Forthcoming Seminars at F-1

26 Mar 2019
Jürgen SchnackMagnetism of free and deposited magnetic molecules
Magnetic molecules possess many interesting properties. In this presentation I focus on some frustration effects such as an enhanced magnetocaloric effect as well as on the modification of magnetic properties in contact with non-magnetic metallic substrates. I am also going to explain very recent developments to calculate magnetic observables for large spin systems.

Geometric spin frustration in low-dimensional magnetic materials such as the two dimensional antiferromagnetic kagome lattice can lead to unusual behavior. Some of these features are present in magnetic molecules and lead to a deeper understanding of extended systems. Among such findings are localized independent magnons, which are responsible for flat bands, giant magnetization jumps and an increased magnetocaloric effect. The latter can also be observed in molecules with the structure of a sawtooth chain. In addition, we could report about the experimental realization of adiabatic demagnetization experiments using heptametallic gadolinium molecules. In the cooling experiment 200 mK could be reached and a rich structure of the isentropes could be observed. When put on a non-magnetic metallic surface, magnetic molecules may change their properties due to the coupling to the conduction electrons. Following an experimental realization of stacked molecules, which form short spin chains, we can show how strong such an interaction needs to be in order to screen the terminal spin completely.

Seminar room for physics (JSI main building)

Seminars Archive

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5 Mar 2019
Marko Žnidarič (FMF, UL)Localized and ballistic eigenstates in chaotic spin ladders and the Fermi-Hubbard model
I will introduce a ladder model with or without disorder that is in general chaotic, but that includes the integrable Hubbard chain as a special case. One can analytically show the existence of atypical eigenstates of such a model that are populated by noninteracting excitations. Depending on parameters they can e.g. exhibit Anderson localization, or, surprisingly, ballistic transport at any disorder strength. These properties differ strikingly from those of typical eigenstates nearby in energy, which give rise to diffusion. Results have implications for possible localization in the presence of non-Abelian symmetries, as well as for phases of matter that are intermediate between full ergodicity and integrability.

Seminar room for physics (JSI main building)

26 Feb 2019
Mikhail KiselevLandau-Zener Interferometry in Multilevel Systems
We propose universal approach to Landau-Zener (LZ) problem in a multilevel system. The problem is formulated in terms of generators of SU(N) algebra and maps the Hamiltonian onto the effective anisotropic pseudospin (N-1)/2 model. The vector Bloch equation for the density matrix describing the temporal evolution of the multilevel crossing problem is derived and solved analytically for two generic cases: i) three-level crossing problem representing a minimal model for a LZ interferometer and ii) four-level crossing problem corresponding to a minimal model of coupled interferometers. It is shown that the analytic solution of the Bloch equation is in excellent quantitative agreement with the numerical solution of the Schroedinger equation for the 3- and 4-level crossing problems. The solution demonstrates oscillation patterns which radically differ from the standard patterns for the two-level Landau-Zener problem:

5 Feb 2019
Tomaž RejecTime-dependent thermoelectric transport in nanosystems: reflectionless Luttinger field approach
Recently the Luttinger field approach was proposed as a way to simulate switching on a temperature gradient across a nanoscale device initially in thermal equilibrium. The time dependent particle and heat currents can then be calculated by propagating the initial equilibrium state of the system in time. Unfortunately applying a uniform Luttinger field in the whole of a lead causes a discrepancy between steady state currents in the long time limit and those predicted by the Landauer-Büttiker formulas as well as artefacts at short times. Here we propose a modified approach where the Luttinger field gradually reaches its final value across a transition region. If the length of the transition region is sufficient, the electrons move through without reflecting. In this way the correct energy distribution of electrons originating from such a lead, corresponding to the new temperature, is established in the scattering region. Our approach is tested on a single quantum dot and a parallel double quantum dot system.

Seminar room for physics (JSI main building)

22 Mar, 2019 Seminar:
Mar 26: Magnetism of fr...
Jürgen Schnack...
14 Mar, 2019 Abroad:
Tutorial Lecture
Jernej F. Kamenik...
4 Mar, 2019 Seminar:
Mar 5: Localized and b...
Marko Žnidarič (FMF, ...
4 Mar, 2019 Abroad:
Contributed Talk
Nejc Košnik...
28 Feb, 2019 Abroad:
Jernej F. Kamenik...
28 Feb, 2019 Abroad:
Invited Talk
Jernej F. Kamenik...
25 Feb, 2019 Seminar:
Feb 26: Landau-Zener In...
Mikhail Kiselev...
11 Feb, 2019 Publication:
Hackl L., Vidmar L., Ri...
Phys. Rev. B 99...
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