Condensed Matter Physics Seminar
2006/2007 | 2007/2008 | 2008/2009 | 2009/2010 | 2010/2011 | 2011/2012 | 2012/2013 | 2013/2014 | 2014/2015 | 2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2024-12-13 (Friday)
room 1.02, Pasteura 5 at 12:15 
Hiroyuki Yamase (NIMS Tsukuba, Japan)Long-range Coulomb interaction on a bilayer lattice system and the resulting charge dynamics
While the long-range Coulomb interaction (~1/r) is usually handled in a continuum space, I here provide its function form on a bilayer lattice system and elucidate the resulting charge dynamics. The results are compared with resonant inelastic x-ray scattering data obtained in Y-based high-temperature cuprate superconductors with Tc close to 100 K.
2024-11-29 (Friday)
room 1.02, Pasteura 5 at 12:15
Wojciech Brzezicki (Jagiellonian University, Kraków and MagTop, Warsaw)Surface chiral metal and warped time-reversal symmetry
We develop theory of dichroism and spin-dichroism for Sr2RuO4 to describe the observed peculiarities in ARPES. It is based on a tight-binding model for t2g electrons used earlier and contains a crucial ingredient: warped time-reversal symmetry. It assures perfectly antisymmetric spin-integrated dichroic signal while keeping spin-resolved signal completely non-symmetric.
2024-11-22 (Friday)
room 1.02, Pasteura 5 at 12:15
Marek Rams (UJ Kraków)On 'Computational supremacy in quantum simulation' of a quench dynamics in transverse-field Ising spin glasses
Quantum computers hold the promise of solving certain problems that lie beyond the reach of conventional computers. Establishing this capability, especially for impactful and meaningful problems, remains a central challenge. One such problem is the simulation of nonequilibrium dynamics of a magnetic spin system quenched through a quantum phase transition. In this respect, a recent article reports on an extensive benchmark of D-Wave quantum annealingprocessor comparing its performance with several leading classical approximation methods, including tensor networks and neural networks. It delineates parameter regions (system size, Ising couplings geometry, quench times) where none of the above classical methods achieve the same accuracy as the quantum annealer within a reasonable timeframe. I'll focus on the limitations of tensor networks, in particular, projected entangled-pairs states ansatz, for performing such simulations.
2024-11-15 (Friday)
room 1.02, Pasteura 5 at 12:15
Jędrzej Wardyn (IFT UW)Exact and numerical results for q-deformed Majumdar-Ghosh model
The Majumdar-Ghosh model is a spin-1/2 chain and one of the few frustrated magnetic models with an exactly solvable ground state. In our study, we look at its q-deformation, a deformation respecting the U_q(su(2)) symmetry of the model. The q-deformation allows us to explore an unusual system offering a bridge between (q=0) transverse field Ising (integrable model) and (q=1) Majumdar- Ghosh model. We derive exact formulas for the dimer order parameter in finite size and in the thermodynamic limit and compare them to numerical results from ED and DMRG. Moreover, we compute numerically several expectation values including magnetisation, ground state energy, and von Neumann entropy in transversal and longitudinal magnetic fields. These measurements give different perspectives on looking at this model and may offer a way to confirm a possible experimental realization in the material Szenicsite.
2024-11-08 (Friday)
room 1.02, Pasteura 5 at 12:15
Błażej Ruba (FUW)Approximate bosonization method for many fermion systems
A progress in the rigorous study of many fermion systems, at least in some scaling regimes, has been made recently using approximate bosonization. This approach is applicable to systems in spatial dimension two and higher, unlike the exact bosonization in dimension one. I will explain the main ideas behind the method and review the existing results on the ground state energy.
2024-10-18 (Friday)
room 1.02, Pasteura 5 at 12:15
Emilia Witkowska (IFPAN)Spin-squeezing generation with ultra-cold atoms in optical lattices in the Mott regime
Entanglement in systems with single-particle control is a well-established resource of modern quantum technology. Spin-squeezing is a great example of such. Applied in an optical lattice clock it can reduce the statistical uncertainty of spectroscopic measurements.During the seminar, I will consider the dynamic generation of spin squeezing with ultra-cold atoms with two internal states loaded into an optical lattice in the strongly interacting regime as realized with state-of-the-art experiments using a quantum gas microscope. I will show how anisotropic interactions and inhomogeneous magnetic fields generate scalable spin squeezing when their magnitudes are sufficiently small, but not negligible. The simple models for collective spin will be shown to describe the dynamics effectively. I will also discuss the effect of nonuniform filling caused by hole doping, at a microscopic level, demonstrating their limiting role in the dynamics and scaling of entanglement.
2024-10-11 (Friday)
room 1.02, Pasteura 5 at 12:15
Mateusz Homenda (IFT UW)Critical Fermi surfaces of two dimensional fermionic systems
During my talk I will readdress the problem of the description of quantum criticality in 2D fermionic systems. Based on the most prominent example, nematic quantum criticality, I will describe the major physical features of the system, such as the Landau damping of collective modes or a non-Fermi liquid behaviour of single particle excitations. I will also explain the main obstacles to formulating a satisfactory theory of critical Fermi surfaces. In the second part of my talk I will present the main result of application of the functional renormalization group method to this problem.