The relationship between charge density waves and superconductivity? It's complicated

July 18, 2018, Ames Laboratory
Temperature dependence of resistivity upon electron irradiation. Resistivities of four different samples: R1 (0, 0.23, 0.47, 0.72, 0.95, 1.18, 1.4, 1.7, and 2.4 C cm−2), R2 (0, 1.57 C cm−2), R3 (0, 3.67 C cm−2), and R4 (0, 4.18 C cm−2). Note that all 0-dose curves for samples R1, R2, R3, and R4 are coincident. Overall resistivity increase with increasing dose was consistently seen for all samples, as shown by the arrows. The inset shows in-situ measurement of resistivity of sample R1 as a function of dose during electron irradiation at 22 K. The blue arrows indicate stops in irradiation, during which the sample was extracted from the irradiation chamber and characterized. Partial annealing of about 30–40% of resistivity increase occurred on warming the sample to room temperature and subsequently cooling down to 22 K. Credit: Nature Communications (2018). DOI: 10.1038/s41467-018-05153-0

For a long time, physicists have tried to understand the relationship between a periodic pattern of conduction electrons called a charge density wave (CDW), and another quantum order, superconductivity, or zero electrical resistance, in the same material. Do they compete? Co-exist? Co-operate? Do they go their separate ways?

For the first time, physicists at Ames Laboratory and their international collaborators were able to explore that relationship in the superconducting and CDW material niobium diselenide (NbSe2), through experiments using swift electron bombardment.

"What we are doing is 'poking' the system by introducing disorder into the crystal lattice," said Ames Laboratory scientist Ruslan Prozorov. "By knocking out some of the ions, impacting electrons create defects in the material. Both quantum ordered states (CDW and superconductivity) respond in certain ways to these additional defects, which we can measure."

The research, which included resistivity measurements, London penetration depth studies, and X-ray diffraction, showed that the relationship between CDW and superconductivity is complicated—in some ways the two states compete with each other, and in others, CDW assists superconductivity.

"Charge density wave competes with superconductivity for the same conduction electrons," said Prozorov. "As CDW is suppressed or disrupted, superconductivity is grabbing the electrons needed to form Cooper's pairs, which form superconducting condensate."

But CDW also assists superconductivity through its coupling to crystal lattice vibrations, called phonons. And phonons act as a "glue" between electrons to form a Cooper pair. At some threshold level of disorder, long-range ordered CDW disappears abruptly, and superconducting transition temperature is abruptly reduced as well.

"It is very important to understand the factors that influence superconductivity, in particular its critical temperature," said Prozorov. "Room temperature superconductors of future technologies will most likely be artificially assembled from individual atoms and single atomic layers fully utilizing basic mechanisms that lead to the enhancement of useful properties. Our research is a step in that direction."

The research is further discussed in the paper, "Using controlled disorder to probe the interplay between charge order and in NbSe2," authored by Kyuil Cho, M.  Kończykowski, S. Teknowijoyo, M.A. Tanatar, J. Guss, P.B. Gartin, J. Wilde, A. Kreyssig, R. McQueeny, A. Goldman, V. Mishra, P.J. Hirschfeld and R. Prozorov; and published in the Nature Communications.

Explore further: Scientists gain insight on mechanism of unconventional superconductivity

More information: Kyuil Cho et al. Using controlled disorder to probe the interplay between charge order and superconductivity in NbSe2, Nature Communications (2018). DOI: 10.1038/s41467-018-05153-0

Related Stories

Charge density wave inhomogeneity and pseudogap in 1T-TiSe2

April 19, 2018

1T-TiSe2 has been widely studied in the past few decades as one of the typical charge density wave (CDW) materials. Recently, superconductivity was realized in this system through Cu intercalation, pressure or electric gating, ...

Superconductivity in an alloy with quasicrystal structure

March 27, 2018

Extraordinary things happen at low temperatures. One of the best examples is superconductivity, a phenomenon wherein the electrical resistance of a solid drops to zero below a critical temperature. Known for a century, superconductivity ...

When crystal vibrations' inner clock drives superconductivity

November 9, 2016

Superconductivity is like an Eldorado for electrons, as they flow without resistance through a conductor. However, it only occurs below a very low critical temperature. Physicists now believe they can enhance superconductivity ...

Recommended for you

A new way to count qubits

September 24, 2018

Researchers at Syracuse University, working with collaborators at the University of Wisconsin (UW)-Madison, have developed a new technique for measuring the state of quantum bits, or qubits, in a quantum computer.

Explainer: The US push to boost 'quantum computing'

September 24, 2018

A race by U.S. tech companies to build a new generation of powerful "quantum computers" could get a $1.3 billion boost from Congress, fueled in part by lawmakers' fear of growing competition from China.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.