Context: 

Recently, a team of researchers from China and Japan reported in the journal Physical Review Letters that they had found strong signs that Niobium Diselenide (Nbse2) can become a Bose metal.

More on the News

• The researchers are cautious in definitively calling NbSe₂ a Bose metal, as the definition of such a state remains somewhat ambiguous. 
• The study's lead investigator, Professor Xiaoxiang Xi from Nanjing University, acknowledged that while the results point to a potential Bose metal state, further work is needed to fully understand and confirm its existence.

About Bose metal

• Certain metals, below a critical temperature, have electrons that experience an attractive force and pair up, but don’t condense into a superconductor.
• Instead of becoming a superconductor, the material just becomes a better conductor and conducts electricity using Cooper pairs (electron pairs), not individual electrons. This state is called a Bose metal.
• The key characteristic of a Bose metal is the partial conductivity where Cooper pairs form but do not exhibit long-range superconducting coherence.
• It is a type of Anomalous Metallic State (AMS) where Cooper pairs (pairs of electrons that typically form in superconductors) fail to condense into a superconducting state. 
• AMSs are studied in condensed matter physics to understand disordered metals (metals with irregular atomic structures or impurities that prevent regular metallic behavior).
• Currently, Bose metals do not have practical applications. 
• Traditionally theories of disordered metals suggest they should either become insulator (zero conductivity) or superconductors (infinite conductivity) at absolute zero temperatures. 
• Bose metals challenge this, as their conductivity lies somewhere between zero and infinity as temperature approaches absolute zero.

Key Findings of Study on Niobium Diselenide:

• Niobium Diselenide (NbSe₂) is a well-known material that becomes a superconductor at low temperatures, exhibiting the typical behavior of expelling magnetic fields when it enters the superconducting state. 
• As magnetic field strength increases, NbSe₂ enters a “mixed state,” where it allows the magnetic field to penetrate in isolated pockets without fully disrupting its superconductivity.
• NbSe2 is a type-II superconductor because it exhibits this dynamic behavior when subjected to a magnetic field.
• In type-II superconductors, the forces acting on electrons become stronger as the material is cooled and magnetized, especially if the material is physically thinner.
• The researchers hypothesized that If a two-dimensional (2D) version of NbSe₂ (essentially a single layer of its molecules) is exposed to a magnetic field in a specific direction , it could create a Bose metal. 
• Their experiments showed signs of this anomalous metallic state, where Cooper pairs formed but failed to condense into a superconducting state; this was confirmed using Raman spectroscopy.
• In the case of NbSe₂, as the material became thinner and subjected to specific magnetic conditions, this Hall resistance disappeared (an indicator that the material’s charge carriers were Cooper pairs rather than individual electrons).

Significance of the Research

• Studies in the field of Bose metal could lead to deeper insights into quantum materials and open new avenues in the development of future technologies, such as quantum computing and highly efficient conductors. 
• This could provide valuable insight into the role of phase fluctuations in disrupting superconductivity and may help refine existing theories on superconducting and non-superconducting materials.