Regular ordered structure of a crystal (left corner), resembles some similarity with e.g. Portuguese tiles. [Fer01]
Crackling noise produced during the compression
of a nanoporous material when it cracks. [Fer07]
Symmetry plays an important role in nature, in technique, as well as in art. Who would not be impressed by the famous Taj Mahal (on the right), which was finished in 1648 in loving memory of Mumtaz Mahal, the wife of the Indian Großmogul. [Fer02]
The symmetry largely determines the properties of crystals. If the symmetry is lowered, e.g. due to the presence of a phase transition at a critical temperature Tc, large changes in physical properties occur over a rather narrow temperature range. This symmetry breaking leads to an enormous increase of functionality (Ferroelectricity, Ferromagnetism, etc.) of a material, which can be used for technical applications. E.g. high sensitive thermal detectors for the search of buried people, etc.
In the present project we go further and study the properties of tiny parts of crystals, the domain walls (picture below). Domain walls are inherently connected to symmetry breaking, i.e. whenever symmetry breaking occurs, there appear different variants of the low symmetry structure with a domain wall between.
What technicians – looking for such application – do not like so much, is the fact, that such domain walls can be pinned by defects, because such pinning slows down any dynamic process in a device.
In the presence of defects the domain wall feels a potential energy that is very irregular and resembles an alpine landscape (image on the right).
Very often in physics it happens that a given subject or problem turns out to be very similar to another one, which at a first glance had looked very different. This happens also in the present case. It turns out that the movement of domain walls in a random potential can be used to better understand earthquakes. Why this is so?
Roughly speaking earthquakes happen when the built up stress- due to the movement of tectonic plates – is abruptly released when week parts of the earth crust break. If an inhomogeneous material breaks it produces a specific noise, called crackling noise.
«Structure and dynamics of interfaces in ferroic materials»
–or how to survive in a disordered world?
Measured power-law distribution of crackling noise in a natural mineral (Schist) from the Großglockner region in Austria. [Fer06]
The simplest experiment for a system that produces crackling noise is to disrupt or crumple a piece of paper. The irregular movement of the crack front releases energy which is power-law distributed. This is very similar to the famous Gutenberg-Richter law in earthquakes. It means that – fortunately – earthquakes with higher magnitude are much less frequent compared to low energy earthquakes.
Measurements of earthquakes over many decades have shown that this law is very nicely fulfilled. The physics behind it – which serves that this damping of high energy events happens – is strongly connected to the physics of interfaces in random potentials.
Domain walls are about 1-10 nm (0.000001 – 0.00001 mm) thick, which means that about 10000 domain walls fit into the thickness of a human hair. The thing that makes such tiny nano-objects fascinating is, that they can have completely different properties as their surrounding. For example such domain walls can conduct current (even superconducting) when the surrounding is insulating, they can be magnetic with non-magnetic surrounding, and for this reason very small devices can be built, which work on the basis of domain wall functionality.
The methods we use include Microscopic methods with various resolution, from optical microscopy (10-6 m) to electron microscopy (10-10 m), as well as group theory and Landau-Ginzburg-Devonshire models, which finally lead to differential equations.
Crackling noise, phase transitions, domain walls
Principal Investigator: Prof. Wilfried Schranz
Handwriting of recent calculations on domain wall problems (to be published) [Fer09]
 Statistical similarity between the compression of a porous material and earthquakes
Jordi Baró, Álvaro Corral, Xavier Illa, Antoni Planes, Ekhard K. H. Salje, Wilfried Schranz,
Daniel E. Soto-Parra and Eduard Víves. Phys. Rev. Lett. 110, 088702, 1-5 (2013)
Selected for a Viewpoint in Physics: Little Earthquakes in the Lab, by Ian Main.
 Strain intermittency due to avalanches in ferroelastic and porous materials
V. Soprunyuk, S. Puchberger, A. Tröster, E. Vives, E.K.H. Salje and W. Schranz
Invited paper for the special Festschrift issue on “Ferroelastics and domain walls”
honouring the 70th birthday of Ekhard Salje. J. Phys.: Condensed Matter 29, 224002 (2017)
 The noise of many needles: Jerky domain wall propagation in PbZrO3 and LaAlO3
S. Puchberger, V. Soprunyuk, W. Schranz, A. Tröster, K. Roleder, A. Majchrowski,
M.A. Carpenter and E.K.H. Salje. APL Materials 5, 046102 (2017)
 See e.g. Low amplitude, low frequency elastic measurements using Dynamic Mechanical
Analyzer (DMA) spectroscopy; E.K. H. Salje and W. Schranz. Z. Kristallographie 226, 1 (2011)
[Fer08] MD Simulation © Wilfried Schranz, Universität Wien
[Fer09] Handwritten calculations © Wilfried Schranz, Universität Wien
[Fer10] Lead zirconate © Wilfried Schranz, Universität Wien
[Fer11] Data schist & Schist energy with time © Wilfried Schranz, Universität Wien
 Crackling noise
James P. Sethna, Karin A. Dahmen & Christopher R. Myers. Nature 410, 242-250 (2001)
Source Material - Attribution
[Fer01] Portuguese tiles © Wilfried Schranz, Universität Wien
[Fer02] Taj mahal © Wilfried Schranz, Universität Wien
[Fer03] Sketch of a domain wall © Wilfried Schranz, Universität Wien
[Fer04] Random energy landscape © Wilfried Schranz, Universität Wien
[Fer06] Großglockner © Wilfried Schranz, Universität Wien
[Fer07] Compression © Wilfried Schranz, Universität Wien
Here you will find the proposed materials framed in a coloured box . The code next to it identifies each item (foto, video, etc.) individually. You will need this code to fill in the form. Additionally, you can have an overview of the materials from all research groups at matter.soundsof.net/materials.
Ultimately, the main goal of this research is two-fold: on one hand, understanding the coupling mechanisms that are responsible for the functionality of domain walls. Because then we could deliberately learn how to address domain walls for e.g. data storage. On the other hand, a deeper knowledge of the origin of the observed dramatic slowing down of the dynamics of domain walls, with the aim to finally avoid it.
Data Schist &
Schist energy with time
Upon this data, the power-law distribution was calculated (see picture). You can download the original Data Files using the links on the right.
Meanwhile, within the present project we have studied quite different systems that produce crackling noise under slow compression, including nano-porous silica, as well as natural porous materials like charcoal and even mica schist from the Großglockner region. All of them showing nice power-law behaviour of the corresponding energy distributions.