Searcharxiv⌕ Search

arXiv subjects

George Kastrinakis

Publications and source records attributed to George Kastrinakis.

At least 19 recordsLinked to original sources
arXiv2023

Theoretical model for the extreme positive magnetoresistance

We present a model for the positive extreme magnetoresistance (XMR), recently observed in a plethora of metallic systems, such as PtSn$_4$, PtBi$_2$, PdCoO$_2$, WTe$_2$, NbSb$_2$, NbP, TaSb$_2$, LaSb, LaBi, ZrSiS and MoTe$_2$. The model is an extension of our earlier work on positive giant magnetoresistance, and uses an elaborate diagrammatic formulation. XMR is a bulk effect (not a surface effect), due to the dramatic sensitivity of the conductivity to the finite magnetic field $H$. This is possible at low temperatures, in the presence of finite disorder elastic spin scattering, and for a special value, predicted from the theory, of the material-dependent effective Coulomb repulsion. Good agreement with experiments is obtained. According to our model XMR is higher in cleaner samples, and anisotropic with regards to the direction of $H$. We discuss in particular compounds containing the elements Pt, Sc, and Rh.

cond-mat.str-el↗
arXiv2023

Zeeman dependence of the quasiparticle scattering rate and ARPES in copper oxides and related materials

Within a strongly interacting Fermi liquid framework, we calculate the effects of the Zeeman energy $\omega_H$ for a finite magnetic field, in a metallic system with a van Hove peak in the density of states, located close to and below the Fermi surface. We find that the chemical potential increases with the square of $\omega_H$. We obtain a characteristic quasiparticle scattering rate linear in the maximum of $\omega_H$ and temperature, both in the normal and the d-wave superconducting state. We predict that ARPES experiments in copper oxides, and related compounds, should be able to elucidate this behavior of the scattering rate, and in particular, the difference between spin up and down electrons.

cond-mat.supr-con↗
arXiv2018

Conductivity of weakly disordered metals close to a "ferromagnetic" quantum critical point

We calculate analytically the conductivity of weakly disordered metals close to a "ferromagnetic" quantum critical point in the low temperature regime. Ferromagnetic in the sense that the effective carrier potential $V(q,ω)$, due to critical fluctuations, is peaked at zero momentum $q=0$. Vertex corrections, due to both critical fluctuations and impurity scattering, are explicitly considered. We find that only the vertex corrections due to impurity scattering, combined with the self-energy, generate appreciable effects as a function of the temperature $T$ and the control parameter $a$, which measures the proximity to the critical point. Our results are consistent with resistivity experiments in several materials displaying typical Fermi liquid behavior, but with a diverging prefactor of the $T^2$ term for small $a$.

cond-mat.str-el↗
arXiv2016

Scattering rate, transport and specific heat in a metal close to a quantum critical point : emergence of a robust Fermi liquid picture ?

We calculate the low temperature one-particle scattering rate and the specific heat in a weakly disordered metal close to a quantum critical point. To lowest order in the fluctuation potential, we obtain typical Fermi-liquid results proportional to T^2 and T respectively, with prefactors which diverge as a power law of the control parameter upon approaching the critical point. The Kadowaki-Woods ratio is shown to be independent of the control parameter only for the case of 3-D FM fluctuations. Our work is relevant for experiments on CeCoIn$_5$ and Sr_3Ru_2O_7.

cond-mat.str-el↗
arXiv2016

Fermi liquid behaviour in weakly disordered metals close to a quantum critical point

