Publications by authors named "Gianluca Giovannetti"

18 Publications

  • Page 1 of 1

Conflicting evidence for ferroelectricity.

Nature 2017 07;547(7662):E9-E10

Department of Chemistry, Life Science and Environmental Sustainability, Parma University and INSTM-UdR Parma, 43124 Parma, Italy.

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http://dx.doi.org/10.1038/nature22801DOI Listing
July 2017

Design of a Mott Multiferroic from a Nonmagnetic Polar Metal.

Phys Rev Lett 2015 Aug 20;115(8):087202. Epub 2015 Aug 20.

Department of Materials Science and Engineering, Northwestern University, Illinois 60208-3108, USA.

We examine the electronic properties of the newly discovered "ferroelectric metal" LiOsO3 combining density-functional and dynamical mean-field theories. We show that the material is close to a Mott transition and that electronic correlations can be tuned to engineer a Mott multiferroic state in the 1/1 superlattice of LiOsO3 and LiNbO3. We use electronic structure calculations to predict that the (LiOsO3)1/(LiNbO3)1 superlattice exhibits strong coupling between magnetic and ferroelectric degrees of freedom with a ferroelectric polarization of 41.2  μC cm(-2), Curie temperature of 927 K, and Néel temperature of 379 K. Our results support a route towards high-temperature multiferroics, i.e., driving nonmagnetic polar metals into correlated insulating magnetic states.
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http://dx.doi.org/10.1103/PhysRevLett.115.087202DOI Listing
August 2015

Hemolysis in patients with antibody deficiencies on immunoglobulin replacement treatment.

Transfusion 2015 May 22;55(5):1067-74. Epub 2014 Dec 22.

Unit of Immunohematology and Transfusion Medicine, Sapienza University of Rome, Rome, Italy.

Background: Immunoglobulin (Ig)G replacement with intravenous or subcutaneous immunoglobulins is a lifelong substitutive therapy in patients with primary antibody deficiencies (PADs). Hemolysis after immunoglobulin therapy was described in patients receiving high immunoglobulin dosages. The issue of hemolysis after immunoglobulin administration at replacement doses has been considered of little clinical significance.

Study Design And Methods: This was a single-center observational study over a 2-year period on immunoglobulin-induced hemolysis in a cohort of 162 patients with PADs treated with immunoglobulin administered at replacement dosages.

Results: Six patients had signs and symptoms of immunoglobulin-induced hemolysis. Two additional asymptomatic patients were identified by a short-term study run on 16 randomly selected asymptomatic patients. Alloantibodies eluted from patients' red blood cells (RBCs) had anti-A and Rh specificities (anti-D and anti-C). The immunoglobulins contained alloantibodies with the same specificities of the antibodies eluted from patients' RBCs.

Conclusion: Hemolysis occurred in patients receiving immunoglobulin at replacement dosages. Polyvalent immunoglobulin preparations contained multiple clinically significant antibodies that could have unexpected hemolytic consequences, as anti-C whose research and titration are not required by the European Pharmacopoeia. The issue of hemolysis in long-term recipients of immunoglobulin treatment administered at replacement dosages should be more widely recognized.
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http://dx.doi.org/10.1111/trf.12939DOI Listing
May 2015

Selective Mott physics as a key to iron superconductors.

Phys Rev Lett 2014 May 28;112(17):177001. Epub 2014 Apr 28.

CNR-IOM-Democritos National Simulation Centre and International School for Advanced Studies (SISSA), Via Bonomea 265, I-34136, Trieste, Italy.

We show that electron- and hole-doped BaFe(2)As(2) are strongly influenced by a Mott insulator that would be realized for half-filled conduction bands. Experiments show that weakly and strongly correlated conduction electrons coexist in much of the phase diagram, a differentiation which increases with hole doping. This selective Mottness is caused by the Hund's coupling effect of decoupling the charge excitations in different orbitals. Each orbital then behaves as a single-band doped Mott insulator, where the correlation degree mainly depends on how doped is each orbital from half filling. Our scenario reconciles contrasting evidences on the electronic correlation strength, implies a strong asymmetry between hole and electron doping, and establishes a deep connection with the cuprates.
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http://dx.doi.org/10.1103/PhysRevLett.112.177001DOI Listing
May 2014

Visceral leishmaniasis presenting with paroxysmal cold haemoglobinuria.

Blood Transfus 2014 Jan 3;12 Suppl 1:s141-3. Epub 2013 Jul 3.

Department of Cellular Biotechnologies and Haematology, Division of Haematology, "Sapienza" University, Rome, Italy.

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http://dx.doi.org/10.2450/2013.0034-13DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3934238PMC
January 2014

Diisopropylammonium bromide is a high-temperature molecular ferroelectric crystal.

Science 2013 Jan;339(6118):425-8

Ordered Matter Science Research Centre, Southeast University, Nanjing 211189, China.

