Dr. Carlos A. Lamas
Investigador Independiente CONICET
Lugar de trabajo: IFLP
lamas@fisica.unlp.edu.ar
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:
A theoretical model for tellurite-sulfates Na2Cu5(TeO3)(SO4)3(OH)4 and K2Cu5(TeO3)(SO4)3(OH)4
Abstract: A 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)
On the neural network flow of spin configurations
Abstract: We 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.
An effective field theory approach for the bilayer honeycomb antiferromagnet
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.
Phase diagram study of a two-dimensional frustrated antiferromagnet via unsupervised machine learning
Abstract: We apply unsupervised learning techniques to classify the different phases of the J1−J2 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)
Current jumps in flat band ladders with Dzyaloshinskii-Moriya interactions
Abstract: Localized 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)
Exploring neural network training strategies to determine phase transitions in frustrated magnetic models
Abstract: The 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
Magnon crystals and magnetic phases in a Kagomé-stripe antiferromagnet
Abstract: In 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)
Optimizing configurations for determining the magnetic model based on ab-initio calculations
Abstract: In 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
arXiv:1809.00743 [pdf, ps, other]
Inducing critical phenomena in spin chains through sparse alternating fields
Abstract: We 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 n−1 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)
arXiv:1712.08216 [pdf, ps, other]
Nematic quantum phases in the bilayer honeycomb antiferromagnet
Abstract: The spin−1/2 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)
arXiv:1704.01588 [pdf, ps, other]
Magnetization process in a frustrated plaquette dimerized ladder
Abstract: The 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)
Quantum phase diagram of a frustrated antiferromagnet on the bilayer honeycomb lattice
Abstract: We 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)
arXiv:1501.06178 [pdf, ps, other]
Dimerized ground states in spin-S frustrated systems
Abstract: We 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)
arXiv:1501.04930 [pdf, ps, other]
Self consistent study of the quantum phases in a frustrated antiferromagnet on the bilayer honeycomb lattice
Abstract: We 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)
arXiv:1406.4872 [pdf, ps, other]
Diagnosing order by disorder in quantum spin systems
Abstract: In 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
arXiv:1403.3737 [pdf, ps, other]
Phase diagram study of a dimerized spin-S zig-zag ladder
Abstract: The 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
arXiv:1312.6324 [pdf, ps, other]
Quantum phases in the frustrated Heisenberg model on the bilayer honeycomb lattice
Abstract: We 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)