Collaborative Research Center 360
Constrained Quantum Matter
Less is more!
We use carefully chosen constraints to design and
manipulate quantum states in solids, seeking to create new quantum
materials and explore conceptual challenges from quantum information
theory to non-equilibrium physics.
Next year will be the TRR360 International Conference in September 2025. Go here to find out about the details!



2025 James C. McGroddy Prize awarded to Hidenori Takagi
We are very proud to announce that one member of the TRR360, Hidenori Tagaki from the MPI for solid-state research in Stuttgart, will be awarded with the 2025 James C. McGroody Prize for New Materials. He is honoured “for seminal theoretical and experimental research, materials design and discoveries that pioneered the exploration of novel forms of topological quantum matter in spin-orbit assisted Mott insulators realized in transition metal oxides”. More information can be found here. The prize will be presented in March 2025.
Next events
Recent Articles
Xu, W. -T.; Rakovszky, T.; Knap, M.; Pollmann, F. Entanglement Properties of Gauge Theories from Higher-Form Symmetries Journal Article Phys. Rev. X 15, 011001, 2025. @article{xu_entanglement_2025, We explore the relationship between higher-form symmetries and entanglement properties in lattice gauge theories with discrete gauge groups, which can exhibit both topologically ordered phases and higher-form symmetry-protected topological (SPT) phases. Our study centers on a generalization of the Fradkin-Shenker model describing ℤ2 lattice gauge theory with matter, where the Gauss law constraint can be either emergent or exact. The phase diagram includes a topologically ordered deconfined phase and a nontrivial SPT phase protected by a 1-form and a 0-form symmetry, among others. We obtain the following key findings: First, the entanglement properties of the model depend on whether the 1-form symmetries and the Gauss law constraint are exact or emergent. For the emergent Gauss law, the entanglement spectrum (ES) of the nontrivial SPT phase exhibits degeneracies, which are robust at low energies against weak perturbations that explicitly break the exact 1-form symmetry. When the Gauss law and the 1-form symmetry are both exact, the ES degeneracy is extensive. This extensive degeneracy turns out to be fragile and can be removed completely by infinitesimal perturbations that explicitly break the exact 1-form symmetry while keeping the Gauss law exact. Second, we consider the ES in the topologically ordered phase where 1-form symmetries are spontaneously broken. In contrast to the ES of the nontrivial SPT phase, we find that spontaneous higher-form symmetry breaking removes “half” of the ES levels, leading to a nondegenerate ES in the topologically ordered phase, in general. Third, we derive a connection between spontaneous higher-form symmetry breaking and the topological entanglement entropy (TEE). Using this relation, we investigate the entanglement entropy that can be distilled in the deconfined phase of the original Fradkin-Shenker model using gauge-invariant measurements. We show that the TEE is robust against the measurement when the 1-form symmetry is emergent but it is fragile when the 1-form symmetry is exact. Our results demonstrate the advantage of higher-form symmetries for understanding entanglement properties of gauge theories. |
Tang, N.; Gen, M.; Rotter, M.; Man, H.; Matsuhira, K.; Matsuo, A.; Kindo, K.; Ikeda, A.; Matsuda, Y.; Gegenwart, P.; Nakatsuji, S.; Kohama, Y. Crystal field magnetostriction of spin ice under ultrahigh magnetic fields Journal Article Phys. Rev. B 110, 214414, 2024. @article{tang_crystal_2024, We present a comprehensive study of the magnetoelastic properties of the Ising pyrochlore oxide Ho2Ti2O7, known as spin ice, by means of high-field magnetostriction measurements and numerical calculations. When a magnetic field is applied along the crystallographic ⟨111⟩ axis, the longitudinal magnetostriction exhibits a broad maximum in the low-field regime around 30 T, followed by a dramatic lattice contraction due to crystal-field (CF) level crossing at 𝐵cf∼65 T. The transverse magnetostriction exhibits a contrasting behavior, highlighting the anisotropic nature of the CF striction. By applying a magnetic field at varying sweep rates, we identify distinct timescales of spin dynamics that are relevant to monopole formation and annihilation, as well as CF-phonon dynamics. Our mean-field calculations, based on a point-charge model, successfully reproduce the overall magnetostriction behavior, revealing the competition between the exchange striction and CF striction. A signature of the CF level crossing is also observed through adiabatic magnetocaloric-effect measurements, consistent with our magnetostriction data. |
