What are Quantum Minerals?

By Sul MulroySep 6 2019

Image Credits: GiroScience/shutterstock.com

The study of quantum materials, i.e. materials with properties lying beyond the standard realms of understanding of contemporary condensed-matter physics, is a growing field with intense interest for the development of technologies including high-density data-storage and computing.

What are Quantum Effects?

Quantum effects become dominant when a system’s size is comparable to the electron wavelength. This typically occurs when a material’s dimensions are on the nanometer scale with new phenomena related to the material’s electronic and magnetic properties arising in smaller domains. The discovery of these properties has driven new fields of research forward to exploit and harness the physical phenomena demonstrated by such materials.

While materials exhibiting the desired properties for such applications are typically synthesized various naturally occurring minerals exhibit quantum properties and numerous developments in solid-state physics were made possible by scientific observations of the properties of naturally occurring minerals. The complex structure of natural minerals is due to the complex and often multiphase modes of formation in the natural environment. This often means synthesis and replication of such minerals via artificial means is not possible. What it does mean is that chemists and physicist can study their unique properties and then apply the knowledge to aid in the formation and characterization of synthetic materials with similar, tunable properties.

Minerals that Exhibit Quantum Properties

Numerous copper minerals exhibit a multitude of quantum properties including dimerized quantum spin dimers. These dimers are essentially antiferromagnetically coupled atoms, i.e. the magnetic moment of each adjacent copper atoms are opposed. This allows a quantum critical point, i.e. the point at which a quantum phase transition occurs, to be reached under the application of a magnetic field. Such minerals include the copper carbonates malachite [Cu₂CO₃(OH)₂] and callaghanite [Cu₂Mg₂(CO₃)(OH)₆·2H₂O] and the copper arsenates urusovite [CuAl(AsO₄)O] and clinoclase [Cu₃(AsO₄)(OH)₃].

Copper bearing phases are also good examples of naturally occurring minerals with quantum spin chains that influence both ferromagnetism, where the magnetic domains of adjacent atoms are aligned and antiferromaganetism, where they are opposed. Interactions between these chains can influence spin-spiral magnetic order allowing suppression of long-range magnetic order. Copper arsenates, sulfates, and molybdates all exhibit this type of quantum behavior. Such properties and their influence on the behavior of minerals displaying them have potential applications in low-temperature processes such as the liquefaction of hydrogen.

Transition metal sulfide minerals also display quantum properties, of particular note are iron sulfides crystallizing in the tetragonal crystal system. These have been shown to exhibit superconductivity, a quantum mechanical phenomena where electrical resistivity almost completely vanishes beneath a certain critical temperature. Unfortunately, the presence of other metals in naturally occurring tetragonal iron sulfides, e.g. mackinawite [(Fe,Ni)_1+xS], will suppress these properties and it is unlikely a pure phase tetragonal iron sulfide will be discovered in the natural environment.

Conclusion

A vast swathe of minerals exhibit quantum properties that influence their magnetic and electrical properties. Even within the field of quantum magnetism there is a plethora of other phenomena types. The complex interactions between electrons and the various metals present in the crystal structure offer chemists an incredible opportunity to discern the various factors that lead to such properties and utilize them in high-tech applications. Understanding the temperatures at which materials and their electrons display quantum properties such as magnetism and superconductivity can aid in the development of high-performance computers as conventional processors typically rely on cooled systems to optimize performance.

Sources and Further Reading

• Bardeen J, Cooper LN, Schrieffer JR (1957) Theory of superconductivity. Physical Review, 108, 1175-1204
• Fu Y, Willander M (2001) Semiconductor quantum materials and their applications in electronics and optoelectronics. In: Nalwa HS, Handbook of Advanced Electronic and Photonic Materials and Devices.
• Inosov DS (2019) Quantum magnetism in minerals. Advances in Physics, 67, 149-252.
• Orenstein J (2012) Ultrafast spectroscopy of quantum materials. Physics Today. http://orensteinlab.berkeley.edu/wp-content/uploads/2015/01/PUB102Orenstein.pdf
• Yin J, Slizovskiy S, Cao Y, Hu S, Yang Y, Lobanova I, Piot BA, Son SK, Ozdemir S, Taniguchi T, Watanabe K, Novoselov KS, Guinea F, Geim AK, Fal’ko V, Mischenko A (2019) Dimensional reduction quantum Hall effect and layer parity in graphite films. Nature Physics, 15, 437-442.

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