Molecular ferroelectrics are highly desirable for their easy and environmentally friendly processing, light weight, and mechanical flexibility. We found that diisopropylammonium bromide (DIPAB), a molecular crystal processed from aqueous solution, is a ferroelectric with a spontaneous polarization of 23 microcoulombs per square centimeter [close to that of barium titanate (BTO)], high Curie temperature of 426 kelvin (above that of BTO), large dielectric constant, and low dielectric loss. DIPAB exhibits good piezoelectric response and well-defined ferroelectric domains. These attributes make it a molecular alternative to perovskite ferroelectrics and ferroelectric polymers in sensing, actuation, data storage, electro-optics, and molecular or flexible electronics.
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http://dx.doi.org/10.1126/science.1229675DOI Listing
January 2013

Microscopic origin of large negative magnetoelectric coupling in Sr(1/2)Ba(1/2)MnO3.

Phys Rev Lett 2012 Sep 7;109(10):107601. Epub 2012 Sep 7.

CNR-IOM-Democritos National Simulation Centre and International School for Advanced Studies (SISSA), Trieste, Italy.

With a combined ab initio density functional and model Hamiltonian approach we establish that in the recently discovered multiferroic phase of the manganite Sr(1/2)Ba(1/2)MnO3 the polar distortion of Mn and O ions is stabilized via enhanced in-plane Mn-O hybridizations. The magnetic superexchange interaction is very sensitive to the polar bond-bending distortion, and we find that this dependence directly causes a strong magnetoelectric coupling. This novel mechanism for multiferroicity is consistent with the experimentally observed reduced ferroelectric polarization upon the onset of magnetic ordering.
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http://dx.doi.org/10.1103/PhysRevLett.109.107601DOI Listing
September 2012

Proximity of iron pnictide superconductors to a quantum tricritical point.

Nat Commun 2011 Jul 19;2:398. Epub 2011 Jul 19.

Dipartimento di Fisica, Università di Roma 'La Sapienza', P. Aldo Moro 2, Roma 00185, Italy.

In several materials, unconventional superconductivity appears nearby a quantum phase transition where long-range magnetic order vanishes as a function of a control parameter like charge doping, pressure or magnetic field. The nature of the quantum phase transition is of key relevance, because continuous transitions are expected to favour superconductivity, due to strong fluctuations. Discontinuous transitions, on the other hand, are not expected to have a similar role. Here we determine the nature of the magnetic quantum phase transition, which occurs as a function of doping, in the iron-based superconductor LaFeAsO(1-x)F(x). We use constrained density functional calculations that provide ab initio coefficients for a Landau order parameter analysis. The outcome is intriguing, as this material turns out to be remarkably close to a quantum tricritical point, where the transition changes from continuous to discontinuous, and several susceptibilities diverge simultaneously. We discuss the consequences for superconductivity and the phase diagram.
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http://dx.doi.org/10.1038/ncomms1407DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3160143PMC
July 2011

High-T(c) ferroelectricity emerging from magnetic degeneracy in cupric oxide.

Phys Rev Lett 2011 Jan 12;106(2):026401. Epub 2011 Jan 12.

Consiglio Nazionale delle Ricerche CNR-SPIN L'Aquila, Italy.

Cupric oxide is multiferroic at unusually high temperatures. From density functional calculations we find that the low-T magnetic phase is paraelectric, and the higher-T one is ferroelectric with a size and direction of polarization in good agreement with experiments. By mapping the ab initio results on to an effective spin model, we show that the system has a manifold of almost degenerate ground states. In the high-T magnetic state noncollinearity and inversion symmetry breaking stabilize each other via the Dzyaloshinskii-Moriya interaction. This leads to an unconventional mechanism for multiferroicity, with the particular property that nonmagnetic impurities enhance the effect.
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http://dx.doi.org/10.1103/PhysRevLett.106.026401DOI Listing
January 2011

Multiferroicity in TTF-CA organic molecular crystals predicted through ab initio calculations.

Phys Rev Lett 2009 Dec 28;103(26):266401. Epub 2009 Dec 28.

Consiglio Nazionale delle Ricerche-Istituto Nazionale per la Fisica della Materia (CNR-INFM), CASTI Regional Laboratory, 67100 L'Aquila, Italy.

We show by means of ab initio calculations that the organic molecular crystal TTF-CA is multiferroic: it has an instability to develop spontaneously both ferroelectric and magnetic ordering. Ferroelectricity is driven by a Peierls transition of the TTF-CA in its ionic state. Subsequent antiferromagnetic ordering strongly enhances the opposing electronic contribution to the polarization. It is so large that it switches the direction of the total ferroelectric moment. Within an extended Hubbard model, we capture the essence of the electronic interactions in TTF-CA, confirm the presence of a multiferroic groundstate, and clarify how this state develops microscopically.
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http://dx.doi.org/10.1103/PhysRevLett.103.266401DOI Listing
December 2009

Above-room-temperature ferroelectricity in a single-component molecular crystal.

Nature 2010 Feb;463(7282):789-92

National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8562, Japan.

