Condensed Matter Physics Seminars

In the first slot of this semester we will meet to reacquaint oursleves with one another. The plan will be for everyone to introduce themselves and what they are currently working on, roughly 3-4 minutes each. This is principally aimed at people in UMCS but as always external guests will be also very welcome to attend and to speak.

The paper is Moiré-Enabled Topological Superconductivity, Kezilebieke, et al, Nano Lett. 22, 328 (2022): https://doi.org/10.1021/acs.nanolett.1c03856

In the dice seminar we all read the paper in advance and then the presenter will be picked at random from the audience the day. PhD students attending for the first time may excuse themselves from presenting. Please do prepare suggestions for the paper for the next dice seminar, which will be on the 22nd March.

The paper is Thermal chiral anomaly in the magnetic-field- induced ideal Weyl phase of Bi1−xSbx, Vu, et al, Nature Materials 20, 1525 (2021): https://doi.org/10.1038/s41563-021-00983-8 

In a dice seminar we will pick a recent article to present. The presenter will be picked from the audience at random! First time PhD student attendees may excuse themselves from presenting.

The spin-squeezed states refer to quantum correlated states with reduced fluctuations in one of the collective spin components, leading to smaller uncertainty of one spin component perpendicular to the mean spin direction than the classical limit. They can be practical in quantum metrology through atomic interferometers and the high-precision of state-of-the-art atomic clocks. In this seminar, I want to explain some aspects of applications of spin squeezing in quantum systems. In addition, I like to speak about the ways that lead to creating squeezed states as well as their faced challenges. In the end, I introduce some open questions in this field.

https://rdcu.be/cJyOw

Up to now, no analytical formalism has been introduced for the interaction of a continuous-mode field with a two-level atom taking into account directly and explicitly all modes of the field that could allow to examine the evolutions of both the atom and the field. In this work, we will address the interaction of a two-level atom with a continuous-mode field, in the weak coupling limit, for any arbitrary initial state of the field. Using a novel re-normalization method we will derive a greatly simplified formulae for the S-propagator of the atom-field such that it depends only on normally-ordered creation and annihilation operators of the field, the decay rate of the atom and the Lamb Shift in atomic frequency. A Lindblad-form master equation is also derived for the atom, which is in full agreement with the GKLS master equation.

https://doi.org/10.1126/science.abl7152

https://doi.org/10.1038/s41535-021-00410-w

Instead of our usual condensed matter physics seminar we invite you to attend this popular science lecture by our colleague Prof. Dr Stefan Poedts.

Recently silicene, a silicon counterpart of graphene, has attracted increasing attention due to its outstanding electronic properties. Therefore numerous experimental and theoretical studies have been devoted to fabrication of silicene, but still its synthesis remains a big challenge. Until now silicene has been fabricated with success, mainly in the epitaxial form on various substrates, for example on Ag(111), Ir(111) or on graphite.

We study the formation of silicene layers on Pb-Si surfaces. We use Low Temperature-Scaning Tunneling Microscopy and Spectroscopy (LT-STM/STS) to characterize structural and electronic properties of the system at liquid helium temperatures. Our STM/STS investigations reveal, that Si deposited onto √3×√3-Pb surface forms nanoribbons, directly bonded to the Si(111) substrate. While the deposition of silicon on the Pb substrate results in two different Si phases: √3×√3 covered and 1 × 1 uncovered silicene structures.

We study the dynamical properties of the one-channel and two-channel spin-1/2 Kondo models after quenching in Hamiltonian variables. Eigen spectrum of the initial and final Hamiltonians is calculated by using the numerical renormalization group method implemented within the matrix product states formalism. We consider multiple quench protocols in the considered Kondo systems, also in the presence of external magnetic field of different intensities. The main emphasis is put on the analysis of the behavior of the Loschmidt echo L(t), which measures the ability of the system’s revival to its initial state after a quench. We show that the decay of the Loschmidt echo strongly depends on the type of quench and the ground state of the system. For the one-channel Kondo model, we show that L(t) decays as, L(t)∼(t·TK)^−1.4, where TK is the Kondo temperature, while for the two-channel Kondo model, we demonstrate that the decay is slower and given by L(t)∼(t·TK)^−0.7. In addition, we also determine the dynamical behavior of the impurity’s magnetization, which sheds light on identification of the relevant time scales in the system’s dynamics.

Elemental two-dimensional (2D) materials play an important role in spintronics, valleytronics, and pseudospintronics. They are also called Dirac materials because their electrons behave like massless Dirac particles obeying Dirac equation instead of Schrodinger equation. Graphene is nowadays a famous material due to its exquisite properties and potential applications. However, silicene (single-layer silicon) is an elemental 2D Dirac material which possesses the same main features that make graphene interesting. Additionally silicene has two advantages over graphene. Firstly it has considerably larger band gap which is very important for electronic applications. Secondly silicene is much more suitable when it comes to actual applications with today’s silicon-based semiconductor industry.

Based on the Dirac-Bogoliubov-de Gennes (DBdG) equation, we take the advantage of a scattering approach to theoretically investigate the electronic transport in silicene-based nanostructures. The main part of our studies focuses on the silicene-based heterostructures of superconductor, normal, insulator and ferromagnetic materials. It is assumed that the superconductivity and ferromagnetism are incduced in silicene via proximity effect. In the final part, we briefly discuss the electronic transport properties of a graphene superlattice in comparison with its silicene-based counterpart.