Mauro M. Doria

Instituto de Física – FIS

Universidade Federal do Rio de Janeiro

C.P. 68528

Rio de Janeiro 21941-972 RJ BRAZIL

Curriculum Vitae Lattes

Teaching

Adviser of recent thesis work

• Rodrigo Carlos Viana Coelho - "Lattice Boltzmann Method for Bosons and Fermions" - master degree - 2014
  
• Edinardo Ivison Batista Rodrigues - "Formula de Lichnerowicz-Weitzenbock aplicada a supercondutores de uma e duas componentes" (co-adviser) master 2013
  
• Antonio Rodrigues de Castro Romaguera - "Propriedades da matéria de vórtices em supercondutores mesoscópicos tridimensionais" - doctorate degree 2007
  

Recent publications and conference participation

Active membership

• University Council of the Federal University of  Rio de Janeiro (Consuni)

• Multisuper Network

• Núcleo de supercondutividade teórica e computacional

Some research activities  in Condensed Matter Physics

just gave room to the new tools based on scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES), resonant inelastic X-ray scattering(RIXS) and others, as  phase diagrams are like maps to be conquered by imagination.
video - the new cartography


Threefold symmetry of confined vortex loops

The formation of vortex patterns induced by magnetic inclusions embedded in a superconducting material is studied here. Since in the absence of an external field, flux lines should be closed, vortex lines are expected to start and end at the magnetic particles. The calculations performed in the framework of the Ginzburg-Landau theory revealed that in some cases the vortex loops becomes confined and they always nucleate in triplets around the magnetic core.

Transverse magnetization and torque in asymmetrical mesoscopic superconductors

The transverse magnetization and the torque that result from the asymmetrical coexistence of vortices with different lengths in mesoscopic superconductors are obtained. The general aspects of our results apply to irregularly shaped grains, and, consequently, can also be relevant to the understanding of inhomogeneous bulk samples with granular structure.


Tilted vortices in a superconducting mesoscopic cylinder

Tilting of the field leads to interesting phenomena caused by the small volume-to-surface ratio, as vortex lines are preferentially oriented along the field direction while they are forced to be perpendicular to the surface. Vortices can enter and leave the cylinder also by simply rotating the applied field. We find the striking result of a single vortex with the lowest free-energy configuration achieved at a tilted angle.

Vortex patterns in a mesoscopic superconducting rod with a magnetic dot

The vortex pattern of a superconducting mesoscopic rod caused by the presence of a magnetic dot on its top are obtained here. The magnetic field falls with the cubic power of the distance and, consequently, is weaker at the bottom surface of the rod as compared to the top one, leading to vortex patterns very distinct from the thin limit cases. The vortices become truly three-dimensional curved lines in space instead of the flat “coin” vortices found in the previous two-dimensional studies. The height of the rod is a key parameter that renders the extreme cases of very short and very long rods different. Notiation (Lgiant,Lmulti) referes to the the central vorticity and the number of lateral vortices, respectively. The fivefold symmetric configuration was selected to the the front page of the Physical Review B  "Kaleidoscope" of March 2010.

Superconducting Strip Could Become an Ultra- Low-Voltage Sensor (Science Daily - April 30, 2012).

The dynamic and static phases of vortices under an applied drive are investigated in a superconducting stripe with an array of weak links. The presence of crossedmagnetic and electric fields introduces interesting regimes resulting in alternating static phases with zero voltage and dynamic phases, which are characterised by non-zero voltage peaks in the superconductor.


Magnetization of a superconducting film in a perpendicular magnetic field

The  magnetization of superconducting films with large aspect ratio width/thickness can be computed either by the usual thermodynamic energy derivative, or by a virial expression obtained here by scaling arguments. The two methods are in perfect agreement according to the present results.The figure below shows the magnetization M of a superconducting infinite film in a perpendicular magnetic field Ba for several film thickness, and Ginzburg-Landau parameter. The solid lines are calculated from the energy-derivative and the dots are from the virial expression rendering excellent agreement.

Current-induced cutting and recombination of magnetic superconducting vortex loops in mesoscopic superconductor-ferromagnet heterostructures

Vortex loops are generated by the inhomogeneous stray field of a magnetic dipole on top of a current-carryingmesoscopic superconductor. Cutting and recombination processes unfold under the applied drive, resulting in periodic voltage oscillations across the sample. We show that a direct and detectable consequence of the cutting and recombination of these vortex loops in the present setup is the onset of vortices at surfaces where they were
absent prior to the application of the external current.

