Unveiling the quantum secrets of matter


The high field magnet will provide the strongest magnetic field for neutron scattering worldwide. But we are not striving just for a world record, no! There are strong scientific motivations. High magnetic fields can unveil properties of matter which are hidden otherwise. What happens deep inside matter, when zillions of atoms and their electrons interact and go through different types of order? How does superconductivity arise and gets suppressed and what triggers phase transitions in strange quantum states? We hope to get a glimpse, why quantum physics sometimes determines material’s properties and sometimes not so much. Understanding matter is the driving force, Bella Lake explains. She is a Professor of Physics and head of the expert team in Quantum Phenomena in Novel Materials at HZB.


What is the interesting point in putting high magnetic field on materials?

Bella Lake: Field is a probe by which you can explore materials. It is a bit like temperature or pressure: You can change the temperature to go through different phases and new phenomena emerge. Similarly, you can change the magnetic field to manipulate your sample and to go through different phases, in order to learn more about it.

Actually, we have at HZB already strong magnetic fields which provide a maximum of 17 Tesla. Why do you need to have the High Field Magnet with up to 25 Tesla? What is the purpose of putting a field a million times stronger than the earth’s magnetic field on a sample?

Bella Lake: Well, to produce an effect that is measurable on a material, you have often to put fields of the order of ten or even more than twenty Tesla onto them. Earth’s magnetic field will not do anything to them. It is a question of the energy scale: With 17 Tesla you can just about in some materials change the phase, but for many materials you just can’t do that with that size of field, you need a stronger field. Higher magnetic fields are used already, for example you can use pulsed fields which attain even 100 Tesla, but these can’t be used with neutron scattering. So it is known that there are new phenomena to be observed, but these are not explored in detail. You could do this with neutron scattering when you have a HFM, because then you can go up into this size of fields and you can make significant advance into exploring these new phenomena.

Why is the combination of the Magnet with neutrons so interesting?

Bella Lake: Well, it is a very obvious combination, because neutrons measure magnetic properties. And magnetic fields strongly influence magnetic properties. Magnetic fields directly affect the magnetism in the sample and neutrons directly measure those properties.

Can you give me an example of actual research question which could get done with the HFM and neutron scattering?

Bella Lake: For example superconductivity in those High-Tc-Superconductors is still not understood in many ways. It is thought to be a complex balance of different phases like charge order or magnetic phases – superconductivity somehow arises between the balance of these phases. With an high magnetic field, you can suppress the superconductivity and enhance the magnetic or charge order phases. Neutrons allow you to make a real microscopic measurement of the details of what’s happening. Until now, that has not been possible. So, if we have 20 Tesla, we can explore it. Another example is a metaelectric phase transition which is not explored. These phase transitions happens in multiferroic materials, where the electric properties like polarization are coupled to the magnetic order. Here a magnetic field does not only change the magnetic order, but also the electrical properties, so it acts like a switch. And this is not explored, it occurs in material when the magnetic field is like 20 Tesla or more, within reach of the new High Field Magnet but beyond the reach of any current magnet. Materials like multiferroics do potentially have uses as switches in data storage, obviously that would be years into the future but at least understanding the process is the first step in getting there. If you understand what is the mechanism maybe you can design materials, just the process of understanding is helpful.

What is your favorite question you want to address with the HFM?

Bella Lake: From a personal point of view? I am interested in a material called strontium copper borate, which goes through a series of phases when you put it into a magnetic field. And these phases have been measured with magnetization. So you see magnetization steps, there are plateaus; as you increase the field, the magnetization will actually level off and then start again rising and level off. And when it levels off, it does so at certain special values of magnetization like 1/8 or 1/4 or 1/3. So it has these special fractional properties. And it is not really understood why, but these fractions correspond to the fractions observed in the Quantum Hall Effect. It ought to be a deep quantum property, a quantum phenomenon, related to the topology of the system. Just to go in there and explore what is happening on that magnetization plateau in detail with neutrons is my goal.

Some people would say that these questions are too esoteric and do not lead to any useful innovation. What would you answer?

Bella Lake: I feel one has to be patient. These research questions do lead somewhere but it needs time. It is like a long term investment, when you put your money in the bank and you look 20 years later and see what has happened. And of course no one item, no one bit of research is ever guaranteed. I can’t say this will help in some way solve a specific problem. But the sum of problems explored together, maybe will. And I feel there is value in understanding, just for its own sake. It is like why do we have art or why do we go traveling. It has its own value.

 

Interview: Dr. Antonia Rötger; first published in HZBZlog