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G. S. Lozano

Publications and source records attributed to G. S. Lozano.

At least 19 recordsLinked to original sources
arXiv2025

Vortex flow anisotropy in nematic superconductors

We investigate the vortex flow anisotropy in the mixed state of nematic superconductors, focusing on the effects of nematic-superconducting coupling on vortex dynamics. Using numerical simulations within a time-dependent Ginzburg-Landau (TDGL) approach, we analyze vortex viscosity in a model featuring an s-wave superconducting order parameter coupled to an Ising-like nematic order parameter, suitable for systems with $C_4$ symmetry. Our results indicate that nematicity induces a significant anisotropy in the flux-flow resistivity, which depends on both vortex core shape anisotropy and normal-phase conductivity anisotropy. These two effects can either compete or cooperate with each other. We discuss the implications of these findings for identifying nematic superconductivity in the superconducting phase. Our work provides new insights into the interplay between nematic and superconducting order parameters, leading to new possibilities for experimental and theoretical exploration of anisotropic transport properties in unconventional superconductors.

cond-mat.supr-con↗
arXiv2019

Nematicity in the superconducting mixed state of strain detwinned underdoped $\text{Ba}(\text{Fe}_{1-x}\text{Co}_x)_2\text{As}_2$

Evidence of nematic effects in the mixed superconducting phase of slightly underdoped $\text{Ba}(\text{Fe}_{1-x}\text{Co}_x)_2\text{As}_2$ is reported. We have found strong in-plane resistivity anisotropy for crystals in different strain conditions. For these compositions, there is no magnetic long range order, so the description may be ascribed to the interplay between the superconducting and nematic order parameters. A piezoelectric-based apparatus is used to apply tensile or compressive strain to tune nematic domain orientation in order to examine intrinsic nematicity. Measurements are done under a rotating magnetic field and the analysis of the angular dependence of physical quantities identifies the cases in which the sample is {\em detwinned}. Furthermore, the angular dependence of the data allows us to evaluate the effects of nematicity on the in-plane superconductor stiffness. Our results show that although nematicity contributes in a decisive way in the conduction properties, its contributions to the anisotropy properties of the stiffness of the superconducting order parameter is not as significant in these samples.

cond-mat.supr-con↗
arXiv2011

Dynamics of superconducting vortices driven by oscillatory forces in the plastic flow regime

We study experimentally and theoretically, the reorganization of superconducting vortices driven by oscillatory forces near the plastic depinning transition. We show that the system can be taken to configurations that are tagged by the shaking parameters but keep no trace of the initial conditions. In experiments performed in $NbSe_2$ crystals, the periodic drive is induced by ac magnetic shaking fields and the overall order of the resulting configuration is determined by non invasive ac susceptibility measurements. With a model of interacting particles driven over random landscapes, we perform molecular dynamics simulations that reveal the nature of the shaking dynamics as fluctuating states similar to those predicted for other interacting particle systems.

cond-mat.supr-con↗
arXiv2010

Depinning and dynamics of AC driven vortex lattices in random media

We study the different dynamical regimes of a vortex lattice driven by AC forces in the presence of random pinning via numerical simulations. The behaviour of the different observables is charaterized as a function of the applied force amplitude for different frequencies. We discuss the inconveniences of using the mean velocity to identify the depinnig transition and we show that instead, the mean quadratic displacement of the lattice is the relevant magnitude to characterize different AC regimes. We discuss how the results depend on the initial configuration and we identify new hysteretic effects which are absent in the DC driven systems.

cond-mat.supr-con↗
arXiv2008

Ordered, disordered and coexistent stable vortex lattices in NbSe_2 single crystals

It is commonly accepted that the peak effect (PE) in the critical current density of type II superconductors is a consequence of an order-disorder transition in the vortex lattice (VL). Examination of vortex lattice configurations (VLCs) in its vicinity requires the use of experimental techniques that exclude current induced VL reorganization. By means of linear ac susceptibility experiments in the Campbell regime, where vortices are forced to oscillate (harmonically) around their effective pinning potentials, we explore quasi-static stable and metastable VLCs in NbSe_{2} single crystals near the PE. We identify three different regions: for T T_{2}(H) configurations are fully disordered and no metastability is observed. In the T_{1}<T<T_{2} region we find temperature dependent stable configurations with intermediate degree of disorder, possibly associated to coexistence of ordered and disordered lattices throughout the PE. A simple estimation of the equilibrium proportion of ordered and disordered domains is provided.

cond-mat.supr-con↗
arXiv2007

Non-Abelian Chern-Simons Vortices

We consider the bosonic sector of a N=2 supersymmetric Chern-Simons-Higgs theory in 2+1 dimensions. The gauge group is U(1)xU(N) and has N_f flavors of fundamental matter fields. The model supports non-Abelian (axially symmetric) vortices when N_f\geq N, which have internal (orientational) moduli. When N_f > N, the solutions acquire additional collective coordinates parameterizing their transverse size. We solve the BPS equations numerically and obtain local (N_f = N) and semi-local (N_f > N) string solutions.