We calculate analytically the low temperature quasi-particle scattering rate, the conductivity, and the specific heat in weakly disordered metals close to a quantum critical point, via the use of a proper fluctuation potential $V(q,ω)$ between the quasi-particles. We obtain typical Fermi liquid results proportional to $T^2$ and $T$ respectively, with prefactors which diverge as power laws of the control parameter $a$ upon approaching the critical point. The Kadowaki-Woods ratio is shown to be independent of $a$ (possibly times a logarithmic dependence on $a$) only for the case of three-dimensional ferromagnetic fluctuations. Our results are consistent with experiments on the eight materials CeCoIn$_5$, Sr$_3$Ru$_2$O$_7$, YbRh$_2$Si$_2$, La$_{2-x}$Ce$_x$CuO$_4$, Tl$_2$Ba$_2$CuO$_{6+x}$, CeAuSb$_2$, YbAlB$_4$, and CeRuSi$_2$.

cond-mat.str-el↗
arXiv2014

Variational wavefunction for multi-species spinful fermionic superfluids and superconductors

We introduce a new fermionic variational wavefunction, generalizing the Bardeen-Cooper-Schrieffer (BCS) wavefunction, which is suitable for interacting multi-species spinful systems and sustaining superfluidity. Applications range from quark matter to the high temperature superconductors. A wide class of Hamiltonians, comprising interactions and hybridization of arbitrary momentum dependence between different fermion species, can be treated in a comprehensive manner. This is the case, as both the intra-species and the inter-species interactions are treated on equally rigorous footing, which is accomplished via the introduction of a new quantum index attached to the fermions. The index is consistent with known fermionic physics, and allows for heretofore unaccounted for fermion-fermion correlations. We have derived the finite temperature version of the theory, thus obtaining the renormalized quasiparticle dispersion relations, and we discuss the appearance of charge and spin density wave order. We present numerical solutions for two electron species in 2 dimensions. Based on these solutions, we show that, for equivalent spin up and down fermions, the Fermi occupation factor (per spin) equals 1/2 deep in the Fermi sea. This constitutes a unique experimental prediction of the theory, both for the normal and superfluid states. Interestingly, this result, obtained in the thermodynamic limit, is consistent with Fermi occupation factor (in-)equalities for finite systems of electrons, derived (in a different context) by Borland and Dennis, J. Phys. B {\bf 5}, 7 (1972) and by Altunbulak and Klyachko, Commun. Math. Phys. {\bf 282}, 287 (2008).

cond-mat.supr-con↗
arXiv2012

A fermionic superfluid state for many spinful species - II

In a previous report (arxiv:0901.2487), we introduced a new fermionic variational wavefunction, suitable for interacting multi-species systems and sustaining superfluidity. This wavefunction contains a new quantum index. Here we introduce a spin triplet version of this wavefunction, with parallel spin pairs only. We also present a single fermion species wavefunction, which may be relevant for the problem of the BCS to BEC transition.

cond-mat.supr-con↗
arXiv2012

A fermionic superfluid state for many spinful species - III

In previous reports (arXiv:0901.2487, arXiv:1007.0745), we introduced a new fermionic variational wavefunction, suitable for interacting multi-species systems and sustaining superfluidity. This disentangled wavefunction contains a new quantum index. Here we introduce a general spin triplet version of this wavefunction.

cond-mat.supr-con↗
arXiv2010

Microscopic Bardeen-Cooper-Schrieffer formulation of the critical temperature of multilayer copper-oxide superconductors

We study superconductivity in multilayer copper oxides, in the frame of a realistic microscopic formulation. Solving the full temperature dependent BCS gap equations, we obtain a maximum in the transition temperature Tc for M=3 or 4 CuO2 layers in the unit cell for appropriate values of the interlayer tunneling (negative pair tunneling), and via the consideration of the doping imbalance between the inner and outer layers. This is the ubiquitous experimental result for Ca intercalated copper oxides, as opposed to other intercalating elements. Further, using a restricted set of parameters, we obtain an exact fit of Tc(M=1-4) for five different Ca intercalated homologuous copper oxide families.

cond-mat.supr-con↗
arXiv2009

An effective 1-band model for the cuprate superconductors

Starting from the copper-oxygen Hamiltonian of the CuO2 planes, we derive analytically an extended 1-band Hubbard Hamiltonian for the electrons on copper sites, through a canonical transformation which eliminates the oxygen sites. The model sustains a variety of phases : checkerboard states, stripes, antiferromagnetism, local pairs and mixtures thereof. This approach may be helpful in understanding what is so special about the CuO2 planes, as opposed to other compounds.

