Scientists from two of Oxfordshire's leading research centres have completed the first painstaking and careful mapping of the features of one of the most exotic states of matter in the Universe. Their work is published this week, 31 March 2011, in the science journal Nature.
The magnetic field - temperature phase diagram for k-(BEDT-TTF)2Cu2(CN)3 obtained from muon spin rotation experiments and including previously reported NMR and thermodynamic measurements
Credit: Francis Pratt / ISIS / STFC
The fruit of their five years of work is a unique and detailed map of a state of matter known as a 'quantum spin liquid', which is found close to absolute zero in a particular example of a chemically-engineered molecular material. The existence of this strange state of matter was proposed in the 1970s but has only recently been confirmed. Until now, there has been very limited information available describing its physical characteristics. By using the extremely sensitive technique of muon spin rotation, the properties of the quantum spin liquid state have been measured over a wider magnetic field range and in considerably greater detail than before.
The research team led by Dr Francis Pratt at the ISIS Neutron and Muon Source at STFC Rutherford Appleton Laboratory includes scientists from ISIS, the University of Oxford and colleagues from Japan and the Swiss Muon Source at the Paul-Scherrer Institute in Switzerland.
"This research is fundamental physics of the purest kind," said STFC's Dr Pratt. "The quantum spin liquid state is extremely fascinating and we can imagine that in the future it could be of use in quantum computing and the writing and deciphering of coded information (cryptography). But right now we are only at the start of a very long journey to understand it fully."
"Since the idea of the quantum spin liquid was first proposed there have been many hundreds of papers published speculating on the properties of quantum spin liquids, but until now there has been very little experimental evidence to compare these ideas with", said Dr Pratt.
Applying a small magnetic field to the quantum spin liquid state found in κ-(BEDT-TTF)2Cu2(CN)3 causes weak magnetism to form demonstrating the delicate nature of the quantum spin liquid state
Credit: Francis Pratt / ISIS / STFC
The quantum spin liquid state that has been mapped by the team is found in 70 milligrams of tiny black crystals of the layered organic material κ-(BEDT-TTF)2Cu2(CN)3 cooled to just a couple of hundredths of a degree above absolute zero. Despite it being extremely difficult to make the tiny plate-like crystals, the material is perfect for these experiments since it is on the border between being an insulator and a metal, a key requirement for the existence of the quantum spin liquid state.
The careful study and precise measurements needed to map the quantum spin liquid state were made using muon spin rotation. In this technique, muons are implanted into the material and sense the way the local magnetic properties vary as the temperature and magnetic field are changed in the experiment.
This research represents the first major experimental step towards understanding the real nature of the quantum spin liquid state. The team would like to do further measurements, but a breakthrough in chemistry is needed to produce more of the material and allow further measurements to be done using other techniques such as neutron scattering.
Contacts and sources: Science and Technology Facilities Council
The research is published in the 31 March 2011 edition of the science journal Nature.
"Magnetic and non-magnetic phases of a quantum spin-liquid"
F L Pratt, P J Baker, S J Blundell, T Lancaster, S Ohira-Kawamura, C Baines, Y Shimizu, K Kanoda, I Watanabe and G Saito
Nature 471, 612–616 (31 March 2011) , doi:10.1038/nature09910
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The magnetic field - temperature phase diagram for k-(BEDT-TTF)2Cu2(CN)3 obtained from muon spin rotation experiments and including previously reported NMR and thermodynamic measurements
The fruit of their five years of work is a unique and detailed map of a state of matter known as a 'quantum spin liquid', which is found close to absolute zero in a particular example of a chemically-engineered molecular material. The existence of this strange state of matter was proposed in the 1970s but has only recently been confirmed. Until now, there has been very limited information available describing its physical characteristics. By using the extremely sensitive technique of muon spin rotation, the properties of the quantum spin liquid state have been measured over a wider magnetic field range and in considerably greater detail than before.
The research team led by Dr Francis Pratt at the ISIS Neutron and Muon Source at STFC Rutherford Appleton Laboratory includes scientists from ISIS, the University of Oxford and colleagues from Japan and the Swiss Muon Source at the Paul-Scherrer Institute in Switzerland.
"This research is fundamental physics of the purest kind," said STFC's Dr Pratt. "The quantum spin liquid state is extremely fascinating and we can imagine that in the future it could be of use in quantum computing and the writing and deciphering of coded information (cryptography). But right now we are only at the start of a very long journey to understand it fully."
"Since the idea of the quantum spin liquid was first proposed there have been many hundreds of papers published speculating on the properties of quantum spin liquids, but until now there has been very little experimental evidence to compare these ideas with", said Dr Pratt.
Applying a small magnetic field to the quantum spin liquid state found in κ-(BEDT-TTF)2Cu2(CN)3 causes weak magnetism to form demonstrating the delicate nature of the quantum spin liquid state
The quantum spin liquid state that has been mapped by the team is found in 70 milligrams of tiny black crystals of the layered organic material κ-(BEDT-TTF)2Cu2(CN)3 cooled to just a couple of hundredths of a degree above absolute zero. Despite it being extremely difficult to make the tiny plate-like crystals, the material is perfect for these experiments since it is on the border between being an insulator and a metal, a key requirement for the existence of the quantum spin liquid state.
The careful study and precise measurements needed to map the quantum spin liquid state were made using muon spin rotation. In this technique, muons are implanted into the material and sense the way the local magnetic properties vary as the temperature and magnetic field are changed in the experiment.
This research represents the first major experimental step towards understanding the real nature of the quantum spin liquid state. The team would like to do further measurements, but a breakthrough in chemistry is needed to produce more of the material and allow further measurements to be done using other techniques such as neutron scattering.
Contacts and sources: Science and Technology Facilities Council
The research is published in the 31 March 2011 edition of the science journal Nature.
"Magnetic and non-magnetic phases of a quantum spin-liquid"
F L Pratt, P J Baker, S J Blundell, T Lancaster, S Ohira-Kawamura, C Baines, Y Shimizu, K Kanoda, I Watanabe and G Saito
Nature 471, 612–616 (31 March 2011) , doi:10.1038/nature09910
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