arXiv subjects

Carlo Di Castro

Publications and source records attributed to Carlo Di Castro.

6 recordsLinked to original sources

arXiv2026

The charge density fluctuations and the Shrinking Fermi Liquid scenario for strange metallicity in cuprates

We interpret the strange metal (SM) properties of slightly overdoped cuprates in terms of the recently proposed Shrinking Fermi Liquid theory. This is based on the pervading presence in the cuprate phase diagram of charge density fluctuations (CDF), which have been identified and characterized in RIXS. These fluctuations are abundant and have a low energy due to the proximity of the charge density wave quantum critical point hidden under the superconducting dome of cuprates, but have a short range and non-critical character with a finite energy M/\gamma ~10 meV as measured above Tc. Here M~ \xi^-2 is determined by the short correlation length \xi, while \gamma encodes the Landau damping ruling the lifetime of the charge fluctuations. Besides these low energy CDF, cuprates also display phonons and a broad continuum of particle-hole excitations, mostly due to spin paramagnons arising from their strongly correlated character. With these experimentally characterized ingredients we show that above Tc the SM properties in transport are well described in terms of fermionic Landau quasiparticles scattering with CDF and phonons. The optical properties can instead be interpreted by the combined effect of low energy CDF determining the temperature dependence, and of the paramagnon continuum determining a linear in frequency scattering rate. Remarkably, the combined effect of these simple ingredients also induces \omega/T scaling properties for frequencies larger than M/\gamma. When superconductivity is suppressed by strong magnetic fields the SM properties extend down to a few Kelvin. By assuming that the CDF dissipation parameter \gamma grows logarithmically by lowering T, we account for all anomalous transport and thermodynamic properties of cuprates (specific heat, Seebeck, heat transport, resistivity, and magnetoresistance) thereby providing a consistent scenario for the SM phase of cuprates.

cond-mat.str-el↗

arXiv2015

Nematic fluctuations and the magneto-structural phase transition in ${\rm Ba(Fe_{1-x}Co_x)_2As_2}$

An inelastic light (Raman) scattering study of nematicity and critical fluctuations in ${\rm Ba(Fe_{1-x}Co_x)_2As_2}$ ($0\le x \le 0.051$) is presented. It is shown that the response from fluctuations appears only in $B_{1g}$ (${x^2-y^2}$) symmetry. The scattering amplitude increases towards the structural transition at $T_s$ but vanishes only below the magnetic ordering transition at $T_{\rm SDW} < T_s$, suggesting a magnetic origin of the fluctuations. The theoretical analysis explains the selection rules and the temperature dependence of the fluctuation response. These results make magnetism the favorite candidate for driving the series of transitions.%Below $T_{\rm SDW}$ the gap of the magnetically ordered phase opens up.

cond-mat.str-el↗

arXiv2014

Self-organized electronic superlattices in layered materials

We show that in layered systems with electronic phase separation tendency, the long-range Coulomb interaction can drive the spontaneous formation of unidirectional superlattices of electronic charge in a completely homogeneous crystalline background. In this self-organized electronic heterostructure, the ratio among the number of crystalline planes in the minority and majority electronic phases corresponds to Farey fractions with the superlattice period controlled by the background charge density and the frustrating Coulomb interaction strength. The phase diagram displays Arnold tongues obeying a modified Farey tree hierarchy and a devil's staircase typical of systems with frustration among different scales. We further discuss the competition of these electronic superlattices, recently observed in iron-based superconductors and mixed valence compounds, with in-plane electronically modulated phases.

cond-mat.str-el↗

arXiv2010

On the possible secondary component of the order parameter observed in London penetration depth measurements

We discuss the effect of a secondary component of the superconducting order parameter on the superfluid density in the cuprates. If we assume a main $d_{x^2-y^2}$ gap, the most stable realization of a mixed order parameter has a time-reversal breaking $d_{x^2-y^2}+ \imath d_{xy}$ symmetry. In this state the nodes are removed and the temperature dependence of the superfluid density changes from the linear behavior of a pure d-wave to a more rounded shape at low temperature. The latter is compatible with the behavior experimentally observed in the in-plane magnetic field penetration depth of optimally doped $La_{2-x}Sr_xCuO_2$ and $YBa_2Cu_3O_{7-δ}$.

cond-mat.supr-con↗

arXiv2007

Disordered loops in the two-dimensional antiferromagnetic spin-fermion model

The spin-fermion model has long been used to describe the quantum-critical behavior of 2d electron systems near an antiferromagnetic (AFM) instability. Recently, the standard procedure to integrate out the fermions to obtain an effective action for spin waves has been questioned in the clean case. We show that in the presence of disorder, the single fermion loops display two crossover scales: upon lowering the energy, the singularities of the clean fermionic loops are first cut off, but below a second scale new singularities arise that lead again to marginal scaling. In addition, impurity lines between different fermion loops generate new relevant couplings which dominate at low energies. We outline a non-linear sigma model formulation of the single-loop problem, which allows to control the higher singularities and provides an effective model in terms of low-energy diffusive as well as spin modes.

cond-mat.str-el↗

arXiv2006

Disordered Electron Systems

These lectures provide an introduction to the theory of disordered interacting electron systems. In particular, we concentrate on those aspects which are fundamental for the problem of the metal-insulator transition due to the interplay of disorder and interaction. After reviewing the problem of disordered non-interacting electrons, we examine the past and recent experimental urgency to take into account interaction effects. We describe, by using the language of standard perturbation theory, how these interactions effects lead to the picture of the renormalized disordered Fermi liquid. This allows us to obtain the renormalization group equations for the disordered interacting electron liquid. The group equations are then discussed by the light of the existing experimental evidence.

cond-mat.dis-nn↗