Video - superconductor-ferromagnet interface

Little-Parks oscillations near a persistent current loop

A persistent current loop is set on the top edge of a mesoscopic superconducting thin-walled cylinder with a finite height. We investigate the Little-Parks effect for variable heights. For a short cylinder the Little-Parks effect is the known one, as there is only one magnetic flux piercing the cylinder. But for a tall cylinder the inhomogeneity of the magnetic field makes different magnetic fluxes pierce the cylinder at distinct heights. The outcome is the onset of  two distinct Little-Parks oscillatory regimes according to the magnetic moment of the current loop. We show how these two regimes, and also the transition between them, can be observed in measurements. Below the oscillations of the critical temperature are shown for cylinders with heights twice and ten times the coherence length for several trapped angular momenta.



The Lichnerowicz-Weitzenböck formula and superconductivity

This formula is intimately connected to a set of commuting local momentum and spin operators. The local momentum operator, constructed over the spin-charged background, is nothing but the so-called covariant derivative introduced by Fock and Ivanenko in 1929 in the context of general relativity to deal with Dirac spinors. The existence of the local momentum operator and its commutativity with the local spin operator are a signal of curvature and torsion, as set by Elie Cartan geometrical formalism, who formulated general relativity in terms of the so called “co-frame”, also known as tetrad or vierbein. We call it “spin-frame”, as we think of it as carrying information about the spin correlations present in the system. “It should be noted that the possibility of relating the torsion of space to an intrinsic angular momentum of matter was first suggested by Cartan in 1923. However it was only in 1925 that the modern concept of spin was introduced by Uhlenbeck and Goutsmith.” (Introduction to Gravitation, Venzo de Sabbata and Maurizio Gasperini). In this  proposal  superconductivity

other degrees of freedom .


Topologically stable gapped state in a layered superconductor

An important concept in condensed matter physics is that of an order parameter, introduced by Lev Landau in the last century to describe the transition to the superconducting state. Interestingly, one of Landau’s first proposals of an order parameter was the supercurrent, also suggested to exist in the microscopic superconducting ground state of Felix Bloch. These ideas were soon dismissed since a spontaneous circulating supercurrent increases the kinetic energy. Nevertheless we find an excited but stable state with these spontaneously circulating supercurrents, containing flow and counter flow in the layers, even without the presence of an external magnetic field.



Coexistence of magnetic and charge order in a two-component order parameter description of the layered superconductors

The pseudogap is a skyrmionic condensate in the temperature range near to the crossing of the pseudogap line transition with the superconducting critical temperature dome.  Then the pseudogap is a condensate that displays both magnetic and charge properties whose patterns are obtained here for states of definite angular momentum. There is a supercurrent circulating in and out of the layers, and so, there is supercurrent within a layer and in between the layers as well. This intrincate supercurrent pattern produces a very low nearly undetectable magnetic field. Assuming a given value for this local magnetic field we predict the pseudogap energy density and find a natural oscillatory frequency of charges in and out of the layers that falls in the THz regime. A natural inhomogeneous charge distribution arises within the layers which is depicted below.

One of the greatest achievements of the Boltzmann equation is to determine the macroscopic hydrodynamical equations of a fluid from a phase-space distribution function, which describes the probability to find particles with microscopic velocity in a given position and time. Nearly 80 years have passed since Uehling and Uhlenbeck  solved the Boltzmann equation for the quantum fluid approximately by determining the small correction to the distribution function of noninteracting particles in case of a weak interaction. We take the Boltzmann equation with the Bhatnagar-Gross-Krook collision operator and consider it for the Bose-Einstein and Fermi-Dirac equilibrium distribution functions. We conclusively show that the Hermite polynomial expansion of the equilibrium distribution functions must be carried to fourth order in such cases. Only in this order it is possible to obtain meaningful macroscopic hydrodynamical equations that lead to the correct viscosity and thermal coefficients. We have also demonstrated the feasibility of the fourth-order lattice Boltzmann method scheme by showing that it numerically describes motion and heating in an energy conserving way.