The seminar of the Superconducting Metamaterials Laboratory National University of Science and Technology MISiS (Moscow, Leninskiy prospekt 4), lecture hall Б-607 (6th floor) on 31st of March at 15:00.
Correspondent person: Andrei Malishevskii, e-mail: email@example.com; phone: +7 916 135 03 25
- Tuneable Spin and Charge Phenomena, Siddharth S. Saxena (Cavendish Labarotory, Cambridge University)
This talk will discuss pressure induced phenomena in the vicinity of ferroelectric and magnetic quantum phase transitions.
Materials tuned to the neighbourhood of a zero temperature phase transition often show the emergence of novel quantum phenomena. Much of the effort to study these new emergent effects, like the breakdown of the conventional Fermi-liquid theory in metals has been focused in narrow band electronic systems. Ferroelectric crystals provide a very different type of quantum criticality that arises purely from the crystalline lattice. In many cases the ferroelectric phase can be tuned to absolute zero using hydrostatic pressure. Close to such a zero temperature phase transition, the dielectric constant and other quantities change into radically unconventional forms due to the fluctuations experienced in this region. The simplest ferroelectrics may form a text-book paradigm of quantum criticality in the solid-state where there are no complicating effects of electron damping of the quantum charge fluctuations. We present low temperature high precision data demonstrating these effects in pure single crystals of SrTiO3 and KTaO3. We outline a model for describing the physics of ferroelectrics close to quantum criticality and highlight the expected 1/T^2 dependence of the dielectric constant measured over a wide temperature range at low temperatures. In the neighbourhood of the quantum critical point we report the emergence of a small frequency independent peak in the dielectric constant at approximately 2K in SrTiO3 and 3K in KTaO3. Looking to the future, we imagine that quantum paraelectric fluctuations may lead to new low temperature states and mediate novel interactions in multi-ferroic systems (e.g. EuTiO3) and ferroelectric crystals supporting itinerant electrons.
- Electrically-induced magnetic atom-like structures in multiferroics, Petr I. Karpov, Sergei I. Mukhin (Department of Theoretical Physics and Quantum Technologies, MISiS)
Electric field control of magnetic structures, particularly topological defects, in multiferroic materials has led to electric field creation and manipulation of single magnetic defects: domain walls and skyrmions.
In this talk a new scenario is discussed of electric field induced multiple self-organized topological defects - magnetic vortices and anti-vortices, in materials with easy plane symmetry. Analytical and numerical calculations will be presented that describe electrically induced "magnetic atoms" consisting of "nuclei" populated with vortices and surrounded with "shells" of anti-vortices [arXiv:1701.01842].
Everyone is welcome! Pass for seminar participants who are not students, graduate students or employees of MISiS, will be carried out upon presentation of passport subject to prior registration for the seminar (until 14:00 the day of the seminar).