Research – Institute of Theoretical Physics – Leibniz University Hannover

The goal of the research unit is the development of many-body standard reference systems with known static and dynamical correlation functions at arbitrary temperature, on the lattice and in the continuum, very much like Bosonization provides standard reference systems near \(T = 0\), namely conformal field theories with central charges \(c = 1\) and known static low-temperature properties.

Correlations in Integrable Quantum Many-Body Systems

Home page of the Research Unit FOR2316

Participating Instutions

Project: Spin chains and vertex models based on superalgebras

Spin chains and two-dimensional vertex models with an underlying superalgebra structure appear naturally in certain statistical physics models, e.g. intersecting loops, and disordered electron systems. In several examples for such models the low energy effective theory describing their critical behaviour has displayed rather unusual properties: the lack of unitarity in these systems allows for continua of critical exponents leading to a fine structure with strong subleading corrections to scaling in the finite size spectrum. This is a signature of non-compact degrees of freedom emerging in the continuum limit of these models. In this project we plan to study the properties of these systems in the context of integrable superspin chains. In particular we want to identify the corresponding conformal field theories and characterize the continuous part of their spectrum. In addition, the effect of boundary conditions on the critical properties will be addressed. To deal with the strong finite-size effects present in these systems we shall develop new analytical methods for the analysis of the spectral problem.

Publications

Frahm, H., & Gehrmann, S. (2024). Finite-size spectrum of the staggered six-vertex model with antidiagonal boundary conditions. Nuclear Physics B, 1006, Article 116655. https://doi.org/10.1016/j.nuclphysb.2024.116655

Gehrmann, S., Kotousov, G. A., & Lukyanov, S. L. (2024). Scaling limit of the ground state Bethe roots for the inhomogeneous XXZ spin - 1/2 chain. Nuclear Physics B, 1006, Article 116624. https://doi.org/10.48550/arXiv.2406.12102, https://doi.org/10.1016/j.nuclphysb.2024.116624

Frahm, H., Gehrmann, S., & Kotousov, G. A. (2024). Scaling limit of the staggered six-vertex model with \(U_q(\mathfrak{sl}(2))\) invariant boundary conditions. SciPost Physics, 16(6), Article 149. https://doi.org/10.21468/SciPostPhys.16.6.149

Gehrmann, S. (2024). The influence of boundary conditions on the emergence of non-compact degrees of freedom in the scaling limit of integrable lattice models. [Doctoral thesis, Leibniz University Hannover]. https://doi.org/10.15488/17537

Frahm, H., Gehrmann, S., Nepomechie, R. I., & Retore, A. L. (2023). The D⁽²⁾₃ spin chain and its finite-size spectrum. Journal of High Energy Physics, 2023(11), Article 095. https://doi.org/10.1007/JHEP11(2023)095

Frahm, H., & Martins, M. J. (2023). U_q[OSp(3|2)] quantum chains with quantum group invariant boundaries. Nuclear Physics B, 995, Article 116329. https://doi.org/10.48550/arXiv.2307.09412, https://doi.org/10.1016/j.nuclphysb.2023.116329

Kotousov, G. A., & Lukyanov, S. L. (2023). On the scaling behaviour of an integrable spin chain with Z_r symmetry. Nuclear Physics, Section B, 993, Article 116269. https://doi.org/10.1016/j.nuclphysb.2023.116269

Frahm, H., & Gehrmann, S. (2023). Integrable boundary conditions for staggered vertex models. Journal of Physics A: Mathematical and Theoretical, 56(2), Article 025001. https://doi.org/10.48550/arXiv.2209.06182, https://doi.org/10.1088/1751-8121/acb29f

Frahm, H., & Martins, M. J. (2022). \(OSp(n|2m)\) quantum chains with free boundaries. Nuclear Physics B, 980, Article 115799. https://doi.org/10.1016/j.nuclphysb.2022.115799

Frahm, H., & Gehrmann, S. (2022). Finite size spectrum of the staggered six-vertex model with \(U_q(sl(2))\)-invariant boundary conditions. Journal of High Energy Physics, 2022(1), Article 70. https://doi.org/10.1007/JHEP01(2022)070

Hobuß, K. (2019). Spin chains and vertex models based on superalgebras. [Doctoral thesis, Leibniz University Hannover]. Leibniz Universität Hannover. https://doi.org/10.15488/8827

Frahm, H., Hobuß, K., & Martins, M. J. (2019). On the critical behaviour of the integrable q-deformed OSp(3|2) superspin chain. Nuclear Physics B, 946, Article 114697. https://doi.org/10.1016/j.nuclphysb.2019.114697, https://doi.org/10.15488/10411

