91 research outputs found
Theory of RF-spectroscopy of strongly interacting Fermions
We show that strong pairing correlations in Fermi gases lead to the
appearance of a gap-like structure in the RF-spectrum, both in the balanced
superfluid and in the normal phase above the Clogston-Chandrasekhar limit. The
average RF-shift of a unitary gas is proportional to the ratio of the Fermi
velocity and the scattering length with the final state. In the strongly
imbalanced case, the RF-spectrum measures the binding energy of a minority atom
to the Fermi sea of majority atoms. Our results provide a qualitative
understanding of recent experiments by Schunck et.al.Comment: revised version, 4 pages, 3 figures, RevTex
Fermi surface reconstruction in hole-doped t-J models without long-range antiferromagnetic order
We calculate the Fermi surface of electrons in hole-doped, extended t-J
models on a square lattice in a regime where no long-range antiferromagnetic
order is present, and no symmetries are broken. Using the "spinon-dopon"
formalism of Ribeiro and Wen, we show that short-range antiferromagnetic
correlations lead to a reconstruction of the Fermi surface into hole pockets
which are not necessarily centered at the antiferromagnetic Brillouin zone
boundary. The Brillouin zone area enclosed by the Fermi surface is proportional
to the density of dopants away from half-filling, in contrast to the
conventional Luttinger theorem which counts the total electron density. This
state realizes a "fractionalized Fermi liquid" (FL*), which has been proposed
as a possible ground-state of the underdoped cuprates; we note connections to
recent experiments. We also discuss the quantum phase transition from the FL*
state to the Fermi liquid state with long-range antiferromagnetic order.Comment: 20 pages, 8 figure
Incommensurate density wave quantum criticality in two dimensional metals
We revisit the problem of two dimensional metals in the vicinity of a quantum
phase transition to incommensurate charge density wave order,
where the order parameter wave vector connects two hot spots on
the Fermi surface with parallel tangents. Earlier theoretical works argued that
such critical points are potentially unstable, if the Fermi surface at the hot
spots is not sufficiently flat. Here we perform a controlled, perturbative
renormalization group analysis and find a stable fixed point corresponding to a
continuous quantum phase transition, which exhibits a strong dynamical nesting
of the Fermi surface at the hot spots. We derive scaling forms of correlation
functions at the critical point and discuss potential implications for
experiments with transition metal dichalcogenides and rare-earth tellurides.Comment: 11 pages, 3 figures; journal versio
Exact solution of a two-species quantum dimer model for pseudogap metals
We present an exact ground state solution of a quantum dimer model introduced
in Ref.[1], which features ordinary bosonic spin-singlet dimers as well as
fermionic dimers that can be viewed as bound states of spinons and holons in a
hole-doped resonating valence bond liquid. Interestingly, this model captures
several essential properties of the metallic pseudogap phase in high-
cuprate superconductors. We identify a line in parameter space where the exact
ground state wave functions can be constructed at an arbitrary density of
fermionic dimers. At this exactly solvable line the ground state has a huge
degeneracy, which can be interpreted as a flat band of fermionic excitations.
Perturbing around the exactly solvable line, this degeneracy is lifted and the
ground state is a fractionalized Fermi liquid with a small pocket Fermi surface
in the low doping limit.Comment: Revised version, 8 page
Electron spectral functions in a quantum dimer model for topological metals
We study single electron spectral functions in a quantum dimer model
introduced by Punk, Allais and Sachdev (Ref. [1]). The Hilbert space of this
model is spanned by hard-core coverings of the square lattice with two types of
dimers: ordinary bosonic spin-singlets, as well as fermionic dimers carrying
charge +e and spin 1/2, which can be viewed as bound-states of spinons and
holons in a doped resonating valence bond (RVB) liquid. This model realizes a
metallic phase with topological order and captures several properties of the
pseudogap phase in hole-doped cuprates, such as a reconstructed Fermi surface
with small hole-pockets and a highly anisotropic quasiparticle residue in the
absence of any broken symmetries. Using a combination of exact diagonalization
and analytical methods we compute electron spectral functions and show that
this model indeed exhibits a sizeable antinodal pseudogap, with a momentum
dependence deviating from a simple d-wave form, in accordance with experiments
on underdoped cuprates.Comment: 13 pages, 7 figure
Signatures of correlated magnetic phases in the local two-particle density matrix
Experiments with quantum gas microscopes have started to explore the
antiferromagnetic phase of the two-dimensional Fermi-Hubbard model and effects
of doping with holes away from half filling. In this work we show how direct
measurements of the system averaged two-spin density matrix and its full
counting statistics can be used to identify different correlated magnetic
phases with or without long-range order. We discuss examples of phases which
are potentially realized in the Hubbard model close to half filling, including
antiferrromagnetically ordered insulators and metals, as well as insulating
spin-liquids and metals with topological order. For these candidate states we
predict the doping- and temperature dependence of local correlators, which can
be directly measured in current experiments.Comment: 15 pages, 7 figure
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