47,442 research outputs found
Local Spin Susceptibility of the S=1/2 Kagome Lattice in ZnCu3(OD)6Cl2
We report single-crystal 2-D NMR investigation of the nearly ideal spin S=1/2
kagome lattice ZnCu3(OD)6Cl2. We successfully identify 2-D NMR signals
originating from the nearest-neighbors of Cu2+ defects occupying Zn sites. From
the 2-D Knight shift measurements, we demonstrate that weakly interacting Cu2+
spins at these defects cause the large Curie-Weiss enhancement toward T=0
commonly observed in the bulk susceptibility data. We estimate the intrinsic
spin susceptibility of the kagome planes by subtracting defect contributions,
and explore several scenarios.Comment: 4 figures; published in PR-B Rapid Communication
Observation of Zeeman effect in topological surface state with distinct material dependence
The helical Dirac fermions on the surface of topological insulators host
novel relativistic quantum phenomena in solids. Manipulating spins of
topological surface state (TSS) represents an essential step towards exploring
the theoretically predicted exotic states related to time reversal symmetry
(TRS) breaking via magnetism or magnetic field. Understanding Zeeman effect of
TSS and determining its g-factor are pivotal for such manipulations in the
latter form of TRS breaking. Here, we report those direct experimental
observations in Bi2Se3 and Sb2Te2Se by spectroscopic imaging scanning tunneling
microscopy. The Zeeman shifting of zero mode Landau level is identified
unambiguously by judiciously excluding the extrinsic influences associated with
the non-linearity in the TSS band dispersion and the spatially varying
potential. The g-factors of TSS in Bi2Se3 and Sb2Te2Se are determined to be 18
and -6, respectively. This remarkable material dependence opens a new route to
control the spins in the TSS.Comment: main text: 17 pages, 4 figures; supplementary: 15 pages, 7 figure
On the Origin of the Checkerboard Pattern in Scanning Tunneling Microscopy Maps of Underdoped Cuprate Superconductors
The checkerboard pattern in the differential conductance maps on underdoped
cuprates appears when the STM is placed above the O-sites in the outermost
CuO-plane. In this position the interference between tunneling
paths through the apical ions above the neighboring Cu-sites leads to an
asymmetric weighting of final states in the two antinodal regions of
-space. The form of the asymmetry in the differential
conductance spectra in the checkerboard pattern favors asymmetry in the
localization length rather than a nematic displacement as the underlying
origin.Comment: 8 pages, 5 figures, final versio
Variational Monte-Carlo studies of Gossamer Superconductivity
We use a partially Gutzwiller projected BCS d-wave wavefunction with an
antiferromagentic weighting factor to study the ground state phase diagram of a
half filled Hubbard-Heisenberg model in a square lattice with nearest neighbor
hopping and a diagonal hopping . The calculations are carried out by
using variational Monte Carlo method which treats the Gutzwiller projection
explicitly. At large on-site Coulomb interaction , the ground state is
antiferromagnetic. As decreases, the ground state becomes superconducting
and eventually metallic. The phase diagram is obtained by extensive
calculations. As compared to the strong effect of , the phase boundaries
turn out to be less sensitive to . The result is consistent with the
phase diagram in layered organic conductors, and is compared to the earlier
mean field result based on the Gutzwiller approximation.Comment: 5 pages, 4 figure
Phase properties of hypergeometric states and negative hypergeometric states
We show that the three quantum states (Plya states, the
generalized non-classical states related to Hahn polynomials and negative
hypergeometric states) introduced recently as intermediates states which
interpolate between the binomial states and negative binomial states are
essentially identical. By using the Hermitial-phase-operator formalism, the
phase properties of the hypergeometric states and negative hypergeometric
states are studied in detail. We find that the number of peaks of phase
probability distribution is one for the hypergeometric states and for the
negative hypergeometric states.Comment: 7 pages, 4 figure
Electrolyte gate dependent high-frequency measurement of graphene field-effect transistor for sensing applications
We performed radiofrequency (RF) reflectometry measurements at 2.4 GHz on
electrolyte-gated graphene field-effect transistors (GFETs) utilizing a tunable
stub-matching circuit for impedance matching. We demonstrate that the gate
voltage dependent RF resistivity of graphene can be deduced even in the
presence of the electrolyte which is in direct contact with the graphene layer.
The RF resistivity is found to be consistent with its DC counterpart in the
full gate voltage range. Furthermore, in order to access the potential of
high-frequency sensing for applications, we demonstrate time-dependent gating
in solution with nanosecond time resolution.Comment: 14 pages, 4 figure
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