet Mott states is fully characterized by even- and odd-class quantum dimer models. The difference between spin singlet Mott states for even and odd numbers of atoms per site can be attributed to a selection rule in the low energy sectors of on-site Hilbert spaces; alternatively, it can also be attributed to an effect of Berry's phases on bosonic Mott states. We also discuss evidence for spin singlet quantum condensate of spin-one atoms. Our main finding is that in a projected spin singlet Hilbert space, the low energy physics of spin-one bosons is fully characterized by a Bose-Hubbard model of interacting spinless bosons carrying charges of Ising gauge fields; the other major finding is spin-charge separation in some one-dimensional Mott states. We propose charge-e spin singlet superfluid for an odd number of atoms per lattice site and charge-2e spin singlet superfluid for an even number of atoms per lattice site in one-dimensional lattices. All discussions in this article are limited to integer numbers of bosons per site.

cond-mat.supr-con↗
arXiv2002

Quantum Spin Nematic States in Bose-Einstein Condensates

We review some recent results on discrete symmetries and topological order in spinor Bose-Einstein condensates (BECs) of $^{23}Na$. For spin one bosons with two-body scatterings dominated by a total spin equal to two channel, the BECs are in quantum spin nematic states at a low density limit. We study spin correlations in condensates at different limits and analyze hidde$ symmetries using a non-perturbative approach developed recently. We further more investigate the influence of hidden $Z_2$ symmetries and U(1) quantum orders in symmetry partially retored states, particularly the effects on topological excitations.

cond-mat.stat-mech↗
arXiv2002

Spin Ordering and Quasiparticles in Spin Triplet Superconducting Liquids

Spin ordering and its effect on low energy quasiparticles in a p-wave superconducting liquid are investigated. We show that there is a new 2D p-wave superconducting liquid where the ground state is rotation invariant. In quantum spin disordered liquids, the low energy quasiparticles are bound states of the bare Bogolubov- De Gennes (${\em BdeG}$) quasiparticles and zero energy skyrmions, which are charge neutral bosons at the low energy limit. Further more, spin collective excitations are fractionalized ones carrying a half spin and obeying fermionic statistics. In thermally spin disordered limits, the quasi-particles are bound states of bare ${\em BdeG}$ quasi-particles. The latter situation can be realized in some layered p-wave superconductors where the spin-orbit coupling is weak.

cond-mat.mes-hall↗
arXiv2002

Spin rotation invariant spin triplet superconducting liquids

Spin ordering and its effect on the low energy quasiparticles in a p-wave superconducting fluid are investigated. We study the properties of a new 2D quantum spin triplet superconducting liquid where the ground state is spin rotation invariant. In quantum spin disordered cases, zero energy skyrmions are topologically stable because of a fermionic zero mode in space-time monopoles which serve as a quantum protectorate.The low energy quasiparticles are bound states of the bare Bogolubov- De Gennes ({\em BdeG})quasiparticles and skyrmions, which are charge neutral bosons at the zero energy limit. Further more, the spin collective excitations are fractionalized ones carrying a half spin and obeying fermionic statistics. In thermally spin disordered superconducting states, a bare {\em BdeG} has an infinity energy and each two {\em BdeG} quasiparticles form spin zero or one bound states.

cond-mat.str-el↗
arXiv2001

Spin correlation and Discrete symmetry in Spinor Bose-Einstein Condensates

We study spin correlations in Bose-Einstein condensates of spin 1 bosons with scatterings dominated by a total spin equal 2 channel. We show the low energy spin dynamics in the system can be mapped into an $o(n)$ nonlinear sigma model(NL$σ$M). $n=3$ at the zero magnetic field limit and $n=2$ in the presence of weak magnetic fields. In an ordered phase, the ground state has a hidden $Z_2$ symmetry and is degenerate under the group $[U(1)\times S^{n-1}]/Z_2$. We explore consequences of the hidden symmetry and propose some measurements to probe it.