hep-th↗
arXiv2007

Non-Abelian Vortices on the Torus

We study periodic arrays of non-Abelian vortices in an $SU(N) \times U(1)$ gauge theory with $N_f$ flavors of fundamental matter multiplets. We carefully discuss the corresponding twisted boundary conditions on the torus and propose an ansatz to solve the first order Bogomolnyi equations which we find by looking to a bound of the energy. We solve the equations numerically and construct explicit vortex solutions.

hep-th↗
arXiv2006

On 1+1 Dimensional Galilean Supersymmetry in Ultracold Quantum Gases

We discuss a 1+1 dimensional Galilean invariant model recently introduced in connection with ultracold quantum gases. After showing its relation to a nonrelativistic 2+1 Chern-Simons matter system, we identify the generators of the supersymmetry and its relation with the existence of self-dual equations

cond-mat.other↗
arXiv2006

Vortex solutions in the noncommutative torus

Vortex configurations in the two-dimensional torus are considered in noncommutative space. We analyze the BPS equations of the Abelian Higgs model. Numerical solutions are constructed for the self-dual and anti-self dual cases by extending an algorithm originally developed for ordinary commutative space. We work within the Fock space approach to noncommutative theories and the Moyal-Weyl connection is used in the final stage to express the solutions in configuration space.

hep-th↗
arXiv2005

Bogomolny equations for vortices in the noncommutative torus

We derive Bogomolny-type equations for the Abelian Higgs model defined on the noncommutative torus and discuss its vortex like solutions. To this end, we carefully analyze how periodic boundary conditions have to be handled in noncommutative space and discussed how vortex solutions are constructed. We also consider the extension to an $U(2)\times U(1)$ model, a simplified prototype of the noncommutative standard model.

hep-th↗
arXiv2003

Rashba coupling in quantum dots: exact solution

We present an analytic solution to the problem of the Rashba spin-orbit coupling in semiconductor quantum dots. We calculate the exact energy spectrum, wave-functions, and spin--flip relaxation times. We discuss various effects inaccessible via perturbation theory. In particular, we find that the effective gyromagnetic ratio is strongly suppressed by the spin-orbit coupling. The spin-flip relaxation rate has a maximum as a function of the spin-orbit coupling and is therefore suppressed in both the weak- and strong coupling limits.

cond-mat.str-el↗
arXiv2003

Non BPS noncommutative vortices

We construct exact vortex solutions to the equations of motion of the Abelian Higgs model defined in non commutative space, analyzing in detail the properties of these solutions beyond the BPS point. We show that our solutions behave as smooth deformations of vortices in ordinary space time except for parity symmetry breaking effects induced by the non commutative parameter $θ$.

hep-th↗
arXiv2002

Anomalies in Noncommutative Dipole Field Theories

We study chiral symmetries of fermionic non commutative dipole theories. By using Fujikawa's approach we obtain explicit expressions of the anomalies for Dirac and chiral fermions in 2 and 4 dimensions.

hep-th↗
arXiv2001

Particle-vortex dynamics in noncommutative space

We study the problem of a charged particle in the presence of a uniform magnetic field plus a vortex in noncommutative planar space considering the two possible non-commutative extensions of the corresponding Hamiltonian, namely the ``fundamental'' and the ``antifundamental'' representations. Using a Fock space formalism we construct eigenfunctions and eigenvalues finding in each case half of the states existing in the ordinary space case. In the limit of $θ\to 0$ we recover the two classes of states found in ordinary space, relevant for the study of anyon physics.

hep-th↗
arXiv2001

Comments on the U(2) Noncommutative Instanton

We discuss the 't Hoof ansatz for instanton solutions in noncommutative U(2) Yang-Mills theory. We show that the extension of the ansatz leading to singular solutions in the commutative case, yields to non self-dual (or self-antidual) configurations in noncommutative space-time. A proposal leading to selfdual solutions with Q=1 topological charge (the equivalent of the regular BPST ansatz) can be engineered, but in that case the gauge field and the curvature are not Hermitian (although the resulting Lagrangian is real).

hep-th↗
arXiv2000

Self-dual Chern-Simons solitons in noncommutative space

We construct exact soliton solutions to the Chern-Simons-Higgs system in noncommutative space, for non-relativistic and relativistic models. In both cases we find regular vortex-like solutions to the BPS equations which approach the ordinary selfdual non-topological and topological solitons when the noncommutative parameter $θ$ goes to zero.

hep-th↗
arXiv2000

Nielsen-Olesen vortices in noncommutative space

We construct an exact regular vortex solution to the self-dual equations of the Abelian Higgs model in non-commutative space for arbitrary values of $θ$. To this end, we propose an ansatz which is the analogous, in Fock space, to the one leading to exact solutions for the Nielsen-Olesen vortex in commutative space. We compute the flux and energy of the solution and discuss its relevant properties.

hep-th↗