168 research outputs found
Molecular Spins for Quantum Information Technologies
Technological challenges for quantum information technologies lead us to consider aspectsof molecular magnetism in a radically new perspective. The design of new derivatives and recentexperimental results on molecular nanomagnets are covered in this tutorial review through thekeyhole of basic concepts of quantum information, such as the control of decoherence andentanglement at the (supra-)molecular level
Magnetocaloric effect in hexacyanochromate Prussian blue analogs
We report on the magnetocaloric properties of two molecule-based
hexacyanochromate Prussian blue analogs, nominally CsNi[Cr(CN)_6](H_2O) and
Cr_3[Cr(CN)_6]_2x12(H_2O). The former orders ferromagnetically below Tc=90 K,
whereas the latter is a ferrimagnet below Tc=230 K. For both, we find
significantly large magnetic entropy changes DSm associated to the magnetic
phase transitions. Notably, our studies represent the first attempt to look at
molecule-based materials in terms of the magnetocaloric effect for temperatures
well above the liquid helium range.Comment: 4 pages, 6 figure
Molecular Spins in the Context of Quantum Technologies
Molecular spins have shown interesting quantum features which make them potential candidates for the implementation of quantum information processing. New challenges related to possible applications in broader class of quantum technologies are currently under discussion. Here, we revisit some key features trying to learn something from experiences in near fields
Coherent coupling of molecular spins with microwave photons in planar superconducting resonators
Within the quest for solid state quantum systems to be
used for fundamental as well as applied research, molecular
spins have recently emerged as a versatile platform with
interesting performances in terms of quantum coherence and
correlation. Molecular units provide well defined environment
to electronic spins and they represent elementary bricks for
complex nano-architectures and nano-devices. Here we review
our recent efforts and results on their efficient integration in
circuit Quantum ElectroDynamics and, more specifically, in
reaching their coherent coupling with microwave photons in
planar resonators. To monitor molecular spin performances
over a wide temperature and magnetic field range we have
first developed microwave planar resonators made of high
Tc superconductors, obtaining excellent performances up
to liquid Nitrogen temperature and in magnetic fields up to
7 Tesla. Ensembles of different molecular spins systems are
then systematically tested. The regime of high spin-photon
cooperativity is achieved with molecular spins diluted in nonmagnetic
matrix at 0.5 K, while the strong coupling regime is
observed with concentrated samples of organic radicals up to
50 K. The possibility to create coherent states among distinct
spin ensembles is further explored in similar spectroscopic
experiments. These results show that molecular spins can be
efficiently integrated in quantum devices
Graphene Spintronic Devices with Molecular Nanomagnets.
The possibility to graft nano-objects directly on its surface makesgraphene particularly appealing for device and sensing applications. Here we reportthe design and the realization of a novel device made by a graphene nanoconstrictiondecorated with TbPc2 magnetic molecules (Pc = phthalocyananine), to electricallydetect the magnetization reversal of the molecules in proximity with graphene. Amagnetoconductivity signal as high as 20% is found for the spin reversal, revealing theuniaxial magnetic anisotropy of the TbPc2 quantum magnets. These results depict thebehavior of multiple-field-effect nanotransistors with sensitivity at the single-molecule level
Observation of different charge transport regimes and large magnetoresistance in graphene oxide layers
We report a systematic study on charge transport properties of thermally reduced graphene
oxide (rGO) layers, from room temperature to 2 K and in presence of magnetic fields up to
7 T. The most conductive rGO sheets follow different transport regimes: at room temperature
they show an Arrhenius-like behavior. At lower temperature they exhibits a thermally
activated behavior with resistance R following a R = R0exp(T0/T)p law with p = 1/3, consistently
with 2D Mott Variable Range Hopping (VRH) transport mechanism. Below a given
temperature Tc, we observe a crossover from VHR to another regime, probably due to a
shortening of the characteristic lengths of the disordered 2D system. The temperature Tc
depends on the reduction grade of the rGO. Magnetoresistance DR/R of our rGO films shows
as well a crossover between positive and negative and below liquid He temperature DR/R
reaches values larger than 60%, surprisingly high for a \u2013 nominally \u2013 non magnetic
material
Microstrip Resonators and Broadband Lines for X-band EPR Spectroscopy of Molecular Nanomagnets
We present a practical setup to perform continuous-wave X-band
electron paramagnetic resonance spectroscopy by using planar microstrip lines and
general purpose instrumentation. We fabricated Ag/alumina and Nb/sapphire microstrip
resonators and transmission lines and compared their performance down to
2 K and under applied magnetic field. We used these devices to study single crystals
of molecular Cr3 nanomagnets. By means of X-band planar resonators we measured
angle-dependent spectra at fixed frequency, while broadband transmission lines
were used to measure continuous wave spectra with varying frequency in the range
2–25 GHz. The spectra acquired at low temperatures allowed to extract the essential
parameters of the low-lying energy levels of Cr3 and demonstrate that this method is
particularly suitable to study small crystals of molecular nanomagnets
Coherently coupling distinct spin ensembles through a high-Tc superconducting resonator
The problem of coupling multiple spin ensembles through cavity photons is revisited by using (3,5-dichloro-4- pyridyl)bis(2,4,6-trichlorophenyl) methyl (PyBTM) organic radicals and a high-T-c superconducting coplanar resonator. An exceptionally strong coupling is obtained and up to three spin ensembles are simultaneously coupled. The ensembles are made physically distinguishable by chemically varying the g factor and by exploiting the inhomogeneities of the applied magnetic field. The coherent mixing of the spin and field modes is demonstrated by the observed multiple anticrossing, along with the simulations performed within the input-output formalism, and quantified by suitable entropic measures
Hall-effect studies in YBa2Cu3O7/PrBa2Cu3O7 superlattices
We measured the resistivity and the Hall coefficient RH in a series of YBa2Cu3O7/PrBa2Cu3O7 multilayers. We found no systematic change of the transport properties with decreasing layer thicknesses down to one unit cell. The resistivity and RH evaluated for the YBa2Cu3O7 layers are slightly higher than in bulk material, suggesting a small decrease of the carrier density in the multilayers. However, we observe no change in the Hall number 1/eRH when the thickness of the YBa1Cu3O7 layers decreases, so that the lowering of Tc observed in the superlattices cannot simply be related to a change in the carrier density. Furthermore, we find that the temperature dependence of RH is very similar to that of bulk materials
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