5,116 research outputs found
Fast pick up technique for high quality heterostructures of bilayer graphene and hexagonal boron nitride
We present a fast method to fabricate high quality heterostructure devices by
picking up crystals of arbitrary sizes. Bilayer graphene is encapsulated with
hexagonal boron nitride to demonstrate this approach, showing good electronic
quality with mobilities ranging from 17 000 cm^2/V/s at room temperature to 49
000 cm^2/V/s at 4.2 K, and entering the quantum Hall regime below 0.5 T. This
method provides a strong and useful tool for the fabrication of future high
quality layered crystal devices.Comment: 5 pages, 3 figure
Dynamic RKKY interaction between magnetic moments in graphene nanoribbons
Graphene has been identified as a promising material with numerous
applications, particularly in spintronics. In this paper we investigate the
peculiar features of spin excitations of magnetic units deposited on graphene
nanoribbons and how they can couple through a dynamical interaction mediated by
spin currents. We examine in detail the spin lifetimes and identify a pattern
caused by vanishing density of states sites in pristine ribbons with armchair
borders. Impurities located on these sites become practically invisible to the
interaction, but can be made accessible by a gate voltage or doping. We also
demonstrate that the coupling between impurities can be turned on or off using
this characteristic, which may be used to control the transfer of information
in transistor-like devices.Comment: 10 pages, 10 figure
Controlling spin relaxation in hexagonal BN-encapsulated graphene with a transverse electric field
We experimentally study the electronic spin transport in hBN encapsulated
single layer graphene nonlocal spin valves. The use of top and bottom gates
allows us to control the carrier density and the electric field independently.
The spin relaxation times in our devices range up to 2 ns with spin relaxation
lengths exceeding 12 m even at room temperature. We obtain that the ratio
of the spin relaxation time for spins pointing out-of-plane to spins in-plane
is 0.75 for zero applied perpendicular
electric field. By tuning the electric field this anisotropy changes to
0.65 at 0.7 V/nm, in agreement with an electric field tunable in-plane
Rashba spin-orbit coupling
Carbon nanotube: a low-loss spin-current waveguide
We demonstrate with a quantum-mechanical approach that carbon nanotubes are
excellent spin-current waveguides and are able to carry information stored in a
precessing magnetic moment for long distances with very little dispersion and
with tunable degrees of attenuation. Pulsed magnetic excitations are predicted
to travel with the nanotube Fermi velocity and are able to induce similar
excitations in remote locations. Such an efficient way of transporting magnetic
information suggests that nanotubes are promising candidates for memory devices
with fast magnetization switchings
Massive scalar field near a cosmic string
The function of a massive scalar field near a cosmic string is
computed and then employed to find the vacuum fluctuation of the field. The
vacuum expectation value of the energy-momentum tensor is also computed using a
point-splitting approach. The obtained results could be useful also for the
case of self-interacting scalar fields and for the finite-temperature Rindler
space theory.Comment: 15 pages, standard LaTeX, no figures. Reference [14] correcte
Experimental observation of quantum entanglement in low dimensional spin systems
We report macroscopic magnetic measurements carried out in order to detect
and characterize field-induced quantum entanglement in low dimensional spin
systems. We analyze the pyroborate MgMnB_2O_5 and the and the warwickite
MgTiOBO_3, systems with spin 5/2 and 1/2 respectively. By using the magnetic
susceptibility as an entanglement witness we are able to quantify entanglement
as a function of temperature and magnetic field. In addition, we experimentally
distinguish for the first time a random singlet phase from a Griffiths phase.
This analysis opens the possibility of a more detailed characterization of low
dimensional materials
Vacuum Polarization at Finite Temperature around a Magnetic Flux Cosmic String
We consider a general situation where a charged massive scalar field
at finite temperature interacts with a magnetic flux cosmic string.
We determine a general expression for the Euclidean thermal Green's function of
the massive scalar field and a handy expression for a massless scalar field.
With this result, we evaluate the thermal average and the
thermal average of the energy-momentum tensor of a nonconformal massless scalar
field.Comment: 22 pages, latex, no figure
Vacuum Polarization in the Spacetime of a Scalar-Tensor Cosmic String
We study the vacuum polarization effect in the spacetime generated by a
magnetic flux cosmic string in the framework of a scalar-tensor gravity. The
vacuum expectation values of the energy-momentum tensor of a conformally
coupled scalar field are calculated. The dilaton's contribution to the vacuum
polarization effect is shown explicitly.Comment: 11 pages, LATEX file, 2 eps figure
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