Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Metallic phase for bosons implies new state of matter


The Heisenberg uncertainty principle places severe constraints on the subatomic world. To illustrate, for particles called bosons, the principle dictates that bosons either condense to form a superconductor or they must remain localized in an insulator. However, experiments conducted during the last 15 years on thin films have revealed a third possibility: Bosons can exist as a metal. Scientists have been struggling to interpret this surprising result.

Phase diagram showing the destruction of superconductivity: 1) The yellow region represents the ordered phase in which all the electron pairs share the same phase (all arrows pointing up), 2) The elusive bose metal is in blue in which all the phases are disordered but form a glass, and 3)
Beyond the electron pairs fall apart and form an insulator. The vertical axis represents temperature and the in-plane axes any of the tuning parameters that destroy superconductivity such as defects or magnetic field.

"The conventional theory of metals is in crisis," said Philip Phillips, a professor of physics at the University of Illinois at Urbana-Champaign. "The observation of a metallic phase for bosons directly contradicts conventional wisdom. A satisfactory explanation requires a new state of matter."

Writing in the Oct. 10 issue of the journal Science, Phillips and Denis Dalidovich -- a former graduate student now working at Florida State University -- analyze the thin-film experiments and offer a new explanation in which the charge-carrying bosons condense into a glass-like, metallic state.

Normally, the charge carriers in metals are electrons -- fermions that are subject to the Pauli exclusion principle, which limits the number of carriers that can occupy the same quantum state. In a superconductor, however, the charge carriers are pairs of electrons -- bosons -- that need not obey the Pauli exclusion principle. As a result, macroscopic occupation of a single quantum state is allowed.

"Like musicians in a marching band, bosons in a superconductor all march in step with one another -- that is, they have the same phase," Phillips said. "When they march out of step, the result is an insulator."

In the experiments (performed at Stanford and the University of Minnesota) that Phillips and Dalidovich analyzed, a thin-film superconductor was transformed into an insulator either by decreasing the film thickness or by applying a perpendicular magnetic field. The signature of a superconductor is zero resistance, while the signature of an insulator is infinite resistance.

"But in these experiments, there was a wide range where the resistance was neither zero nor infinite -- it was a finite value that seemed to persist all the way down to zero temperature," Phillips said. "And if you have a finite resistivity at zero temperature, that is called a metal."

According to the conventional theory of metals, "that metallicity shouldn’t be there," Phillips said. "So these experiments that destroy superconductivity, but don’t immediately produce an insulator, pose a serious theoretical question."

Over the years, new states of matter have been proposed that had exotic magnetic or topological textures associated with the bosons. But these states lacked a key property of a metal -- finite conductivity at zero temperature. A better explanation for the intervening metallic phase is that bosons are condensing into a glass-like state.

Glasses are inherently dynamical objects, Phillips said. "They look solid, but there is no crystalline structure and therefore no true ground state. Bosons moving in such a glassy environment fail to localize because no unique ground state exists."

To illuminate what such a state looks like, consider again the marching band proceeding up a very long hill, Phillips said. The musicians will tire at different rates and fall out of step. But the new marching patterns will propagate through the band. While the band as a whole is out of step, there will be local regions of order where groups of musicians still march in step at the same rate.

"In a similar fashion, when you disrupt the phases in a superconductor, you don’t end up immediately with an insulator," Phillips said. "Instead, you have a dynamic system in which the phases have local order while overall there is disorder." Such an intermediate phase in which there is local order but global disorder lies outside the conventional rubric.

The researchers’ findings are relevant to topological glasses in general, including the much-studied vortex glass state that has been argued to have zero resistance and to explain the ground state of high-temperature, copper-oxide superconductors in a perpendicular magnetic field.

"Recent experiments by researchers at Maryland and Caltech show that the resistivity does not vanish in the vortex glass state," Phillips said. "The resistivity remains finite, so it now appears that the vortex glass is metallic and not a superconductor, consistent with the glassy Bose metal proposed." This agreement lends further credence to the glassy model proposed to explain the strange Bose metal state of matter.

Funding was provided by the American Chemical Society and the National Science Foundation.

James E. Kloeppel | UIUC
Further information:

More articles from Physics and Astronomy:

nachricht Physicists from Hannover Predict Novel Light Molecules
26.02.2020 | Leibniz Universität Hannover

nachricht From China to the South Pole: Joining forces to solve the neutrino mass puzzle
25.02.2020 | Johannes Gutenberg-Universität Mainz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: High-pressure scientists in Bayreuth discover promising material for information technology

Researchers at the University of Bayreuth have discovered an unusual material: When cooled down to two degrees Celsius, its crystal structure and electronic properties change abruptly and significantly. In this new state, the distances between iron atoms can be tailored with the help of light beams. This opens up intriguing possibilities for application in the field of information technology. The scientists have presented their discovery in the journal "Angewandte Chemie - International Edition". The new findings are the result of close cooperation with partnering facilities in Augsburg, Dresden, Hamburg, and Moscow.

The material is an unusual form of iron oxide with the formula Fe₅O₆. The researchers produced it at a pressure of 15 gigapascals in a high-pressure laboratory...

Im Focus: From China to the South Pole: Joining forces to solve the neutrino mass puzzle

Study by Mainz physicists indicates that the next generation of neutrino experiments may well find the answer to one of the most pressing issues in neutrino physics

Among the most exciting challenges in modern physics is the identification of the neutrino mass ordering. Physicists from the Cluster of Excellence PRISMA+ at...

Im Focus: Therapies without drugs

Fraunhofer researchers are investigating the potential of microimplants to stimulate nerve cells and treat chronic conditions like asthma, diabetes, or Parkinson’s disease. Find out what makes this form of treatment so appealing and which challenges the researchers still have to master.

A study by the Robert Koch Institute has found that one in four women will suffer from weak bladders at some point in their lives. Treatments of this condition...

Im Focus: A step towards controlling spin-dependent petahertz electronics by material defects

The operational speed of semiconductors in various electronic and optoelectronic devices is limited to several gigahertz (a billion oscillations per second). This constrains the upper limit of the operational speed of computing. Now researchers from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, and the Indian Institute of Technology in Bombay have explained how these processes can be sped up through the use of light waves and defected solid materials.

Light waves perform several hundred trillion oscillations per second. Hence, it is natural to envision employing light oscillations to drive the electronic...

Im Focus: Freiburg researcher investigate the origins of surface texture

Most natural and artificial surfaces are rough: metals and even glasses that appear smooth to the naked eye can look like jagged mountain ranges under the microscope. There is currently no uniform theory about the origin of this roughness despite it being observed on all scales, from the atomic to the tectonic. Scientists suspect that the rough surface is formed by irreversible plastic deformation that occurs in many processes of mechanical machining of components such as milling.

Prof. Dr. Lars Pastewka from the Simulation group at the Department of Microsystems Engineering at the University of Freiburg and his team have simulated such...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

70th Lindau Nobel Laureate Meeting: Around 70 Laureates set to meet with young scientists from approx. 100 countries

12.02.2020 | Event News

11th Advanced Battery Power Conference, March 24-25, 2020 in Münster/Germany

16.01.2020 | Event News

Laser Colloquium Hydrogen LKH2: fast and reliable fuel cell manufacturing

15.01.2020 | Event News

Latest News

Physicists from Hannover Predict Novel Light Molecules

26.02.2020 | Physics and Astronomy

Turbomachine expander offers efficient, safe strategy for heating, cooling

25.02.2020 | Power and Electrical Engineering

The seismicity of Mars

25.02.2020 | Earth Sciences

Science & Research
Overview of more VideoLinks >>>