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Dr. Carlos A. Lamas


Dr. Carlos A. Lamas

Investigador Independiente CONICET


Lugar de trabajo: IFLP


Temas de interés:

  • Strongly correlated systems 
  • Magnetic properties
  • Classical and quantum phase transitions
  • Machine learning



Actividades docentes:


  • Profesor Adjunto, Facultad de Cs Exactas, UNLP

           Primer Semestre:    Matemáticas en Física

           Segundo Semestre: Seminario de física del sólido 



Cursos de posgrado:


Introducción a las redes neuronales y sus aplicaciones





Publicaciones recientes:  




  1. arXiv:2210.15416  [pdfother

    cond-mat.str-el cond-mat.mtrl-sci

    A theoretical model for tellurite-sulfates Na2Cu5(TeO3)(SO4)3(OH)4 and K2Cu5(TeO3)(SO4)3(OH)4

    Authors: I. L. Bartolom/'eL. ErricoV. FernandezM. MateraA. V. Gil RebazaC. A. Lamas

    AbstractA theoretical model for two new tellurite-sulfates, namely Na2Cu5(TeO3)(SO4)3(OH)4 and K2Cu5(TeO3)(SO4)3 (OH)4 is determined to be compatible with ab-initio calculations. The results obtained in this work show that some previous speculations in the literature about the couplings are correct, obtaining a model with a mixture of ferromagnetic and antiferromagnetic… ▽ More

    Submitted 27 October, 2022; originally announced October 2022.

    Comments: 7 pages, 8 figures

    Journal ref: Phys. Rev. B 106, 195119 (2022)



  1. arXiv:2203.06652  [pdfother


    On the neural network flow of spin configurations

    Authors: Santiago AcevedoCarlos A. LamasAlejo Costa DuranMauricio B. SturlaTomás S. Grigera

    AbstractWe study the so-called neural network flow of spin configurations in the 2-d Ising ferromagnet. This flow is generated by successive reconstructions of spin configurations, obtained by an artificial neural network like a restricted Boltzmann machine or an autoencoder. It was reported recently that this flow may have a fixed point at the critical temperature of the system, and even allow the comput… ▽ More

    Submitted 13 March, 2022; originally announced March 2022.



  1. arXiv:2109.11687  [pdf, other


    An effective field theory approach for the bilayer honeycomb antiferromagnet

    Authors: S. Acevedo, C. A. Lamas, P. Pujol

    Abstract: The spin-3/2 Heisenberg antiferromagnet on the bilayer honeycomb lattice is a minimal model to describe the magnetic behavior of Bi3Mn4O12(NO3). We study this model with frustrating inter-layer second-neighbor couplings, taking into account quantum and thermal fluctuations. We use a path integral formulation in terms of coherent states to describe the low energy physics of the model.… ▽ More

    Submitted 23 September, 2021; originally announced September 2021.



    arXiv:2101.10161  [pdfother

    cond-mat.str-el cond-mat.stat-mech

    Phase diagram study of a two-dimensional frustrated antiferromagnet via unsupervised machine learning

    Authors: S. AcevedoM. ArlegoC. A. Lamas

    AbstractWe apply unsupervised learning techniques to classify the different phases of the J1J2 antiferromagnetic Ising model on the honeycomb lattice. We construct the phase diagram of the system using convolutional autoencoders. These neural networks can detect phase transitions in the system via `anomaly detection', without the need for any label or a priori knowledge of the phases. We present diff… ▽ More

    Submitted 6 April, 2021; v1 submitted 25 January, 2021; originally announced January 2021.

    Comments: 11 pages, 15 figures

    Journal ref: Phys. Rev. B 103, 134422 (2021)




  1. arXiv:2009.04970  [pdfother

    cond-mat.str-el quant-ph

    Current jumps in flat band ladders with Dzyaloshinskii-Moriya interactions

    Authors: S. AcevedoP. PujolC. A. Lamas

    AbstractLocalized magnons states, due to flat bands in the spectrum, is an intensely studied phenomenon and can be found in many frustrated magnets of different spatial dimensionality. The presence of Dzyaloshinskii-Moriya (DM) interactions may change radically the behavior in such systems. In this context, we study a paradigmatic example of a one-dimensional frustrated antiferromagnet, the sawtooth chain… ▽ More

    Submitted 6 April, 2021; v1 submitted 10 September, 2020; originally announced September 2020.