Abdeldaim, A. H.; Gretarsson, H.; Day, S. J.; Le, M. D.; Stenning, G. B. G.; Manuel, P.; Perry, R. S.; Tsirlin, A. A.; Nilsen, G. J.; Clark, L. Kitaev Interactions Through an Extended Superexchange Pathway in the jeff = 1/2 Ru3+ Honeycomb Magnet RuP3SiO11 Journal Article Nat. Commun. 15, 9778, 2024. @article{abdeldaim_kitaev_2024, Magnetic materials are composed of the simple building blocks of magnetic moments on a crystal lattice that interact via magnetic exchange. Yet from this simplicity emerges a remarkable diversity of magnetic states. Some reveal the deep quantum mechanical origins of magnetism, for example, quantum spin liquid (QSL) states in which magnetic moments remain disordered at low temperatures despite being strongly correlated through quantum entanglement. A promising theoretical model of a QSL is the Kitaev model, composed of unusual bond-dependent exchange interactions, but experimentally, this model is challenging to realise. Here we show that the material requirements for the Kitaev QSL survive an extended pseudo-edge-sharing superexchange pathway of Ru3+ octahedra within the honeycomb layers of the inorganic framework solid, RuP3SiO11. We confirm the requisite state of Ru3+ in RuP3SiO11 and resolve the hierarchy of exchange interactions that provide experimental access to an unexplored region of the Kitaev model. |
Kamenskyi, D.; Vasin, K.; Prodan, L.; Kutko, K.; Khrustalyov, V.; Pavlov, S. G.; Hübers, H. -W. Terahertz Resonant Emission by Optically Excited Infrared-Active Shear Phonons in KY(MoO4)2 Journal Article Adv. Sci. 12, 2407028, 2024. @article{kamenskyi_terahertz_2024, Abstract The generation of monochromatic electromagnetic radiation in the terahertz (THz) frequency range has remained a challenging task for many decades. Here, the emission of monochromatic sub-THz radiation by optical phonons in the dielectric material KY(MoO4)2 is demonstrated. The layered crystal structure of KY(MoO4)2 causes infrared-active shear lattice vibrations to have energies below 3.7 meV, corresponding to frequencies lower than 900 GHz where solid-state-based monochromatic radiation sources are rare. Directly excited by a 5 ps long broadband THz pulse, infrared-active optical vibrations in KY(MoO4)2 re-emit narrowband sub-THz radiation as a time-varying dipole for tens of picoseconds, which is exceptionally long for oscillators with frequencies below 1 THz. Such a long coherent emission allows for the detection of more than 50 periods of radiation with frequencies of 568 and 860 GHz. The remarkably long decay time together with the chemical stability of the employed material suggests a variety of possible applications in THz technology. |
Impressions from past events




































The research programme
We seek to design and utilize new quantum states by taking advantage of the recently developed capability to tailor electron systems in complex materials through a variety of complementary constraints, focusing on spin-momentum locking, gauge structures of interacting spin systems, and kinetic constraints.
News
Here you can find all the important news around the project ConQuMat: recent publication, internal events for project members and opening for various positions.
Outreach - Öffentlichkeitsarbeit
Dive with us into the fascinating world of quantum matter! (science communication offers in German)
Es gibt viele Angebote, um die Forschung aus dem Projekt ConQuMat der Öffentlichkeit zugänglich zu machen. Egal ob durch einen Blog, Spiele oder Erlebnisveranstaltungen – tauchen Sie mit uns in die faszinierende Welt der Quantenmaterie ein!