Advanced Seminar on Condensed Matter Physics (AG Klingeler)

Sommersemester 2023

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INF 227, SR 1.403
Friday 11:00

5.5.2023 11:00
Prof. Silvia Picozzi, D'Annunzio University
INF 227, SR 1.403
26.5.2023 14:00
Dr. Nan Tang, Augsburg University
INF 227, HS 2 (different room/time)

Spin ice is a prototypical state of frustrated magnets, in which Ising spins form a short-range "2-in, 2-out" correlation instead of a long range order due to geometrical frustrations of pyrochlore lattice. Local Ising anisotropy induced by the competition between crystal electric field effect and magnetic interactions play important roles to stabilize such spin-ice correlations. Generally, frustrated magnets show characteristic magnetostrictive responses and in this study, we measured both magnetization and magnetostriction of classical spin ice Ho2Ti2O7 and quantum spin ice Pr2Zr2O7 under high magnetic fields to explore the regime beyond the Ising limit. In the talk, I will give an extensive introduction on basics of spin ice, and present the latest experimental results and the corresponding simulations by McPhase.

5.6.2023 13:15
Dr. Evgeny Alekseev, FZ J├╝lich
INF 227, SB 1
12.6.2023 14:00
Dr. Koushik Karmakar, HZ Berlin
INF 227, SB 1.107

Quantum magnets are known to exhibit peculiar properties at the quantum level due to the interaction between the spins of individual atoms or molecules. These materials have a special ordering of the magnetic moments that arise due to the interplay of various quantum effects such as quantum fluctuations, frustration, and entanglement. However, to realize these quantum behaviours one needs access to high-quality materials. In this seminar, we will discuss the challenges of growing high-quality single crystals of different quantum magnets. Two methods we will focus on are the floating-zone growth (travelling-solvent-floating-zone) method and the Czochralski (top-seeded-solution-growth) method to obtain single crystals of materials such as spin-chains, spin-liquids, and high-Tc superconductors. We will see how high-quality single crystals of these quantum magnets allow us to explore their emerging physics at low temperatures including gapless magnetic excitations and novel magnetic ground states.

11.7.2023 10:00
Prof Kwang-yong Choi, Department of Physics, Sungkyunkwan University, Republic of Korea
INF 227, tba
The spin-1/2 antiferromagnetic Heisenberg model on a Kagomé lattice offers an excellent framework for investigating complex quantum entangled states. In particular, it allows for the exploration of a quantum spin liquid in the absence of an external field, as well as magnetic analogs of liquid, solid, and supersolid phases near magnetization plateaus. In this talk, we will address the experimental realization of these predicted novel phases in the material YCu3(OD)6+xBr3-x (x≈0.5) on a Kagomé lattice.
By combining thermodynamic and Raman spectroscopic techniques, we provide compelling evidence for the existence of fractionalized spinon excitations in YCu3(OD)6+xBr3-x (x≈0.5). These excitations exhibit a Dirac nodal structure, although their spectral weight at low energies is modified by the presence of bond randomness. Our preliminary NMR data reveal an inhomogeneous ground state due to inevitable perturbations. More significantly, we observe the 1/9 magnetization plateau at an accessible field range of μ0H1/9=15-21 T undiscovered hitherto in S=1/2 Kagomé antiferromagnets. Our findings highlight the significance of YCu3(OD)6+xBr3-x as a model material, which enables the investigation of field-induced quantum entangled states within the 1/9 plateau phase.