Ferroelectrics are electro-active materials that can store and switch their polarity (ferroelectricity), sense temperature changes (pyroelectricity), interchange electric and mechanical functions (piezoelectricity), and manipulate light (through optical nonlinearities and the electro-optic effect): all of these functions have practical applications. Topological switching of pi-conjugation in organic molecules, such as the keto-enol transformation, has long been anticipated as a means of realizing these phenomena in molecular assemblies and crystals. Croconic acid, an ingredient of black dyes, was recently found to have a hydrogen-bonded polar structure in a crystalline state. Here we demonstrate that application of an electric field can coherently align the molecular polarities in crystalline croconic acid, as indicated by an increase of optical second harmonic generation, and produce a well-defined polarization hysteresis at room temperature. To make this simple pentagonal molecule ferroelectric, we switched the pi-bond topology using synchronized proton transfer instead of rigid-body rotation. Of the organic ferroelectrics, this molecular crystal exhibits the highest spontaneous polarization ( approximately 20 muC cm(-2)) in spite of its small molecular size, which is in accord with first-principles electronic-structure calculations. Such high polarization, which persists up to 400 K, may find application in active capacitor and nonlinear optics elements in future organic electronics.
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http://dx.doi.org/10.1038/nature08731DOI Listing
February 2010

Multiferroicity in rare-earth nickelates RNiO3.

Phys Rev Lett 2009 Oct 7;103(15):156401. Epub 2009 Oct 7.

Institute Lorentz for Theoretical Physics, Leiden University, 2300 RA Leiden, The Netherlands.

We show that charge ordered rare-earth nickelates of the type RNiO3 (R = Ho, Lu, Pr and Nd) are multiferroic with very large magnetically-induced ferroelectric (FE) polarizations. This we determine from first principles electronic structure calculations. The emerging FE polarization is directly tied to the long-standing puzzle of which kind of magnetic ordering is present in this class of materials: its direction and size indicate the type of ground-state spin configuration that is realized. Vice versa, the small energy differences between the different magnetic orderings suggest that a chosen magnetic ordering can be stabilized by cooling the system in the presence of an electric field.
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http://dx.doi.org/10.1103/PhysRevLett.103.156401DOI Listing
October 2009

Magnetically induced electronic ferroelectricity in half-doped manganites.

Phys Rev Lett 2009 Jul 17;103(3):037601. Epub 2009 Jul 17.

Institute Lorentz for Theoretical Physics, Leiden University, Leiden, The Netherlands.

Using a joint approach of density functional theory and model calculations, we demonstrate that a prototypical charge ordered half-doped manganite La1/2Ca1/2MnO3 is multiferroic. The combination of a peculiar charge-orbital ordering and a tendency to form spin dimers breaks the inversion symmetry and leads to a ferroelectric ground state with a polarization up to several microC/cm2. The presence of improper ferroelectricity does not depend on the hotly debated structural details of this material: in the Zener-polaron structure we find a similar ferroelectric response with a large polarization of purely magnetic origin.
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http://dx.doi.org/10.1103/PhysRevLett.103.037601DOI Listing
July 2009

Electronic correlations decimate the ferroelectric polarization of multiferroic homn2o5.

Phys Rev Lett 2008 Jun 5;100(22):227603. Epub 2008 Jun 5.

Institute Lorentz for Theoretical Physics, Leiden University, P.O. Box 9506, 2300 RA Leiden, The Netherlands.

We show that electronic correlations decimate the intrinsic ferroelectric polarization of multiferroic manganites RMn2O5, where R is a rare earth element. Such is manifest from ab initio band structure computations that account for the Coulomb interactions between the manganese 3d electrons--the root of magnetism in RMn2O5. Including these leads to an amplitude and direction of polarization of HoMn2O5 that agree with experiment. The decimation is caused by a near cancellation of the ionic polarization induced by the lattice and the electronic one due to valence charge redistributions.
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http://dx.doi.org/10.1103/PhysRevLett.100.227603DOI Listing
June 2008

Multiferroicity induced by dislocated spin-density waves.

Phys Rev Lett 2007 Jun 20;98(25):257602. Epub 2007 Jun 20.

School of Physics and Astronomy, Scottish Universities Physics Alliance, University of St. Andrews, North Haugh KY16 9SS, United Kingdom.

We uncover a new pathway towards multiferroicity, showing how magnetism can drive ferroelectricity without relying on inversion symmetry breaking of the magnetic ordering. Our free-energy analysis demonstrates that any commensurate spin-density-wave ordering with a phase dislocation, even if it is collinear, gives rise to an electric polarization. Because of the dislocation, the electronic and magnetic inversion centers do not coincide, which turns out to be a sufficient condition for multiferroic coupling. The novel mechanism explains the formation of multiferroic phases at the magnetic commensurability transitions, such as the ones observed in YMn(2)O(5) and related compounds. We predict that in these multiferroics an oscillating electrical polarization is concomitant with the uniform polarization. On the basis of our theory, we put forward new types of magnetic materials that are potentially ferroelectric.
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http://dx.doi.org/10.1103/PhysRevLett.98.257602DOI Listing
June 2007