Nematic Quantum Critical Fluctuations in BaFe_{2-x}Ni_{x}As_{2}

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Critical Phenomena

Background:

• Nematic fluctuations are crucial in understanding the complex phase diagrams of iron-based superconductors.
• Distinguishing between quantum and thermal critical fluctuations has been challenging due to similar experimental signatures.

Purpose of the Study:

• To systematically investigate nematic fluctuations in electron-doped BaFe_{2-x}Ni_{x}As_{2} under uniaxial pressure.
• To differentiate the contributions of quantum and thermal fluctuations to the observed resistivity.
• To explore the behavior of nematic fluctuations across various doping levels, especially around the optimal doping concentration.

Main Methods:

• In-plane electrical resistance measurements were performed on BaFe_{2-x}Ni_{x}As_{2} samples subjected to uniaxial pressure.
• Systematic variation of doping levels (x) and applied pressure was employed.
• Analysis focused on the pressure-dependent resistivity along the (100) and (110) crystallographic directions.

Main Results:

• A significant pressure-dependent resistivity along the (100) direction was observed across all doping levels, contradicting simple Ising-type nematic models.
• This (100) resistivity signal peaked at the optimal doping concentration, indicating a strong association with nematic quantum critical fluctuations.
• Thermal fluctuations from striped antiferromagnetic order were identified as dominant in the underdoped regime along the (110) direction.

Conclusions:

• The observed (100) resistivity suggests that the nematic quantum critical point is not adequately described by a simple Ising-type nematic model.
• The findings point towards a strong coupling between quantum critical fluctuations and fermions, or potentially a higher symmetry phase around optimal doping.
• Thermal fluctuations play a significant role in the underdoped region, influencing the nematic behavior along the (110) direction.