Research team takes big step towards making a Bose metal

Sub: Sci

Sec: Msc

Introduction

A Bose metal is an anomalous metallic state (AMS) with unique electrical properties.
It is a state where Cooper pairs exist but do not condense into a superconductor.
This makes Bose metals a significant area of research in condensed matter physics.

Conductivity in Metals

Metals conduct electricity due to free-moving electrons in a lattice of atomic nuclei.
Conductivity varies with temperature:
At room temperature (20ºC), zinc has a conductivity of 16.9 million siemens per meter.
At -272.3ºC, zinc becomes a superconductor with infinite conductivity.

Superconductivity and Cooper Pairs

Superconductors exhibit zero resistance below a critical temperature.
At low temperatures, electrons pair up due to weak attractive forces, forming Cooper pairs.
These pairs undergo a phase transition, leading to superconductivity.

Anomalous Metallic States (AMS)

Some metals improve their conductivity at low temperatures but do not become superconductors.
They conduct electricity via Cooper pairs instead of electrons but lack long-range superconducting coherence.
This state is termed a Bose metal.

Bose Metal: A Challenge to Traditional Theories

Classical theories suggest that at absolute zero, metals should either:
Become superconductors (infinite conductivity) or
Become insulators (zero conductivity).
A Bose metal defies this expectation by maintaining a conductivity between zero and infinity.

Recent Research on Bose Metals

Until now, Bose metals were only theoretically predicted.
On February 13, 2025, researchers from China and Japan found strong evidence of a Bose metal in niobium diselenide (NbSe₂).

Role of Magnetic Fields

Superconductors expel magnetic fields when cooled below their critical temperature.
Type-II superconductors like NbSe₂ allow magnetic fields to enter in isolated pockets.
When a 2D version of NbSe₂ is subjected to a specific magnetic field, it exhibits properties of a Bose metal.

Experimental Findings

Researchers used Raman spectroscopy to confirm the presence of Cooper pairs in non-superconducting NbSe₂.
Hall resistance vanished as the thickness of NbSe₂ increased, indicating charge transport via Cooper pairs instead of electrons.

Theoretical Implications

The study suggests AMS is characterized by fluctuating local pairing that does not condense into superconductivity.

Findings challenge existing theories about:

Future Prospects

Bose metals currently lack practical applications.
However, they provide a rich playground for physics research, which could drive future technological advancements.