cond-mat.mes-hall↗
arXiv2001

Hidden topological order in $^{23}Na (F=1)$ Bose-Einstein Condensates

We show the existence of a new hidden topological order in $^{23}Na$ (F=1) Bose-Einstein condensates (BEC) with antiferromagnetic interactions. Occurrence of this order is due to the confinement of hedgehogs in BEC where a spin Josephson effect takes place. However, a topological long range order is also argued to coexist with a short range spin correlation, as a result of topological order from disorder.

cond-mat.stat-mech↗
arXiv2001

Spin-1/2 Collective Excitations in BEC of Interacting Spin-1 Atoms

We construct spin-1/2 collective excitations in BEC of interacting spin-1 atoms. These excitations exist in states with a maximal global degeneracy. The stability and energy of these objects are determined by interactions with spin fluctuations and are studied based on a duality relation between hyper-monopoles and magnetic monopoles in physical space.

cond-mat.stat-mech↗
arXiv2001

Spinor Bosonic Atoms in Optical Lattices: Symmetry Breaking and Fractionalization

We study superfluid and Mott insulator phases of cold spin-1 Bose atoms with antiferromagnetic interactions in an optical lattice, including a usual polar condensate phase, a condensate of singlet pairs, a crystal spin nematic phase, and a spin singlet crystal phase. We suggest a possibility of exotic fractionalized phases of spinor BEC and discuss them in the language of topological defect condensation and $Z_2$ lattice gauge theory.

cond-mat.stat-mech↗
arXiv1999

Ferromagnetic correlations in quasi-one-dimensional conducting channels

We propose a model which explains the experimental observation of spontaneous spin polarization of conducting electrons in quasi- one-dimensional GaAs/AlGaAs channels. We show that a ferromagnetic order is a generic property of a quasi-one-dimensional conducting channel embedded in a Wigner crystal. We also discuss gate voltage, magnetic field and temperature dependences of the channel's conductance.

cond-mat.mes-hall↗
arXiv1999

Wave Function Mismatches and Coulomb Drag

In this paper, I study the topological excitations in a pairing state in double layer systems at Landau level filling factor $ν=1/2$ in the presence of disorders. Due to mismatches between single particle wave functions of composite Fermions in different layers, the sensitivity of the Chern number of the pairing state, with respect to changes of impurities, is infinity. Consequently, Goldstone mode in this pairing state is strongly damped at low temperature. It is argued that this leads to a unique temperature dependence of the drag resistance at low temperature.

cond-mat.mes-hall↗
arXiv1999

A novel superconducting glass state in disordered thin films in Clogston limit

A theory of mesoscopic fluctuations in disordered thin superconducting films in a parallel magnetic field is developed. At zero temperature, the superconducting state undergoes a phase transition into a state characterized by superfluid densities of random signs, instead of a spin polarized disordered Fermi liquid phase. Consequently, the ground state belongs to the same universality class as the 2D XY spin glass. As the magnetic field increases further, mesoscopic pairing states are nucleated in an otherwise homogeneous spin polarized disordered Fermi liquid. The statistics of these pairing states is universal depending on the sheet conductance of the 2D film.

cond-mat.mes-hall↗
arXiv1999

Quantum Phase Pumping

In this Letter, we consider the adiabatic charge transport through a normal mesoscopic sample sandwiched by superconductors without modulation of local chemical potentials. The deformation of coherent quasiparticles in the normal metal in the presence of periodically changing phases in the superconductors leads to a charge transport. Both the magnitude and the phase dependence of the charge transferred per period through the sample strongly depend on temperature.

cond-mat.mes-hall↗
arXiv1999

Coulomb drag as a signature of the paired quantum Hall state

Motivated by the recent Coulomb drag experiment of M. P. Lilly et. al, we study the Coulomb drag in a two-layer system with Landau level filling factor $ν=1/2$. We find that the drag conductivity in the incompressible paired quantum Hall state at zero temperature can be finite. The drag conductivity is also greatly enhanced above $T_c$, at which the transition between the weakly coupled compressible liquids and the paired quantum Hall liquid takes place. We discuss the implications of our results for the recent experiment.

cond-mat.mes-hall↗