Frahm, H., & Martins, M. J. (2018). The fine structure of the finite-size effects for the spectrum of the OSp(n|2m) spin chain. Nuclear Physics B, 930, 545-562. https://doi.org/10.1016/j.nuclphysb.2018.03.016, https://doi.org/10.15488/3390

Frahm, H., & Hobuß, K. (2017). Spectral flow for an integrable staggered superspin chain. Journal of Physics A: Mathematical and Theoretical, 50(29), Article 294002. https://doi.org/10.1088/1751-8121/aa77e7

Datasets

Frahm, H. & Gehrmann, S. (2024). Dataset: Bethe ansatz data for the staggered six-vertex model with antidiagonal boundary conditions. DOI:10.25835/hl5nqg81

Frahm, H. & Martins, M. J. (2023). Dataset: Finite size data for \(U_q[OSp(3|2)]\) quantum chains with quantum group invariant boundaries. DOI:10.25835/ypipefbz

Frahm, H.,Hobuß, K., & Martins, M. J. (2019). Dataset: Finite size data for the q-deformed OSp(3|2) superspin chain. DOI:10.25835/0064330

Quasi particles in topological quantum liquids such as the fractional Quantum Hall states and certain two-dimensional frustrated magnets display unconventional quantum statistics. The conserved topological charge of these non-Abelian anyons is protected and has spawned interest for such systems in the context of quantum computation. In this project we plan to study the properties of interacting many-anyon systems whose construction is based on the mathematical structures describing the fundamental operations of fusion and braiding. Upon fine-tuning of the interactions these models can be embedded into a family of commuting operators. We shall develop functional methods to exploit local identities present in these integrable models for the solution of their spectral problem. Our investigation of integrable anyon chains will be complemented by studies of non-integrable deformations thereof to gain understanding into the emergence of unconventional boundary degrees of freedom and their realization as topological quantum impurities in electronic systems.

Publications

Showing results 1 - 8 out of 8

Westerfeld, D., Großpietsch, M., Kakuschke, H., & Frahm, H. (2023). Factorization of density matrices in the critical RSOS models. Journal of Statistical Mechanics: Theory and Experiment, 2023, Article 083104. https://doi.org/10.1088/1742-5468/aceeef

Westerfeld, D. (2022). Functional methods for correlation functions of integrable face and anyon models. [Doctoral thesis, Leibniz University Hannover]. Leibniz Universität Hannover. https://doi.org/10.15488/11992

Ardonne, E., Finch, P. E., & Titsworth, M. (2021). Classification of Metaplectic Fusion Categories. Symmetry, 13(11), Article 2102. https://doi.org/10.3390/sym13112102

Frahm, H., & Westerfeld, D. (2021). Density matrices in integrable face models. SciPost Physics, 11(3), Article 057. https://doi.org/10.21468/SciPostPhys.11.3.057

Borcherding, D., & Frahm, H. (2019). Condensates of interacting non-Abelian SO(5)_Nf anyons. Journal of High Energy Physics, 2019(10), Article 54. https://doi.org/10.1007/JHEP10(2019)054

Borcherding, D., & Frahm, H. (2018). Condensation of non-Abelian SU(3) N_f anyons in a one-dimensional fermion model. Journal of Physics A: Mathematical and Theoretical, 51(49), Article 495002. https://doi.org/10.48550/arXiv.1808.05808, https://doi.org/10.1088/1751-8121/aaea9b

Borcherding, D., & Frahm, H. (2018). Signatures of non-Abelian anyons in the thermodynamics of an interacting fermion model. Journal of Physics A: Mathematical and Theoretical, 51(19), Article 195001. https://doi.org/10.48550/arXiv.1706.09822, https://doi.org/10.1088/1751-8121/aaba1e

Finch, P. E., Flohr, M., & Frahm, H. (2018). Z_n clock models and chains of so(n)₂ non-Abelian anyons: Symmetries, integrable points and low energy properties. Journal of Statistical Mechanics: Theory and Experiment, 2018(2), Article 023103. https://doi.org/10.1088/1742-5468/aaa788

Projects in Holger Frahm's Research Group

FOR 2316: Correlations in Integrable Quantum Many-Body Systems

Correlations in Integrable Quantum Many-Body Systems

Participating Instutions

Project: Spin chains and vertex models based on superalgebras

Publications

Datasets

Project: Non-Abelian anyons

Publications