cond-mat.supr-con↗
arXiv2005

Low temperature dephasing saturation from elastic magnetic spin disorder and interactions

We treat the question of the low temperature behavior of the dephasing rate of the electrons in the presence of elastic spin disorder scattering and interactions. In the frame of a self-consistent diagrammatic treatment, we obtain saturation of the dephasing rate in the limit of low temperature for magnetic scattering, in agreement with the non-interacting case. The magnitude of the dephasing rate is set by the strength of the magnetic scattering rate. We discuss the agreement of our results with relevant experiments.

cond-mat.dis-nn↗
arXiv2005

Quasiparticle scattering rate in overdoped superconducting cuprates

We calculate the quasiparticle scattering rate in the superconducting state of the overdoped cuprates, in the context of the Eliashberg formalism for a Fermi liquid with strong van Hove singularities close to the chemical potential. For a $d_{x^2-y^2}$ superconducting gap, we demonstrate analytically that the scattering rate is linear in the maximum of temperature or energy, but with different intercepts and momentum dependence. We discuss our results in view of angle-resolved photoemission experiments. We also discuss the case of a s-wave gap.

cond-mat.supr-con↗
arXiv2004

Metal-insulator transition in 2D: the role of interactions and disorder

We present a model for the metal-insulator transition in 2D, observed in the recent years. Our starting point consists of two ingredients only, which are ubiquitous in the experiments: Coulomb interactions and weak disorder spin-orbit scattering (coming from the interfaces of the heterostructures in question). In a diagramatic approach, we predict the existence of a characteristic temperature $T_o=T_o(n,ω_H)$, $n$ being the density of carriers, and $ω_H$ the Zeeman energy, below which these systems become metallic. This is in very good agreement with experiments, and corroborates the fact that varying $n$ and $ω_H$ are equivalent ways into/out of the metallic regime. The resistivity, calculated as a function of temperature and $\om_H$ in the metallic state, compares favorably to experiment. We comment on the nature of the transition, and calculate the specific heat of the system.

cond-mat.dis-nn↗
arXiv2002

Dephasing from interactions and spin disorder

We calculate the dephasing rate of the electrons in the presence of interactions and elastic spin disorder scattering. In the frame of a self-consistent diagrammatic treatment, we obtain saturation of the dephasing rate in the limit of zero temperature for spin-orbit disorder in 2 dimensions. This result is in agreement with relevant experiments.

cond-mat.dis-nn↗
arXiv2001

Interface roughness and planar doping in superlattices: weak localization effects

We examine the effects of interface roughness and/or planar impurity doping in a superlattice, in the frame of a weak disorder description. We find that these two types of disorder are equivalent, and that they can be viewed as effective "bulk" disorder, with anisotropic diffusion coefficients. Our results offer quantitative insight to transport properties of multilayers and devices, which contain inadvertently structural disorder at the interfaces.

cond-mat.dis-nn↗
arXiv2001

A common origin for the resistivity of Cd$_2$Re$_2$O$_7$, the cuprates, and Sr$_2$RuO$_4$?

We propose an explanation for the temperature dependence of the resistivity of Cd$_2$Re$_2$O$_7$, including the regime above the structural phase transition at $T$=200 $^o$K. The mechanism involved relies on the existence of a strong van Hove singularity close to the Fermi surface, which is evidenced by relevant band structure calculations. The same mechanism has successfully described the $T$-linear resistivity of the cuprates and Sr$_2$RuO$_4$, and the one-particle scattering rate in the former materials, as corroborated by recent experiments. We describe a few predictions for Cd$_2$Re$_2$O$_7$ and Cd$_2$Os$_2$O$_7$.

cond-mat.str-el↗