    Journal ref: Phys. Rev. B 102, 195139 (2020)


  1. arXiv:2009.00661  [pdfother

    physics.comp-ph cond-mat.stat-mech cond-mat.str-el

    Exploring neural network training strategies to determine phase transitions in frustrated magnetic models

    Authors: I. CorteS. AcevedoM. ArlegoC. A. Lamas

    AbstractThe transfer learning of a neural network is one of its most outstanding aspects and has given supervised learning with neural networks a prominent place in data science. Here we explore this feature in the context of strongly interacting many-body systems. Through case studies, we test the potential of this deep learning technique to detect phases and their transitions in frustrated spin systems,… ▽ More

    Submitted 30 June, 2021; v1 submitted 1 September, 2020; originally announced September 2020.

    Journal ref: Computational Materials Science Volume 198, October 2021, 110702

  1. Magnon crystals and magnetic phases in a Kagomé-stripe antiferromagnet

    Authors: S. AcevedoC. A. LamasM. ArlegoP. Pujol

    AbstractIn this work we analyze the magnetization properties of an antiferromagnetic Kagomé stripe lattice, motivated by the recent synthesis of materials exhibiting this structure. By employing a variety of techniques that include numerical methods as Density Matrix Renormalization Group and Monte Carlo simulations, as well as analytical techniques, as perturbative low energy effective models and exact s… ▽ More

    Submitted 8 September, 2020; v1 submitted 29 August, 2019; originally announced August 2019.

    Comments: 14 figures, 11 pages

    Journal ref: Phys. Rev. B 100, 195145 (2019)


  1. arXiv:1907.03376  [pdfother

    cond-mat.str-el cond-mat.mtrl-sci physics.atom-ph quant-ph

    Optimizing configurations for determining the magnetic model based on ab-initio calculations

    Authors: J. M. MateraC. A. LamasL. A. ErricoA. V. Gil RebazaV. I. Fernández

    AbstractIn this paper, it is presented a novel strategy to optimize the determination of magnetic couplings by using ab-initio calculations of the energy. This approach allows determining efficiently, in terms of a proposed effective magnetic spin model, an optimal set of magnetic configurations to be simulated by DFT methods. Moreover, a procedure to estimate the values of the coupling constants and thei… ▽ More

    Submitted 7 July, 2019; originally announced July 2019.

    Comments: 8 pages, 4 figures

    Journal ref: Computational Materials Science Volume 178, 1 June 2020, 109628


  1. arXiv:1809.00743  [pdfpsother

    cond-mat.str-el quant-ph

    Inducing critical phenomena in spin chains through sparse alternating fields

    Authors: M. CerezoR. RossignoliN. CanosaC. A. Lamas

    AbstractWe analyze the phase diagram of the exact ground state (GS) of spin-s chains with ferromagnetic XXZ couplings under n-alternating field configurations, i.e, sparse alternating fields having nodes at n1 contiguous sites. It is shown that such systems can exhibit a non-trivial magnetic behavior, which can differ significantly from that of the standard (n=1) alternating case and enable mec… ▽ More

    Submitted 9 January, 2019; v1 submitted 3 September, 2018; originally announced September 2018.

    Comments: 11 pages, 6 figures, final version

    Journal ref: Phys. Rev. B 99, 014409 (2019)


  1. arXiv:1712.08216  [pdfpsother


    Nematic quantum phases in the bilayer honeycomb antiferromagnet

    Authors: H. ZhangC. A. LamasM. ArlegoWolfram Brenig

    AbstractThe spin1/2 Heisenberg antiferromagnet on the honeycomb bilayer lattice is shown to display a rich variety of semiclassical and genuinely quantum phases, controlled by the interplay between intralayer frustration and interlayer exchange. Employing a complementary set of techniques, comprising spin rotationally invariant Schwinger boson mean field theory, bond operators, and series expansions we… ▽ More

    Submitted 21 December, 2017; originally announced December 2017.

    Comments: 6 pages, 3 figures

    Journal ref: Phys. Rev. B 97, 235123 (2018)



  1. arXiv:1704.01588  [pdfpsother


    Magnetization process in a frustrated plaquette dimerized ladder

    Authors: F. EliasM. ArlegoC. A. Lamas

    AbstractThe magnetic phase diagram of a plaquette dimerized antiferromagnetic system is studied by using a combination of numerical and analytical techniques. For the strongly frustrated regime, series expansions and bond operators techniques are employed to analyze zero magnetization plateau, whereas low energy effective models are used to study the complete magnetization process. The interplay between f… ▽ More

    Submitted 5 April, 2017; originally announced April 2017.

