1,721,114 research outputs found
The Ancient Romans’ Route to Charge Density Waves in Cuprates
Full text linkAn account is given of the main steps that led the research group in Rome, to which the author belongs, to the formulation of the charge-density-wave scenario for high-T-c superconducting cuprates. The early finding of the generic tendency of strongly correlated electron systems with short range interactions to undergo electron phase separation was subsequently contrasted with the homogenizing effect of the long-range Coulomb interaction. The two effects can find a compromise in the formation of incommensurate charge density waves. These charge density waves are inherently dynamical and are overdamped as a consequence of the possibility to decay in electron-hole pairs, yet tend to maintain a (quantum) critical character, which is mirrored in their marked momentum and frequency dependence and in their strong variation with temperature and doping. These dynamical incommensurate charge density waves act as mediators of pairing lading to high-T-c superconductivity, and provide the scattering mechanism that produces the observed violation of the Fermi-liquid paradigm in the metallic phase
Effect of carrier confinement on exchange coupling in dilute magnetic semiconductors with self-organized nanocolumns
No full textThe "carrier-confinement" model for phase-separated dilute magnetic semiconductors is proposed, in which the carrier scattering by ferromagnetic strings embedded into a semiconductor host leads to the appearance of quasi-one-dimensional spin-polarized states inside the energy gap of the three-dimensional spectrum. Quasiparticle excitations from these states to the band edge mediate an efficient interstring exchange even in the absence of free carriers in the host. The related exchange integral can switch between ferromagnetic and antiferromagnetic with varying both the interstring distance and the filling of the quasi-one-dimensional spin-polarized states. We discuss the applicability of our model for the description of the magnetic behavior of the array of Mn-rich nanocolumns inserted into a Mn-depleted host in phase-separated (Ge,Si):Mn alloys
Effect of a lattice dimerization on a system with coexisting charge and spin density waves
No full textOxide interfaces: Spin-to-charge current conversion
No full textThe concept of spintronics (short for spin transport electronics) was first developed in the 1980s and rests on the idea that information can be stored, transferred and processed by means of the spin of the electrons, and that spins can be manipulated not only by magnetic fields but also by electric fields. Among the various pathways towards spintronics proposed so far, the most promising seems to be related to the spin Hall effect: in the presence of spin–orbit interactions, the motion of electrons is coupled to their spin so that a charge current flowing through a specimen characterized by a sizable spin–orbit interaction produces a transverse spin current, polarized in the direction perpendicular to both currents (charge-to-spin conversion). The converse (spin-to-charge conversion) can also be achieved. Edouard Lesne and colleagues1 now report that, taking advantage of the strong spin–orbit coupling existing at certain oxide interfaces such as LaAlO3/SrTiO3, gate-tunable spin-to-charge conversion with unprecedentedly high efficiency is achievable
Gap and pseudogap evolution in underdoped cuprates
No full textWe describe the spectral properties of underdoped cuprates as resulting from a momentum-dependent pseudogap in the normal-state spectrum. Such a model accounts, within a BCS approach, for the doping dependence of the critical temperature and of the leading-edge shift observed in the cuprates. We also reproduce the T-c - T* bifurcation near optimum doping
Ground-state magnetic properties of the Kondo lattice model at low electron densities
No full textThe infinite-size version of the density-matrix renormalization-group approach in real space is applied to the Kondo lattice model in one dimension, providing a more accurate determination of the zero-temperature magnetic properties for electron densities n less than or equal to 0.5. The paramagnetic state of the free model evolves into a state with ferromagnetic correlations, by increasing the strength of the Kondo coupling, in agreement with previous numerical results. The change in the magnetic properties is produced by the competition between the RKKY mechanism, which favours the paramagnetic state in the weak-coupling region, and the Kondo screening, which leads to the formation of tightly bound singlets in the strong-coupling region, enforcing ferromagnetic correlations in the system
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