Cecilie Glittum

• Zhang, Zhao & Glittum, Cecilie (2026). Resonating valence bond ground states on corner-sharing simplices. SciPost Physics. 20(4). doi: 10.21468/scipostphys.20.4.121. Full text in Research Archive Show summary

  The Hubbard model in the U\to∞ U → ∞ limit has been known to have resonating valence bond (RVB) ground states on certain corner-sharing simplex lattices. Examples include both the quasi-1D sawtooth lattice with open boundary and a larger class of higher dimensional lattices without boundaries. The two types of results were obtained by different approaches which do not apply to one another. In the second class of lattices, the simplest simplex is a tetrahedron. We hereby generalize both results by studying the singly hole-doped system on the quasi-1D lattice of a tetrahedron chain, which can be considered a stripe of the pyrochlore or checkerboard lattices. The energy level ordering of irreducible representations of each tetrahedron shows that a chain of them has exponentially degenerate partial RVB or dimer-monomer ground states where each tetrahedron hosts one spin- 1/2 1 / 2 monomer and one spin- 0 0 dimer. The exact ground states in the infinitely long chain limit are analytically solved by introducing basis transformations between local Hilbert spaces of neighboring tetrahedra, and its energy agrees with the extrapolation of numerical exact diagonalization results of finite sized systems.

• Glittum, Cecilie & Syljuåsen, Olav Fredrik (2026). The finite-temperature behavior of a triangular Heisenberg antiferromagnet. Journal of Physics: Condensed Matter. ISSN 0953-8984. 38(13), p. 135801–135801. doi: 10.1088/1361-648x/ae4f4b. Full text in Research Archive Show summary

  We investigate the classical antiferromagnetic Heisenberg model on the triangular lattice with up to third-nearest neighbor exchange couplings using the Nematic Bond Theory. This approach allows us to compute the free energy and the neutron scattering static structure factor at finite temperatures. We map out the phase diagram with a particular emphasis on finite-temperature phase transitions that break lattice-rotational symmetries, spiral spin liquids and the broad specific heat hump that is ubiquitous in the antiferromagnetic 120 degree phase. We identify this specific heat hump as signaling the onset of an exponentially increasing correlation length. Further, we map out the temperature of the specific heat hump and the transition temperatures of the symmetry-breaking transitions throughout the exchange-coupling space. Along the line J3 = J2 / 2 , the Fourier-transformed exchange coupling exhibits a degenerate ring-like minimum, giving rise to spiral spin liquid behavior at intermediate temperatures. We investigate the structure factor of the spiral spin liquid as function of J2 and identify the corresponding low-temperature order, which coincides with the single-q spiral states of maximum spin-wave entropy along the degenerate ring.

• Glittum, Cecilie & Syljuåsen, Olav Fredrik (2023). Sublattice pairing in pyrochlore Heisenberg antiferromagnets. Physical review B (PRB). ISSN 2469-9950. 108(1), p. 1–6. doi: 10.1103/PhysRevB.108.014413. Full text in Research Archive Show summary

  We argue that classical pyrochlore Heisenberg antiferromagnets with small further-neighbor couplings can order in a state where pairs of sublattices form antiparallel spirals. The spiral ordering wave vectors of the two pairs are in general different from each other, and are constrained by which sublattices are being paired. This sublattice pairing state generally breaks inversion and most rotation symmetries. Its existence depends on the antiferromagnetic nearest-neighbor coupling which favors the spins on each tetrahedron to sum to zero. To substantiate our argument, we extend the nematic bond theory; a diagrammatic large-Ns method, to non-Bravais lattices, and demonstrate that the predicted state is indeed realized at low temperatures in a large region of exchange coupling space. We also carry out a spin wave calculation which suggests that the sublattice pairing state is coplanar.

• Glittum, Cecilie & Syljuåsen, Olav Fredrik (2021). Arc-shaped structure factor in the J1-J2-J3 classical Heisenberg model on the triangular lattice. Physical review B (PRB). ISSN 2469-9950. 104(18). doi: 10.1103/PhysRevB.104.184427. Full text in Research Archive

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• Glittum, Cecilie (2020). Nematic Bond Theory of Frustrated Heisenberg Models on Triangular and Honeycomb Lattices. Universitetet i Oslo. Full text in Research Archive Show summary

  The newly developed Nematic Bond Theory enables an efficient way of studying phases and phase transitions in classical frustrated magnets with Heisenberg interactions. We extend here the Nematic Bond Theory to hold for non-Bravais lattices, and develop in addition an approximate expression for the free energy, which can be calculated at low computational cost. Using these extensions, we study classical frustrated Heisenberg models on triangular and honeycomb lattices. On the triangular lattice, we derive the phase diagram for the J1-J2-J3 Heisenberg model with ferromagnetic nearest neighbour interactions. In addition to detect lattice-nematic phases, we also find a novel symmetry broken state, which shows an extended maximum in the spin correlation function. We conjecture that this state is caused by domain wall excitations. The honeycomb lattice is studied to benchmark the Nematic Bond Theory on a non-Bravais lattice. For the antiferromagnetic J1-J2 Heisenberg model, we find that the Nematic Bond Theory shows good agreement with the literature for both symmetry broken lattice-nematic phases and symmetric spin liquid states.

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