    Comments: 14 pages, 6 figures

    Journal ref: Phys. Rev. B 95, 214426 (2017)


  1. Quantum phase diagram of a frustrated antiferromagnet on the bilayer honeycomb lattice

    Authors: Hao ZhangCarlos A. LamasMarcelo ArlegoWolfram Brenig

    AbstractWe study the spin-1/2 Heisenberg antiferromagnet on a bilayer honeycomb lattice including interlayer frustration. Using a set of complementary approaches, namely Schwinger bosons, dimer series expansion, bond operators, and exact diagonalization, we map out the quantum phase diagram. Analyzing ground state energies and elementary excitation spectra, we find four distinct phases, corresponding to t… ▽ More

    Submitted 11 February, 2016; v1 submitted 9 December, 2015; originally announced December 2015.

    Comments: 12 pages, 12 figures

    Journal ref: Phys. Rev. B 93, 235150 (2016)




  1. arXiv:1501.06178  [pdfpsother

    cond-mat.str-el quant-ph

    Dimerized ground states in spin-S frustrated systems

    Authors: C. A. LamasJ. M. Matera

    AbstractWe study a family of frustrated anti-ferromagnetic spin-S systems with a fully dimerized ground state. This state can be exactly obtained without the need to include any additional three-body interaction in the model. The simplest members of the family can be used as a building block to generate more complex geometries like spin tubes with a fully dimerized ground state. After present some numer… ▽ More

    Submitted 8 September, 2015; v1 submitted 25 January, 2015; originally announced January 2015.

    Comments: 10 pages, 9 figures

    Journal ref: Phys. Rev. B 92, 115111 (2015)


  1. Self consistent study of the quantum phases in a frustrated antiferromagnet on the bilayer honeycomb lattice

    Authors: M. ArlegoC. A. LamasH. Zhang

    AbstractWe study the frustrated Heisenberg model on the bilayer honeycomb lattice. The ground-state energy and spin gap are calculated, using different bosonic representations at mean field level and numerical calculations, to explore different sectors of the phase diagram. In particular we make use of a bond operator formalism and series expansion calculations to study the extent of dimer inter-layer pha… ▽ More

    Submitted 20 January, 2015; originally announced January 2015.

    Comments: 27th International Conference on Low Temperature Physics

    Journal ref: J. Phys.: Conf. Ser. 568 042019 (2014)


  1. arXiv:1406.4872  [pdfpsother


    Diagnosing order by disorder in quantum spin systems

    Authors: C. A. LamasD. C. CabraP. PujolG. L. Rossini

    AbstractIn this paper we study the frustrated J1-J2 quantum Heisenberg model on the square lattice for J2 > 2J1, in a magnetic field. In this regime the classical system is known to have a degenerate manifold of lowest energy configurations, where standard thermal order by disorder occurs. In order to study its quantum version we use a path integral formulation in terms of coherent states. We show that th… ▽ More

    Submitted 18 June, 2014; originally announced June 2014.

    Comments: 8 pages, 3 figures

    Journal ref: Eur. Phys. J. B, 88 7 (2015) 176



  1. arXiv:1403.3737  [pdfpsother

    quant-ph cond-mat.stat-mech cond-mat.str-el

    Phase diagram study of a dimerized spin-S zig-zag ladder

    Authors: J. M. MateraC. A. Lamas

    AbstractThe phase diagram of a frustrated spin-S zig-zag ladder is studied through different numerical and analytical methods. We show that for arbitrary S, there is a family of Hamiltonians for which a fully-dimerized state is an exact ground state, being the Majumdar-Ghosh point a particular member of the family. We show that the system presents a transition between a dimerized phase to a Néel-like… ▽ More

    Submitted 20 January, 2015; v1 submitted 14 March, 2014; originally announced March 2014.

    Comments: 14 pages, 6 figures. Some typos were corrected, and notation was clarified

    Journal ref: J. Phys.: Condens. Matter 26 (2014) 326004



  1. arXiv:1312.6324  [pdfpsother


    Quantum phases in the frustrated Heisenberg model on the bilayer honeycomb lattice

    Authors: Hao ZhangM. ArlegoC. A. Lamas

    AbstractWe use a combination of analytical and numerical techniques to study the phase diagram of the frustrated Heisenberg model on the bilayer honeycomb lattice. Using the Schwinger boson description of the spin operators followed by a mean field decoupling, the magnetic phase diagram is studied as a function of the frustration coupling J2 and the interlayer coupling J. The presence of b… ▽ More

    Submitted 6 January, 2014; v1 submitted 21 December, 2013; originally announced December 2013.

    Comments: 10 pages, 9 figures

    Journal ref: Phys. Rev. B 89, 024403 (2014)







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